JTJN7 IJKW Wining: dept. LIBRARY UNIVERSITY OF CALIFORNIA. Class HEAT ENERGY AND FUELS PYROMETRY, COMBUSTION, ANALYSIS OF FUELS AND MANUFACTURE OF CHARCOAL, COKE AND FUEL GASES BY HANNS v. JUPTNER / PROFESSOR, IMPERIAL AND ROYAL TECHNICAL INSTITUTE, VIENNA TRANSLATED BY OSKAR NAGEL, Pn.D. "HE UNIVER iF NEW YORK McGRAW PUBLISHING COMPANY 239 WEST 39TH STREET 1908 . .' B COPYRIGHT, 1908, BY THE McGRAW PUBLISHING COMPANY NEW YORK Stanbopc ipress F. H. GILSON COMPANY BOSTON. U.S. A TRANSLATOR'S PREFACE PROFESSOR HANNS VON JUPTNER has divided the study of chemical engineering into two groups, namely: energy and matter ; and beginning with a general discussion of the various forms of energy, has written four volumes covering the subject both theoretically and practically. The present volume deals with heat energy and fuels, and contains a large amount of carefully tabulated data in conven- ient form for use. A great deal of this data is new and will be welcomed by chemists, metallurgists and engineers. Although the book is intended for use in universities and engineering schools it is of equal value to practising engineers, since it gives not only the fundamental principles, but also the latest experimental data and practice. Among the topics of greatest practical interest are : Measure- ment of high temperatures and late data on the melting points of various substances ; discussion of incomplete combustion, combustion temperatures and combustion at constant volume and constant pressure, and an immense amount of data on solid, liquid and gaseous fuels and their production. The chapters on the gasification of fuels, which contain the results of the author's own experiments as well as those of Strache and Jahoda, are of especial value. The book has been extremely well received in Europe, where it is widely used both in schools and in practice as a text-book and handbook. THE TRANSLATOR. NEW YORK, November, 1908. iii 181331 CONTENTS INTRODUCTION. CHAPTER PAGE I. GENERAL REMARKS 1 II. FORMS OF ENERGY 11 VOLUME I. HEAT ENERGY AND FUELS. Part I. Heat Measurement, Combustion and Fuels. I. THE MEASUREMENT OF HIGH TEMPERATURES (PYROMETRY) . . 37 II. PYROMETRY (Continued) 53 III. PYROMETRY (Conclusion). OPTICAL METHODS OF MEASURING TEMPERATURES 68 IV. COMBUSTION HEAT AND ITS DETERMINATION 91 V. DIRECT METHODS FOR DETERMINING THE COMBUSTION HEAT 110 VI. INCOMPLETE COMBUSTION 117 VII. COMBUSTION TEMPERATURE 127 VIII. FUELS (In General) 141 IX. WOOD 145 X. FOSSIL SOLID FUELS (In General) 155 XI. PEAT 166 XII. BROWN COAL (Lignite) 173 XIII. BITUMINOUS AND ANTHRACITE COALS 178 XIV. ARTIFICIAL SOLID FUELS 188 XV. CHARCOAL 191 XVI. PEAT-COAL, COKE AND BRIQUETTES 214 XVII. COKING APPARATUS 230 XVIII. LIQUID FUELS . 241 XIX. GASEOUS FUELS 243 XX. PRODUCER GAS 246 XXI. WATER GAS 268 XXII. DOWSON GAS, BLAST FURNACE GAS AND REGENERATED COM- BUSTION GASES 287 XXIII. APPARATUS FOR THE PRODUCTION OF FUEL GASES 292 INDEX 303 'OF THE UNIVERSITY ^N^LIFO* HEAT ENEKGY AND FUELS INTRODUCTION. CHAPTER I. GENERAL REMARKS. IF we consider the immense strides that technical science has made in the second half of the nineteenth century; if we observe how prosperity is increasing, especially in the countries prominent in engineering; and how, as a natural sequence, the standing and influence of engineers are constantly growing in these countries, we are forced to ask by what means all this has come to pass in other words, to what circumstances are we indebted for this remarkable progress? A close study of the development of technical science shows its close connection with the natural development of mankind. At first, man had no other resource in his struggle with wild animals and natural forces than himself, that is, the organs given him by nature. Necessity taught him how to protect himself from cold by means of clothes, to seek protection from expo- sure to the weather, and led him to build dwellings. Nature gave him a cave for his first home, but he soon learned to construct artificial shelters. In his struggles with wild animals he tried to increase his efficiency. For this purpose he first tried to lengthen his reach with a stick. Then he found that a thrown stone was able to act far beyond the immediate range of his arm. He soon found that there were expedients for using the strength of his muscles to greater advantage, and he began to devise primitive tools in the widest sense of the word. His problem now was to select the material most adapted to his purposes from the mineral, vegetable and animal kingdoms; thus his knowledge of nature was considerably increased. As l 2 HEAT ENERGY AND FUELS the material suitable for his tools and implements could not always be found near at hand, man had to get it by barter, and we have the beginning of commerce and traffic. It was a great advance in the progress of civilization when man learned to use fire; this discovery is of special inter- est to us as chemical industry depends on it. In close connection are the manufacture of burned clay-vessels (the beginning of ceramics) and the production of metals, both of which are of the greatest importance in the development of civilization, as they furnish materials that are especially suited for the manufacture of implements and arms of various kinds. Herewith are connected other improvements, such as the prep- aration of food by boiling, broiling, roasting and baking, the preparation of alcoholic beverages, the use of fermentation in baking bread, dyeing, tanning, etc. At first man lived alone" or banded in small families. With increasing civilization, especially after the beginning of agriculture and cattle-breeding, which enabled a number of people to live together by insuring the necessities of life, clans were formed by the union of families, and therefrom, grad- ually, the nations. Thus division of labor was made possi- ble; the individual members of such families or clans were enabled to devote their time to the solution of certain tasks, according to their individual skill and inclination. Gradual evolution along these lines, in the course of thousands of years, resulted in the differentiation of skilled labor into distinct trades and professions, and on this foundation modern engineering and the modern industrial system developed. In the Middle Ages the skilled artisans were working by rule of thumb, and frequently kept their methods of working secret. At that time there was no engineering science in existence in the modern sense of this word. This is but natural, since the process of reasoning was hampered by insufficient and conflicting data; and was, moreover, entirely different from our modern way of thinking, the base of which is natural science. This interfered with the progress of the trades and the development of progressive methods. The period of Renaissance only brought a change by guiding us back to the observation of nature. This change, naturally, could take place only slowly and gradually, as there is no more difficult task for a man, not GENERAL REMARKS 3 accustomed to it from his youth, than to observe and think accurately; on the other hand, the scientists formed at that time an entirely separate class, just as did the trades and profes- sions, and a long time was required before the gap between the two was bridged over, so that science and the trades could work together. At first the sciences had to be developed, before being utilized in the trades ; but soon at least in some directions mutual relations presented themselves, which decreased the gap, at the same time advancing both science and the trades. Thus the invention of the printing press made it possible to communicate one's thought or word easily to all the world, while the invention of the steamboat and railroad brought people in different countries directly together. Commerce became a world power and opened new markets. Competition started and with it came the necessity of making improvements. In this way in the course of the nineteenth century modern engineering and the technical sciences originated, which now represent one of the most influential factors in modern civiliza- tion. But this enormous progress was directly based upon the correct practical application of the natural sciences. Whereas formerly science was the foundation on which modern engineering developed, the reverse is now often the case. Every new scientific invention is still carefully followed up by the engineer and utilized for practical purposes, even more than ever before. But it often now happens that the engineer promotes science by making a scientific research in order to solve a technical problem. This indicates what must be demanded now of a good engineer. He must have a thorough scientific education and must be able to work scientifically in unexplored fields; he must gain practical experience, which necessitates highly developed powers of observation, and he must have the faculty of utilizing the results of science in practice. For this purpose he must be able to think logically, scientifically and technically, for these two requirements are by no means identical. We have seen above how the trades were gradually trans- formed to modern industries. Like all great changes, this transformation involved serious complications; the conflict 4 HEAT ENERGY AND FUELS between capital and labor originated capitalism and socialism. Between capital, that makes the creation of large industries possible, and labor, which first of all represents the producing power in the industries, stands the engineer, the mental leader. His is the task not only to keep up order and discipline in the enterprise, but also to act as mediator between those two opposite parties. This is not easy, nor pleasant, but it is a very important duty. Its fulfillment requires energy toward both sides, and sometimes even apparent harshness; but also a good heart and the earnest desire to find out the causes that are at the bottom of the endeavors on both sides. Every worker, including the engineer, who works with his intellect, is right in asking for reasonable wages, and it is per- fectly right and proper that the capitalist, who lends his money to the enterprise, should expect a profit out of it. This is the main cause of the conflict. The industrial enterprise as such must also earn something. It is necessary to put aside capital for protection against unforeseen events and against menacing competition, for making enlargements, etc. Every industry must, therefore, endeavor to make a profit. If the management of an enterprise is to remain in the hands of the engineer he has, therefore, to be familiar with commercial questions and economic problems. Like all others the chemical industry needs buildings, appa- ratus, machines, and means of transportation, and the chemical engineer should know something about these mechanical appli- ances, not only in the interest of the industry, but also to insure him his position, as otherwise the business management will be given into the hands of a business man, and the technical man- agement into the hands of other (non-chemical) engineers. This will be especially the case in places where labor is scarce and wages high, as it then becomes necessary to reduce the operating expenses by the installation of mechanical appliances. Attention has to be paid also to the welfare of the working- man by the provision of baths, hospitals, schools, etc., which also requires special knowledge. Finally the engineer must have a very important faculty, that is, to keep cool in danger. This faculty has its own com- mercial value, since on it human lives often depend. Related therewith is courage, which in moments of danger enables a GENERAL REMARKS 5 man to be cautious and quick, to consider all possibilities, and to act for the greatest good. Much is, therefore, expected of an engineer, and the question is, how shall the chemical engineer acquire all these qualities and this knowledge? Coolness and courage are traits of character that each must acquire for himself; hence we cannot consider them here. Nor can practical -experience be taught in a school, by a teacher or text-book, since practical experience is not the knowledge of such facts as are stated in technical text-books, but rather the faculty of making proper use of such facts in practice. This faculty is best acquired in practice if the eyes are kept open. Instruction, however, can help a man to educate himself in correct technical thinking, as we will proceed to show. It is the task of the school to give to its students a thorough scientific education, i.e., to give them, as far as possible, a thorough theoretical foundation. The school must encourage original research and independent scientific reasoning; it must increase the powers of observation and judgment, and must show by concrete examples how scientific results are used in practice. But this is not so easy a task as appears at first sight. First of all the data available for lectures on chemical engineering are so limited that it is absolutely impossible to discuss and treat in detail all the branches of the industry. Only such branches of chemical engineering can be treated in detail as are either of great industrial importance (like fuels, combustion, the industry of heavy chemicals, iron and steel metallurgy, etc.) or those branches which seem especially adapted to develop in an engineer the faculties sketched above. Special stress is to be laid on the discussion of the theoretical basis of the various processes, and the discussion of apparatus is to be limited to the most important types. It may frequently happen that such typical examples are not taken from latest practice, but from older methods of operation, if the latter show the fundamental process with greater clearness. While this principle also holds good for the writing of a text- book on chemical engineering, we are permitted to cover a wider field; for limitation in the selection of the various industries is not as essential as in lectures. However, even a text-book, the 6 HEAT ENERGY AND FUELS object of which is first of all to supplement lectures, should not be too voluminous. Compared to a book the personal lecture has a great advantage, in that the teacher can observe from the attentiveness of his students whether he is understood; and if not he can explain his subject more in detail. A text-book can, therefore, never entirely replace the lecture, but may be very useful in supple- menting it. However, neither lecture nor text-book alone can accomplish the same ends as university or college instruction, since the latter has two additional aids in excursions and laboratory work. The latter should not be limited to analytical work; on the con- trary the student ought to be a good analyst when he starts to work in the chemical engineering laboratory. Naturally he has to do analytical work also in this period, but this should not be his principal work. In this stage synthetic work should be kept in the foreground, with solutions of problems such as may actually occur in practice ; it is even advisable that the students learn to design plants and to make critical reports on designs which have been worked out. This goes far beyond the ordinary limits of chemical engineer- ing instruction and increases the work of the teacher; but it brings valuable results. This kind of instruction, however, is very difficult in the ordinary laboratories and necessitates the installation of special technological schools. Their erection would simultaneously amend another defect of present methods of instruction. As above mentioned, instruction as given now cannot but be encyclopedical and is very far from being a thorough technical education. This, however, can be remedied by giving the students in special schools an opportunity to acquaint themselves more in detail with a limited field of chemical engineering according to their choice without changing the present encyclopedic instruction in the whole engineering field. Excursions are also an important means of instruction, as the student has a chance to see actual industrial works, and to observe operations carried out on a large scale. If they are to be useful and profitable, a number of conditions should be fulfilled. The number of the participants should not be too great; if the number of the students is very large they must be divided into several parties. At first only short excursions GENERAL REMARKS should be made to stimulate the faculty of observation of the students. An excursion must not be made before the processes used in the works to be visited have been discussed in the lectures. Interest in excursions and resorption of the things observed are increased by exercises in designing, and by working out projects, as we have already mentioned. It would also be advantageous if a professor of mechanical engineering would participate in these visits. Such excursions should be aided and facilitated by the government, railroads and manufacturers. It hardly requires mentioning that a well arranged museum or collection of things of technical interest is also of great assistance in instruction. If we now turn to our subject proper chemical technology we find it difficult to define exactly the word " technology." The name of our science, literally translated, means " disci- pline of the arts" (r^V, Aoyos). So we might conclude to define as technology the mechanics of all possible arts, from all the fine arts to the handicrafts. This, however, is not the case, as neither the fine arts and handicrafts nor agriculture and mining belong to the sphere of technology. On the other hand, in various trades, which are not included in engineering science, the same appliances and methods are used as in engineering. The problem becomes even more complicated if we keep in mind that in technical processes not only substances are trans- formed but also energies so as to assume a more useful and more convenient form. We could, therefore, define technology as the science of the methods by which materials and forms of energy as we find them are transformed so as to become more useful and valuable. To what extent the value of a substance is increased by the work of the engineer is shown by the following example, taken from a paper of the English ironmaster, Ldwthian Bell : Scale of Iron. Price per Kg. Scale of Iron. Price per Kg. Pig iron 01 Needles from same 1 3 Rail-steel 014 Fine wire 1 4 Gas-pipes Bessemer steel Bessemer steel wire 0.02 0.02-0.025 0.3 Fine needles from same . Chronometer springs .... Finest watch-springs. . . . 1.68 3.00 2000.00 8 HEAT ENERGY AXD FUELS The transformation of substances and energies always requires a certain amount of work and always involves the practical loss of a fraction of the substance or energy. To carry out the desired transformation, it is necessary to install a plant with buildings and proper appliances, such as machines, furnaces, etc. The running (operating) expenses are calculated as follows: (a) First cost of plant (to be depreciated). (b) The operating expenses proper (wages, cost of raw materials, transportation, taxes, etc.). (c) Reserves for protection against all emergencies. On the other hand, the unavoidable loss of material and energy in every process means a loss of capital and an increase of the operating expenses. For effecting the greatest possible economy all these expenses and losses have to be reduced to a minimum. The reduction of the first cost and operating expenses depends, first of all, on the methods used; and, generally speaking, the method of operation will be the more economical 1. The lower the first cost (capital invested). 2. The cheaper the labor and the raw material used. 3. The quicker the working (which means careful planning). 4. The more convenient the location (with respect to labor market and shipping facilities). 5. The smaller the loss of raw material and energy. In this respect a method can be made profitable in many cases by utilizing again the losses (at least partly) either by using them again in the same process or by converting them into marketable by-products. 6. The quality and the selling price of the finished product are naturally also of the greatest importance. The object of a process can be of*two different kinds: The object may be, for instance, a change of form (disinte- gration, agglomeration 'into larger pieces, change of shape) or a mechanical separation into products of different values. In the case of energies the object may be to transform them into use- ful forms. This is the case in utilizing the energy of a water- fall or of the wind by means of water-wheels and wind-mills; or in the change of certain forms of energies into others, as in GENERAL REMARKS 9 electric generators. The science that treats on these subjects is mechanical engineering. Secondly, the object may be to transform raw materials by chemical changes into substances of a different chemical com- position, or to transform chemical energy into other forms of energy (mechanical energy, heat, light and electricity). All such processes are in the sphere of chemical engineering. Both branches of technology, however, are so closely related that it is impossible to draw a sharp line between the two. The manufacture of paper, for instance, and iron-foundry work is frequently treated in text-books of both mechanical and chemical engineering, while the purification of sulphur occurring in nature and of the native metals is often described only in chemical works, notwithstanding the fact that only mechanical and physical processes are involved. The chemical engineer has to use frequently, besides chemical, also mechanical means, and in many cases he has to be well informed as to water-wheels, steam-engines, blowers, pumps, etc. Mechanical and chemical changes are often so closely combined (as in annealing sheet metals, welding of iron, hardening of steel, etc.), that a correct idea of the respective processes can only be formed from a chemical-mechanical point of view. According to these explanations chemical technology can be divided into two main groups : 1. Chemical technology of the energies. 2. Chemical technology of materials. This book will treat of the first. In the chemical technology of materials use must be made of energy for forming the desired products, while in the chemical technology of energies materials must be employed as carriers of chemical energy. No strict division can therefore be made between these groups, but it presents many advantages for instruction. We therefore comprise under " chemical technology of the energies" the science of the change of chemical into other forms of energy and will consider the transformation of chemical energy into (a) Heat (by combustion, generated or consumed by other chemical processes; firing and refrigeration). 10 HEAT ENERGY AND FUELS (6) Mechanical energy (explosives and internal combustion engines). (c) Radiant energy (mainly light, i.e., chemical illumination; transformation into heat-rays is considered under a). (d) Electricity (galvanic cells and storage batteries). Especially in the case of production of heat from fuel, and in the case of explosives and illuminants, it is hardly possible to separate chemical technology of energies from the materials that furnish the chemical energy to be transformed, so that we will find it necessary to consider also the technology of these materials. CHAPTER II. FORMS OF ENERGY. ENERGY is the power to do work, if we call work a change of state in general. The performance of all our industrial operations requires a considerable amount of energy, for instance, mechanical energy in the working of metals, disintegrating of phosphates, cements, and other raw materials for conveying and transporting materials; heat energy for melting metals and burning of lime, cement and ceramic products; electric energy for illuminating, refining of copper, production of aluminum and chlorine; light energy for illuminating and photography; chemical energy in the production of chemical compounds, as chlorate of potash, explosives, etc. Energy cannot be made from nothing, but has to be procured from the natural reservoirs of energy in which it is accumu- lated. We are, however, enabled to draw from the accumu- lated energies of nature, and by means of certain machines to transform them into other forms of energy, but without increas- ing the total amount. This is, for instance, done in steam engines, electric generators and batteries, etc. Of the natural reservoirs of energy, the following are of industrial importance : 1. Live motors (man, horse, etc.). 2. Falling water (waterfalls, creeks, rivers). 3. Moving air (wind motors and sailing vessels). 4. Substances in which chemical energy is stored. The .most important of these are the fuels. All these available sources of energy are actually only inter- mediate reservoirs, their energy having been obtained from the sun in a more or less direct way. The sun is, therefore, the original source of all energy, of all heat, of all electric energy and of all chemical phenomena on the surface of the earth. 11 12 HEAT ENERGY AND FUELS The sun transmits energy to the waterfalls by heating and evaporating sea water; transmits energy to all plants by decom- posing the carbon dioxide of the air by means of its rays, trans- forming the plants in the ground into fossil coal. It is evident that by this transmission a large amount of solar energy is lost. We have to add, for instance, to the water for evaporation the total latent evaporating heat, which is again liberated by the condensation to liquid water and a large part of the water condensed in the mountains cannot be utilized, partly on account of practical reasons, partly on account of its seeping into the ground, and partly on account of the evapora- tion on its downward way; therefore the experiments for directly utilizing the radiant energy of the sun deserve our most earnest consideration. Precisely speaking, however, all these losses are only losses to the industrial world and not to the earth, as, for instance, by the condensation of water- vapor, the air layers, in which this phenomenon takes place, are warmed up. The radiant energy of the sun is, therefore, the only source from which the energy-content of our earth can be increased, and the radiation of the earth is the only source of energy- Before going into the details of the chemical technology of energies it might be well to say a few words about the differ- ent forms of energy. All possible changes occurring in a system can be referred to three fundamental quantities: The mass (M), the space, which can be conceived as the cube of length or distance (L 3 ), and the time (T). All these changes can be reduced to changes of energies and we can therefore measure all forms of energy by using as units mass, distance and time. If we allow a system to go through certain changes without adding or deducting energy, so that it returns again to the first state, then the system contains again the same form and the same quantity of energy as in the beginning. Energy cannot be lost or generated, but only transformed into other forms. The mathematical expressions for all forms of energy can be divided into two factors, the capacity factor and the intensity factor. The former is more or less unchangeable, while on the FORMS OF ENERGY 13 latter depends the equilibrium. Equilibrium between two quantities of energy is only attained when the intensities are equal. If we indicate the energy, intensity factor and capacity factor with E, I and c, respectively, we have and therefore dE = Idc + cdi; dE it c is constant we have = c: di if i is constant we have - = i. dc This defines exactly the nature of these energy factors. The following are the known forms of energy : 1. Mechanical energy. 2. Heat. 3. Electric and magnetic energy. 4. Chemical energy. 5. Radiant energy. 1. Mechanical energy occurs in the following forms: (a) Kinetic or actual energy. (6) Energy of space, which can be (1) Energy of distance. (2) Energy of surface. (3) Energy of volume. (a) The mathematical expression for kinetic energy is According to the way by which this expression is split into factors we get as capacity factor either m, which quantity is absolutely unchangeable, or mv, which is only relatively unchangeable, while as factor of intensity we obtain half the square of velocity f J or the velocity itself (v). The unit of kinetic energy is the Erg (E), which is the energy contained in the mass of a gram, when moving with a 14 HEAT ENERGY AND FUELS velocity of 1 centimeter per second. The dimension of the kinetic energy (expressed by M, L and T), is The energy of space occurs in three different forms in which the capacity factor is represented by distance, surface and vol- ume respectively. We have Form of energy. Capacity. Intensity. Energy of distance = distance X force Energy of surface = surface (area) X tension Energy of volume = volume X pressure. The energy of distance acts between two points in the direc- tion of their connecting line. If we indicate the length (dis- tance) with I and the force with /, we have E = If, and therefore the force a 3 di is equal to the ratio of change of energy to change of distance (length). If the energy of distance is transformed exclusively into kinetic energy (as in the ordinary mechanical and astro- nomical problems) this equation expresses the acceleration, a, and then corresponds to the ordinary definition of force. The energy of surface is active on the surface of liquids and solids. Its intensity of factor, the tension, is identical with the constant of capillarity. The energy of volume appears in gases. Its factors are volume and pressure. We have, therefore, the following expressions for the dimen- sions of the energies of space and its factors : Capacity. Intensity. Energy. distance (L) force = [EL~ l ] E surface (L 2 ) tension - [EL~ 2 ] E volume (L 3 ) pressure - [EL~ 3 ] E We know of two kinds of energy of distance, one of which (called gravity) acts between two . material points so that the FORMS OF ENERGY 15 energy increases with the distance and reaches a minimum when the points are in direct contact. It is governed by Newton's law of gravitation. If we indicate the energy of dis- tance with Ed, the two masses acting upon each other with m and m 2 , their distance with r, we can express this law by the equation in which c t and j 2 are constants. If r = GO and Ed = c v it reaches a maximum. The differential of this equation gives us the ordinary form of this law : dE . mn The quantity c t is unknown; the second constant k 2 is, expressed in the centimeter-gram-second system, j 2 = 6.6 X 10- 8 . On the surface of the earth the force of gravity can be con- sidered constant for moderate altitudes, and the energy of dis- tance is directly proportionate to the altitude. The second kind of distance energy occurs for instance in electrically charged balls, and is distinguished from the former by reaching its maximum value at infinitely small instead of infinitely large distance between the bodies acting upon each other. For this energy we have E = j 2 , and for the force dE . m^n., Tr = ~ h r* This force has therefore the same formula as in the first case, but is negative. While the gravity is an attracting force, this force is repulsive. We have seen above that two masses acting upon each other, under the influence of gravity, tend to approach each other; whereby the distance energy is decreased, being partly trans- formed into kinetic energy. 16 HEAT ENERGY AND FUELS The decrease of distance energy, corresponding to a decrease in I of dl is If we suppose ra x = M mass of the earth and m 2 = m mass of a falling body, r = R the radius of the earth and dr = dh is an incre- ment of the fall-distance, corresponding to an infinitely small change of distance energy, we have . M . Mm dE d = j 2 m ah, an expression wherein j 2 - =/ (gravity). ri ti Thence we can write dE d = fdh. As the lost distance energy is completely transformed into kinetic energy of the equation dE k = mv dv we can make both expressions equal : fdh = mv dv. By integration between o and h and o and v respectively we obtain rh rv fj dh = m J v dv or //i = - - , as the fundamental law for the mutual transforma- Zi tion of kinetic and distance energy. If we put into fdh = mv dv for the acceleration the value v = - - . we get Galileo's law of fall : at fdt = m dv, or dv ^l dt m Equilibrium between kinetic energy and distance energy can only exist if the two masses, acting upon each other, are moving around their common center of gravity. Analogous to the two kinds of distance energy we can imagine two kinds of surface energy; however, we know only one of them, i.e., the one that tends to decrease the surface. FORMS OF ENERGY 17 The cause of this is called tension (y). therefore - dE v = RT , v and -, -fi [T -, J v or, for constant temperature, - E,, = RT S~ J y By integration between v l and v 2 we get RTlog 1 - = E/ - E,!'. *'i There is little known of the relation between volume-energy, volume, and pressure, except in the case of gases. For the equilibrium between volume and distance energy such as takes place, for instance, in a cylinder filled with gas, in UNIVER: H L. ! PC f FORMS OF ENERGY 19 which a pressure is exerted upon the gas by a piston working without friction, we have j dh = p dv. The cross section of the cylinder being q, dv = q dh, then pq = f, i.e., the force equals the product of gas-pressure and cross- sectional area. Before mentioning the other forms of energy we want to consider a few general important considerations. If there is no equilibrium in a system between the forms of energy present, the system is undergoing a change so that the decrease of one form of energy is greater than the increase of the other. Then energy goes over from places of higher inten- sity to those of lower intensity whereby it is sometimes trans- formed into other forms of energy; to what extent such a transformation takes place depends on the nature of the system, which inasmuch as it effects a transformation of energy is called a machine. In the above supposed case of unbalanced energy the neces- sary change of state of the system can take place in various ways. A lifted stone, for instance, can fall vertically to the earth or can slide down an inclined plane. It will select, in fact, the way along which it attains in the same length of time the greatest possible kinetic energy. The generalization of this principle is: Of all possible transformations of energy the one will take place that will produce in a given time the largest transfer of energy from the original form to some other. 2. Heat was the first form of energy to be recognized as an independent quantity. In connection with this form of energy two important laws were formulated, which laws also hold for all the other forms of energy : (a) Thermodynamic law: Heat can be transformed into mechanical work and other forms of energy and vice versa. This transformation takes place according to certain definite 20 HEAT ENERGY AND FUELS laws. This law is based upon the fact that energy cannot be made nor destroyed, but only transformed from one form into another. Clausius has formulated this same law as follows: the energy of the universe is constant. (b) Thermodynamic law: Heat cannot go of its own accord from a colder to a warmer body. Applying this law to all forms of energy we can say: If two bodies are in equilibrium with a third with respect to certain forms of energy, they are also in equilibrium with each other as regards the same forms of energy. If we add to a body the heat dQ at the absolute temperature T, we have / ^=0 (= for reversible, < for non-reversible processes). The second law has, furthermore, another important meaning. In a reversible process, carried out between very narrow limits of temperature (between T and T + dt), the heat quantity added to the system being Q, the infinitely small part of this added heat can be transformed into work or other forms of energy. This is a law of special importance in the study of energy. As, according to above explanation, we have for reversible processes / = 0, must be the total differential *J 1 1 of a quantity which just as the energy depends only on the state of the body, but not on the way by which this state was reached. Clausius calls this quantity "entropy," and it is generally denoted by s, and by introducing this quantity into the second principle we get dQ = T ds. Like all other forms of energy the heat can be decomposed into two factors, one of intensity and the other of capacity. The former is the temperature, while the latter, according to circumstances, is represented by the entropy or heat-capacity. FORMS OF ENERGY 21 The general equation of energy being E = ci, and the total differential dE = c di + idc we have for a constant c (dc = 0) ; dE j. c, di and for constant i (di = 0) For the heat we have i = T. If we add to a substance the heat quantity dQ, so that no other form of energy is generated (with- out being considered) and if we determine the relation between the heat added and the increase of temperature effected thereby, we have dE = c dt, wherein c stands for the heat capacity of the substance. In melting and evaporation and solidifying or condensation respectively, and also in many chemical processes taking place at constant temperature we have dE = dcT or analogous to the former equation dE = dsT. The total values of the entropy being unknown we have to transform these equations by referring them to two states marked by index 1 and 2 : (s, - s 2 ) dT = (c, - c a ) di. We have, for instance, assuming equilibrium between heat and volume-energy, (! - s 2 ) dT = (^ - v 2 ) dp, or, s l s 2 dp v, -v^df' 22 HEAT ENERGY AND FUELS If we indicate the latent heat of the process referred to (chemical reaction, etc.) by I we have I and therefore which expression is correct for all changes of the state of aggre- gation and all chemical changes of state, that are connected with a change of volume. We can transform it into 7 /7T 7 = (v l - v 2 ) dp (Clapeyron's equation). 4. As coefficient of capacity of chemical energy the gram- atom of the elements or the gram-molecule is generally used, while as coefficient of intensity the " chemical potential " or simply " potential " is used (J. Willard Gibbs). For the latter quantity we have, according to the general energy-equation, dE % = dc The individual values of the quantities of chemical intensity being unknown, we can only consider their sum as appearing in equations of chemical reactions. If, for instance, E l and E 2 represent the total chemical energy-content of a system in the beginning and end state respectively, q being the energy gen- erated (liberated) in going from 1 to 2, we have If we divide now both sides of the equation by the capacity c of the system (c remaining constant in the processes under consideration) we get fi.fiys, c c c or, i, = i 2 + - - FORMS OF ENERGY 23 As the capacity c is always a positive quantity we have, if q = - ^ = i 2 ; i t > i 2 if q > and ^ < i 2 if q < 0. Thence chemical equilibrium can only take place if the inten- sities of the forms of chemical energy before and after the transformation are equal; otherwise if this is possible such a transformation will take place that the intensity decreases (and on account of the equality of the capacities the total chemical energy of the system will also decrease). If instead of one single chemical substance, as in the case above, there are several, it must be remembered that to every one of them there corresponds a certain quantity of chemical energy and also of intensity, so that we can write an energy- equation for every substance. If we go back to the ele- ments, i.e., to the individual kinds of atoms present, and mark their number before and after the transformation with n/, n 2 , n 3 ' . . . and n/', n 2 ", n a ", . . . , respectively, their energy content with #/, E 2 ', E 3 ', . . . , #/', EJ',EJ f t and the energy of reaction connected with the transformation with q', q" ', q'", we have, for every kind of atom, H 2 O 58294 6 CO + } O 2 > CO 2 C + O 2 CO C + O 2 -> C0 2 N 2 + O 2 -> 2 NO 2 CO > CO 2 + C 68182.4 28674.5 96856.9 43000.0 39507.9 CO 2 + H 2 > CO + H 2 O - 9887 8 C + H,O > CO + H 2 29620 1 C + 2 H 2 O - CO 2 + 2 H 2 -19732.3 As the direction of chemical reactions is not independent of the temperature, the chemical changes of state do not neces- sarily depend upon the chemical energy alone, but also upon other forms of energy. When considering a measure of chem- ical affinity the chemical energy alone is not sufficient, and we have to use, therefore, the change of the free energy of the system, in which the quantity q appears as independent of the temperature (chemical energy). We have seen above that chemical equilibrium can only take place if the intensity of the chemical energy before the change equals the intensity after the change. Otherwise such a change of state should take place that the intensity of this energy in the system decreases. If, notwithstanding, this transformation does not occur, the reason for this can only be looked for in the compensating effect of other forms of energy. This is of the FORMS OF ENERGY . 27 greatest importance, as is shown by Ostwald in the following explanation : "In chemical energy the possibility of compensating differ- ences of intensity is apparently very general, as can be seen from the fact, that in many cases it can be preserved without loss, practically speaking, for an indefinite length of time. The possibility of using chemical energy (i.e., of transforming it into other forms) is necessarily connected with the pres- ence of differences of chemical intensities, which can be kept up (i.e., compensated) as long as desired. "The forms of compensating energy can only in rare cases be observed. This is the reason why we know so little about the presence of a function of chemical intensity. We see that in spite of the possibility of transformation of the chemical energy into other forms, for instance, in a mixture of oxygen and hydrogen, no such transformation takes place as long as the temperature remains below a certain point. In such cases we speak of a 'passive resistance.' We can explain these phenomena by supposing that a compensation of the differences of chemical intensity, by other forms of energy, actually takes place, and that between the stage of oxy hydrogen-gas and of water at low temperatures intermediate stages are contained, which for the transformation (the other energy-quantities remaining constant) would at first effect an increase of the intensity factor; afterwards a very considerable decrease of the same, corresponding to the state of water, would take place. Such states are called metastabile." 3. Electric Energy. The magnitude of intensity of electric energy is called electromotive force, or potential difference. While, however, the intensity of heat, the temperature, is counted from an absolute zero point, being therefore always positive, no such point has been found for electric potential. It is therefore necessary to use an arbitrary zero-point whereby positive and negative potential-values are obtained. The quantity of electricity is used as a factor of capacity. If we denote the same with E v the potential with n and the electrical energy with E e , we have E E Hi = y 71 or, E e = En. 28 HEAT ENERGY AND FUELS For the quantities of electricity the law of conservation can be expressed as follows: The total quantity of electricity is con- stant, and equal quantities of positive and negative electric energy are always present. If two quantities of electricity, + E and E, concentrated in mathematical points at a distance r from each other, act upon each other, the potential difference being TT, they exert upon each other a force /, which is given by the equation 3 k' E ^- f- -* K depends on the nature of the medium between the two electric quantities, and is called its dielectric constant. If we call the distance traversed by the two electric quantities under the influence of this force dr, we have for the electric energy and therefore for a change of the distance from r' to r, If we make r' = & , we have E-E -**', r If E l and E 2 are both positive or both negative, we see that is positive, i.e., the electric energy increases with the decreasing distance, or: the two electric quantities of like sign repel each other. If, however, E 1 is positive and E 2 negative, 77"E1 ~p or vice versa, - becomes negative; electric quantities of unlike signs attract each other. FORMS OF ENERGY 29 If we have two infinitely large quantities of electricity of opposite sign stored in reservoirs having a potential difference TT, and we connect these two electricity reservoirs by means of a conductor, electric energy will flow from both into the con- ductor in the same way that heat-energy passes to a cold body. Thereby the two electric quantities neutralize each other in the conductor, the electric energy being transformed into heat. This shows how the electric current is produced. If the two quantities of electricity are not infinitely large the generation of a uniform electric current (i.e. the preserva- tion of the same potential-difference between two cross sections of the conductor) will only be possible if the electric energy consumed in the conductor in the time-unit is constantly replaced at the source of the electric current. If we refer this process to the time-unit, calling the ratio of quantity of elec- tricity to time - = ij intensity of current, this intensity of current must be proportional to the potential difference n and furthermore be dependent on a coefficient, the quantity of which is determined by the quality of the conductor. This coefficient is the conductance Z; its reciprocal value r = - is L called the resistance of the conductor. We thereby arrive at Ohm's law : i = ln 7T r We have seen above that in the conductor free electricity is neutralized, or electric energy is converted into heat. If the potential difference across the ends of the conductor is n and if no other energy except heat is generated, we will have, if we call the heat quantity formed from electric energy " W," W = Qx. W Considering also the time -- = q, t QTT we have q = . 30 HEAT ENERGY AND FUELS As = i (intensity) and as according to Ohm's law TT = rr, I/ we can write q = i 2 r y i.e., the rate at which heat is generated in a conductor is pro- portional to the resistance and to the square of the intensity. This is Joule's law. Another important law of electrochemistry is Faraday's: All motions of electricity in electrolytes take place only with simultaneous motion of ions, so that with equal quantities of electricity chemically equivalent quantities of the various ions are moved. This law is correct for every kind of electricity- movement in conductors of the second class. Of special interest for us is the transformation of chemical into electrical energy as we find it in galvanic batteries. It was thought at first that herein the chemical energy is per- fectly transformed into electricity. This, however, is not correct. In general we can express these conditions by the equation : wherein E e means electrical energy, E c chemical energy, Q the quantity of electricity transferred in the electrolyte, - the poten- tial difference and T the absolute temperature. The radiant energy is the least known of any form of energy. Ostwald says in regard to the energy of radiation : " The law of the conservation of energy shows a discrepancy, as we know some phenomena in which energy present dis- appears beyond the power of our senses and means of obser- vation. It does not, however, disappear absolutely, as we can get back a quantity of energy equal to the amount lost. But in all these cases it can be proved that a certain (generally very little) time has elapsed during which the energy has left one part of the system under observation, but has not yet appeared in the other part. From the fact that the energy reappears after a certain time, we make the conclusion by analogy that it existed during this interval in a different form; as long as it was present in this form, it was imperceptible to FORMS OF ENERGY 31 us until after its retransformation into one of the forms of energy that we can perceive with our senses." This form, in which the energy has no connection with, and no relation to our senses, is called radiant energy or energy of radiation. By the regular relation between the disappearance of energy from one place and its reappearance at another place, we conclude that energy, if transformed into radiant form, travels through the space with a velocity of 3 X 10 10 cm. per second. This is called the velocity of transmission of light (ray) ; it is correct, however, for radiating energy in general, from which light may originate. Electric energy is easily changed into radiant energy, which travels at the same speed, as energy originated from heat and chemical energy, which is generally called light. Based upon W. Weber's work Maxwell found, by comparing the formula for the electro-dynamic effect (long distance) and for the motion of light, that the principal con- stants 4 are identical, and Hertz lately demonstrated by means of experiments that the periodical motions of radiant energy, through space, generated by rapid electric oscillations, are governed by the same law as the optical motions. To infer, therefore, as is done generally at present, that light is an electromagnetic phenomenon, is as incorrect as if one should conclude, from the fact that burning phosphorus emits light, that the light is a chemical phenomenon. We have, in all these cases, transformations of other forms of energy into radiant energy, that follow their own laws and can be recon- verted by proper means into every other form of energy. Radiant energy can, as the other forms of energy, be pro- duced from other forms of energy or changed into the same. Its relation to mechanical energy is the least known. It cannot be said with certainty at present whether direct change of the latter into radiant energy takes place at all. I was not able to find a single positive proof of this transformation. This is the cause of the fact that the mechanical energy, which acts in the movement of the stellar bodies, remains essentially unchanged, while the other formations which contain other kinds of energy, that are more easily transformed into radiation, do not show such a constancy. The transformation from radiant into me- chanical energy has also not been proved beyond doubt ; possibly such a transformation takes place in Crooke's radiometer. 32 HEAT ENERGY AND FUELS Theoretically we should expect in every substance that yields radiant energy, a mechanical counter effect in the form of a pres- sure which works contrary to the direction of the radiation. On the other hand a pressure in the direction of the radiation corresponds to every absorption of radiant energy. This pres- sure is equal to the radiant energy contained in unit volume. At the very great velocity of the radiation this amount is gen- erally very small. Contrary to mechanical energy thermic energy is very easily transformed into radiation. This change is so frequent and so regular that the thermic energy is often called u radiating heat. 7 ' This name is as misleading as the definition of heat as a kind of motion; for the heat after transformation into radiant energy is not heat, just the same as mechanical energy, after transformation into heat, has ceased to exist as mechanical energy; in the new state the energy follows new laws and cannot be called by the old name. * The change of heat into radiant energy cannot be followed up in an absolute manner, since we have no means of measuring the radiant energy itself, being forced to convert the same into another form of energy; we have to reconvert it in this case into heat by placing in front of the radiant bodies, bodies absorbing the rays and transforming them into measurable heat. In other words the receiver has to be as sensitive a thermometer as possible. The receiver has to contain a certain heat of certain temperature, and must therefore also radiate, and the heat-quantity, which is perceptible on account of the absorbed radiation, is the difference between the latter and the emitted heat. VOLUME I. THE CHEMICAL TECHNOLOGY OF HEAT AND FUELS. VOLUME I. THE CHEMICAL TECHNOLOGY OF HEAT AND FUELS. THE chemical technology of heat treats of the methods used in the industries for the transformation of chemical energy into heat. This transformation generally takes place by means of a chemical process called combustion, which in all commercial processes used up to the present time consists of oxidation. The oxygen required is taken either from the atmosphere or from oxides, the latter being thereby reduced. Lately experiments that look very promising have been made to produce pure oxygen on a large scale or to increase the oxygen content of the air for obtaining an increased effect in the combustion. The materials which are used commercially for generating heat are called fuels. They are either used as they occur in nature (natural fuels) or are made to undergo certain changes before being used (artificial fuels). The object of combustion, as above stated, is the trans- formation of chemical energy into heat. It will therefore be necessary to become acquainted with the methods of measur- ing the generated heat and also with the methods that enable us to determine the energy-content of the fuels. Primarily, we are concerned with the measurement of the intensity factors of heat energy, i.e. the temperature, since the capacity-factors (the specific heats) are generally known, and hence do not have to be determined in every case. Second in order comes the experimental determination of the calorific value. These determinations are of two kinds, depend- ing on whether the quantity of heat yielded by the combustion of a certain quantity of fuel is to be determined, or whether the highest temperature that can be reached theoretically by combustion, is to be ascertained. Finally it will be necessary to study in detail the process of combustion. 35 36 HEAT ENERGY AND FUELS All these points are considered in Part I of this work. Part II contains the science of firing, i.e. all the processes that favor the utilization of the combustion heat, or reduce the unavoid- able heat losses, and also the discussion of the different methods of industrial firing. Part III is added as an appendix, treating of the various chemical methods of heat abstraction (refrigeration). PAET I. HEAT MEASUREMENT, COMBUSTION AND FUELS. CHAPTER I. THE MEASUREMENT OF HIGH TEMPERATURES (PYROMETRY). THE measurement of temperature is of the utmost importance in the industries, because on the one hand certain processes and reactions take place only within certain limits of temperature, and on the other hand an increase of temperature above a certain value means an increase of heat loss and a waste of fuel. Instruments for measuring temperature are generally called thermometers; thermometers used for measuring high temper- atures, however, are called pyrometers. Widely different prop- erties of certain substances which vary with temperature have been used or proposed for the measurement of tempera- ture: Change of length and volume of various substances, variation in the pressure of gases and vapors, melting points of different substances, heat given up by hot substances in cool- ing, color of emitted light, change of electric resistance and thermoelectric behavior, heat-conductivity, etc. We are going to describe below the most important instru- ments of this kind : 1. Ordinary thermometers, in which the apparent expansion of a liquid (generally mercury, at low temperatures, alcohol) in a containing glass vessel, is measured. Since the ordinary thermometers can be used only up to the vicinity of the boiling point of mercury (358 C. at atmospheric pressure), tempera- tures up to about 500 C. require instruments that contain a quantity of hydrogen or nitrogen above the mercury, instead of a vacuum. When used they have to be heated up slowly, i.e. gradually inserted into the medium or space, the temperature of which is to be measured. 37 /*&' 3*^ f OF THE " f UNIVERSITY i 38 HEAT ENERGY AND FUELS For exact measurements of temperature the following errors have to be considered : 1. Reading error. 2. Graduation error. 3. Error due to pressure (inside or outside). 4. Error due to meniscus. 5. Erroneous determination of the fixed points. 6. Error due to time lag of thermometer. 7. Error due to glass-expansion. We want to consider, in a few words, the most important of these sources of error. To obtain correct readings the visual ray has to be perpen- dicular to the graduation. For exact measurements of temperature it is a disagreeable fact that thermometers, after some time, show incorrect read- ings, the freezing point being apparently moved upwards, and returning to the original position only after being heated to high temperatures for several months. This phenomenon is called depression. This depression is in close relation to the composition of the glass : TABLE II. DEPRESSION FOR VARIOUS COMPOSITIONS OF GLASS. Depres- sion. SiO 2 A1 2 O 3 CaO MgO PbO K,O Na 2 O Degree 0. 0.08 0.09 09 50.83 72.04 65.42 69.04 1.04 2.42 0.93 0.89 0.52 8.20 13.67 12.21 27.98 11.08 1.63 19.46 18 52 15.32 0.10 56.74 0.66 0.18 29.86 12.48 11 65 00 2 04 13 58 19 51 07 0.12 0.15 0.20 0.24 72.09 69.52 64.48 70.29 1.45 3.86 1.48 2.29 11.20 9.13 5.68 9.55 0.12 0.71 12.71 1.88 3.07 3.55 14.51 13.41 13.77 12.81 2 48 31 75 65 1 34 6 11 5 68 11 50 35 74 72 1 35 9 10 5 86 9 03 0.36 0.37 0.40 0.40 0.48 61 66.42 66.55 63.47 60.56 68.30 70.29 3.35 1.31 1.77 1.14 1.28 2.49 10.70 13.37 10.10 10.21 10.41 8.68 30 14.55 15.50 12.24 3.52 8.27 12 06 4.57 3.07 11.95 24.45 12.08 5 38 0.66 72.44 1.60 9.23 11.29 6.00 THE MEASUREMENT OF HIGH TEMPERATURES 39 TABLE III. DEPRESSION FOUND BY WIEBE. Depres- sion. Si0 2 Fe 2 3 A1 3 3 CaO MgO Mn 2 O 3 As,0 3 K 2 O Na 2 O _ 0.04 0.15 64.45 64.66 0.53 .81 0.24 12.36 13.38 0.22 0.27 Trace Trace PhO 0.89 0.87 20.09 18.89 0.86 1.48 0.15 0.38 0.38 0.40 0.44 0.65 07 49.49 64.49 68.62 69.58 66.53 66.74 70 0.61 0.53 0.46 0.43 0.30 .35 0.42 2.37 2.09 2.18 0.21 1.20 11.56 7.36 7.90 9.44 8.68 16.5 0.67 0.38 0.36 0.30 0.21 0.22 33.90 Mn 9 O 3 0."77 0.34 Trace Trace 0.08 0.35 Trace 0.27 0.74 12.26 17.14 3.56 3.97 3.95 10.57 13 5 1.54 3.75 16.89 15.35 16.15 12.72 07 70 15.0 15 1 05 66 6 14 14 Other tests made by Abbe and Schott also proved that lead- potassium glass, potassium-lime glass or sodium-lime glass show the lowest depression, which, however, increases if potassium and sodium are present in a glass simultaneously. According to these observations a standard-thermometer glass of the following composition is manufactured by Schott & Genossen in Jena : Silicic acid 67 per cent Boracic acid 2 per cent Alumina 2.5 per cent Lime 7 per cent Oxide of zinc 7 per cent Soda (caustic) 14.5 per cent This glass, after previously being heated to 100 C. shows a transient fall of the zero-mark of only 0.05 to 0.06 C. The correction of the thermometer-reading on account of the meniscus is made by means of the equation :* T = t + 0.000148 n(t - t'), wherein T means corrected temperature. t means observed temperature. if means average temperature of the meniscus. n means length of the meniscus in thermometer- degrees. * (See also the following table of Thorpe.) 40 HEAT ENERGY AND FUELS 3 8 PQ a B C Difference: 0.6 A1 2 O 3 , 6 SiO 2 . 26 0.3 0.7 7.2 72 ) 27 0.3 0.7 20 200 28 1 10 29 1 8 30 1 6 31 1 5 32 4 33 3 34 2.5 35 2.0 36 1.5 38 1.0 Cramer has made melting cones for measuring lower tem- peratures in the brick industry. They can be bought in two sizes (6 and 10 cm. high) from the Royal Porcelain Factory in Charlottenburg or from the Chemical Laboratory for Clay Industry, Berlin, N. W., Kreuz str. 6. 58 HEAT ENERGY AND FUELS TABLE XI. COMPOSITION OF PYROSCOPES FOR LOW TEMPERATURES. Molecules. Nr K 2 O CaO PbO A1 2 3 Fe 2 3 Si0 2 BA 01 02 03 04 05 0.3 0.3 0.3 0.3 0.3 0.7 0.7 0.7 0.7 0.7 0.3 0.3 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0.2 3.95 3.90 3.85 3.80 3.75 0.05 0.10 0.15 0.20 0.25 06 3 7 3 2 3 70 30 07 08 09 010 Oil 012 013 014 0.3 0.3 0.3 0.3 Na 2 0.5 0.5 0.5 5 0.7 0.7 7 0.7 0.5 0.5 0.5 5 0.3 0.3 0.3 0.3 0.8 0.75 0.70 65 0.2 0.2 0.2 :":: 3.65 3.60 3.55 3.5 3.6 3.5 3.4 3 3 0.35 0.40 0.45 0.5 1.0 1.0 1.0 1 015 5 5 60 3 2 1 016 017 018 019 020 021 022 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.55 0.50 0.40 0.30 0.20 0.10 3.1 3.0 2.8 2.6 2.4 2.2 2.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 C. Bischof, who thoroughly investigated these pyroscopes, found even the highest melting point far below that of melting platinum. The melting points of Nos. 13, 14, 15 and even 17 are only slightly above that of melting palladium (1500 C.); furthermore these pyroscopes show various irregularities among themselves. However, notwithstanding these defects the Central Association of German Manufacturers recommended the official adoption of the Seger-cones, March 28, 1904. The table on following page contains some new data relative to the melting temperatures of all these cones (measured with Le Chatelier pyrometer). Only the following of these melting points are correctly determined: Nr. 022 melts at dark red glow, Nr. 010 at the melting point of silver, Nr. 1 near the melting point of an alloy containing 90 per cent gold and 10 per cent platinum, Nr. 10 at PYROMETRY 59 the point where felspar begins to soften, and Nr. 36 at about the melting point of platinum. The other temperatures are only approximate. TABLE XII. MELTING POINTS OF PYROSCOPES. Nr. Deg. Cent. Nr. Deg. Cent. N, Deg. Cent. 022 590 02 1110 19 1510 021 620 01 1130 20 1530 020 650 1 1150 21 1550 019 680 2 1170 22 1570 018 710 3 1190 23 1590 017 740 4 1210 24 1610 016 770 5 1230 25 1630 015 800 6 1250 26 1650 014 830 7 1270 27 1670 013 860 O 1290 28 1690 012 890 9 1310 29 1710 Oil 920 10 1330 30 1730 010 950 11 1350 31 1750 09 970 12 1370 32 1770 08 990 13 1390 33 1790 07 1010 14 1410 34 1810 06 1030 15 1430 35 1830 05 1050 16 1450 36 1850 04 1070 17 1470 38 1890 03. 1090 18 1490 | ! 7. Color imetric pyrometers. With these instruments the temperature is derived from the quantity of heat that is given off by a heated body when cooling off in the calorimeter. This method was strongly recommended by Pouillet, Regnault, Carnelley, Violle and others, and introduced into industrial practice by Weinhold, Fiodier and others. In order to reduce the radiation heat losses from the calo- rimeter to a minimum, the instrument is so designed that it becomes only slightly heated. In an apparatus to be used for scientific purposes the temperature rise of the calorimeter is measured by a mercury thermometer comprising 2 degrees and divided into T ^ degrees. At first an iron cylinder was used as the thermometric sub- stance, i.e., the substance which gives off the heat to be measured in the calorimeter. The use of iron, however, proved to be 60 HEAT ENERGY AXD FUELS unsatisfactory on account of its easy oxidation and of its non- uniform cooling. If we take the heat given off and the tem- perature as co-ordinates, we obtain a curve with two points of inflexion, corresponding to the allotropic change of state of the iron. This shows that the temperatures calculated could not be correct. This is the reason why platinum substances and a mercury- thermometer divided in T 7 degrees are used in laboratories, and in the industries a nickel-cylinder (the heating of this metal is very regular) and a mercury-thermometer divided in T V degrees whose scale, therefore, can be larger. A rise of about 50 C. in the calorimeter-temperature is sufficiently exact for practical purposes. The nickel-cylinder is put into a small pipe of fire-proof material, fitted with a removable iron handle. After the pipe with the cylinder has been in the furnace whose temperature is to . be measured for fifteen minutes, one can be sure that equilibrium of temperature has been established. The pipe is now taken out of the furnace, emptied into the calorimeter, the calorimeter-water stirred and the increase of temperature read and recorded. The following tests made by the Compagnie Parisienne du Gaze show the regularity of the heating law for nickel : tCJ = 50.5 63.5 89.5 103 117.5 134 150 166 t = 400 500 700 800 900 1000 1100 1200 We give below a few melting temperatures determined by Violle and also by Holborn and Day. TABLE XIII. MELTING POINTS OF METALS. Metal. Violle. Holburn arid Day. Silver Degrees 954 Degrees 961 5 Gold 1045 1064 Copper 1055 1065 Palladium 1500 1500 Platinum . . 1779 1780 PYROMETRY 61 Below we describe a few pyro-calorimeters that were con- structed for practical use. The latest type of Weinhold's pyrometer for determining high temperatures is illustrated in Fig. 7. The calorimeter- vessel proper CC is made of thin sheet brass. It holds about 1 Kg of water, is cylindrical at the bottom and conical at FIG. 7. WeinhokTs Pyrometer. the top. The ratio of the height to the diameter is so chosen as to make the surface as small as possible, in order to reduce to a minimum the loss or gain of heat by radiation or conduc- tion. A cylindrical vessel of tin-plate BE with a loose conical cover DD surrounds the calorimeter- vessel, which is carried by three cork-pieces, cemented into BB, and so arranged as to maintain a space of 1 cm. between the walls of the containing vessel and the calorimeter. BB is fastened in a wooden box HH. As wood and still air are very poor conductors of heat, and as bright sheet metal prevents radiation of heat, by this method an excellent heat-insulation is effected. The center 62 HEAT ENERGY AND FUELS one of the three cylindrical openings in the calorimeter- vessel serves for introducing -the metal ball, which is bored through in three directions perpendicular to each other. The thermometer T is inserted through a cork in the shortest neck. The shaft of the circulating device R is inserted through the narrow neck. This device (Fig. 8) consists of an impeller with six inclined paddles which move in a slim brass tube, open at the top and the bottom. Its shaft is rectangular at the top, FIG. 8. Circulating Device (for 7). FIG. 9. Brass Wire Basket. so that the pulley S can be attached. By means of a cord passing over three guide-pulleys and a crank wheel, attached to the outside of the wooden box, R can be rapidly rotated. The lively circulation of water caused thereby facilitates the equalization of the temperature in the calorimeter. The thermometer T is provided with a scale divided in 0.1 degrees, on which, however, 0.01 degrees can be estimated. The thin cylindrical mercury-reservoir of the thermometer (50 to 60 mm.'s long) extends nearly the entire height of the calorimeter. The hot metal ball is kept in the brass- wire basket (Fig. 9). Its cover can be turned around a hinge, and is provided with a pin attached rectangularly downward. If the basket with PYROMETRY 63 the cover open is let down into the neck of the calorimeter, the cover and also the basket remain hanging upon the edge of the neck. If now the ball is allowed to fall through the neck, it hits the pin and thereby closes the cover. This causes the basket with the ball to fall upon the bottom of the calorimeter, so that finally the cover almost touches the surface of the water, which, before putting in the basket and the ball, should reach to the lower edge of the neck. To assure the right amount of water in the calorimeter, a pipette is used, which is fastened to a disk of metal, wood, or cork, so that its lower end is exactly flush with the entry of the neck to the calorimeter. At first water is put in until it stands a few millimeters high in the neck, then the disk of the pipette is laid upon the edge of the neck and the excess water sucked out. By throwing the hot ball into the calorimeter not only the water contained in the latter but also the calorimeter-vessel is heated up. To determine the quantity of heat absorbed by the instrument, the quantity of heat absorbed by the vessel has also to be considered. This is done by ascertaining the quantity of water that would be necessary to absorb the same quantity of heat as the calorimeter, i.e., by determining the water- value of the calorimeter. For this purpose the brass calorimeter-vessel, together with the stirring arrangement and the basket K (but without the pulley S and thermometer T with cork) is weighed in a dry state. The weight found, multiplied by the specific heat of brass (0.095) , gives the water- value of the empty calorimeter. The water-value of the thermometer is difficult to find, but can be neglected on account of the small quantity involved. After inserting the thermometer with the cork the apparatus is weighed a second time, and finally after putting in the cooling water it is weighed for the third time. The difference of the second and third weight gives the water content of the calorimeter. The water-value of the filled calorimeter is the sum of this water content and the water-value of the empty calorimeter. If, for instance, the empty calorimeter without thermometer weighs 210 g., with thermometer 236 g., with water 1240 g., we have: Water value of the empty calorimeter = 210 X 0.095 = 19.95 g. Water content of the calorimeter =1240- 236 = 1004.00 g. Water value of the filled calorimeter = 1004 + 19.95 = 1023.95 g. 64 HEAT ENERGY AND FUELS The water-value of the empty calorimeter is more conveniently determined by putting into the instrument a weighed quantity of water, then throwing in a test ball of a certain temperature (for instance 100 C.) and measuring the increase of temperature. If we divide the heat given off by the ball by the increase of tem- perature and deduct therefrom the weight of the calorimeter, we obtain the water-value of the dry instrument. The balls used weigh from 60 to 80 g. For introducing them into the space, the temperature of which is to be measured, a pair of tongs made of heavy iron wire or bar iron, provided with cup-shaped jaws, is used (Fig. 10) , or a spoon with cover, and fitted FIG. 10. Tongue. FIG. 11. Spoon. with a long handle (Fig. 11). The weight of the ball has to be determined before use. If the balls are of the size mentioned it is sufficiently accurate to weigh to the nearest decigrams. When using, the calorimeter is filled with fresh water, the wire basket put in, and immediately before inserting the ball - the circulation device is started, and kept in motion until the thermometer shows a constant temperature, which is read and recorded (initial temperature of the calorimeter). When intro- ducing the ball, care has to be taken not to injure the thermometer and the driving cord of the circulation device. Directly after throwing in the ball, the circulation device is worked until the thermometer becomes stationary when the temperature (final temperature) is read and recorded. The difference between initial and final temperature multiplied by the water-value of the filled calorimeter expressed in kilo- grams gives the heat-quantity (in calories) transmitted from the ball to the. calorimeter. Therefrom the quantity of heat given off by a 1 Kg. ball is calculated, and by comparing this figure with a table in which the heat (c. t.) is calculated from the specific heat of the metal, the temperature is found. Considerably simpler in construction is the calorimeter of Dr. Ferdinand Fischer (Fig. 12). The cylinder A, which is made of thin copper plate and has a diameter of 500 mm., is suspended PYROMETRY 65 in the wooden base B. The space between both is filled with fibrous asbestos or mineral wool. The apparatus is closed by a thin brass or copper plate, having a large opening d (20 mm. diam.) for the stirrer c and for throwing in the metal cylinder, and a small opening for the thermometer 6, which is a normal thermometer built by Geissler in Bonn. It has a very small mercury reservoir; its scale has a range of from to 50 C., and is divided into 0.1 degrees, so that 0.01 degrees can easily be estimated ; a strap a of thin cop- per plate protects it from being FIG. 12. Fischers Calorimeter. FIG. 13. Siemens Water Pyrometer. broken by the stirrer. The stirrer consists of a round copper disk, soldered to a copper rod. The latter is melted into a glass rod, that serves as handle. If, for instance, the copper vessel weigh 35.905 g., the stirrer without glass rod weigh 6.445 g., then the water-value of the calorimeter is 0.094 (35.905 + 6.445) - 3.98 g., including the thermometer about 4 g. If the calorimeter water weigh 246 g., the water-value of the filled calorimeter is 250 g. 66 HEAT ENERGY AND FUELS For measuring the temperature doubly bored cylinders of plati- num, wrought iron or nickel are used. For the first case, i.e., with platinum cylinders weighing 20 g., such a quantity of water is put in that the total water- value amounts to about 125 g., with the two other metals to twice that amount. In a manner similar to that given above the cylinders are exposed in the medium the temperature of which is to be measured and thrown into the calorimeter through the cover opening d. The cylinder falls upon the disk of the stirrer, and now by raising and lowering the latter a uniform heating of the calorimeter-water is effected, so that at the end of about one minute the thermometer reaches the final temperature. No corrections are made for evaporation of water or heat transmission by radiation or conductivity, as the evaporation is extremely small and the insulation of the calorimeter perfect. If the calorimeter-water reaches a temperature of about 40 de- grees it has to be changed. The calculation of the temperature is made as in the former case. TABLE XIV. HEAT CAPACITIES OF PLATINUM, ETC. I kit iuu in Iron. Nickel. tc. According to Violle. Post. Pion- chon. Eu- chenne. Calculated from the Average Specific Pion- chon. Eu- chnne. Heat. cal. cal. cal. cal. cal. cal. cal. 100 3.23 10.8 11.0 11.0 10.8 11.0 12.0 200 6.58 22.0 22.5 23.0 21.5 22.5 24.0 300 9.75 35.0 36.5 37.0 32.5 42.0 37.0 400 13.64 39.5 41.5 42.0 43.0 52.0 50.0 500 17.35 67.5 68.6 69.5 54.0 65.5 63.5 600 21.18 86.0 87.5 84.0 65.0 78.5 75.0 700 25.13 108.0 111.5 106.0 76.0 92.5 90.0 800 29.20 132.0 137.0 131.0 87.0 107.0 103.0 900 33.39 157.0 157.5 151.5 98.0 123.0 117.5 1000 37.7 187.5 179.0 173.0 109.0 138.5 134.0 1100 42.13 150.0 1200 46.65 166.0 1300 51.35 1400 56.14 1500 61.05 1600 66.08 1700 71.23 1800 76.50 PYROMETRY 67 One of the simplest and oldest but also most widely used instru- ments is the water-pyrometer of C. H. Siemens (Fig. 13). It con- sists of a copper vessel A holding 568 cu. cm. of water. In order to reduce the loss by radiation it is surrounded by two vessels, one being filled with felt, the other being empty. The mercury thermometer is protected by a perforated metal-shell and has besides the ordinary scale a movable brass scale c (similar to a vernier), that gives the temperature directly without calculation. After filling the calorimeter with water the zero mark of the pyrometer-scale is set upon the temperature of water, as shown by the mercury thermometer. A hollow copper cylinder of a certain heat-capacity is now exposed in the medium, the tem- perature of which is to be measured, and after remaining there 10 to 15 minutes is thrown into the calorimeter- water. The temperature required is obtained by adding to the tem- perature read off the pyrometer-scale c, the temperature of the calorimeter- water. The manipulation of this instrument is there- fore extremely simple, naturally at the expense of accuracy. For calculating the temperatures the following data of the heat capacities of platinum, iron and nickel from degrees to t degrees can be used. CHAPTER III. PYROMETRY (Conclusion). OPTICAL METHODS OF MEASURING TEMPERATURES. THE instruments used for this purpose are based upon the relation between temperature and emission of light from heated substances. (a) If a substance is gradually heated up, it starts at a certain temperature to emanate light-rays, the brightness of the latter increasing with the temperature. The color of the emanated light changes in a definite manner with the temperature. In many industries, after some practice, the approximate tempera- ture of a furnace can be estimated with the naked eye without any instruments, from the brightness of the glowing walls and the heated substances. The oldest data relative to the temperature of these so-called glow-colors were given by Pouillet. The temperatures of the glow-colors have been determined by means of a Le Chatelier-Pyrometer, by Maunsel White and F. W. Taylor, and by Howe. The table on following page contains the results of these investigations. The extreme rays of the spectrum show plainly the changes of brightness and color; but the yellow rays in the center, on account of their brightness, cover up all the others. The experi- ment was therefore tried of absorbing the latter by means of blue cobalt-glass. A glowing substance, viewed with such a glass, appears at relatively low temperature very red, and at high temperature strongly blue; thence with this method more reliable results are obtained than with the naked eye. (6) The optical pyrometer of Mesure and Nouel (Figs. 14, 15) can be obtained from E. Ducretet in Paris. The direct observation of the glow-colors is rather difficult since it depends on individual qualification and momentary dis- position. The eye can never determine the color shades with PYROMETRY absolute exactness, being only able to estimate by comparison. In a dark furnace-room the dark red of a melting metal can easily be taken as bright red, and vice versa in a light room, so FIGS. 14 and 15. Lunette Pyrome'trique (Pyroscope). that the result of such observation varies according to observer, light and time of observation. TABLE XV. TEMPERATURES CORRESPONDING TO GLOW COLORS. Pouillet. Howe. White and Taylo r. Heat Color. Deg. Cent. Heat Color. Deg. Cent. Heat Color. Deg. Cent. Beginning glow . Dark red glow . . Beginning cherry red. Cherry red Bright cherry red. Dark yellow. . . . 525 700 800 900 1000 1100 First trace ( in dark of visible < red ( in daylight ? Dark red < Full cherry red Bright red 470 475 550 to 625 700 850 Dark red Dark cherry . . . Cherry red Bright cherry. . Orange 566 635 746 843 899 Bright yellow. . . 1200 Full yellow < 950 to Bright orange . 941 White glow Bright white. . . . 1300 1400 Bright yellow White glow 1000 1050 1150 Yellow Bright yellow. . White glow. . . . 996 1079 1205 Dazzling white < 1500 to 1600 The object of the pyrometric tube of Mesure and Noue'l is the correction of this defect; it allows the determination of the 70 HEAT ENERGY AND FUELS temperature of a substance by simple observation and enables us to determine more distinctly the shade of the color. The apparatus is based upon the phenomenon of circular polarization and consists mainly of two Nicol-prisms, the polarizer P and the analyzer A. Between these two prisms is arranged a quartz-disk Q, 11 mm. thick, split perpendicularly to the main- axis. At the zero position of the instrument the planes of inci- dence of the two Nicol-prisms are perpendicular to each other. The correctness of the position of the prisms can easily be verified by taking off Af , and removing the quartz-disk. Oppo- site to the eye-piece L at the other end of the tube is the objective G, consisting of a plane-glass or a well-polished diverg- ing glass. The following phenomenon can be observed by looking with this apparatus towards a source of light. After passing through the Nicol-prism P the light is polarized. Without a quartz- plate, i.e. with the second (perpendicular to the first) Nicol- prism following the first, this polarized light would be reflected by the cut surface of the Nicol-prism, and the field of view would appear dark. The quartz-plate, however, causes a turning of the plane of polarization that is proportional (according to Biot's law) to the thickness of the quartz-plate and approximately inversely proportional to the wave length of the ray (light). Thereby certain colors of the spectrum are extinguished by interference, and a mixed color is observed in the apparatus, de- pending on the temperature of the luminous body. By turning the analyzer the mixed color is changed, and whenever the instru- ment is set upon the same color-shade the temperature of the substance under observation can be inferred from the position of the polarizer. For this purpose the analyzer inside the tube is made so that it can be rotated. For measuring the displacement angle the instrument has a fixed mark / and is provided with a scale that can be rotated with the eye-piece and the analyzer. Since the length of the wave of the emitted light varies with the temperature, by slowly turning the analyzer certain colors that are changing with the temperature of the luminous body can be observed. The change from one color to another corresponds to a certain displacement-angle, varying with the temperature of the glowing substance. Hereby we arrive at a position where the color, by the slightest PYROMETRY 71 further rotation, changes quickly from blue to red. Between these two colors is observed a purple-violet shade formed by the most extreme rays of the spectrum; this shade is character- istic for measuring the angle of displacement. (Another shade [lemon-yellow], between green and red, can also be used for this purpose.) The position of hand I on the graduated arc C gives the angle from which the temperature is figured. For determining the scale of temperature Pouillet's data on glow temperatures and the melting point of silver (954 C.) and platinum (1775 C.) according to Violle are used. TABLE XVI. GLOW TEMPERATURE OF SILVER. Heat. Displace- ment. Tempera- ture, Cent. Color: Beginning cherry red Cherry red Degrees. 33 40 Degrees. 800 900 Bright cherry red 46 1000 Orange 52 1100 Yellow 57 1200 Bright yellow Bright white Dazzling white Dazzling white Dazzling white 62 66 69 71-72 73-74 1300 1400 1500 1600 1700 Sunlight : 84 8000 Below are given the results of some measurements with this instrument : TABLE XVII. DATA ON POLARISCOPIC PYROMETERS. (A) Measurements by the Author. Angle. Tempera- ture, Cent. Bessemer steel in the pan Degrees. 59 Degrees. 1260 Open-hearth furnace, empty 61.75 1290 " after charging the above steel " middle of charge " " " towards end of charge 59.5 58.5 63 5 1275 1245 1340 Heating furnace 50.5 1050 HEAT ENERGY AND FUELS (E) Measurements of J. Weiler in the Bessemer converter: Deg. Cent. While blowing . 1330 At the end . . . . 1580 Slag 1580 Steel in pan 1640 Preheated block.. 1200 Block under hammer 1080 Blast furnace for gray iron : Beginning of melting zone 1400 Steel crucible furnace 1600 Brick kiln 1100 Heat colors : red heat 525 Cherry 800 Orange ' 1100 White 1300 Dazzling white. 1500 (C) Measurements of Le Chatelier: Angle. Deg. Cent. Degrees. Sun 84-86 8000 Gas-flame 65-70 1680 Red glowing platinum 40-45 800 To keep out side-light it is of advantage to fasten a protecting tube in front of the objective. For the determination of low temperatures a convergent lens is placed before the instrument. (c) Temperature can also be judged from the proportion of the intensities of two certain kinds of rays (for instance red and green) that are emitted from the heated substance. Table XVIII gives the difference of the emission of red, green and blue rays of different substances compared to a black substance. Crova has constructed a pyrometer based upon these data; however, it requires very great care in manipulation. (d) Analogously the intensity of a single ray of a certain wave length can be used for measuring temperature. One would think, at the first thought, that the intensity depends on the emitting PYROMETRY 73 capacity of the glowing substance, this capacity varying widely as is shown by the above figures. Actually, however, with most substances the variation in the emission is equalized by the capacity of reflection, which varies in the opposite sense. Fur- thermore the capacity of emission of most of the substances used in the industries is not considerable. TABLE XVIII. EMISSIVE POWER OF VARIOUS SUBSTANCES. Deg. Cent. Red. Green. Blue. Magnesia . 1300 10 15 20 Magnesia 1550 0.30 0.35 0.40 Lime 1200 0.05 0.10 0.10 Lime 1700 0.60 0.40 0.60 Oxide of chromium 1200 1 00 1 00 1 00 Oxide of chromium 1700 1 00 1 40 30 Oxide of thorium 1200 50 50 70 Oxide of thorium 1760 60 50 35 Oxide of cerium 1200 8 1 00 1 Oxide of cerium 1700 9 90 85 Welsbach mixture 1200 25 40 1.0 Welsbach mixture 1700 50 80 1.0 The Cornu-Le Chatelier optical pyrometer is based upon this principle (Fig. 16). The instrument takes the form of a tube, through which the glowing substance is viewed. A reflector FIG. 16. Optical Pyrometer (Cornu-Le Chatelier). consisting of a glass-plate with parallel faces throws the image of a small flame into the eye-piece. A red glass in front of the eye-piece cuts off all but certain rays. Absorbing glasses can be put in front of the objective glass, so that only ^ of the 74 HEAT ENERGY AND FUELS incident light is allowed to go through. Between these glasses and the objective a transparent piece of onyx (Fig. 17) is inserted by means of which the light can be reduced at will. The observation is made by reducing the red light of the glowing sub- stance, whose temperature is to be deter- mined, by means of the darkening glasses and the onyx, until it is equal in brightness lamp. The apparatus is calibrated by direct By this method the follow- loo FIG. 17. Piece of Onyx for Reducing the Light. to the standard comparison with an air-pyrometer. ing intensities of light (red rays A = 659) were measured : TABLE XIX. INTENSITIES OF LIGHT. Red -glowing coal (600) .... Melting silver (950) Stearine candle, gas burner Pigeon lamp ... 0.0001 0.015 1 1 1 Melting palladium (1550) Melting platinum Incandescent lamp Arc light 4.8 15 40 10000 Argand burner with glass . . Welsbach burner 1.9 2.05 Sunlight (noon) Melting Fe 2 O 3 (1350).... 90000 2.25 By this method at first a thermo-element was calibrated, by means of which the intensity of emission of black ferric oxide at different temperatures was determined. It was found that the law for the change of intensity of the red rays with the temperature can be expressed by the formula : 3210 T wherein T is the absolute temperature. The following intensities (in candlepower) were obtained for different temperatures : TABLE XX. LIGHT INTENSITIES FOR VARIOUS TEMPERATURES. Intensity. Temperature in Deg. Cent. Intensity. Temperature in Deg. Cent. 0.00008 600 39.0 1800 0.00073 700 60.0 1900 0.0046 800 93.0 2000 0.020 900 1800 3000 0.078 1000 9700 4000 0.24 1100 28000 5000 0.64 1200 56000 6000 1.63 1300 100000 7000 3.35 1400 150000 8000 6.7 1500 224000 9000 12.9 1600 305000 10000 22.4 1700 PYROMETRY 75 As can be seen from this table the intensities increase rapidly. Hence, if in the determination of high temperatures an error of 0.1 candlepower is made in the measurement, the error in the temperature does not amount to more than from 2 to 3 C., which error can be entirely neglected. The flame in the furnace must be avoided during the obser- vation as otherwise incorrect results are obtained. This method is very good for measuring high temperatures, it is less exact, however, for low temperatures. Le Chatelier made the following measurements with this instrument : TABLE XXI. TEMPERATURE DETERMINATIONS (Le Chatelier). Deg. Cent. Open-hearth steel furnace 1490 to 1580 Glass furnace 1375 to 1400 Porcelain furnace 1370 Porcelain furnace, new 1250 Incandescent lamp 1800 Arc light 4100 Sunlight 7600 Blast Furnace. Deg. Cent. At the tuyeres 1930 Pig iron, beginning 1400 Pig iron, end 1520 Bessemer Process. Deg. Cent. Slag 1580 Steel flowing into pan 1640 Reheating of ingot 1200 End of forging 1080 Open-hearth steel: Steel flowing, beginning 1580 Steel flowing, end 1420 Casting into form 1490 Fery has made some changes in this instrument. Wanner's optical pyrometer is based upon the same principle. If we denote the intensity (of light) as /, the length of wave as 76 HEAT ENERGY AND FUELS i X, the absolute temperature as T and two constants as c^ and c 2 , we have, according to Wien : c c * T - J- P AT . "/I 5 As we have no absolute measure for the intensity, we can only compare same with another luminous body; for the latter we have and therefore an equation containing only one constant. This equation is perfectly correct only for absolutely black bodies, but can also be used for measuring temperatures in a furnace on account of the reflection going in all directions in the interior of the furnace. When determining flame temperatures great care has to be taken. If the flame temperature is the same as that of the surrounding furnace- walls, this method can be used as it is; if, however, only glowing gases are present, colored for instance by sodium, correct furnace temperatures are not obtained except when the flame allows the rays used in the measurement to pass unabsorbed. Converter-gases are rather opaque to red (the color used in the Wanner pyrometer), especially so when many solid particles are burning in the flame. Hence too low a temperature will be obtained. In the optical pyrometer the light is decomposed by a straight prism, and by means of a small slit nothing but the light corre- sponding to Frauenhofer's line c is allowed to go through. As, according to above equation, the measurement of temperature is based upon the comparison of two luminous substances, a small electric lamp is used as the standard luminous body. The lamp is attached to the front of the apparatus, and the light enters the instrument by means of a comparing-prism, while the light radiating from the glowing substance, whose temperature is to be measured, enters directly. The two intensities are compared by means of two Nicol-prisms, one of which (the PYROMETRY 77 analyzer) can be turned with the eye-piece. The angle, that can be read from a circular scale, serves as the measure of intensity, while the corresponding temperature is read from a table. If a luminous body is viewed through the apparatus, the field of view appears divided into two halves of unequal brightness. The eye-piece is turned until both parts show the same bright- ness, the angle read and recorded and the temperature found from the table. The entire apparatus, whose optical parts are manufactured by Franz Schmidt and Haenisch in Berlin, is about 30 cm. long, is shaped like a telescope and is easy to handle. Three storage batteries furnish the electricity for the little 6- volt lamp. Since the light-intensity of this lamp depends on the e.m.f. of the storage batteries, it is necessary to adjust the lamp from time to time by means of amyl-acetate lamps. On account of the increasing weakness of light at low tem- peratures, 900 C. is taken as the lowest working point. The upper limit can be selected at pleasure. TABLE XXII. TEMPERATURE-MEASUREMENTS WITH THE WANNER PYROMETER. (a) In blast-furnaces. Slag. Pig iron Pig iron from mixer Pig iron flowing into converter. Steel when turning converter. . . Slag when turning converter . . . Slag, flowing out Pig iron, starting of flow Pig iron in a prismatic form. . . . Pig iron getting solid Slag from mixer Slag from converter Pig iron from blast furnace Steel from converter . : Iron from cupola Deg. Cent. 1402 1370 1317 1284 1260 1240 1460 1555 1424 1372 1384 1372-1330 1230 1012 1384 1330 1230 1225 1211 1239 (6) Thomas-process. (Temperature of converter-gases during charge) 1310, 1381, 1472, 1310, 1331, 1472 and 1494 C. The temperature of the converter is much higher. The tem- perature of the slag, three minutes after stopping the blower, was found to be 1700 C. 78 HEAT ENERGY AND FUELS (c) Various measurements. Zirconium in oxygen gas blast 2090 C. Electric arc light with retort coal 3560-3610 C. Of other optical pyrometers we mention the apparatus of Holborn-Kurlbaum and of Morse, in which the intensity of the electric standard lamp is varied. The thermo-electric telescope of Fery (Fig. 18) is based upon the measurement of the total radiated energy of a glowing substance. [^*^f?j^^-:-^=*|SSK FIG. 18. Fury's Thermo-electric Telescope. The total radiation of energy of a substance according to the Stefan-Boltzmann law is : E = K (T 74 - TV). In this equation E is the energy radiated from a black body at absolute temperature T to a body of the temperature T and K is a constant. The correctness of this law within the widest temperature limits was proved by Lummer, Kurlbaum, Pring- sheim, Paschen and others. The following table gives the observations of Pringsheim and Lummer: TABLE XXIII. RADIATION OF ENERGY. 1 Black Body. 2 Absolute Tempera- ture Ob- served. 3 Reduced Deflection. 4 K 10 10 5 Absolute Tempera- ture Cal- culated. 6 T Ob- served T Calculated. Boiler (kettle) Saltpetre kettle Do 373.1 492.5 723 156 638 3320 127 124 124 8 374.6 492.0 724 3 Degrees. -1.5 + 0.5 1 3 Do Fire brick furnace Do Do 745 810 868 1378 3810 5150 6910 44700 126.6 121.6 123.3 124 2 749.1 806.5 867.1 1379 -4.1 + 3.5 + 0.9 _ i Do ...'... 1470 57400 123 1 1468 + 2 Do 1497 60600 120 9 1488 + 9 Do 1535 67800 122 3 1531 + 4 > Average 123.8 PYROMETRY 79 The temperatures given in column 2 are referred to the tem- perature-scale of Holborn and Day, in which the thermo-electro- motive force of the Le Chatelier-element (Pt + Platinum Rhodium) is calibrated with a nitrogen-thermometer. Under column 3 we have the radiant energy of the black body at the observed temperature, measured bolometrically (and the gal- vanometer-deflection reduced to the same units). The bolometer temperature was 290 absolute. The following observations of Lummer and Kurlbaum show the anomalies that have to be considered with other than black bodies. (See the following pages.) The radiant energy of ferric oxide is from 4 to 5 times as great as that of polished platinum, but nevertheless considerably smaller than that of a black body. With increasing temperature however the radiation of non-black bodies increases faster than that of absolutely black substances. In Fery's thermo-electric telescope (Fig. 18) the image of the glowing surface whose temperature is to be measured falls upon the soldered joint of a copper thermo-element, a galvanometer being inserted in the circuit of the latter. The solder becomes heated, and the thermo-e.m.f. generated is measured by the galvanometer. The image of the glowing surface is thrown upon the solder by means of the eye-piece 0. The objective F is made of fluor spar, which absorbs very little of the radiant energy. Some instruments are made with glass objectives. TABLE XXIV. RADIANT ENERGY OF VARIOUS SUBSTANCES. Absolute Temperature. K E T r. Black Body. Polished Plati- num. Ferric Oxide. 372.8 492 654 795 1103 1481 1761 290.5 290 290 290 290 290 290 108.9 109.0 108.4 109.9 109.0 110.7 4.23 5.56 8.14 12.18 16.69 19.64 33.1 36.6 46 .'9 64.3 80 HEAT ENERGY AND FUELS The following table shows the close agreement of results, determined with different optical pyrometers, used to measure the temperature of the electric arc light. 1 TABLE XXV. COMPARISON OF PYROMETRICAL MEASUREMENTS. Observer. Absolute Tempera- ture. Method. Le Chatelier , . . Violle 4370 3870 Photometry: intensity of red light. Calorimetry specific heat Wilson & Gray 3600 of coal. Total radiation of cupric ox- Wanner 3700-3900**) ide (empirical equation). (According to the coal used) Fery.. 3600-4000 photometry; Wien's law. W^ave length of maximum Lummer & Prinsrsheim 3750-4200 radiation (Wien's law), do Fery .... . 3760**) Total radiation* Stefan- Boltzmann's law. Temperature of the black body. Methods based upon the change of electric resistance. Tem- perature can also be measured by the change in the electric resistance of a spiral platinum wire, wound around a rod of fire- clay and protected from the outside by a clay- vessel (Fig. 19). FIG. 19. Spiral Platinum Wire (protected). The law governing the relation between resistance and tem- perature is represented by a parabola. This principle was first used by Siemens, but soon abandoned in practice as the plati- num is affected by silicon, phosphorus and the gases of reac- tion, whereby its resistance is considerably changed. At first a platinum tube was put around the platinum wire, which made the apparatus too fragile and too expensive. It was soon found that a porcelain-tube would do just as well. The apparatus therefore is very apt to break, and is hardly used except for very accurate measurements in laboratories. i Waidner & Burgess: The temperature of the arc (Phys. Rev. 19, Nr. 4). PYROMETRY 81 TABLE XXVI. COMPARISON OF PYROMETRICAL MEASUREMENTS. (Fischer.) Pyrometer of Steinle & Hartung (Graphite Pyrometer). Siemens (Resistance Pyrometer) . Fischer (Calori- meter) . eter (Geissler). Degrees. 358 Degrees. 361 728 612 700 260 101 102 612 266 98 100 602 261 99.5 99.8 103 99 99.8 103 101 99 8 843 751 754 910 862 837 778 761 858 751 848 744 730 511 449 440 312 308 304 294 290 287 Upon the same principle are based the pyrometers of Hart- mann and Braun in Bockenheim-Frankfurt am Main, of Callendar and others. The results of some measurements with these instruments are given in Table XXVII: TABLE XXVII. MEASUREMENTS WITH HARTMANN AND BRAUN'S PYROMETER. Deg. Cent. Melting point: Tin Bismuth Cadmium Lead Zinc , . Zinc Magnesium, 1% impurities Antimony Aluminium, 99 . 5% Al . . . . Silver Gold Copper K 2 S0 4 K 2 SO 4 solidifying point. . . Na 2 SO 4 melting point Na 2 SO 4 solidifying point. . . Na 2 CO 3 , melting point. . . . 232 (Callendar and Griffiths, Hey- cock and Neville) 270 Callendar and Griffiths. 322 Do. 329 Do. 421 Do. 419 Heycock and Neville. 633 629.5 654.5 960.5 1062 1080.5 1084 1067 902 883 850 Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. 82 HEAT ENERGY AND FUELS Henri Le Chatelier' s thermo-electric pyrometer. This instru- ment is based upon the measurement of the current produced by heating the soldered joint of a thermo-element. The solder immediately reaches temperature-equilibrium with the body or space whose temperature is to be measured, and the instrument can be set at quite a distance from the place to be investigated, which is of considerable advantage. The selection of the metals for the thermo-element is of impor- tance. Iron or nickel cannot be used, as these metals, when heated at one point, set up local currents. Generally one wire is of platinum and the other of platinum containing 10 per cent of indium or rhodium. For measuring the current Le Chatelier uses a Deprez d'Arsonval aperiodic galvanometer fitted with a mirror and scale, or a needle-galvanometer, built according to his instructions by Pellin in Paris. Kaiser and Schmidt in Berlin and Siemens and Halske use needle-galvanometers. According to the investigations of H. Le Chatelier the relation between the electromotive force and the temperature difference between the soldered joint and the extremity of an element consisting of platinum and palladium can be expressed by the equation : y ^ e - 4 ' 3 (t ~ + 1000 (e - He found t - t = 100 445 954 1060 1550 e - 500 2950 10,900 12,260 24,030 By using a thermo-element consisting of platinum and a plat- alloy, the equation takes a different form. TABLE XXVIII. MEASUREMENTS WITH THERMO-ELEMENTS. Bar us. Le Chatelier. Holborn and Wien. Pt-Pt 90 + Ir 10 Pt Pt 90 + Rh 10 Pt Pt 90 +Rh 10 t e t e t c Degrees. 300 500 700 900 1100 2,800 5,250 7,900 10,050 13,800 Degrees. 100 357 445 665 1060 1550 1780 550 2,770 3,630 6,180 10,560 16,100 18,200 Degrees. 100 200 400 600 800 1000 1200 1400 1600 565 1,260 3,030 4,920 6,970 9,080 11,460 13,860 16,220 PYROMETRY 83 All these observations when plotted show similar curves. For Le Chatelier's observation we have : log e = 1.2196 log t + 0.302. Wherein e is expressed in microvolts. The best way is to calibrate the instrument by direct observa- tions. For this purpose the data given in Table XXIX can be used- TABLE XXIX. DATA FOR CALIBRATING PYROMETERS. Boiling point of water Boiling point of naphthaline Melting point of zinc Boiling point of sulphur Melting point of aluminium Melting point of salt Melting point of silicate of sodium. Boiling point of zinc Melting point of silver Melting point of gold Melting point of palladium Melting point of platinum Deg. Cent. 100 218 420 445 655 (667) 800 883 930 960 (961.5) 1045 (1064) 1500 1780 (The figures in parentheses were determined by Holborn and Wien). The boiling points of water, naphthaline and sulphur are de- termined by heating the substances to the boiling point in an in- sulated glass tube closed at the bottom; then the soldered joint of the thermo-element is immersed in the vapor. The melting point of zinc is observed by enclosing the thermo-element in a porcelain tube (Fig. 20), and immersing it in the molten metal. i 4 FIG. 20. Thermo-element in Porcelain Tube. FIG. 21. Crucible. When determining the melting point of gold a few milligrams of gold are placed under the thermo-element, which is put into a crucible filled with sand (Fig. 21) and heated above 1000 degrees, 84 HEAT ENERGY AND FUELS at the same time carefully watching the movement of the galva- nometer. When the gold starts to melt, the galvanometer remains stationary until all the gold is melted, when the temperature continues to rise at a steady rate. When measuring the temperature of steel-furnaces, etc., the thermo-element must be enclosed in an iron pipe. For porcelain- furnaces where temperature measurements are made constantly, the thermo-element, which is protected by a glazed earthenware pipe, is permanently attached to the furnace but does not extend into the interior of the furnace. It is heated by a specially arranged circular recess. This instrument is made in Germany by W. C. Heraeus in Hanau, and by Kaiser and Schmidt in Berlin, as shown in Fig. 22; FIG. 22. Holborn-Wien Pyrometer. it is specially constructed for industrial use. In the report of the "physikalisch-technische Reichsanstalt," the advantages of the Holborn-Wien modification of the Le Chatelier pyrometer are PYROMETRY 85 set forth ; the reading of the instrument is so simple that a fairly intelligent workingman can learn, in a short time, how to use it. Furthermore the instrument is durable, the accuracy is not impaired by high temperatures, the reading apparatus can be at quite a distance from the furnace and one indicating device can be used for a number of ther mo-elements. The thermo-element consists of a pure platinum wire 0.6 mm. in diameter and 1500 mm. long, one end of which is melted to- gether with the end of another wire consisting of an alloy of 10 per cent rhodium and 90 per cent of platinum. The purity of the metals used is of importance if the same thermo-electromotive forces are to be obtained. The opposite ends of the wire are con- nected to a circuit. By heating the solder a small e.m.f. is generated (about 0.001 volt per 100 degrees temperature differ- ence between the soldered end and the free end). This e.m.f. is measured by means of a galvanometer provided with two scales, one graduated in microvolts, and the other in temperature- degrees. According to Holborn and Wien, the accuracy of the instrument at 1000 C. is 5 C. FIG. 23. Arrangement of Element. When in use the wires of the element must not come in contact with substances that react with platinum or its alloys. This is prevented by suitably mounting the instrument in a porcelain- 86 HEAT ENERGY AND FUELS tube, which at the same time provides the insulation of the wires. These porcelain shells can stand temperatures up to 1600 degrees. Fig. 23 shows how the element is mounted. A hard rubber disk, having an opening in the center is slid from the bottom over the outer porcelain-tube. This disk has a recess which fits about the head B of the porcelain-tube. A layer of asbestos-cord is wound in between A and B. The upper hard rubber disk is provided with two small openings, through which the wires of the element are drawn and a recess for the porcelain insulating tube. The disk I is permanently connected with disk A by means of three brass screws. Two binding screws, which serve as terminals, are attached to C. Asbestos cord is wrapped around the outer porcelain-tube, the latter being forced into the iron pipe D. D is provided at the lower end with a removable cap and at the upper end with a bell E to which the hard rubber-head of the mounted element is fastened by means of three iron screws. The temperatures of molten metals, slags, etc., are preferably determined with floating pyrometers of spheroidal shape. TABLE XXX. TEMPERATURE DETERMINATIONS, OPEN-HEARTH STEEL FURNACE. (Le Chatelier.) Deg. Cent. Gas leaving producer 720 Gas entering regenerator 400 Gas leaving regenerator 1200 Air leaving regenerator 1000 Flue gases at bottom of flue 300 Furnace, beginning of puddling 1550 Furnace, end of discharge '. 1420 Casting-pan, beginning 1580 Casting-pan, end 1490 GLASS FURNACE. Furnace, during refining 1400 Glass, during refining 1310 Glass, during work 1045 Heating of bottles 585 Rolling plate-glass 600 ILLUMINATING GAS MANUFACTURE. Furnace on top 1 190 Furnace on bottom 1060 Retort at end of distillation 975 Flue-gases 680 PYROMETRY 87 The Hartmann and Braun pyrometer is based upon the same principle. The thermo-elements, up to 1000 C., consist of plati- num and platinum-nickel, up to 1600 C. of platinum and plati- num-rhodium. The nickel element is twice as sensitive as the rhodium element. CERAMICS. Burning temperature of hard porcelain 1400 C. Burning temperature of china porcelain 1275 C. Burning temperature of bricks 1100 C. Wiborgh's Thermophone (Fig. 24). This consists of a fire- clay cylinder, containing a small copper-cartridge filled with dynamite. The thermophone is brought into the space, whose tem- perature is to be measured, and the length of time observed until an explosion takes place (light detonation). The temperature is then read from a table. To ascertain the time required for heating the cartridge by heat-conduction to the explosion-temperature (150 C.), Fourier's equation is used': FIG. 24. VTZ In this equation, t is the outside temperature; y, the tem- perature of a point in the interior, at a distance x from the surface after a time, 2, and 6, the original temperature of the clay-body. C is the heat conductivity of the substance; c, the specific heat of the substance; d, the weight of 1 cu.m. of the substance, in kg., and z, time in hours; x, the distance of the point observed, from surface of test-body, in meters. 88 HEAT ENERGY AND FUELS Table XXXI can be used for ascertaining the temperature. TABLE XXXI. DATA ON WIBORGH'S THERMOPHONE. I II I ii i n I n i 1 a i 1 1 i w T3 C 1 c i 02 13 C I 00 3 3 fi i rf o c I 3 i t T3 C 1 3 C i | 300 3 33 2 46 4 1140 46 2 36 44 2 320 340 360 380 400 3 2 2 2 2 6.0 45.6 29.6 17.0 6 6 2 2 1 1 25.2 9.2 56.8 46.8 38.6 1160 1180 1200 1220 1240 45.6 45.2 44.6 44.2 43.8 35.6 35.2 35.0 34.6 34.2 43.6 43.2 42.8 42.4 42 420 1 58 1 32 1260 43 4 33 8 41 6 440 460 480 500 520 540 560 KQfl 1 1 50.6 44.2 39.0 33.8 30.0 26.4 23.0 20 1 1 1 1 1 1 1 1 26.2 21.4 17.2 13.4 10.2 7.4 4.8 2 4 1280 1300 1320 1340 1360 1380 1400 1420 43.0 42.6 42.2 41.8 41.4 41.2 40.8 40 4 33.4 33.2 32.8 32.6 32.4 32.2 32.0 41.2 40.8 40.4 40.0 39.6 39.2 38.8 38 6 fion 17 2 1 4 1440 40 2 38 2 620 14 8 58 1460 39 8 38 640 660 680 700 12.6 10.4 8.6 6 8 56.6 55.0 53.6 52 2 1480 1500 1520 1540 39.4 39.2 39.0 38 6 37.8 37.4 37.2 36 8 720 5 2 50 8 1560 38 4 36 6 740 760 3.6 2 2 49.8 48 6 1580 1600 38.0 37 8 36.4 36 2 780 800 820 1.0 59.8 58 4 47.6 46.6 45 6 1620 1640 1660 37.6 37.4 37 36.0 35.6 35 4 840 57 4 44 8 680 36.8 35.2 SfiO KR 4. 44 1700 36 6 35 880 900 920 940 QfiO ... 55.4 54.4 53.6 52.8 KO n . . . 43.2 42.6 41.8 41.2 40 fi 1720 1740 1760 1780 1800 .. .. 36.4 36.2 36.0 35.8 35 6 ... 34.8 34.6 34.4 34.2 34 Q80 51 2 40 900 34.6 33.0 1000 1020 1040 1060 1030 1100 1120 ... 50.6 49.8 49.2 48.6 48.0 47.2 46.8 39.4 38.8 38.2 37.8 37.4 37.0 36.4 44.6 2000 2100 2200 2300 2400 33.8 33.0 32.2 31.6 31.0 1 32.2 31.4 30.8 30.2 29.6 PYROMETRY 89 The thermophone has to be kept in a dry place, and when used, must have an initial temperature of from 18 to 22 C. (a) When determining the temperature in reverbatory- or muffle-furnaces, stacks, etc., or in all cases where the thermo- phone rests upon a solid base and is surrounded by hot gases, the time elapsing between the insertion of the thermophone and the explosion is read and the temperature taken from Table I. (6) When determining the temperature of liquid metals, such as zinc, lead, copper, silver or gold, an iron pipe, closed at the bottom, 30 mm. inside, 34 to 36 mm. outside diameter, is inserted in the molten metal; after a few minutes, when the pipe has attained the same temperature as the metal, the thermophone is slid into the pipe. In this case the temperature is read from Table II. (c) When measuring high temperatures of molten metal and slag, such as iron, steel, etc., the thermophone is thrown upon the surface of the metal and slag, and the temperature is taken from Table III. The above table is made out for = 20 C. If the air-temperature differs from this a correction must be made according to equation : if y = 150, 6 = 20, we have: If at an air temperature of 0' = 30 degrees a temperature of 2000 degrees is found, the correction is = -142, and the measured temperature is t' = 2000 - 142 - 1858 C. The results obtained with the thermophone are very satis- factory. Contact of the thermophone with basic slags has to be avoided, since in such cases the explosion takes place too early, which gives too high results. 90 HEAT ENERGY AND FUELS TABLE XXXII. COMPARATIVE DATA ON WIBORGH'S THERMOPHONE. Temperature- Measurements. Air Pyrometer. Thermophorie. Heating furnace 784 5 Deg. Cent. 772 764 Heating 875.0 888 878 Open-hearth steel upon acid slag. . . upon steel over 2400 1812 upon strongly basic slag over 2400 In practice automatic registering pyrometers are very useful as they make a continuous control of the temperature-changes possible. Because of lack of space they cannot be described in this book. Suggestions for Lessons. Practice in handling various pyrometers; Adjustment of same; Determination of melting points, heating and cooling curves; Comparative temperature-measurements with different pyro- meters. CHAPTER IV. COMBUSTION HEAT AND ITS DETERMINATION. HEAT value, fuel value, thermal value, calorific value or ther- mal efficiency is the quantity of heat developed from a certain quantity of fuel in complete combustion. It is generally expressed in calories. This quantity is called absolute thermal value, etc., if it is referred to the unit of weights, specific thermal value, if referred to the unit of volume. Pyrometric thermal efficiency is called the temperature that can theoretically be reached by combustion of the fuel. We are going to speak first of the absolute thermal value or, chemically expressed, of the determination of the combustion- heat, which is generally figured in calories, sometimes however given in per cents of the thermal value of pure carbon, or as "evaporating-power," or in comparison with some other fuels, or as the quantity of lead reduced by 1 g. of fuel. The expression of the thermal value in calories is easily under- stood as it means the number of large calories furnished by the combustion of 1 kg. of fuel. If this quantity is divided by 8080 (the thermal value of 1 kg. of charcoal according to Favre and Silbermann) the thermal value is obtained, expressed in terms of the heat- value of pure carbon. The expression of the thermal value of a fuel by its " evapo- rating power" was first proposed by Karmarsch. It means the quantity of water transformed into steam by 1 kg. of fuel and is obtained by dividing the thermal value expressed in calories with 652 (the heat-quantity, necessary, according to Regnault, to transform 1 kg. of water at C. into steam at 150 C.). For certain purposes the thermal value of one fuel is compared with the value of another fuel, i.e. the fuel quantity equivalent to the other is given. Generally 1 cubic meter of soft logwood .is taken as unity which has a thermal value of about 900,000 cal. Table XXXIII will be useful for transformations. 91 92 HEAT ENERGY AND FUELS TABLE XXXIII. THERMAL TRANSFORMATION VALUES. Thermal Value in Calories Referred to 1 Kg. of Evaporating Power. Logwood. Pure Carbon. 1 0.00012376 0.0015337 0.000001111 8080 1 12.39 0.00898 652 0.080693 1 0.000724 900.000 111.4 1380 1 In determining the thermal value account has to be taken of the quantity of hydrogen present which is oxidized to water. According as we assume that this water is completely condensed or completely changed to steam , we obtain the highest and lowest calorific values, respectively. The following methods have been proposed for determining the fuel value : 1. Direct determination of the thermal value. (a) On a small scale, in calorimeters. (6) On a large scale, in steam-boilers. 2. By means of empirical formula based on certain chemical tests. (a) Calculation of the thermal value from the chemical composition (elementary analysis). (6) Calculation of the thermal value from the quantity of oxygen required for complete combustion (Berthier's method). (c) Based on simple chemical tests. (1) Direct determination of the thermal value. These methods undoubtedly give the best results. Several details have to be considered; all losses or gains of heat have to be avoided. This is easier accomplished in small than in large apparatus. The determination of the thermal value on a small scale, how- ever, has a disadvantage in that it is very difficult to get a good average sample small enough to be burned in a small apparatus. The only apparatus to be recommended are those in which a single reliable determination can be made simply and quickly, COMBUSTION HEAT AND ITS DETERMINATION 93 so that a great number of determinations can be made on any one sample without difficulty. We shall consider here only some of the most widely used calorimeters. Of the calorimeters in which combustion with oxygen under atmospheric pressure takes place we shall describe only the calorimeter of F. Fischer (Fig. 25). The oxygen for combustion is led (sometimes after being washed with caustic potash and dried) through the gas pipe a and the platinum pipe r. The latter is fitted loosely in the cover e of the combustion- chamber A (made of 95 per cent silver) and reaches into the platinum- crucible t, which contains about 1 g. of the fuel to be tested. The com- bustion gases escape through the platinum-net u and then upwards between crucible and ring V through s, i and e into the pipes c and 6. The platinum-net u, upon which some soot is deposited, finally gets so hot that the soot is burned. The calorimeter- vessel B, which contains 1500 g. of water, is surrounded by a layer of mineral wool C and the wooden case D. The two thermo- meters t serve for measuring the temperature of the calorimeter water and of the escaping gases respectively ; w is a stirrer, operated , , . FIG. 25. Fischer's Calorimeter. by m and the silk-cord o. By means of a magnifying glass one one-hundredth of a degree can be observed and recorded. Calorimeters in which combustion in oxygen takes place under pressure, as for instance the apparatus of Berthelot, Mahler, Stohman, etc., are very convenient. In all these methods the combustion of the fuel takes place in a closed chamber, in which the fuel is enclosed with a sufficient amount of compressed 94 HEAT ENERGY AND FUELS oxygen. The increase of temperature of a certain mass of water (calorimeter-water) into which the apparatus is immersed, is observed and recorded. The calorimetric bomb of Mahler is illustrated in Fig. 26 and consists of the following parts: (1) A bomb B made of excel- lent steel somewhat softer than gun-steel. This steel has an FIG. 26. Calorimeter Bomb (Mahler). absolute strength of 55 kg. per sq. mm. and 22 per cent elonga- tion. The quality of the steel was carefully selected on account of the strength and also on account of the enameling, of which we will speak later. The bomb has a capacity of 654 cu. cm. and its walls are 8 mm. thick. This capacity is much larger than that of Berthelot's bomb, the object being to obtain ari oxygen surplus even when using a gas not entirely pure. Fuel-gases are also studied with this bomb. The fuel gases often contain as much as 70 per cent of inactive substances, which make it necessary to take con- siderable quantities when testing in order to obtain a measurable increase of temperature in the calorimeter. The oval shape was selected in order to facilitate the forging and enameling. The bomb is nickel-plated on the outside, and coated with enamel on the inside to prevent any bad effects from nitric acid, which is always formed by combustion. This enamel takes the place of the platinum-lining in Berthelot's apparatus. The bomb is closed with a threaded plug packed with sheet lead. The plug is provided with a taper threaded cock, which COMBUSTION HEAT AND ITS DETERMINATION 95 serves as inlet for the oxygen and through which is inserted a well insulated electrode E, which is attached to a platinum rod F that extends towards the interior. Another platinum rod, also fastened to the plug, carries a platinum cap for receiving the fuel to be tested. (2) The other parts of the apparatus are the calorimeter D, the calorimeter- jacket A and the stirrer S. They differ in details from Berthelot's apparatus and are less expensive. The spiral-shaped stirrer of Berthelot is replaced here by a simple and easily operated circulation device which allows the production of a uniform circulation. (3) We may further mention: the thermometer, which is divided in T o degree, the source of electricity P and a watch or minute-glass. (4) Mahler uses oxygen from an oxygen-bomb. Since the most favorable pressure for burning 1 g. of bituminous coal is about 25 atm., and since the bombs contain 1200 liters (120 atm.), one of these vessels is sufficient for about 100 determi- nations. A pressure-gauge (manometer) inserted between the oxygen-bomb and calorimeter-bomb allows the pressure of the oxygen to be controlled. The pressure used with solid and liquid fuels is 25 atm. ; with gases rich in carbon (illuminating gas, etc.) 5 atm., and with poor gases (producer gas, etc.) 1 atm. To insure the complete combustion a certain excess of oxygen must be present; too great an excess, however, would lower the combustion tempera- ture and thereby cause incomplete combustion. The two insulated electric conductors which pass through the plug are connected inside the bomb by a spiral made of 0.1 mm. iron- wire, that extends into the fuel and causes ignition after the state of incandescence is reached. The fuel is contained in a small vessel of platinum, which is connected in the electric circuit. In a bomb containing 650 cu. cm., 1 g. of fuel is used. Slightly volatile liquids can also be used directly. When measuring gases the bomb is evacuated and filled with gas at certain temperature under pressure, which process is repeated twice for removing every trace of air. It is necessary that the calorimeter- water and jacket water be in temperature-equilibrium with the air of the room. All the 96 HEAT ENERGY AND FUELS apparatus is allowed to stand in the test room for 24 hours pre- vious to the test, immersed in a sufficient amount of water. The apparatus has to be protected from the sun and from draughts, which will cause a variation of temperature. The constants of the calorimeter are determined by burning a known quantity of a certain substance of known thermal value, for instance, 1 g. of naphthaline yielding 0.70 cal. When making a determination, 1 g. of the powdered fuel is weighed and put into the small vessel. The powder should not be too fine, as otherwise it might be carried away by the current of oxygen. If a fine powder is to be used it is wrapped up in paper of known weight and known thermal value. The bomb is closed and the oxygen allowed to enter slowly so as to avoid blowing away the powder. When the desired pressure is reached the cock is closed and the bomb cut off from the manom- eter. The bomb is put into the calorimeter, five minutes being allowed for equalizing the temperature. The vessel must be held upright to avoid spilling the powder. The stirrer is moved rap- idly and continuously for three minutes in order to obtain a uni- form temperature of the water, and the temperature of the calorimeter read and recorded. The fuel is ignited by impressing 10 volts on an iron- wire; the temperature is read and recorded every minute for six minutes. The temperature equilibrium of the bomb and calorimeter is generally perfect after three minutes. The readings during the next three minutes are used to correct the heat lost by radiation. It is generally sufficient to add to the increase of temperature recorded three minutes after ignition the decrease of temperature observed during the two following minutes. This is not abso- lutely correct, but sufficiently so for commercial purposes. The exact corrections give results varying not more than ^^ from the correction mentioned. A second correction relates to the combustion heat of the iron- wire in oxygen, which amounts to 1.600 cal. per 1 g. iron, and to the heat liberated by the formation of a small quantity of nitric acid. The latter quantity has to be determined for very accurate work, but can be neglected in commercial tests, the error amount- ing to less than -3^ and being nearly compensated by the error in the correction for cooling. 1 g. HN0 3 yields by its forma- tion 0.230 cal. COMBUSTION HEAT AND ITS DETERMINATION 97 EXAMPLE : One g. of naphthaline is used for combustion. Water-content of calorimeter 2200 g. Water-value of bomb, etc 480 g. Total 2680 g. Measurements of temperature : Before Test. Combustion. Cooling. 0' 17.52 1' 17.52 2' 17.52 3' 20.15 4' 21.06 5' 21.11 6' 21.09 1' 21.07 8' 21.09 Rise in temperature observed 3.59 Correction for cooling 0.04 Total ~33 Quantity of heat, 3.63 X 2.68 - 9.728 cal. Correction for iron, 0.025 X 1.60 = 0.040 cal. Difference 9.688 cal. If a correction for the nitric acid formed had been made the result would have been 9.685 cal. Mahler found in a lecture, i.e. under conditions which pro- hibited the attainment of temperature-equilibrium in the calorim- eter, 8373 cal. as the fuel-value of a bituminous coal, while in the laboratory, when taking all precautions, he obtained a value 1.3 per cent lower. If the coal contains considerable amounts of sulphur, same has to be considered. The sulphur is completely oxidized to sulphuric acid and can be determined by well-known methods after washing the bomb with water. The other calorimeter-bomb, in which combustion is effected with oxygen under pressure, is arranged in a somewhat similar manner. All determinations made in such apparatus have two defects. They give a thermal value at constant volume while in practice all combustion takes place at constant pressure; on the other hand they give the so-called upper thermal value, as the hygro- scopic water of the coal, and the coal formed by combustion is cooled to air-temperature, i.e. condensed, so that the thermal value determined in the bomb includes the latent heat of evapora- 98 HEAT ENERGY AND FUELS 2440 g. tion of the water, which can never be utilized in firing. To counteract this last defect Krocker proposes to put the bomb after combustion into an oil- bath at from 105 to 110 C., arid to absorb the evaporated water in a calcium chloride appa- ratus ; finally, to pass dry air through the bomb. Since he uses very exact corrections for the cooling of the calorimeter, we give an example of his method. Temperature of the room 20 degrees. Water in calorimeter = 2100 g. Water value of the apparatus 340 g. Weight of iron- wire and coal-brickette = 1.0959 g. Weight of iron-wire alone = 0.0187 g. Weight of coal-brickette alone 1.0772 g. Weight of the chloride of calcium apparatus : (a) Before test 48.2169 g. (b) After test 48.7605 g. Weight of total water 0.5436 g. Weight of water in 2 0.0250 g. Weight of water in coal 0.5186 g. = 48% TABLE XXXIV. TEMPERATURE CHANGE. First Test. Main Test. After 1 'eat. No. Reading. Differ- ence. Reading. Differ- ence. Reading. Differ- ence. Note. r = t = t=* T' = v' = 1 18.750 + 18.759 18.759 21.744 _ The coal 2 18.753 0.003 19.170 21.742 0.002 was burned 3 18.753 0.000 20.530 21.739 0.003 as furnish- 4 18.756 0.003 21.240 21.729 0.010 ed without 5 18.756 0.000 21.590 21.720 0.009 being made 6 18.757 0.001 21.723 21.713 0.007 air dry. 7 18.758 0.001 21.749 21.749 21.707 0.006 g 18 7^8 flOfl 01 7fl4 003 g 18 759 001 2 990 10 18.759 0.000 jm 187.759 0.009 173.798 0.040 ver. 18.756 0.001 21.725 0.005 COMBUSTION HEAT AND ITS DETERMINATION 99 The temperature of the calorimeter water rose 2.990 C. For correcting the temperature the formula of Regnault-Stoh- mann-Pfauneller is used : + 7{ \ W - nr j- (n - l)v. v means herein average of temperature-differences of the preliminary test. T means herein average of temperature-readings of the pre- liminary test. t v t 2 . . t n means herein the temperature-readings of the main test. v' means herein average of temperature-differences of final test. T' means herein average of temperature-readings of final test. n means herein number of readings of main test. For our example we have : v - v' = 0.001 + 0.005 =.0.006 T' - T = 21.725 - 18.756 = 2.969 *. + <_ 40.488 _ 2Q011 o 2 2 n-l (t) = 123.002 i nr = 1 x 18.756 - 131.292 ( n - 1) v = 6 X 0.001 - 0.006. The correction therefore is : 006 Corr - = < ^ (- 046 + 20 - 244 . + 123.012 - 131.292) - 0.006 = 0.012. Corrected increase of temperature = 2.990 -f 0.012 = 3.002. Heat generated in calorimeter 3.002 X 2440 = 7324.8 cal. 100 HEAT ENERGY AND FUELS If we deduct herefrom 2.92 cal. (that are developed from 0.0187 g. iron-wire in combustion) we get the thermal value of the coal: 7324.8 - 29.9 1.0772 = 6772 cal. For the acids formed Krocker deducts 8 cal. (as average), whereby the thermal value of the coal becomes : 7324.8 - 29.9 - 8 -T0772- Altogether 0.5436 g. of water were absorbed by the calcium chloride. According to previous tests 0.025 g. of same come from the compressed oxygen, so that for the coal burned we have 0.5436 - 0.025 g. - 0.5186 g. of water (48 per cent of the coal burned). The latent heat of evaporation is: 0.48 X 600 - 288 cal. so that we get as useful thermal value of the coal (lower heat- value) 6764 - 288 = 6476 cal. Since the quantity of hygroscopic water in coal varies widely, only dried coal should be used for the determination of fuel values. Furthermore since the determination of the water content of the calorimeter is a tedious operation, it is of advan- tage to determine the hydrogen content of coal by elementary analysis. A calorimeter constructed by S. W. Parr, professor in the State University at Champaign, 111., for determinating fuel values is more and more widely used on account of its low cost. This calorimeter is based upon the same principle as the calorimeter- bombs, i.e. the combustion takes place in an enclosed space, so that during the process no gases can enter or escape. The oxygen is used in solid form and the products of combustion obtained are transformed into solid compounds, therefore combustion takes place at low pressure, and the expensive bomb is done away with. COMBUSTION HEAT AND ITS DETERMINATION 101 Fig. 27 shows the assembled apparatus, Fig. 28 the reaction- vessel (the cartridge). The calorimeter proper consists of a nickel-plated copper- vessel A, which contains somewhat over 2 liters and a vessel (7, made of wood fiber and surrounded by if FIG. 27. Parr Calorimeter. FIG. 28. Reaction Vessel (for 27). another similar vessel, B. The entire apparatus is closed by the double-cover G, made of one piece. Thereby such an excel- lent heat-insulation is effected that the maximum temperature attained in the reaction remains constant for five minutes, without falling even 0.001. The reaction vessel D is a heavy, nickel-plated, brass cylinder having a cubic content of about 35 cu. cm. ; it is closed at top and bottom with screw plugs and leather gaskets. The lower plug, I, rests upon a pivot-step bearing, F, connected to the cylinder E. The upper plug is provided with a tube H, which extends through the cover, G, and carries the pulley, P. The four blades, h, h, are attached to D. If the device is set in motion (by mean's of a Raabe-turbine) at sufficiently high speed (150 rev. per min.) the calorimeter-water moves in the direction of the arrows and a perfectly uniform temperature distribution is obtained in the calorimeter. From Fig. 28, which shows the reaction vessel (cartridge) on a larger scale it can be seen that the tube H contains a small 102 HEAT ENERGY AND FUELS tube L which is open at one side and ends at the bottom in a conical valve K. The latter is kept closed by the spiral spring M until pressure is applied to N. In the cover, G, a hole (8-9 mm. wide) is provided, through which a thermometer divided at least in ^o degrees, but better in T o degrees, is suspended. The scale of the thermometer goes from 15 to 26 degrees and is 38 to 40 cm. long. It is of impor- tance to have the graduated part of the thermometer absolutely and perfectly cylindrical. The manipulation of the instrument is as follows: After putting the double- vessel, CB, upon a solid table the calorimeter- vessel, A, is filled outside of the wooden jacket with exactly 2 liters of water (preferably distilled water), care being taken to keep the outside of A and the inside of C dry. The temperature of the water should be about 2 degrees below the temperature of the room. A is now put into the wooden vessel, CB, the reaction- vessel, D, is dried perfectly by slightly heating on the sand-bath, the lower cover, 7, is tightly screwed on and about 10 g. of per- oxide of sodium (sifted through 1 mm. mesh) put in. Next 0.5 or 1 g. of the fuel and other substances, to be mentioned later, are introduced into the reaction-vessel, and the cover (whose valve if it should have gotten wet, has to be dried) put on. While pressing N upwards, the charge is well shaken, then lightly tapped to settle the mass on the bottom, the valve K tried to see if it works easily, hh attached and vessel D inserted in A. The cover, G, is now put on, also pulley, E, and the cord put over the latter, then the thermometer, r, is arranged as shown in the figure. The stirrer is operated (about 3 minutes) until the thermometer reading is perfectly constant, the reading recorded but the motor kept going to the end of the test. Ignition is effected by means of a glowing piece of iron wire 10 mm. in length and 2.5 mm. in diameter, weighing about 0.4 g. Such a piece can be used frequently until its weight is considerably less than 0.4 g. At a temperature of 700 degrees this wire carries 0.4 X 0.12 X 700 = 33.6 cai., which corresponds to an increase of temperature of 0.016 degrees in the calorimeter. As readings are made with an exactness of 0.005 degree, correc- tion is made by subtracting from the temperature recorded 0.015 degree. The iron wire is seized by means of curved tweezers, heated to red glow in a Bunsen flame, allowed to fall through N COMBUSTION HEAT AND ITS DETERMINATION 103 into the reaction-vessel ; then N is pressed down with the tweezers and quickly released, so that the iron falls out of K without any gas escaping at L. A noise is heard for several seconds, and the temperature rises first rapidly then slowly. After 4 or 5 minutes the maximum is reached, which remains constant for about 5 minutes, then the reading is recorded. The test now being finished, the motor is stopped and the apparatus taken apart. Cylinder, D, is put into a dish filled with warm water, wherein its contents are dissolved accompanied by the generation of heat. After neutralizing the solution with hydrochloric acid it is easily noticed whether unburned particles of coal are present, in which case the test is unsuccessful. This, however, happens only with anthracite, when persulphate of potash has not been added. With bituminous coal an addition of tartaric acid is sufficient, while with lignite simply double the amount of coal is used, without the addition of anything. Vessel, D, is immediately washed and dried. The water-value of the calorimeter is 123.5 g. (which should be checked) ; we have therefore, including the calorimeter-water, 2123.5 g. According to numerous tests (with an increase of temperature = t' - t) 73 per cent of the heat generated is from the combustion proper, 27 per cent from the reaction of the products of combustion . with Na 2 and Na 2 2 respectively. If 1 g. of coal has been burned (lignite), 0.73 X 2123.5 (If - t) = 1550 (t' t) cal. are generated. We have therefore simply to deduct 0.015 degree (for the heat introduced with the hot iron-wire) from the recorded difference of temperatures t' t and to multiply the quantity obtained -by 1550, to get the thermal-value of 1 g. of coal. With bituminous coals, of which 0.5 g. is used, the difference of temperature recorded would have to be multiplied by 3100. Previously however 0.85 degree has to be deducted for 0.5 g. of tartaric acid and 0.4 g. of iron at 700 degrees. With anthracite the following points have to be observed: 1.0 g. of persulphate and 0.4 g. of iron effect an increase of temperature of 0.155 degree; on the other hand, 0.5 g. of tartaric acid and 0.4 g. of iron effect, as we have seen above, an increase of 0.85. Since only one piece of iron is used for ignition we have to deduct the corresponding increase of temperature and we therefore have as correction for 0.5 g. tartaric acid, 1.0 g. of 104 HEAT ENERGY AND FUELS persulphate and 0.4 g. of iron, 0.85 + 0.155 - 0.015 = 0.99 degree. If the sodium peroxide is too moist, the results obtained are too high; in such a case a second test is made with 0.5 g. of tartaric acid and about 7 g. of sodium peroxide. If now the temperature of the calorimeter increases more than 0.85 degree, this has to be considered in the main test by deducting 0.15 degree for every 0.1 degree of observed additional increase. This correction however can be avoided if the peroxide is kept in air-tight cans of 50 g. or 100 g. capacity. Care must be taken not to throw the mixture of coal and peroxide into water, as otherwise an explosion might take place. This is also the reason why the interior of the valve has to be kept absolutely dry. Parallel tests made by Lunge and Parr with Parr's calorimeter and Mahler's bomb gave the results shown in Table XXXV. TABLE XXXV. TESTS WITH PARR'S CALORIMETER. Kind of Coal. Water. Ash. Thermal Value. Differ- ence. Additions. Mah- ler. Parr. Ruhr flaming coal ...... 2.6 7.1 7685 7688 ) ?695 7703 ( 7 ' + 10 0.600 g. Tartaric acid Ruhr coal. . . . 1.3 6.6 8059 8075 -f 16 0.5 g. Tartaric acid 1.000 g. Persulphate Anthracite... 1.5 6.7 7981 7967 ) 7Q90 8013 \ 7 " + 9 0.600 g. Tartaric acid Coke......... 0.6 13.0 6640 6649 ) fiftfi7 6726 \ 6687 + 47 0.500 g. Tartaric acid Welsh Anthracite. . 2.0 4.2 8049 8044 ) 8Q21 7998 \ 8021 -28 0. 600 g. Tartaric acid English Anthracite. . 2.4 4.6 8365 8324 ) 8 26 8327 J * 62b -39 O.SOOg. Tart, acid + 1.000 g. Persulphate Belgium Braisette. . . 2.4 10.7 7409 7378 ) 7QO , 7409 } 7394 -15 O.SOOg. Tartaric acid Saar coal .... 4.9 11.7 6594 6634 + 40 0.500 g. Tartaric acid Cardiff coal. . 2.2 7.2 7872 7936 + 64 0.500 g. Tartaric acid Saar coal. . . . 3.5 8.4 7146 7161 ) ?184 7207 \ 7 " + 38 0.500 g. Tartaric acid Lignite Briquette. . . 15.17 5037 5084 ) 5Q76 5068 ( 5076 + 39 No addition but 1.000 g. of coal first dried then burned COMBUSTION HEAT AND ITS DETERMINATION 105 Test-boilers used for determining the thermal value of fuels on a large scale differ from ordinary boilers ; the heat-losses in com- mon boilers are not sufficiently uniform. Therefore an especially constructed calorimeter-boiler has to be used (see Muspratt). It should be kept in mind in all determinations of heating values that these values vary with the pressure and the tem- perature at which the combustion takes place. This is of importance, as we can hereby calculate the thermal efficiency of a fuel under different conditions, and in commercial work, where combustion takes place at constant pressure, the figures obtained in the bomb (constant volume) have to be corrected. These variations of the combustion heat are based on the well-known energy principle : the sum of the energy-quantities accumulated in the interior of a system, when the latter changes from one state to another, is exclusively dependent on the initial and final state and independent of the intermediate state. In the special case where the initial and the final state are alike (cir- cular process), this sum is equal to naught. In the following consideration the heat generated by the system and delivered outside and also the increase of volume of the system is taken as positive. Relations between combustion heat at constant volume and at constant pressure. The combustion heat at constant pressure is greater than at constant volume. If combustion takes place at C. the difference of the two combustion-heats is, in cal., 0.54 times the contraction of molecular-volume which takes place in the combustion. If we burn a gas-mixture at constant pressure we obtain a heat quantity Q. At first the volume of the gas is increased by the heat, then it decreases, while cooling off to the starting tem- perature, to a volume which is smaller than the initial volume. The difference of volumes corresponds to the contraction effected by decrease of the number of molecules present during com- bustion. .If we allow the combustion to take place in a cylinder (closed at one end, and fitted with an air-tight piston which can move up and down without friction) , we can lift this piston after com- bustion and when the gases have cooled down to the initial temperature, so that the products of combustion occupy the ' original volume. The work expended thereby is APV. 106 HEAT ENERGY AND FUELS If, however, the combustion takes place at constant volume, the heat quantity q is generated. According to the above explanations we have q = Q - APV, or since we have = 0- q == 428 ' If the system contains n mols we have according to Boyle-Gay- Lussac's law, PV If we substitute for T = 273, P = 10,333 kg. per sq. m., F = 0.02242 cu. m., we have 1033 X 0.02242 X 273 = Q n - 273 X 428 = Q - n 0.5411 cal. We can obtain the same value much easier by considering that we have for 1 mol of the gases M (c p - c v ) = 1.982 cal. and that the gas-equation referred to absolute temperature rests on the supposition that the gas laws are correct down to absolute zero and that the gases at this temperature occupy no volume. We have q = Q- APV = Q-M(c p -c v )T 1.982 X 273 1000 = Q - 0.5411 cal. per mol. COMBUSTION HEAT AND ITS DETERMINATION 107 This equation enables us to transform combustion heats obtained (in the bomb) with constant volume into combustion, heat of constant pressure. Per mol. of the substance burned we have : TABLE XXXVI. Reaction. Combustion Heat Contrac- at Constant tion in Mols Volume. Pressure. H 2 + = H 2 0.. CO + O - CO 2 1.5 5 68.2 67 9 69.0 68 2 \ (H 2 + CO) + O CH 2 + 2O 2 = CO 2 = \ (H 2 + C0 2 ) + 2H 2 O 1 2 68.0 212.4 68.5 213.5 * (2C 2 H 2 + 50 2 ) = 2CO 2 + H 2 O 1.5 314.9 315.7 All these calculations refer to the case where water is formed in the combustion (upper heat value). For getting the lower heat value the latent heat of evaporation of water (10.8 cal. per mol) has to be deducted. It follows also from equation pv = RT that wherever 1 mol of a gas at any pressure, p, is generated or disappears, the external work pv = RT = 1.982 T cal. will be consumed or generated. For the average air-temperature of 18 C. this quantity of work therefore is 1.982 (273 + 18) = 582 cal. In cases where, as in the bomb, the gases are actually generated or disappear, this phenomenon is taken into account by the com- bustion heat, which is measured directly. This, how r ever, is not the case in Parr's calorimeter, since here no gaseous oxygen is originally present and since the products of combustion formed disappear again. The determination of carbon is here not affected, the formation of C0 2 taking place without change of volume. It is different with hydrogen, since a contraction takes place during its combustion, but not in Parr's calorimeter. Therefore this calorimeter does not give the combustion heat at constant volume, but at constant pressure, which accounts for the fact that the results found with Parr's calorimeter are higher than the results found with the bomb. The following law can be derived directly from the energy principle above mentioned : The heat generated in a direct reaction is the sum of all heat quantities that are generated, provided that from a given 108 HEAT ENERGY AND FUELS initial state the final state is reached by various consecutive reactions. This law can be used for calculating reaction heats that cannot be measured directly, for instance, the heat of formation of carbon-monoxide : C + 2 = C0 2 generated q = 94.3 cal. C + = CO generated q l = x cal. CO + = C0 2 generated. . . q 2 = 68.2 cal. We have according to our law, q = q, + q r Therefore 1 = 94.3 - 68.2 = 26.1 cal. By this method the heat of formation of all organic compounds is calculated by deducting from their combustion-heats the heat of the elementary components, for instance : C + H 4 + 2 2 = C0 2 + 2 H 2 0g = 94.3 + 2 X 69.0 = 232.3 cal. C + H 4 = CH 4 q, =x cal. CH 4 + 2 2 = C0 2 + 2 H 2 0g 2 = 213.5 cal. 1 = 232.3 2 - 213.5 = 18.8 cal. Vice versa we can calculate from the heats of formation of organic compounds (which are found in the thermo-chemical tables) their heats of combustion, for instance : C 2 (Diamond) + H 2 = C 2 H 4 q = - 58.1 cal. 2 C 2 + 2 2 = 2 C0 2 qi =+ 188.6 cal.] H 2 + = H 2 (liquid) &= + 69.0 cal.j C 2 H 2 + 5 O = 2 C0 2 + H 2 (liquid) q 3 = x 3 = 188.6 + 69.0 - (- 53.1) = 315.7 cal. Relations between combustion heat and combustion tem- perature. The combustion heat changes with the temperature. The change depends on the fact whether the difference of specific heats of the system before and after combustion is positive or negative. We will show this by an example : COMBUSTION HEAT AND ITS DETERMINATION 109 We will calculate the combustion heat of hydrogen at 1000 C., supposing that the water formed remains in form of steam. We have then at 15 C. : H 2 + = H 2 (steam) . . . q l5 = + 69.0 - 10.8 = +58.2 cal. If we burn the hydrogen at 15 C. and heat the steam formed to 1000 degrees, we have : ,,1000 q l6 _ I cdt = 58.2 - 11.0 M5 = 47.2 cal. If we heat hydrogen and oxygen to 1000 degrees and then burn them at this temperature, we have /i oo (c, + c 2 ) dt + g 1000 = - (7.5 + 3.7) + q l(m .5 - - 11.2 + g 1000 and from this : /1000 (c -c, -cjdt = 58.4 cal. ,5 In this case the difference is small, in others much greater. We have, for instance, for CO + = C0 2 , 1000 ?dt= 68.2 - 12.4 = 55.8 cal. ,1000 f c a ) dt + q l(m = g 1000 - 11.1 15 and therefore q m = 66.9 cal. 7 ! Ju If we indicate the heat-capacities of the system in the initial and final state by c l and c u we can express this (KirchhofFs) law by the general formula : & = ft + ( c i + C H) tfi - 0- CHAPTER V. INDIRECT METHODS FOR DETERMINING THE COMBUS- TION HEAT. (a) Calculation of the thermal value from the elementary analysis. The fuels used in the industries are mixtures of different, not entirely known, chemical compounds. As these compounds have different thermal values it is evident that the calculation of the thermal value from the elementary analysis does not yield exact results. Furthermore the making of an elementary analysis is more complicated and more tedious than the combustion in a bomb, the difficulty of getting a good average sample being the same in both cases. For certain fuels, however, by using the proper empirical formula a result can be obtained that is sufficiently good for many practical purposes. For bituminous coal the following formula is used (Dulong) : 8080 C + 34600 (H - J 0) q - while for lignite, peat and wood, the formula = 8080 C + 29633 H t - 637 (W + W t ) q = 100 is used. In these equations C is the per cent of carbon; H, the per cent of hydrogen ; 0, the per cent of oxygen, and H t , the per cent of disposable hydrogen (H, = H - 0). W means the per cent of chemically combined water (W = | 0). Wj means the per cent of hygroscopic water. NOTE. Every coal even dry coal contains carbon, oxygen and nitro- gen. It was formerly thought that the O with a part of H was present as chemically combined water. The excess of H was called "disposable hydrogen." 110 METHODS FOR DETERMINING COMBUSTION HEAT 111 8080 means the combustion heat of carbon (Favre and Silber- mann). 34,600 means the combustion heat of hydrogen to water. 29,633 means the combustion heat of hydrogen to steam. 637 means the heat of evaporation of water. If a coal contains combustible sulphur, i.e. sulphur in other form than sulphate, some heat in the combustion is also generated by the sulphur, which is taken into consideration by adding to the above formula the product of the percentage sulphur S by W cal. (b) Berthier's method for determining the thermal value. Berthier's method is based on the determination of the oxygen- quantity required for the complete combustion of the fuel and on Welter's law, the incorrectness of which was proven long ago. This method however is still in use on account of its extraordinary simplicity. Welter supposed that, by burning a certain and constant quantity of oxygen with any other element, always the same amount of heat would be generated. This however is not the case, since 1 kg. of oxygen in combination with the following substances generates the following amounts of heat : Carbon to carbon dioxide 3030 cal. Hydrogen to water 4272 cal. Hydrogen to steam 4192 cal. As Berthier's calculation is based on the quantity of heat corresponding to the combustion of carbon to carbon dioxide by means of oxygen, it is evident that the results will generally be too low and the lower the more disposable hydrogen is contained in the fuel. Berthier proceeded as follows: 1 g. (of graphite 0.5 g.) of the finely ground fuel is weighed exactly and mixed with sifted litharge, which is free of metallic particles. The mixture is put into a test-cup (Fig. 29), covered with from 20 to 25 g. of litharge, care- fully put into a red-hot muffle-furnace, covered FIG. 29! Berthier's an< ^ quickly heated to red -glow; in from Coal Tester. three-fourths to one hour the operation is finished and the litharge according to the fuel quantity reduced, by oxidizing the fuel : 2 PbO + C = 2 Pb + CO,. 112 HEAT ENERGY AND FUELS From the weight of the metallic lead obtained, the quantity of oxygen combined with the fuel can be calculated. The test-cup is now removed from the muffle, shaken up several times to combine the small lead-particles, that may be distributed through the litharge, with the main lead mass and allowed to cool. The cup is now broken, the piece of lead brushed clean, and the litharge examined for particles of lead. In calculating the thermal value, the hydrogen present is not taken into consideration, i.e. it is assumed that only the oxygen has combined with carbon. Since 1 kg. carbon re- duces about 34 kg. of lead and yields by combustion 8080 cal., the weight of the lead obtained is simply divided by 34 multiplied by 8080 for getting the absolute thermal value of the fuel in question. Sulphur would have to be determined separately and taken into consideration as explained above. Various modifications of Berthier's test were recommended. Forchhammer suggested the use of oxychloride of lead in place of litharge. Munroe uses instead of the test-cup a gas-pipe provided with a plug at one end, while Strohmeyer oxidizes the fuel by means of cupric oxide, treating the residuum with hydro- chloric acid and ferric chloride and determining the ferrous chloride formed by titration. (c) Other empirical methods for determining the fuel value. An important advance is the empirical formula of Dr. Otto Gmelin, based upon a few simple operations, which gives very much better results than Berthier's process. Gmelin assumed that the coals are mixtures of various chem- ical compounds, which compounds differ from each other not only chemically, but also physically. He selected such a physical property, the ability of retaining hygroscopic water and based his empirical formula upon this property: q = [100 - (H 2 + "ash")] 80- C (6 H a O), in which equation H 2 means the hygroscopic water, "ash, " the ash-content of the fuel in per cent and C a coefficient which changes with the moisture of the coal and has the following values : METHODS FOR DETERMINING COMBUSTION HEAT 113 Hygroscopic water below 3 per cent C = - 4 Hygroscopic water between 3 and 4.5 per cent. . C = + 6 Hygroscopic water between 4.5 and 8.0 per cent C = + 12 Hygroscopic water between 8.5 and 12.0 per cent C = + 10 Hygroscopic water between 12 and 20 per cent . C = + 8 Hygroscopic water between 20 and 28 per cent . C = + 6 Hygroscopic water over 28 per cent C = + 4 Seven years later the author tried to utilize more simple properties that would be more independent of accidental circum- stances than the moisture, and also be related to the chemical composition and therefore to the combustion-heat of the fuels. He selected the behavior of fuels in dry distillation and the determination of the oxygen required for complete combustion. He proceeds as follows: About 1 g. of the finely powdered fuel is weighed in a platinum- crucible and after determining the moisture W by drying at 100 C. is heated (observing ordinary precautions) until combustible gases are given off. The loss of weight in per cent represents the gas-yield G. The residuum P per cent is now completely burned in the open, inclined crucible whereby the ash content A and the fixed carbon or coke-carbon K is found. The latter however always contains negligible quantities of oxygen, hydrogen and nitrogen. The quantity of oxygen required S is most conveniently determined with about 5 g. of fuel by Berthier's method. The quantity of oxygen required for burning the fixed carbon is found by the following equation : o2 ^ o _, The oxygen for completely burning the gaseous products of distillation is : The combustion heat of the fixed carbon was (as average) empirically determined as 7630 cal. per 1 kg. of carbon, while the combustion heat of the gaseous products of distillation varies 114 HEAT ENERGY AND FUELS according to the quality of coal and composition of the gases of distillation. The nature of a fuel is indicated by the ratio (weight) of /C\ gaseous products of distillation and fixed carbon f J; and even more so by the ratio of the oxygen required for the volatile /S N matter to the oxygen required for the fixed carbon ( ) The latter ratio is used empirically for determining the thermal- value of a fuel by means of the equation : wherein C is a coefficient, the value of which depends on the o quality of the fuel (wood, peat, lignite, coal) and the ratio - . TABLE XXXVII. RATIO OF S g TO Sfc. Sg Values of C for s k Wood and Peat. Lignite. Bitum. Coal. 0.25 5500 5600 0.50 4930 4300 3500 1.00 4830 3420 3250 1.50 4750 3350 3225 2.00 4660 3350 3210 2.50 4570 3360 3200 3.00 4470 3370 3180 3.50 4360 3170 4.00 4255 3500 3150 4.50 4150 3140 5.00 4045 3700 3130 5.50 3940 3120 6.00 3830 3950 3100 6.50 3080 7.00 3070 7.50 3060 8.00 3050 In order to make the formula independent of the kind of fuel and to base the calculation of the thermal value entirely upon the content of moisture, ash, gas, fixed carbon and oxygen required for combustion, the different fuels were divided into METHODS FOR DETERMINING COMBUSTION HEAT 115 four groups according to their ability to give off gas when dry and free of ash and the value of C calculated for each of the S groups according to the different values of -^ The following &k table by means of which the thermal value can be determined without any knowledge of the quality of the fuel is easily understood. TABLE XXXVIII. DATA FOR DETERMINING THERMAL VALUES. GROUP I II III IV Gas given off by the Fuel (dry and free of ash). - 33% 33-47.5% 47.5-75% 75- 100% gg 8k Values of the Coefficient C. 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.54 0.55 0.60 0.70 1 0.80 0.90 1.00 . 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 4900 4550 4230 3960 3730 3540 3380 3250 3150 3086 3070 3000 2900 2850 2850 2850 5100 4800 4500 4220 4010 3850 3710 3600 3512 3490 3400 3280 3210 3166 3130 2955 5250 4900 4600 4350 4170 4020 3932 3910 3820 3690 3600 3558 3550 3550 3550 5050 4815 4619 4480 4230 4170 4120 4070 4020 3970 3920 3870 3820 3770 The following empirical formulas have since been proposed By G. Arth: = 34,500 (H - I 0) + 8080 C + 2162 S q ~ 100 116 HEAT ENERGY AND FUELS By E. Goutal (a modification of Jiiptner's formula) : q = 8150 C + AM. M is the quantity of volatile matter, A a coefficient the value of which is : Volatile substances = 2 to 15 per cent. . . . A = 13,000 Volatile substances = 15 to 30 per cent. . . . A = 10,000 Volatile substances = 30 to 35 per cent. . . . A = 9500 Volatile substances = 35 to 40 per cent. . . . A = 9000 The international union of the steam-boiler-inspection societies has adopted the following formula : = [SOOO C + 2900 ( H - - } L \ 8 / 2500 S - 600 lp* 100 in which W means the quantity of hygroscopic water. The differences against direct calorimetric determinations are (L. C. Wolff) : For bituminous coal ................. 2 per cent For lignite ......................... 5 per cent For peat ........................... 8 per cent For cellulose ....................... - 7.9 per cent For wood ........ . .................. 12 per cent By D. Mendeleeff : q = 81 C + 300 H - 26 (0 - S). D. de Paepe has substituted for the value M in Goutal 's f . 100 M formula the expression - - - SUGGESTIONS FOR LESSONS. Practice in handling various combustion-calorimeters; deter- mination of water-value and error-limit. Comparative determination of the combustion heat by different methods. Calculation of combustion heat at constant pressure from the combustion heat at constant volume and vice versa. Calculation of combustion heats for given combustion tem- peratures. CHAPTER VI. INCOMPLETE COMBUSTION. THE complete combustion of the fuels used in the industries yields carbon dioxide and water. The chemical composition of the fuel being known, the quantity of oxygen theoretically required for complete combustion is easily calculated. This quantity is called the theoretical quantity of oxygen necessary for complete combustion. The average composition of dry air, free of carbon dioxide, being Oxygen. . Nitrogen. 21 per cent vol. 23 per cent weight 79 per cent vol. 77 per cent weight it is a simple matter to calculate the theoretical quantity of air required for complete combustion. (In many cases it is sufficient to calculate approximately and to assume the composition of air: 20 per cent vol. O and 80 per cent vol. N.) The CO 2 content of the air varies from 0.04 to 0.06 per cent. In densely inhab- ited buildings it can go as high as 0.5 and even 0.9 per cent vol. The quantity of moisture in the. air varies considerably. Air saturated with moisture contains per 1 cu.m. Degrees C g. H 2 0. Degrees C. g. H 2 0. -10 + 5 + 10 + 15 + 20 2.284 4.871 6.795 9.36-2 12.746 17 157 + 25 + 30 + 35 + 40 + 100 22.848 30.095 39.252 50.700 588.730 The moisture of the air is generally below saturation and above ^ the quantity required for saturation. In heating tests the moisture of the air has to be determined by means of a hygrometer or psychrometer. In practice, however, this theoretical quantity of air is not sufficient for complete combustion and therefore an excess of air has to be used. 117 118 HEAT ENERGY AND FUELS The reason for this is the difficult and incomplete mixture of the gases to be burned with the combustion air and the occurrence of incomplete reactions. The incomplete combustion can therefore furnish various products, as follows: CO, or C + C 2 H 4 + } C0 2 + J C > (~^(~\ I o TT /-vi 1 v^v/9 ~T~ ^ -*"i-9} or 2 CO + 2 H 2 CO + CH 4 , or CO + C + 2 H 2 , or C 2 H 2 + H 2 0, etc. The number of different reactions that can take place simul- taneously and in parallel is frequently very great. The number of reactions and the quantity of products depend on the pre- vailing conditions. In all these cases we speak of a chemical equilibrium which depends on the so-called equilibrium-conditions. Such condi- tions are: Temperature, pressure, electric state and the mutual relation of the elementary components present, i.e. the concen- tration. By a change of the conditions, the state of equilibrium is changed as follows (Henry Le Chatelier) : Any change in an equilibrium factor causes a change in the system which is directly opposite to the change in the factor. This law is best explained by an example : 1. Any increase of temperature causes a change, which tends to decrease the temperature of the system and vice versa. Example : (a) Dissociation: C0 2 - CO + - 68.2 cal. H 2 -> H 2 + O - 58.2 cal. In both reactions heat is absorbed and therefore both are caused or facilitated by increase of temperature. The reaction 2 CO - C + C0 2 + 42.0 cal. in which heat is liberated, is facilitated by decrease of tem- perature. Carbon monoxide is therefore more stable at high INCOMPLETE COMBUSTION 119 than at low temperatures. In the presence of platinum, iron or especially nickel in fine, spongy form this reaction takes place completely at about 300 C. (6) Incomplete reactions : C0 2 + H 2 - CO + H 2 O - 10 cal. CH 4 + CO -> C 2 H 2 + H 2 - 39 cal. In both reactions absorption of heat takes place; they are therefore caused and facilitated by increase of temperature. At low temperature more C0 2 + H 2 , or CH 4 + CO; at high temperature more CO + H 2 or C 2 H 2 + H 2 0, will be present. The reaction CO + H 2 - C0 2 + H 2 + 10 cal. will naturally be facilitated by lowering the temperature. 2. Any increase of outside pressure causes a change of equi- librium, by which the pressure is decreased and vice versa. Examples : (a) Dissociation: 2 C0 2 -* 2 CO + 2 2 H 2 -> 2 H 2 + 2 . By the dissociation of C0 2 or H 2 the volume, or (at constant volume) the pressure is increased 50 per cent. The dissociation will therefore increase with decreasing pressure and decrease with increasing pressure. (6) Incomplete reactions : C 2 H 2 + H 2 -CH 4 + C. The volume of solid carbon, which is exceedingly small, need not be considered. The volume, however (or at constant volume the pressure), of the CH 4 formed is only half of the volume of the original mixture of C 2 H 2 and H 2 . The reaction is there- fore facilitated by increasing the pressure. This is proven by explosion in closed vessels, whereby the quantity of CH 4 and C increases with the pressure. The equilibrium CO + H 2 + C0 2 + H 2 is (if the water is in form of steam) independent of the pressure, as we have on both sides the same volume and therefore also the same pressure. 120 HEAT ENERGY AND FUELS The reaction 2 CO = C + C0 2 is decreased by decreasing the pressure because the volume and therefore also the pressure of C0 2 is only half that of 2 CO. 3. Any increase in concentration of a substance in a system causes a change in the state of equilibrium, in which a certain quantity of this substance is removed and vice versa (mass- action). The quantitative expression for the relations between chemical equilibrium and equilibrium-conditions is different if the equilibrium at a certain temperature or the equilibrium at any temperature is considered. In the first case, i.e. for the isothermic equilibrium, the law of mass-action; in the second, general case, van't Hoff's or Le Chatelier's equation has to be applied. For gas-mixtures the latter equation is preferable as the numerical concentration results directly from the volumetric composition of the gases. We want to consider now an example of great importance in the industries. DISSOCIATION OF CARBON DIOXIDE. At high temperature carbon dioxide is decomposed according to the equation : If RJ Le Chatelier's equation in general form is : Q T dT + (N"-N') IP + n 2 l C 2 - ^X/ C, = constant. In this equation Q T stands for the total heat of reaction (sum of heat generated and external work performed by the reaction, both expressed in cal.) at the temperature T, P is the pressure of the system, N" and N' the number of molecules on the right and left side of the equation, n l anU n 2 the number of molecules, C 1 and C 2 the concentrations of the different substances taking part in the reaction, index 1 meaning the initial system, and 2 the final system. INCOMPLETE COMBUSTION l2l If we use the common instead of the natural logarithms and if we make = 500, we can write our equation : H 500 + 2.3026 (N"~ N') log P + 2.3026 2 log C 2 -5^ log Cj = constant. N" - N' = 1.5 - 1 =O.5, therefore L log Cj = log / = log If we make the total concentration of the system after the establishment of equilibrium = 1, we have Assuming that no surplus-oxygen is present, we conclude from the reaction equation : C,, = JC M . (2) We call x the ratio between the dissociated carbon dioxide, (i.e. the carbon monoxide formed) and the quantity of C0 2 that would be present if no dissociation had taken place, i.e. C co + C C02 , the coefficient of dissociation, and we have x = _ Cco - (3) There can be deduced from (1) and (2) the following equations + f C0 2 to be independent of temperature, and taking Q = 68.2 cal., we have fiT x^ + 1.1513 log P + 2.3026 log (1 _ x) (2 + ^ = Constant; or as for P = 1 at., log P = 0. therefore - 34100 Constant= - ^rp t 2.3026 log Q ^ = - 11.7192; + 1.1513 log P + 2.3026 log K = - 11.7194, T or 14809 logK - (^ _ 1L 7i92 - 1.1513 log P) ^ .3026 - 5.0895 - 0.5 log P. INCOMPLETE COMBUSTION 123 From this Le Chatelier has calculated the values of x given in Table XXXIX. TABLE XXXIX. COEFFICIENTS OF DISSOCIATION. (Le Chatelier). Temperature Degrees C. Pressure in Atmospheres. 0.001 0.01 0. 1 1 10 100 1000 1500 2000 2500 3000 3500 4000 0.007 0.07 0.40 0.81 0.94 0.96 0.97 0.003 0.035 0.125 0.60 0.80 0.85 0.90 0.0013 0.017 0.08 0.40 0.60 0.70 0.80 0.0006 0.008 0.04 0.19 0.40 0.53 0.63 0.0003 0.004 0.03 0.09 0.21 0.32 0.45 0.00015 0.002 0.025 0.04 0.10 0.15 0.25 The results of these calculations agree with the observations made at 1500 C. on the density of carbon dioxide. If we keep in mind that it is the partial pressure of carbon dioxide that is dealt with here, we can make from the above table the following conclusions, which are of importance in practice : 1. Smelting furnaces. In smelting furnaces the maximum temperature reached is 2000 C., and the maximum partial pressure of carbon dioxide is about 0.2 at. There is therefore about 5 per cent of the latter dissociated, which decreases the capacity of the furnace to a small extent (maximum ^V, but generally much less on account of the excess of air used, which diminishes the dissociation of carbon dioxide). 2. Illuminating flames. The luminous flame-zone, in which the separated carbon is burned, seems to have in ordinary flames a temperature of about 2000 C. ; in regenerative-burners the temperature is higher. On account of the high percentage of hydrogen in illuminants, the C0 2 partial pressure falls below 0.1 at. Therefore the dissociation can go above 10 per cent, the flame-temperature decreasing accordingly. The illu- minating power, which increases much faster than the temper- ature, decreases to a much larger extent, which shows that the dissociation is an important factor in illuminating flames. 124 HEAT ENERGY AND FUELS 3. Explosives. Their combustion- temperature is in most cases below 2500 C. and always below 3000 C. As the pressure of carbon dioxide herein goes into thousands of atmospheres, the dissociation does not have to be considered. On account of the very high pressures, in using the equili- brium equations for explosives, the law of Boyle-Gay-Lussac (PV = nRT) must not be used ; it is necessary to introduce into the equation a constant b : P(V -b) = nRT. Similar conditions prevail in the dissociation of water. As we have seen above, we have (if no excess of oxygen is present) : 2x x C co =;;--> quantity of oxygen = - - x 2 + x 2 + x and - 2 (1 - x) = 2 (1 - x) 2 + x 2+x Sum = _ If we have (n + 1) times the quantity of oxygen, the equation for the reaction reads as follows : CO, + (n) 2 = CO + (n + J) 2 and we have, after the equilibrium has been established, x* mols CO (1 - x 9 ) mols C0 2 - + n } mols 2 INCOMPLETE COMBUSTION 125 and therefore - x' 2* Therefore 2 c m =- 2- ^ + 2n **& 1 - x 7 2 + a/ + 2n n 2 (1 - z') ^ h 2" / 2 + ^ + 271 2 xf / x' + 2 n Y (CJ (Cg 2 + '. c' + 2 n \2 + x' + 2 n / x' ( ^ + 2n 2 (1 - z') 2 + a/ + 2 n / ^ + a/(2n) V2 + xf + 2ri 1 - xf (I - xf) (2 + ^ + 2 n)* As K necessarily has the same value as in the former case, we can say : x* x'* + x' (2 n)* u (1 - x) (2 + x)* ~ (1 - z') (2 + x f + 2 n)* ' If we had used twice the theoretical amount of oxygen, n would have been equal to one (n = 1) and we would have x* xf* + x'V2 < x'* + x' \/2 (1 - x) (2 + )* (1 - xf) (2 + x' + 2)* (1 - a/) (4 + a/* + 1.4142 ' = (1 - xf) (4 + 126 HEAT ENERGY AND FUELS We found (see above) i = 0.05 for C0 2 at 2000 C. and 0.2 at partial pressure. Substituting this value, we get : 0.05* xf* + 1 4142 x' an equation from which x' can easily be calculated. We see at a glance that x' is smaller than x. CHAPTER VII. COMBUSTION-TEMPERATURE. THE maximum temperature that a fuel could produce if burned completely, without any loss of heat, with the theoretical quantity of air, we call pyrometric heating-effect. It is gener- ally calculated from the equation : wherein q stands for the quantity of heat generated by com- bustion, and c and p for the specific heat and the quantity of components contained in the products of combustion respec- tively. This temperature however can never be attained in practice. The temperatures of industrial fires and fire-places depend on : 1. The quantity of heat furnished by the fuel, which consists of . (a) The heat of combustion proper and (6) The heat previously stored, i.e. the heat-content of the substances used. 2. The heat carried away by the products of -combustion which may be latent (for instance, CO leaving a blast-furnace). 3. The heat lost by radiation. 4. The heat generated or absorbed by the substances to be treated. 5. The quantity of heat used for forming and expanding the gases generated in the fire. There is a relation between all these quantities, which can be deduced from the principle of conservation of energy. Proceeding from the fuel, air and substances to be worked, in the first stage, the sum of all heat-quantities introduced into or generated in the fire, is independent of the order in which the transformations take place, depending only on the first and last stage. 127 128 HEAT ENERGY AND FUELS We therefore can say that the quantity of heat introduced into the furnace is equal to the quantity taken out of the furnace. The heat introduced into or generated in the furnace equals the heat taken from the furnace. These quantities of heat consist of : 1. Heat introduced into the furnace by fuel, air and sub- stances to be worked (by their own temperature). 2. Heat of combustion. 3. Heat of reaction of the substances to be worked. 4. Heat content of the combustion gases. 5. Heat content of the finished products. 6. Loss of heat by radiation. Since the absolute heat-content of the substances as they enter or as they leave the furnace cannot be determined, we have to be satisfied with a relative determination generally referred to a certain normal condition, which serves as a base for the cal- culations. As such the temperature of melting ice is generally used. Let us imagine an ideal furnace which perfectly insulates the heat and in which no working products are present. If we introduce into this furnace fuel and air of a certain temperature (say 0C.), allow combustion of same and then cool the com- bustion gases to the initial temperature (0 C.), we have the equation : Heat of combustion = Heat of cooling. A. The heat of comb.ustion is a known quantity. The heat of cooling is the difference of the heat-content of the combustion products at the temperature at which they leave the furnace and at the starting temperature (here C.), to which we imagine them cooled again in the end. In our ideal furnace, the heats of combustion and of cooling are equal. The products of com- bustion leave the furnace at the combustion temperature, which, as we will see, is easily calculated. The heat content is equal to the weight of the combustion prod- ucts multiplied by their specific heat and their temperature. If we use the absolute temperature, we obtain the total heat con- tent; if we use the temperature in centigrade we obtain the heat- quantity, by which the substance in question is richer than at 0C. COMBUSTION -TEMP ERA TURE 129 In calculating the pyrometric heating , effect, formerly the specific heat was taken as constant, i.e. independent of- tem- perature. The following are the figures used : TABLE XL. SPECIFIC HEAT OF GASES AND VAPORS AT CONSTANT PRESSURE (Referred to Unit Weight.) Name. Interval of Tem- perature. Degrees. Specific Heat. Observer. Air Air 0100 200 0.23'741 23751 Regnault Oxygen Nitrogen Hydrogen . . 13207 0200 12 198 0.21751 0.2438 3 4090 a Carbon monoxide Carbon monoxide 23 99 26 198 0.2425 2426 Wiedemann u Carbon dioxide Carbon dioxide Water Vapor Methane Ethylene 15100 11214 128217 18208 24100 0.20246 0.21692 0.48051 0.59295 0.3880 Regnault H (i it Wiedemann By means of these figures the temperature of combustion of carbon in pure oxygen is calculated as follows: t = 8080 = 10201 C.* 3.667 X 0.217 The combustion of coal in the theoretical amount of air should give: t = 8080 = 2719 C.f 3.667 X 0.217 + 8.929 X 0.244 while the combustion of carbon with double the volume of air would yield J 8080 3.667 X 0.217 + 8.929 X 0.244 + 11.596 X 0.238 8080 0.792 + 2.179 + 2.760 1410 C. * By the combustion of 1 kg. carbon to CO 2 8080 cal. are generated; 3.667 kg. CO 2 are thereby formed, having a specific heat of 0.217. t 8.929 kg. nitrogen are present in the air of combustion besides 2.667 kg. oxygen. | 11.596 kg. is the weight of the surplus air. 130 HEAT ENERGY AND FUELS TABLE XLI. COMBUSTION DATA ON VARIOUS UNITS. Combustion of Combus- tion Heat in Cal. Combustion Temperature in Degrees C. With Pure Oxygen. With the necessary air Volume. With double the air Volume. Hydrogen to steam Carbon (amorphous) to carbon dioxide Carbon (amorphous) to carbon monoxide Wood dried at 120 Wood ordinary with 20 per cent hygroscopic water Of 1 unit (weight) 28780 8080 2400 3600 2750 6860 Of 1 Liter 6.0 Of 1 Mol. 191930 313200 68370 125930 773400 Degrees 6670 10201 Degrees 2665 2719 1400 2500 1900 2400 2530 2440 2750 3040 2860 2790 Degrees 1410 1300 1100 1340 Coke 7500 7160 8620 7180 6940 Illuminating gas Methane CH 4 to CO 2 and H 2 O Ethylene C 2 H 4 to CO 2 and H 2 O . . Carbon monoxide CO to CO 2 .". . . Water gas CO + H 2 to CO 2 + H 2 O Benzole C 6 H 6 to CO 2 and H 2 O ... If the combustion of fuel and air takes place at any other temperature than degrees, proper allowances must be made. If we had to burn, for instance, 1 kg. of hydrogen of 50 C. with exactly the theoretical amount of dry air of 20 C., the quantity of heat available after combustion is figured as follows : 170.45 cal. 34.88 cal. 1 kg. of hydrogen of 50 C. contains 1 X 3.409 X 50 8 kg. of oxygen of 20 C. contain 8 X 0.217 X 20 26.64 kg. of nitrogen (which are present in the combustion-air besides the oxygen) of 20 degrees contain 26.64 X 0.244 X 20. . 65.00 cal. Sum of the heat supplied before combustion . . = 270.33 cal. The combustion of 1 kg. of hydrogen to steam yields Heat quantity available after combustion. ... = 29,050.33 cal. 28,780.00 cal. COMBUSTION-TEMPERATURE 131 On the other hand the heat capacity of the combustion pro- ducts is : Steam (1 + 8) X 0.4805 .................. 4.325 cal. Nitrogen 26.64 X 0.244 ................... - 6.500 cal. Total ............................... 10.825 cal. The temperature of combustion therefore is : 29,050.33 If the temperature of hydrogen and air before combustion had been C., the temperature of combustion (according to Table XLI) would have been 2665 degrees. The heating of the hydrogen to 50 degrees and of the air to 20 degrees therefore increases the temperature of combustion by 2683 - 2665 = 18 C. The results of these methods of calculation are too high, as the specific heat of substances increases considerably with the temperature. The law governing the relations of specific heat and temperature (for gases) can be expressed according to Le Chatelier 'by one of the general equations C p = 6.5 + aT or C v = 4.5 + aT. C P and C v stand for the average specific heat of 1 gram- molecule at constant pressure or constant volume respectively, T is the absolute temperature, a has the following values for different gases : for 2 atomic gases (H 2 , N 2 , 2 , CO) ....... a = 0.0006 for CO 2 ............................... a = 0.0037 for H 2 ............................... a = 0.0029 for C 2 H 4 ...... ........................ a = 0.0068 The total heat content of a gas at the temperature T = C P XT or C v X T and the difference of the heat content of a gas between T and T is C p (T - T ) and C v (T - T ) respectively. For simplifying the calculation the following table gives the values of C p (T - T 9 ), also the difference (C p - C v ) (T - T ) = A X P (V -V ) = nAR (T - T ), i.e. the external work according to H. Le Chatelier. 132 HEAT ENERGY AND FUELS TABLE XLII. DATA ON EXTERNAL WORK. Temperature C. 200 1.4 1.8 1.9 0.4 400 2.8 3.7 4.0 0.8 600 4.3 6.0 6.4 1.2 800 5.8 8.2 9.0 1.6 1000 1200 1400 1600 CO, N 2 , O 2 , H 2 .. HO 7.4 11.0 12.4 2.0 9.0 14.0 15.5 2.4 10.7 17.0 19.2 2.8 12.5 20.3 23.1 3.2 CO 2 Work AR(T-T ) Temperature C. 1800 2000 2200 2400 2600 2800 3000 CO, N 2 , 2 , H 2 H 2 CO 2 Work AR(T T ) 14.2 24.0 27.3 3.6 16.0 28.3 32.0 4.0 17.3 32.5 38.2 4.4 19.1 36.8 43.7 4.8 21.0 41.5 49.6 5.2 22.9 46.4 55.4 5.6 24.8 51.3 61.7 6.0 EXAMPLE: Calculation of the combustion heat of hydrogen in air. Pure dry air contains in 100 mols. 20.8 2 + 79.2 N v or about 20 2 + 80 N v or about 4 mols. N for every mol. 0. The combustion of hydrogen with the theoretical amount of air therefore corresponds to the equation : In this equation we have at constant pressure a combustion heat of 58.2 cal. = 58,200 cal. for every mol. of burned hydrogen. The products of combustion consist of 1 mol. steam (H 2 0) and 1 mol. nitrogen. Since the combustion heat is equal to the cooling heat, we have : 58,200 = 6.5 (T - T ) + 0.0029 (T 2 - T 2 ) + 2 [6.5 (T - T ) + 0.0006 (T 2 - T Q 2 )] = 19.5 (T - T ) + 0.0041 (T 2 - T 2 ). If TO = C. and x the temperature (in C.) to be found, we have T = 273 and T = 273 + x and 58,200 = 19.5 x + 0.0041 (546 x + x 2 ). COMBUSTION-TEMPERATURE 133 This is a quadratic equation the solution of which is not at all difficult, but most conveniently obtained by graphical con- struction. We know that the combustion-temperature is in the neighborhood of 2000 C. Calculating the cooling heats for temperatures in this neighborhood we have, using Table XLI : 1800 2000 C. 2200 C. 2400 G. H2O.. . 24 28 3 32 5 36 8 2N 2 28 4 32 34 6 38 2 Total 52.4 60.3 67.1 75.0 The combustion temperature in question therefore must be between 1800 and 2000 C. By taking the cooling-heats as ordi- nates and the temperatures as abscissas we obtain the curve shown in Fig. 30. By marking on the ordinate-axis the heat- FIG. 30. Diagram for Combustion Temperatures. generation (58.2 cal.) drawing from here a horizontal line to its intersection with the curve, and a vertical line through the intersection point, we see that the vertical line intersects the axis of temperature at a point corresponding to the required combustion-temperature (1960C.). An analogous calculation is applied if the combustion takes place at constant volume (for instance, in Mahler's bomb) . The combustion heat at constant volume (taking the water as steam) is 58 calories. The heat 134 HEAT ENERGY AND FUELS necessary for heating is obtained by deducting the external work 3 AR (T - 7 7 ) : 1800 2000 2200 2400 Heat required at constant pressure External work 52.4 10.8 60.3 12.0 67.1 13.2 75.0 14.4 Difference 41 6 48 3 KQ q fin fi From Fig. 31 we see that the combustion-temperature is 2320 C. In this calculation the dissociation is not considered; therefore so. iooo 2200" 606 2320 VOP FIG. 31. Diagram for Combustion Temperatures. the calculated temperatures are slightly too high. The dis- sociation however can be taken into consideration by inserting in the temperature equation the coefficient of dissociation as a function of the temperature. Generally, however, a different method is pursued. As an example we will discuss the combustion of carbon monoxide. Calculating the combustion-temperature without considering the dissociation, we find as the result 2100 C. We know from the preceding chapter that the coefficient of dissocia- tion of carbon dioxide at this temperature and at a partial pressure of 0.20 atm. is 0.06. The heat-generation resulting from combustion therefore is 68 (1 - 0.06) = 64 cal. COMBUSTION-TEMPERATURE 135 In calculating the cooling-heat of the combustion-products we have to take 0.06 less C0 2 (the amount dissociated at this temperature), and we have to add 0.06 CO + 0.03 2 , whereby the heat required for heating is decreased by 0.06 (33.8 - 1.5 X 16.6) = 0.6 X 8.9 = 5.34 cal. The heat of combustion is therefore 2050 instead of 2100 C. Analogous calculations show the following values for the combustion-temperature of different gases with air containing 20 per cent of oxygen at an initial temperature of C., without considering the dissociation: TABLE XLIII. COMBUSTION-TEMPERATURE OF VARIOUS GASES. At Constant Pressure. Volume. H 2 .. I960 C 2100 C 2040 C 1850 C 1525 C 2320 C 2430 C 2370 C 2150 C I860 C CO k (CO + H,) CH 4 to CO 2 + 2H 2 O CH 4 to CO + 2H 2 O By comparing these with the previously calculated tempera- tures of combustion (which were obtained by assuming the specific heats to be constant) the excess of the latter can be noted. COMBUSTION-TEMPERATURE OF SOLID SUBSTANCES. The same method of calculation can be applied to the com- bustion of solid substances as carbon, coals, etc. We suppose again the air to contain 20 per cent volume of oxygen. For sim- plifying the calculation such quantities of the solid fuel are used that the volume of the gases of combustion (reduced to C. and 760 mm. pressure) is 22.42 liters, i.e. corresponds to a mol., because the volumetric composition of the combustion gases then shows directly the number of mols of the different gas- constituents present. 136 HEAT ENERGY AND FUELS We will now consider the combustion heat of amorphous carbon, which differs from that of diamond or graphite. 12 g. diamond yields 94.3 cal. 12 g. graphite yields 94.8 cal. 12 g. amorph. carbon yields 97.6 cal. According to the equation C +0 2 +4N 2 = C0 2 +4N 2 ; the composition of the combustion gases is : C0 2 20 per cent volume N 2 80 per cent volume In order to obtain a molecular volume (22.42 liters) of com- bustion-gases 0.2 gram-atoms of carbon must be burned, which yields by the combustion : Q = 0.20 X 97.6 = 19.5 cal. The heating of the combustion-products requires : 2000 C. 2200 C. For CO 2 6 40 7 64 For 4N 2 12 80 13 84 Total .... 19.20 21.48 The combustion-temperature in question therefore is 2026 C. Actually, however, not only C0 2 is formed by the combustion, but also, according to circumstances, either free oxygen (dis- sociation), or carbon monoxide or steam (from hygroscopic water). Accordingly we get the following results: COMBUSTION OF AMORPHOUS COAL. Theoretically, if C0 2 is formed exclusively. . . 2026 C. With 5 per cent oxygen 1950 C. With 5 per cent carbon monoxide 1930 C. Theoretically, with 25 g. of water per 1 kg. carbon... 1950 C. Combustion to carbon monoxide 1250 C. COMBUSTION-TEMPERATURE 137 COMBUSTION-TEMPERATURE OF A NATURAL COAL. The combustion-temperature of a natural coal is figured by a similar method. As an example we take bituminous coal of Commentry showing the following composition : C 75.2 per cent H 5.2 per cent ~ 8.2 per cent N 1.0 per cent Hygrosc. H 2 3.4 per cent Ash 7.0 per cent Total 100.0 per cent The composition of the combustion gases is calculated as follows : C0 2 = 752 : 12 = 62.7 (1) H 2 hygroscopic = 34 : 18 = 1.9 > ~7 q ~v from coal = 52 : 2 = 26.0 \ ' N : By the combustion there are formed : C0 2 with 62.70 H 2 with 13.00 Total 75.70 From the coal 2.50 Difference 73.20 This 73.2 corresponds to 4X73.2= 292.8N) N from coal 10 : 28 = 0.4 Np Total from (1), (2), (3) 383.8 volume. , The volumetric composition of the combustion-gases therefore is: CO, 10 38 X 3 g 2 " 7 = 16.34 per cent voL . 7.27 per cent vol. XT 100 X 293.2 N - = 76.39 per cent vol. ooo.o Total ...... 100.00 per cent vol. 138 HEAT ENERGY AND FUELS From this we can figure the heat of the combustion gases : 1800 C. 2000 C. 2200 C. 17.053 19.508 21.820 The combustion heat is Q = 19.888 cal. and the combustion-temperature 2034 C. COMBUSTION-TEMPERATURE OF PRODUCER GAS. As we shall see later there are frequently used in the industries gaseous fuels, which allow a better utilization of heat. The ideal composition of such a producer gas is : CO + 2 N 2 . Theoretically, this gas requires for combustion i(0 2 ) +2N 2 and yields C0 4 N 2 . The combustion of CO + } (0 2 ) + 4 N 2 gives 68 cal. If the gas is heated before combustion to 1000 C., 5.5 X 7.3 = 40 cal. are required. The total amount of heat, therefore, on which the calculation of the combustion-temperature has to be based is 68 + 40 = 108 cal. TABLE XLIV. HEAT OF THE COMBUSTION PRODUCTS 2000. 2200 C. 2400 C. CO 2 .. 4N, 32.0 64 38.2 69 2 43.7 76 4 Total 96 107 4 120 1 Combustion-temperature = 2220 C. , The same gas gives under different conditions : Theoretically, cold 1500 C.; cold, 5 per cent 1210 C. Gas + air 500 I860 C.; cold, 5 per cent CO 1320 C. Gas + air, 1000 2220 C. COMBUSTION-TEMPERATURE 139 The air used for the production of producer gas always contains varying quantities of water vapor or steam, which is decom- posed by coming in contact with glowing coal, so that the gas contains less nitrogen. With an average content of 250 g. of water per kilogram of coal, the gas obtained contains per gram- atom of carbon : CO + t (H 2 ) + 4 (N 2 ). The combustion-temperature of this gas is : Gas + air: cold 1550 C. Gas + air: 500 1930 C. Gas + air: 1000 2230 C. In practice however the composition of producer gas differs from the above, since it always contains some C0 2 and H 2 and also (if bituminous coal or lignite is used) gaseous hydrocarbons. As an example the following analysis of such a gas is given (referred to 1 mol. of gas mixture) : CO 0.20 vol. H 2 ....- 0.10vol. C0 2 0.05 vol. H 2 0.02 vol. N 0.63 vol. Total 1.00vol. The combustion of this gas yields : TABLE XLV. COMBUSTION OF PRODUCER GAS. Combustion Products. Combustion Heat. CO 2 . . 25 13 6 cal H 2 O. ... 12 5 8 cal N 2 1 23 Total 1.60 19. 4 cal. The calculation shows the following combustion-temperature: Gas and air: cold 1350 C. Gas and air: 1000. . . 2150 C. 140 HEAT ENERGY AND FUELS SUGGESTIONS FOR LESSONS. Calculation of the combustion-temperature of a fuel of known composition and combustion heat, using different quantities of combustion air, at different temperatures of fuel and air. Calculation of the combustion-temperature if the composition of the combustion gases (at different temperature of fuel and air) is given, besides the composition and the thermal value of the fuel. CHAPTER VIII. FUELS. (IN GENERAL.) WE call "fuel" any substance which combines with oxygen accompanied by the generation of heat and therefore can be used in practice as a source of power. Under the term "fuel" in the widest sense of the word we include solids and liquids containing carbon (wood, peat, coal, coke, oil, tar, alcohol, etc.) and gases containing carbon or hydro- gen (illuminating gas, natural gas, producer gas, water gas, etc.) and also various other substances, the oxidation of which is used in the industries as a source of heat. Some of the latter sub- stances are : Sulphur, which is used in southern Italy for smelting crude sulphur (the reason being that no other fuel can be obtained as cheaply). Sulphides (FeS 2 ) are used as fuel in the roasting of ore. In the Bessemer process the silicon of the crude iron (acid process) or the phosphorous (basic process) is used as fuel. TABLE XL VI. CLASSIFICATION OF FUELS. Kind of Fuel. a) Natural. b) Artificial. A. Solid Wood, peat lignite bi- Charcoal coke (bri- B. Liquid C. Gaseous tum, coal, anthracite. Oil Natural gas quettes). Tar, tar oil, alcohol, etc. Illuminating gas pro- ducer gas, water gas, Dowson gas, blast furnace gas, acetylene, etc. 141 142 HEAT ENERGY AND FUELS Lately Goldschmidt has introduced aluminium as a fuel (ther- mit). A mixture of fine-grained aluminium and certain oxides (Fe 2 3 , etc.), when ignited, continues to burn and generates considerable heat: Fe 2 O 3 + 2 Al = A1 2 3 + 2 Fe. This process is used for the reduction of metals, preparation of metals and alloys, free of carbon, generation of high temperatures for weld- ing, melting, casting, etc. In this work we will treat only the first two groups given above, which are commonly called fuels in the true sense of the word. A. SOLID FUELS. (a) Natural Solid Fuels, Wood, Peat, Lignite, Coal and Anthracite. All these fuels contain: 1. Ash, which remains after combustion. 2. Hygroscopic water, sometimes called moisture. 3. A substance containing the combustibles and consisting mainly of carbon and variable quantities of hydrogen, oxygen and nitrogen. The composition of this substance free of water and ash is as follows for the different fuels : TABLE XLVII. COMPOSITION OF FUELS. Composition of the Sub- Vola- stance (free of Water and Ther- tile Ashl mal Fuel. A&LL) , Value. Coke. Mat- c% H% + N% Cal. ters. Wood 51 6 43 4700 non-coking . . . Peat 58 6 36 5900 non-coking . . "70 " Lignite 70 5 25 6500 non-coking . . . 50 Bitum. coal: lean, long flam- ing 8084 5.5 1210 8200 badly coking.. 3540 fat, long flaming 8488 5 910 8600 coking 3035 fat, short flam- ing 8690 54.5 75.5 8700 coking 1623 lean, short flam- ing 9093 4.53.5 5.54.5 8600 badly coking . 614 Anthracite 95 2 3 8200 non coking. . . 3 The ash content varies from about 5 per cent to 15 per cent. The amount of hygroscopic water depends on the humidity of FUELS 143 the atmosphere, and the nature and porosity of the fuel; it generally increases in direct proportion with the volatile matter. Coke forms an exception as it sometimes contains considerable water, which however is not hygroscopic but was introduced by the manufacturing process (cooling of the hot coke with water). The coking of fuels by heating is of great practical importance, preventing small-size coal from falling through the grate bars. Small-sized lean coal is troublesome to burn on a grate. On the other hand coking too much may cause trouble, as thereby a considerable amount of coal is prevented from burning up and the grate cannot be properly cleaned. Some lean fuels have the property of disintegrating in heat and falling through the grate before being burned up. The natural solid fuels are of great importance for the indus- tries on account of their low cost. They can be classified in (a) Vegetable fuels : wood. (/?) Fossile fuels : peat, lignite, coal and anthracite. (6) Artificial Solid Fuels. For certain purposes it is of advantage to use fuels richer in carbon than the ones occurring in nature. This is done by subjecting the natural solid fuels to dry distillation, whereby the following products of decomposition are formed : 1. Gases. 2. Tar. 3. Tar- water. 4. Carbonaceous residuum. The relative quantity of these substances depends on the nature of the substance from which it originated, and the tem- perature of distillation. With increasing temperature the quan- tity of gas is increased, but the content of heavy hydrocarbons and therefore the illuminating power decreased. The advantages of the coked fuel are : 1. A fuel of higher thermal value : (a) The content of carbon of the coked fuel being higher than that of the raw fuel. (b) The gaseous products of distillation requiring a great amount of heat for their gasification in using crude fuel. 144 HEAT ENERGY AND FUELS Thereby the cost of transportation per heat unit is decreased. 2. Coked fuel burns without smoke. 3. Coked fuel does not cake or form clinkers. 4. The sulphur content of the raw fuel is decreased by coking. 5. Valuable by-products are furnished by the coking process. On the other hand we have to consider the following disadvan- tages of coking. 1. The coking entails a certain expense due to heat, fuel, wages and machinery. 2. Coked fuel never burns with a long flame, which is essential in certain cases. 3. Coking increases the ash content. According to the raw material used the coked products are called: .- (a) Charcoal. (6) Peat coal. (c) Coke. (d) Briquettes. CHAPTER IX. WOOD. THE industrial importance of wood as fuel is not very great. It is, however, used to a large extent for building and con- struction purposes which makes a detailed discussion desirable. According to the trees from which the woods originate they may be classified as: (a) Leaved woods: maple, birch, beech, oak, alder, ash, linden, poplar, elm, willow, etc. (b) Coniferous woods : red pine, pine, larch, fir. TABLE XLVIII. CLASSIFICATION OF WOODS ACCORDING TO SPECIFIC GRAVITY. Hard Woods. Soft Woods. Specific Gravity (air dry) Specific Gravity (green) >0.55 >0.90 Specific Gravity (air dry) Specific Gravity (green) < 0.55 < 0.90 Beech Oak Ash Maple Elm Birch Alder = 0.77 = 0.71 = 0.67 = 0.64 = 0.57 = 0.55 = 0.54 Silver fir Red pine Fir Larch Linden Willow Trembling poplar Poplar Black poplar = 0.48 = 0.47 = 0.55 = 0.47 = 0.44 = 0.48 = 0.43 = 0.39 = 0.39 The specific gravity of wood is somewhat variable : it is greater the slower the growth of the tree, i.e., the dryer the soil. Some- times the following classification is used. 1. Hard woods (leaved woods only) : oak, beech, white beech, ash, maple, birch, etc. 2. Soft woods (soft leaved woods) : chestnut, linden, trem- bling poplar, willow, etc. 3. Coniferous woods : fir, silver fir, etc. 146 146 HEAT ENERGY AND FUELS The specific gravities given above include the pores of the wood. Excluding the pores these figures are considerably higher (Rumford). See Table XLIX. TABLE XLIX. SPECIFIC GRAVITY OF WOOD SUBSTANCE. Wood. Speci fie Gravity. Wood. Specific Gravity. Oak 1 5344 Birch 1 4848 Beech 1 5284 Linden 1 4846 Elm 1 5186 F*ir . ... 1 4612 Poplar 1 . 4854 Maple 1.4599 The following figures relative to specific gravity of woods will be of interest: TABLE L. SPECIFIC GRAVITY OF VARIOUS WOODS. Kind of Tree. Bris- son. Hartig. Wernek. Winkler. Muschen- brock. Green. Seasoned. Well Seasoned. Well Seasoned. Scarlet oak Beech Elm 0.85 0.67 0.75 0.84 1.0754 0.9822 0.9476 0.9250 0.9121 0.9036 0.9036 0.9012 0.8993 0.8941 0.8699 0.8633 0.8614 0.8571 0.8170 0.7795 0.7654 0.7634 0.7155 0.7075 0.5907 0.5474 0.4735 0.5502 0.6592 0.6440 0.5550 0.4716 0.5910 0.5749 0.5001 0.4390 0.3656 0.4302 0.3931 0.4302 0.3931 0.5289 0.6441 0.5452 0.5788 0.4205 0.5779 0.6337 0.5699 0*4303 0.3838 0.3480 0^4402 0.663 0.560 0.518 0.441 0.485 0.618 0.619 0.598 0.552 0.493 0.434 0.549 0*443 0.431 0.346 0.418 0^501 0.929 0.852 0.600 0^755 0.734 0^550 0.874 oisoo 0.604 0.383 Larch ' Pine '.... Maple Ash Birch Service Fir 0.55 Red pine Mealy pear Chestnut Alder Linden 0.80 0.60 Black poplar Aspen Italian poplar Sallow Pomegranate Ebony Dutch box Medlar Olive French box Spanish mulberry. Spanish yew 1.35 1.33 1.32 0.94 0.92 0.91 0.89 0.80 WOOD 147 Another classification of woods is based on the following properties : The youngest wood of a tree trunk is called sap-wood. It contains more sap and is lighter in color than the older wood. In some trees the older wood hardly changes (maple, birch, white beech, etc.) ; in some the sap-wood is darker and dryer (linden, red pine, fir tree, etc.) ; in some trees a darker, dryer and stronger wood is formed in the course of time, which is called heart-wood (ebony, walnut, larch, fir, etc.). The weight of wood piles is of more importance than the specific gravity. The net cubic contents of a wood pile is the volume of wood substance including the pores. Its weight in kilograms is 1000 times the specific gravity of the wood. The gross cubic contents of a pile depends upon the density of the pile and the moisture of the wood. Furthermore, the density depends upon the shape and form of the pieces of wood (cord wood, stove wood and brush wood). The moisture decreases with the length of time the wood is stored, down to from 12 to 13 per cent. The actual contents of the wood pile is the volume of wood substance in a certain volume of wood pile. TABLE LI. ACTUAL CONTENT IN PER CENT OF DIFFERENT WOODS. Kind of Wood. Mini- mum. Maxi- mum. Aver- age. Cord wood of leaved wood, logwood and billet wood of coniferous trees, strong, smooth and straight. . Cord wood of leaved and coniferous woods, weak, smooth and straight Cord wood of coniferous woods, strong and weak, knotty and crooked Stove wood of leaved wood, strong, smooth, straight Cord wood of leaved wood, strong and weak, knotty and crooked Stove wood of leaved and coniferous wood, strong and weak, smooth and knotty, straight and crooked Brushwood from trunk, coniferous wood Brushwood from trunk, leaved wood Brushwood from branches, coniferous wood Brushwood from branches, leaved wood Rootwood (leaved and coniferous tree) 73 68 63 58 53 48 42 77 72 67 62 57 52 48 75 70 65 60 55 50 45 148 HEAT ENERGY AND FUELS TABLE LII. WEIGHTS OF WOOD IN PILES. (Woods cut in winter.) Kind of Tree. Green. Seasoned. Cord wood. Stove- wood. Brush. Cord wood. Stove- wood. Brush. Bark. Heart- wood. Bark. Heart- wood. Weight in Kilograms of 1 Solid Cubic Meter. Red pine Pine 892 950 741 790 717 690 923 878 881 937 929 937 968 955 1019 979 926 869 '903 930 1045 986 781 457 554 548 687 734 741 445 503 669 734 "797' 334 551 624 469 703 696 762 "717" 511 516 702 673 780 712 484 Larch Silver fir Oak Red beech Hornbeam Birch Linden Maple Norway maple 978 1051 933 CHEMICAL COMPOSITION. Wood is composed chemically of (1) fiber and (2) sap. The wood fiber consists mainly of cellulose C 6 H 10 5 (C, 44.44 per cent; H, 6.17 per cent; 0, 49.39 per cent). Besides cellulose we find other organic matter, both nitrogenous and non-nitroge- nous, which are generally called "incrustating materials. " They increase towards the center and cause the dark color. The analyses given in .Table LIII show the variations in the composition of different woods dry and free of ash: (H. Che- vandier). TABLE LIII. COMPOSITION OF DIFFERENT WOODS. Kind of Tree. C Per cent. H Per cent. OandN Per cent. Maple Oak 49.80 50 64 6.31 6 03 43.89 42.05 1 28 Pine .... 49 94 6 25 43 81 Willow . 51 75 6 19 41 08 98 WOOD 149 The average composition therefore is : C H O and N 49.2 6.1 44.7 The sap is a solution of various organic (protein, tannic acid, vegetable acids, starch, sugar, essential oils, resins) and inorganic substances in water. Considering the use of wood as fuel, only the content of resin, water and ash has to be considered. With increasing content of resin, the thermal value increases. In order to determine the resin content Hampel treated Austrian woods with 90 per cent alcohol. Table LIV gives the per cents dissolved. TABLE LIV. RESIN CONTENT OF WOODS. Kind of Tree. Taxus baccata L. (yew) Abies excelsa E) C (fir) i r.5i4 J.734 Larix europflBa D C (larch) .807 744 Acer pseudoplatanus L (maple) 69 Fraxinus excelsior L (ash) 47 Fajrus silvaticus L (red beech) 44 Betula alba L (birch) 167 Per cent. The ash content of various woods may be taken from Table LV. TABLE LV. ASH CONTENT OF VARIOUS WOODS. Fresh Old Trunk Branch Brush Wood. Wood. Wood. Wood. Wood. Pine 0.12 0.15 Oak 1.94 1.49 1.32 Oak 0.15 0.11 Beech 0.73 1.54 0.72 Pitch pine . 0.15 0.15 Aspen 1.49 2.38 Birch 0.25 0.30 Willow.... 2.94 3.66 The ash content depends largely on the ash content of the soil. The moisture changes with the seasons, is the lowest in winter and the highest in spring. It also changes with the different trees. 150 HEAT ENERGY AND FUELS Kind of Tree. H 2 O Per cent. English Name. Carpinus betulus Salix caprea 18.6 26 Hornbeam Sallow Acer pseudoplatanus Sorb us aucuparia. . . 27.0 28 3 Maple Fraxinus excelsior 28 7 Ash Betula alba . Qf) "RirpVi Quercus robur 34 7 Oak Pinus silvestris 39 7 Pinp Pinus larix 48 6 TABLE LVI. MOISTURE IN VARIOUS WOODS. Kind of Tree. Hornbeam (Carpinus betulus) . . Sallow (Salix caprea) Maple (Acer pseudoplatanus) . . Service tree (Sorbus aucuparia) Ash (Fraxinus excelsior) Birch (Betula alba) Oak (Quercus robur) Pine (Pinus silvestris, L.) Larch (Pinus larix) Water Content. 18.6 26.0 27.0 28.3 28.7 30.8 34.7 39.7 48.6 The researches of Vrolle (Table LVII) show how great are the variations in the ash content, for instance, in the case of the cherry tree. TABLE LVII. ASH CONTENT OF VARIOUS PARTS OF A CHERRY TREE. Part of Tree. C Per cent. H Per cent. + N Per cent. Ash Per cent. Leaves. . . 45 015 6 971 40 910 7 ug Upper point of branch, bark Upper point of branch, wood 52.496 48.359 7.312 6.605 36.637 44.730 3.454 304 Middle part of branch, bark Middle part of branch, wood Lower part of branch, bark Lower part of branch, wood Trunk, bark 48.855 49.902 46.871 48.003 46 267 6.342 6.607 5.570 6.472 5 930 41.121 43.356 44.656 45.170 44 755 3.682 0.134 2.903 0.354 2 657 Trunk, wood . . . 48 925 6 460 44 319 296 Upper part of root bark . 49 085 6 024 48 761 1 129 Upper part of root, wood Middle part of root, bark Middle part of root, wood Lower part of root 49.324 50.367 47.399 45.063 6.286 6.069 6.259 5.036 44.108 41.920 46.126 43.503 0.231 1.643 0.223 5.007 WOOD 151 Henneberg's researches show how the ash content depends on the soil. Table LVIII shows the composition of beech wood ash: TABLE LVIII. ASH ANALYSES. Kind of Soil. Components. Limestone. Per cent. Gypsum. Per cent. Sandstone. Per cent. Carbonate of potash 6 7 ) ( 4.7 Carbonate of soda 11 J 14.6 J3.2 Sulphate of potash 4 4 3 4 23.3 Chloride of sodium .... 7 trace 5.0 Soluble salts . . . 22 8 18.0 36.2 Carbonate of lime 27 4 30.9 21.1 Magnesia : Phosphates Silicic acid 17.7 15.6 16 9 12.2 9.7 28 7 12.4 10.9 18,4 Insoluble components 77.6 81.5 61.0 For metallurgical purposes the quantity of phosphorus in wood is of interest. R. Akerman and Sarnstrom found that : 1. Leaved wood contains from 4 to 5 times as much phos- phorus as coniferous trees. 2. The quantity of phosphorus in the same kind of wood varies 100 per cent according to the country of origin. 3. Fir wood cut in winter contains more phosphorus than when cut in spring or summer. 4. The trunk contains the least, branches, twigs and especially the bark contain the most. 5. The phosphorus of sap-wood can to a large extent easily be washed out. The moisture of wood depends considerably on the season (Schuebler) : Percentage of Water. jvina 01 iree. End of January. Beginning of April. Ash . . 28 8 38 6 Maple. 33 6 40 3 Horse chestnut . . 40 2 47 1 Fir tree ' 52 7 61 6 Fresh ash 28-29 38-39 Red pine (root) 52 61 152 HEAT ENERGY AND FUELS The moisture varies in the different parts of the trees. It is higher in the outer parts than in the inner parts, higher in the branches than in the trunk. It also depends on the soil and climatic conditions. Air drying reduces the moisture after two summers to about 20 per cent, in very dry summers to from 15 to 16 per cent. For drying wood more perfectly higher temperatures have to be applied. Woods exposed for two years to 125 C. and 225 C. lost water as shown in Table LIX. (Violette) : TABLE LIX. DATA ON THE SEASONING OF WOOD. 100 Parts of Wood give off Water. Temperature. Oak. Ash. Elm. Walnut. 125 C 15.26 14.78 15.32 15.55 150 C 17.93 16.19 17.02 17.43 175 C 32.13 21'. 22 36.94 21.00 200 C 35.80 27.51 33.38 41.77 225 C 44.31 33.38 40.56 36.56 At 200 C. dry distillation begins. Wood dried at higher temperature reaclily absorbs water. Wood (shavings) dried at 136 C. absorbed in 24 hours in winter from 17 to 19 per cent, in summer from 6 to 9 per cent water. By drying, the volume is decreased; by moistening, increased. TABLE LX. THERMAL VALUE OF VARIOUS WOODS (per kg.) . Kind of Wood. Pb reduced by 1 Part of Wood. Calories. Specific Gravity. \ir-dried wood (20% water) 3600 Dried wood (10% water) 4100 White beech air dried. .. . 12 5 3100 0.770 Oak, air dried. 14.05 24003000 0.708 Maple, air dried 14.16 3600 0.645 Pine air dried 13 27 0.550 Willow air dried 13 10 0.487 Linden, air dried .... 14.48 34004000 0.439 Birch, air dried 14.08 0.627 Fir tree air dried 13 86 0.481 The heat of combustion of cellulose per kilogram is as follows, (if the water formed appears in liquid form) for: WOOD 153 Purified cotton 4200 cal. From paper . 4188.1 cal. From ammoniacal solution of cupric oxide 4174.1 cal. Purified with bromine water and ammonia . 4191.9 cal. Average . 4188.5 cal. For water vapor 3591 cal. Boise has found the evaporating power of different kinds of wood to be as given in Table LXI. TABLE LXI. EVAPORATING POWER OF WOOD. Kind of Tree. Water. Ash. Kilograms of Water transformed into Steam by 1 Kilo- gram of Wood. Unseasoned. Seasoned. Unseasoned. Seasoned. Per cent. Wood. Old pine . 16.1 19.3 14.7 12.3 18.7 22.2 14.3 12.5 1.92 1.73 0.95 1.00 1.13 1.43 1.39 2.17 2.29 2.15 1.11 1.14 1.39 1.84 1.62 2.48 4.18 3.62 - 3.84 3.72 3.54 3.39 3.49 3.62 5.11 4.77 4.67 4.39 4.60 4.63 4.25 4.28 Young pine Alder Birch Oak Old red beech Young red beech White beech Winkler has found the comparative fuel value of woods, considering the same volume, to be as given in Table LXII. TABLE LXII. COMPARATIVE FUEL VALUE OF VARIOUS WOODS (Winkler). Kind of Wood (dry). Red Pine = 100. Red Beech = 100. Oak 169 118 Elm 156 109 Maple ... 153 106 Birch 152 105 Beech 143 100 Fir 112 78 Willow 110 77 Poplar ... 109 76 Pine . 106 74 Red pine 100 70 Linden 92 64 154 HEAT ENERGY AND FUELS Since wood, when used as fuel, is almost always measured instead of weighed, this table is of considerable importance, also on account of the volume being less affected by moisture than the weight. If we call best beech wood equal to 100 we get the following scale for the value of woods. I. Fuel quality = 100: beech, birch, pine rich in resin, mountain pine, acacia. II. Fuel quality = 95 to 90: maple, elm, ash, larch rich in resin, chestnut, ordinary pine. III. Fuel quality = 85 to 75: red pine, fir, Siberian stone pine. IV. Fuel quality = 70 : linden. V. Fuel quality = 65 to 60 : alder, poplar, oak, aspen. VI. Fuel quality = 55 to. 50: willow. These values naturally depend also on the use the wood is to be put to. For quickly raising the temperature, for instance, soft wood, especially coniferous wood is used. For domestic use 1.5 cu. m. of soft wood take the place of 1 cu. m. of hard wood. The different parts of a tree have a different fuel quality. Taking trunk wood as = 1, we have Trunk wood 0.90 to 0.80 Branch wood 0.90 to 0.75 Twig wood 0.85 to 0.80 Root wood 0.65 to 0.50 Root wood, rotten 0.40 Wind-fallen wood. . . 0.85 to 0.50 CHAPTER X. FOSSIL SOLID FUELS. (IN GENERAL.) ALL fuels containing carbon are of vegetable origin and differ from each other according to the kind of the plant from which they come and the quality and quantity of the transformation of the vegetable fiber. The course of carbonification is entirely different if the vegetable masses are covered with water, and if the plants are isolated from the atmosphere by layers of clay. Geologically these fuels can be divided in: 1. Younger fossil coals : (a) Peat. (b) Brown coal (lignite). 2. Older fossil coals (bituminous coal and anthracite) . These coals are formed by a process called natural carbonification (carbonaceous decomposition), which was studied by the Swiss geologist, A. Balzer. Balzer states that in this process two kinds of substances have to be dealt with, namely : products of decomposition and resid- uum of decomposition. We can obtain some idea of the nature of the products of decomposition from the methane in the mines; the gases in the fresh coal; the changes of fresh coal in the atmosphere (which changes are a continuation of the process of carbonification), and from certain laboratory experiments on the behaviour of wood in an atmosphere of oxygen. The methane in the coal mines is a real product of decom- position. The gases held in absorption by coals are of the same nature. Meyer found that 100 g. of coal yield from 17 to 59 cu. cm. of a gas containing carbon dioxide, oxygen, nitrogen, methane, ethane and probably butylene. It is undecided how much of the nitro- gen has its source in the vegetable matter and how much in the atmosphere. 155 156 HEAT ENERGY AND FUELS Relating to the behavior of wood in an atmosphere of oxygen, Saussure observed that wood shavings enclosed in an oxygen atmosphere transformed the latter into the same volume of carbon dioxide. The same observation was made by Liebig for moist and old wood. Wiesner found that the first stage of decomposition of wood consists in the appearance of gray color, whereby the intercellular substance vanishes and practically pure cellulose remains. Moist lignite absorbs oxygen from the atmosphere and generates carbon dioxide. Liebig made the conclusion from his experiments, that first of all the hydrogen of the wood is oxidized, while the oxygen of the hydrate water combines with the carbon of the wood to form carbon dioxide. Considering the fact that methane is formed during the transformation of wood into coal, he calculates that cannel coal can be explained as wood fiber less 3 molecules CH 4 , 3 mol. H 2 and 9 mol. C0 2 . Brown coal is oak wood less 2 H 2 and 3 C0 2 , etc. Relating to the influence of the exclusion of air in the forma- tion of coal, Bischof stated that atmospheric oxygen is not essential and that the coal deposits must have been formed mainly under exclusion of oxygen, water having served as the seal in the sea, on the shores and in meadows. In some cases the water was replaced by sand and clay deposits. The ash content of coals proves this fact. The oxygen which is found dissolved in sea water certainly did not have much effect, since according to Hayes, metals kept at a certain depth in the sea are not oxidized. As to the chemical expression of the carbonaceous decom- position Balzer says : According to Bischof there are three ways possible for the decomposition to take place according as carbon dioxide and water, carbon dioxide and methane, or carbon diox- ide, water and methane are formed. The one of these processes which takes place is determined by the amount of the react- ing air, temperature and pressure. When vegetable products during the carbonaceous age were carried by rivers into basins of salt or fresh water, where formation of coal took place, large quantities of methane were formed. If by some geological change the basin becomes dry, the process goes on principally as oxidation. If now a considerable amount of sediment is deposited the formation of coal has to continue, though slowly, without oxygen. FOSSIL SOLID FUELS 157 TABLE LXIII. CHEMICAL COMPOSITION OF FUELS. Uninflammable Coal. OO OO O 1 * w 1 1 1 1 WW MWB O 00 <* 00 CC B B S 1 OO OO O o o BITUMINOUS COALS. . i O O O 1 1 1 ^F| h"1 "n OO 00 OO o" o" o" "*< i I CQ o oooo o : 1 I 1 1 : o" O~O*"o~O~ o" ; Jb urther by absorbed oxygen Remains sand coal . . . T>,, 1 U.. AJUIUCU uy UAygeri Remains graphite BROWN COALS. g g PQ xs O I oooo . . . . ; ; W i CO (M rt< . os - 1 ; : : g ^ * 1 : : : : : a o" o"o~o~ o' ; : | S3 i i *" 8 : : : : : * Bituminous Wood. o 0,0 o : : : : :| W WW B~ : : 1 - ~ ' - ; i| ; s ^s ill ;2 H i ooo o 5 : : : : -g :B *^'H<' c3 co Ico TS Oo3 a> Q o3 c>&iWiO WOOD. : ct 1 '^ o' S S> > a ^ ^S a*3 9 Sg l|lf ^S S g^ooS 'jco*'^"^ o "5^'^ ^3 ^fl Ocooi c3^-^co 'S'^TJ'C 00"^^ On So o_i_i i , <_ ^G^j^^flG^fcHa)^ 158 HEAT ENERGY AND FUELS According to Balzer the influence of temperature is as follows : Low temperature decreases the velocity of coal formation. The temperature in the deepest part of the Atlantic Ocean at from 49 to 57 degrees latitude is 2.1 C. In regions where the lowest winter temperature of the air is 4 C., the deepest layers of water have a constant temperature of from 5 to 6 C. The carbonifica- tion, which is a "voluntary" decomposition of organic subtances, is certainly an exceedingly slow reaction at this temperature, and must have been much slower yet in the glacial age. The influence of pressure is as follows : It is uncertain whether an increase in pressure increases or decreases the velocity of car bonification and the optimum of pressure is also unknown. We cannot make any deductions from the fact that CaC0 3 remains undecomposed at high pressure since in organic reactions with closed glass-tubes the generation of gas and chemical reaction ordinarily takes place at high pressure and high tem- perature. Paraffin is decomposed by high pressure and high temperature in hydrocarbons of the methane and ethylene series. In such cases the reactions taking place change with changes in temperature and pressure. A certain semi-soft condition of the wet mass can be con- sidered as advantageous for the reaction. Valuable information relating to the changes of coals in the atmosphere at ordinary and higher temperature are given by Richter. It is known that coal absorbs oxygen of the air. Charcoal absorbs nine times its volume of oxygen. Coals absorb gases as readily as a dry sponge absorbs water. If coal is sat- urated with one gas, some other gas can be absorbed in addition. With the assistance of moisture the oxygen is com- pressed in the coal, ozonised and thereby becomes chemically active, causing an increase of temperature. (Self-ignition of powdered coal.) Richter observed that the capacity of coal for absorbing oxygen increases up to 200 degrees, at which temperature the absorption stops. Hydrogen and oxygen are absorbed in the proportion 2 : 16. On account of oxidation in the air deteriora- tion of coal takes place, shape and color are changed, thermal value and coking capacity decreased. Since only a part of the hydrogen of the coal is oxidized the FOSSIL SOLID FUELS 159 hydrogen must be present in different combinations, which is important for the theory of the constitution of coals. Considering the residuum of decomposition Balzer mentions the constitution of the wood-substance. The coals are chemical derivatives of cellulose, consequently of the wood-substance. The constitution of these substances and their relations to each other are not positively known. It seems, however, that cellulose does not occur in a free state in wood. From fir wood we can isolate by extraction with ordinary solvents a yellowish- white substance having the formula C 30 H 46 21 , which is only slightly soluble in ammoniacal cupric oxide, being thereby essen- tially different from cellulose. By boiling with hydrochloric acid, glucose and lignose (C 18 H 26 O n ) was formed. The latter, which is also insoluble in ammoniacal cupric oxide, is trans- formed by boiling with nitric acid, into cellulose and certain substances of the aromatic series. From these reactions we can conclude that fir wood contains, besides the cellulose-group, a sugar-forming and an aromatic group, so that its composition is much more complicated than that of cellulose. What is the relation of wood substance to coal? It is known that in the carbonaceous decomposition the relative quantity of carbon and ash increases and the quantity of hydrogen, oxygen and nitrogen decreases. The different qualities of coal from peat to anthracite show different stages of this process, but the formation of one kind of coal from the other cannot be expressed by a chemical equation. Balzer makes the following hypotheses relative to the con- stitution of coals : 1. The coals are mixtures of complicated carbon compounds (organic substances), 2. Which form a continuous (or possibly homogeneous) series. 3. The carbon ring of these compounds is complicated and somewhat analogous to aromatic compounds. Balzer states that besides the carbonaceous decomposition proper a destructive distillation can take place, for instance, by contact with hot bodies or fires. In Hessen, Germany, molten basalt has in this way transformed lignite into anthracite coal, the anthracite deposit changing gradually into the lignite deposit. In some places eruptive porphyry has transformed lignite at the contact points into coke. 160 HEAT ENERGY AND FUELS Supposing an increase of temperature towards the center of the earth, we can assume 100 C. at a depth of 2600 m. Products of distillation formed in these regions can condense in the upper regions, the lower layers forming the retort, the upper the con- densing chamber. Balzer believes that this reaction takes place with petroleum, which is " distilled" from coal deposits, bitu- minous slates, etc. Since petroleum occurs in silurian, devonian and tertiary formations it is apparent that the place of " occurrence" is different from the place of "formation, " which can be explained by distillation, above referred to. Supposing that the carbon in the coals is present as such, we consider the coal deposits as end products, while according to the above mentioned statement they are in a process of contin- uous transformation, which hpwever cannot be fully explained at present. The fact that the temperature in coal mines increases with the depth faster than elsewhere is of practical importance and theoretical interest. A case where it was believed that hot springs were the cause of the high temperature of the mine waters was investigated to find out whether the formation of coal is accompanied by a sufficient generation of heat to explain the high temperatures. The following results were obtained : TABLE LXIV. AVERAGE COMPOSITION OF FUELS. (Muck.) Thermal Value, kg-cal. Wood 50% C 6 % H 43 i^. 33 ^-*-. 30 0.95^ 1.67 2.71 1.46 0.67 to 6.33 ^-*-s 38 >^, 40 >^^, 37 1.16 0.77 1.41 2.51 1.56 >*, 35 ^M^S 31 >-, 28 N , 28 7? 2.84~ 1.68 ^5 ***** 46 "32.88 32.40 29.67 i*^' 77 "^' 37 27.20 31.81 ^0 ~I4 24 -*-' 39 ,*^,' 71 /-' 25 *-'. 32.76 34.15 30.32 26.21 26.87 to f 49.01 i^W 35 ,^*S 59 . ' 56 42.42 42.70 29.24 31.51 33.04 ,^^" 35 /^*-s 64 ^56 ,i_- 56 7J ^21.51 35.43 2.55 1.83 1.99 7.90 5.58 4.61 3.33 2.70 2.04 3.50 8.20 to 21.17 3.80 0.91 14.25 2.6 1.57 8.10 21.60 0.89 to 14.76 9.86 6.60 2.31 3.72 0.57 1 09 18.53 2.92 8.43 3.32 12.59 20.28 4.21 7.87 5.02 t _o 16.7 16.0 17.0 15.17 to 21.7 0.405 0.619 to 0.072 Pale, red- brown. Dark brown, dense. Dark brown. Same. Incompletely decomposed. Solid and dense. Somewhat lighter. Light, felty mass. Dense Kane ....Do. ....Do. . . . .Do. Re"gnault . . . .Do. . . . .Do. Walz. . . . .Do. ....Do. Mulder . . . .Do. . . . .Do. Braunin- ... g fi r o. ....Do. ....Do. ( Nessler and ( Petersen Jaeckel. ....Do. ...Do Websky. . . .Do. ...Do. ...Do. Do Rammstein, Rheinfalls. Steinwenden, Rheinfalls. Niedermoor, Rheinfalls. Prussia . . . . Friesland Light Holland Bremen Bremen Schopfloch, Wurt- temberg. Sindelfingen, Wiirttemberg. Baden 20.6 18.0 11.77 to 18.55 17.63 19.32 18.83 * * * Dark brown, dense, heavy Same Dark brown, dense. Same Heavy, dense, brown. Light, loose. Red brown, heavy Berlin, Havelnie- der. Berlin, Havelnie- der. Hamburg, Moor . . . Grunewald Harz . Harz Limm Hundsmiihl Haspelmoor Neustadter Hiitte. Montanger. 15.50 10.31 17.11 15.72 15.50 23.17 p 1.07 Pressed-peat. Do Peat prepared after Challe- ton. Same . Kraut. ...Do. ...Do. Do. Neufchatel Kolbermoor Switzerland Schonen Pressed-peat . Same Wagner. Goppels- roder. Jacobsen. Very dense . . . * Calculated free of ash. 172 HEAT ENERGY AND FUELS by evaporation, trickling of the water into the ground, by pounding, treading and beating. The boards are then removed and the mass cut with sharp knives into regular bricks. (6) The mass, compressed from the top is beaten into forms, (a) Containing only one brick (beaten peat). (/?) Containing space for several bricks (molded peat). 3. Machine peat. (a) Without pressure (machine peat proper). The cut peat is formed into bricks and dried. Occasionally it is pre- viously carded so as to get a denser product. (b) With pressure (pressed peat). (a) Dry pressed : small-sized peat is sifted, dried by heat, and briquetted in a heavy brick press. Such peat is expensive on account of the cost of drying and is dis- integrated by heat. (/?) Wet pressed, most of the water is removed by pressure. There are many constructions of peat-brick presses in successful use. Peat molded in the form of balls or eggs is very convenient to handle and makes firing easy. Analyses of some dry peats are given on page 171. CHAPTER XII. BROWN-COAL (LIGNITE). BROWN-COAL is the next stage of carbonaceous decay and was formed mostly by transformation of plants rich in resin (conifer- ous trees, palm tree and cypress; later, also leaved trees). The specific gravity of this coal varies from 0.8 to 1.8 (in coals very high in ash), but in most cases from 1.2 to 1.5. It has various colors, and the touch is generally brown. In the air brown-coal easily absorbs oxygen and evolves carbon dioxide, whereby on account of the loss in carbon, the thermal value is decreased ; at the same time the temperature is increased and in large piles causes spontaneous combustion. Brown coal does not occur before the tertiary period. The gases found in brown-coal deposits consist generally of carbon dioxide (not of hydrocarbons as in soft-coal deposits). Zitowich published the gas analyses of such coals (Table LXXI). TABLE LXXI. ANALYSES OF GASES FOUND IN BROWN-COAL. (Zitowich). In Bohemian Patent-Brown Coal. In Earthy Coal of Inferior Quality. CO 2 89.66 1.80 8.03 0.51 82.40 3.00 14.15 0.45 83.99 1.04 14.91 0.65 CO N .... Sum 100.00 100.00 100.59 Gases from : Julius-Mine in Bruex (Bo- hemia) . Coal from Rossitz. Coal from Habichtswald. CO, 37.62 35.13 31 91 9 CO CEL 33.34 29.04 36.06 28.81 30 20 19 N O.. C.,H f . 173 174 HEAT ENERGY AND FUELS While previously the brown-coals were classified as lignite or fibrous brown-coal, earthy brown-coal and conchoidal brown- coal, Zinken has suggested the following classification : 1. Common brown-coal. Compact, more or less dense and strong. The fracture may vary in character from dense to earthy; in structure it may be more or less conchoidal; in appear- ance it may vary from dead to slightly brilliant; in color from light brown to dark brown, and light-brilliant touch. This coal is between earth coal and pitch-coal, and is produced in all sizes. 2. Earthy brown-coal. More or less brittle, light to dark brown, showing dead, uneven fracture, without any organic structure. The lighter varieties burn with a long, the dark ones with a short, but intense flame. 3. Lignite or fibrous brown-coal. More or less fossil wood- substance, yellow to dark brown, specific gravity 0.5 to 1.4, fracture depending on the nature of the wood. 4. Slate-coal. Slaty, dense, dark-brown to black. 5. Paper-coal. Thin, elastic layers of gray to dark-brown color. 6. Leaf-coal. Formed of very thin leaves of plants. 7. Reed-coal. Reed-like strips formed into ribbon-like layers. 8. Moor-coal. Compact without wood-texture, of even, uneven or conchoidal fracture, sometimes slaty, mostly loose, spongy and brittle ; dark brown to pitch black. Specific gravity 1.2 to 1.3. Occurs mostly in the lower part of lignite deposits. 9. Pitch-coal. Compact, brittle to tough, mostly weak, black- brown to pitch black; has the lustre of pitch or wax. Brown touch; fracture imperfect to conchoidal. Specific gravity 1.2 to 1.3. Occurs near volcanic rocks. 10. Lustre-coal. Compact, conchoidal, jet black, very brilliant. The hardest and strongest variety. Specific gravity 1.2 to 1.5. 11. Gagat (from the river Gages in Licia). Dense, conchoidal, pitch-black. So strong that it can be worked into ornaments. 12. Stalky brown-coal. Like common brown coal but stronger. The average composition of brown coals is : Carbon 50 to 65 per cent Disposable Hydrogen 1 to 2 per cent Water chemically combined 20 to 30 per cent Water hygroscopic 10 to 25 per cent Ash 5 to 10 per cent BROWN-COAL 175 The quantity of nitrogen present is nearly always less than 1 per cent. The quantity of water varies as follows : Fresh-mined coal 30 to 40 per cent Sometimes up to 60 per cent In air-dry coal 10 to 30 per cent Coal which has been completely dried at 100 degrees absorbs in the air from 10 to 15 per cent of moisture. The ash varies from 1 per cent to over 50 per cent ; it may contain from 1 to 2 per cent, and sometimes more, sulphur combined with iron (detrimental sulphur). The organic components in brown-coal are mainly ulmic acid, its derivatives and resinous substances. Otherwise the compo- sition varies considerably even in coals from the same mine. The following table shows the composition of some brown- coals : TABLE LXXII. COMPOSITION OF BROWN-COALS. Gas. Coke. Composition of Coal in Per cent. Sulphur. S-j . 8 Place. v Yield: s & Per cent. C H N H 2 O Ash. I* jo 1 * H i H I. Austria Hun- gary: (1) Styria: Johnsdorf. . . 25.73 63.32 6.03 4.92 0.96 Leoben 30.07 54.82 10.77 4.34 Trifail 49.95 3.67 16.'93 0~97 20.15 8.43 1.64 4386 (2) Bohemia: Teplitz 44.93 3.21 12.51 0.64 34.28 4.43 0.50 3925 Dax 50.12 4.06 13.14 0.65 25.50 6.53 0.93 4630 II. Germany. Elbogen 26.0 77.64 7.85 14.51 Cologne 63.42 4.98 27.11 III. France. Dax 46.6 74.19 5.88 20.13 Middle Alyses 48.0 72.19 5.36 22.45 IV. Ireland: Lough Neagh . 58.56 5.95 26.85 As can be seen from the above table the composition of brown- coal of the same origin and mine varies considerably. It is, 176 HEAT ENERGY AND FUELS therefore, very difficult to get an exact average sample for analy- sis. For determining the non-uniformity in the composition, the author broke several small pieces from a piece of coal (of Johnsdorf) about the size of a fist. The results of the analysis are given in Table LXXIII. TABLE LXXIII. COMPOSITION OF BROWN-COALS. No. of Test. Percentage of Hygroscopic Moisture. Yield in Gas. Percentage. Percentage of Coal Resid- uum. Percentage of Ash. 1 8.49 28.57 53.85 9.09 2 8.02 29.07 53.57 9.34 3 7.77 27.95 54.79 9.49 4 7.63 28.41 54.15 9.81 5 6.87 31.67 52.31 9.15 6 9.13 ' 29.76 53.27 9.94 7 8.17 28.81 53.21 9.81 8 7.24 31.90 51.54 9.32 Average. . 7.91 29.52 53.33 9.37 Another series of tests with the same piece are given in Table LXXIV. TABLE LXXIV. COMPOSITION OF BROWN-COALS. Weight of the Lead Regulus Oxygen in kg. in Grams. Theoretically No. of Test. Grams Used. Required for Directly Found. Per 1 g. Fuel. Burning 1 kg. of Fuel. 1 1.00 21.98 21.98 1 . 6990 2 1.00 22.31 22.31 1 . 7245 3 5.00 110.30 22.06 1.7052 4 5.00 109.38 21.88 .6910 5 5.00 111.59 22.795 .7252 6 5.00 111.36 22.68 .7216 7 5.00 111.68 22.34 .7269 8 5.00 115.42 23.08 .7841 9 5.00 110.09 22.02 .7021 10 5.00 112.52 22.50 .7393 Average . . 22.3645 1.72189 BROWN-COAL Table LXXV gives several analyses of brown-coal ash. TABLE LXXV. COMPOSITION OF BROWN-COAL ASH. 177 Coal Ash from .... Artern. Helmstedt. Gross- Priessen. >5 d * 1 w Lignite from Meissner. Seegraben b. Leoben. Fohnsdorf. tic 3 1? r Analyst Krem- ers. Var- ren- trapp. O. Kot- tig. Son- nen- schein. Jliptner SiO 2 . . 3.12 9.17 17.27 33.83 20.67 15.45 13.52 1.23 36.01 12.35 23.7 5.05 1.13 15^62 3.64 2.38 0.38 1.55 20.5 30.3 14^7 18.1 io!o 3.4 1.9 2.88 0^23 Trace 14.62 39.28 13.47 6!l3 17.47 5.32 15.96 2.52 0^15 10.86 12.17 45.44 so, P 2 O. Cb a ... A1 2 O 29.50 32.18 11.57 5.57 Fe 9 O,.. MnO Mn.O 4 . . 7.43 34.15 0.94 |o.47 19.86 15.67 0.38 jll-71 2.35 16.60 Trace J9.91 CaO 20.56 2.16 0.99 1.72 23.67 2.58 1.90 45.60 T67 1.86 MgO K 2 O Na,O Chlorine Total 99.40 96.39 100.00 101.81 98.9 100.00 100.00 100.00 CHAPTER XIII. BITUMINOUS AND ANTHRACITE COALS. A. BITUMINOUS COAL. THE older fossil coals, ordinarily called bituminous coals, are mostly black in color and have a high lustre; no organic structure can be discerned without a microscope. The fracture varies. The coals are not hard but brittle. In destructive distillation they yield more solid residuum and less water than the fuels previously treated and their tempera- ture of ignition is higher. The great commercial importance of bituminous coals early caused their division into groups, many different schemes being proposed. Schondorf based his classification on the coking quality: Coke rough, f loose I. Sand-coal. fine, sandy < molten hard, loose in the center. . II. Molten sand-coal and black. ' molten hard all over III. Sinter coal. Coke gray and solid, opening like a bud III. Baked-sinter-coal. Coke smooth, metallic, strong V. Baking coal. Gruner based the following classification on the character of the flame: I. Long-flame sand-coals (sand-coal rich in gas) can be used for reverbatory furnaces and as inferior gas coal. They burn with long, smoky flame, crack in the heat, and disintegrate without baking. Sand coal. Composition of coal substance: C = 75 to 80 per cent J. H = 5.5 to 4.5 per cent + N = 19.5 to 15.5 per cent The ratio of (0 + N) to H equals 3 or 4. By destructive distillation these coals yield from 50 to 60 per cent of sandy to slightly molten coke, evaporate from 6.7 to 7.5 178 BITUMINOUS AND ANTHRACITE COALS 179 times their weight of water and have a thermal value of 8000 to 8500 cal. The soot-coal, which is of fibrous structure and contains only 3 per cent of hydrogen also belongs to this class. II. Long-flame baking coals (long-flame caking coals, gas-coals, sinter and baking coals rich in gas) are used mainly as flaming coals and gas-coals, less suitable for coking (however, in special ovens a coke of medium quality can be produced). They burn with a long, smoky flame, get soft in the heat and fritted. (Coals standing in quality between these coals and the long-flame sand- coals are called sinter-coals). Composition of coal substance: C = 80 to 85 per cent H = 5.8 to 5 per cent O + N = 14.2 to 10 per cent The ratio of (0 + N) to H equals 2 or 3. Coke residuum of destructive distillation 60 to 68 per cent (per- fectly molten, not baked). These coals evaporate 7.6 to 8.3 times their weight of water and generate 8500 to 8800 cal. III. Baking coals proper (medium-flame caking coal, forge coal), especially adapted to coking, gas making and heating. Burn with less smoke and more brilliant flame than the previous kinds, melt in the heat and bake together to solid masses. Composition of coal substances : C = 84 to 89 per cent H = 5 to 5.5 per cent + N = 11 to 5.5 per cent O + N H = I or 2. Coke residuum by destructive distillation from 68 to 74 per cent; the coke is molten and more or less puffed. These coals evaporate from 8.4 to 9.2 times their weight of water and generate from 8800 to 9300 cal. IV. Short-flame baking or caking coals (coking coal poor on gas). Best coking and boiler coal. Difficult to ignite, burns with an illuminating, short, slightly smoky flame. Cakes some- what in the heat. 180 HEAT ENERGY AND FUELS Composition of coal substance: C - 88 to 91 per cent H = 5.5 to 4.5 per cent + N = 6.5 to 4.5 per cent + N == = about 1. H Coke-residuum of destructive distillation from 74 to 82 per cent. The coke is molten, and compact. These coals evaporate from 9.2 to 10 times their weight of water, and generate from 9300 to 9600 cal. V. Anthracitic coals (poor in gas, older sand-coals) . Especially adapted to shaft furnaces, boilers and domestic uses. Cannot be coked. Difficult to ignite ; burn with short, weak and practically non-smoking flame. Cakes slightly in the heat and frequently disintegrates. Composition of coal-substance : = 90 to 93 per cent H = 4.5 to 4 per cent + N = 5.5 to 3 per cent + N H = about 1. Residuum of destructive distillation from 82 to 90 per cent, slightly molten, mostly sandy. These coals evaporate from 9 to 9.5 times their weight of water and yield from 9200 to 9500 cal. A similar classification was made by Hilt. If we determine the ratio (in weight) of volatile matter to the coke dried at 100 degrees and free of ash, we get the results shown in Table LXXVI. TABLE LXXVI. CLASSIFICATION OF COAL. (Hilt.) Kind of Coal. T Anthracite . . 1 : 20 to 1 9 II. III. TV Semi-caking sinter-coal (poor in gas) Caking or baking coal Baking gas-coal 1 : 9 1 : 5.5 1 : 2 to to to 1 :5.5 1 :2 1:15 V Sinter-coal rich in gas 1 : 1.5 to 1 : 1.25 VT Sand-coal rich in gas . . 1 1 25 to 1 1 11 Ratio of Residuum, Free of Ash and Vol- atile Matter. BITUMINOUS AND ANTHRACITE COALS 181 Expressing the volatile matter as given in Table LXXVI in per cents free of ash, we get the results given in Table LXXVII. TABLE LXXVII. CLASSIFICATION OF COAL. (Hilt.) Kind of Coal. Volatile Matter. Per cent. T Anthracite \ 5 to 10 II Semi caking coal 10 to 15 5 III Caking coal 15 5 to 33 3 IV Baking gas-coal 33 3 to 40 v Sinter-coal rich in gas 40 to 44 4 VI. Sand -coal rich in gas 44.4 to 48 Dr. E. Muck based a classification on simple laboratory experi- ments. If a small quantity (about a teaspoonful) of finely powdered coal is quickly heated, preferably in a platinum crucible, until no flame is visible at the cover, the quality of the cooled residuum varies according to the coal used, as follows: Powder, just like the coal-powder used . . I. Sand-coal. Somewhat molten, partly powder II. Molten sand-coal. Molten but not puffed. III. Sinter-coal. Molten, somewhat puffed IV. Caking sinter-coal. Thoroughly molten and puffed up in a form similar to a potato V. Caking coal. The properties are the same in using the fuel on a large scale. In heating under admission of air (grate-firing), I, II, and III do not melt; but IV and V do melt to such an extent as to clog the grate openings, so that only I, II and III can be used under boilers and for household purposes. If melting (caking) coals III and IV are slowly and gradually heated, they do not melt properly and the coke-residuum is poor- looking, soot-black and strongly puffed. This also takes place at high temperature and too large an air supply, since the fusible coal substance is destroyed by long heating (partial degasifica- tion) and excess of air (oxidation). If caking coal is heated for 182 HEAT ENERGY AND FUELS some time in the open air (to about 300 degrees), it no longer cakes at all if afterwards heated to a high temperature. Depending on the fact, whether the coal sample is heated to high (normal test) or low temperature (puffing test) the coke obtained shows different volume and color. After heating to a high temperature the volume is smaller than after heating to a low temperature. The color after the normal test is more or less brilliant, silver- white, after the puffing test black and not brilliant. We find the same phenomena in coke ovens at low and high temperature. Considering besides the quality of the coke, the fusibility and the flame of the coal, the classification given in Table LXXVIII can be used (Muck). TABLE LXXVIII. CLASSIFICATION OF COALS. Elementary Compo- Yield sition of the Coal, Quality. Dry and Free of Ash, in Per cent. in Coke, Per Quality of Coke. Specific Gravity. cent. c H O I. Dry bituminous 75 5.5 19.5 50 Powdered or 1.25 coal with long to to to to fritted. flame. 80 4.5 15.0 60 II. Baking bitum. 80 5.8 14.2 60 Molten and ri- 1.28 coal with long to to to to mous. to flame, or gas coal. 85 5.0 10.0 68 1.3 III. Baking coal 84 5.0 11. .0 68 Molten and 1.3 proper, or forge to to to to compact. coal. 89 5.5 5.5 74 IV. Baking bitu- 88 5.5 6.5 74 Molten, very 1.3 minous coal with to to to to compact, to short flame, or 91 4.5 5.5 82 slightly ri- 1.35 coke-coal. mous. V. Semi-anthracitic 90 4.5 5.5 82 Fritted or pow- 1.35 coal. to to to to dered. to 93 4.0 3.0 90 1.4 From these figures we see the relation and connection between the properties of the coals and their chemical compositions. But there are also cases of isomerism where coals of about identical composition show an entirely different behavior in heat. BITUMINOUS AND ANTHRACITE COALS 183 TABLE LXXIX. CLASSIFICATION OF COALS. Occurrence. Composition of Coal, Dry and Free of Ash, in Per cent. Yield of Coke, Per cent. Quality of Coke. C H O-f-N Niederwuschnitz, Saxony . . Zwickau Saxony 82.34 82.59 87.47 '87.79 4.73 4.76 5.03 4.78 12.93 12.65 7.50 7.24 66.43 77.29 75.80 77.60 Sandy. Caked. Slightly molten. Caked and strongly puffed. Alma Mine, Floz 4, West- phalia. President Mine, Dickebank, Westphalia. Coal deposits are not at all homogeneous, and we can generally distinguish the following components: 1. Malting coal, jet black, brittle, brilliant, easily split per- pendicularly to its layers. 2. Dull coal, brown to gray-black, hardly any brilliancy, stronger and less brittle. Is not scissile and shows rough frac- ture. Malting coal is the only constituent of sand and sinter-coals, semi-baking, and is the principal constituent of the baking and coking coals, while gas-coal consists of alternate layers of malting and dull-coal. A coal extremely rich in dull coal is called cannel- coal. Since the malting coal occurs in every kind of coal, it is self-evident that it has widely varying composition and fusibility. The dull coal is usually richer in ash -and always richer in hydro- gen and gas than the malting coal. 3. Fibrous coal is widely distributed in all parts of the coal- deposits, forms generally thin layers, is similar to charcoal (there- fore called mineral charcoal) is infusible, low in volatile matter and is therefore detrimental in coke and gas production. 4. Bituminous shale, i.e. slate impregnated with coal sub- stance, is frequently similar to cannel-coal. The coal substance of bituminous slate is rich in hydrogen. The moisture of freshly mined coals varies. In air-dry state they contain from 2 to 4 per cent, sometimes up to 8 per cent of water. The ash varies from 2 to 20 per cent. For some special metallurgical uses, the com- 184 HEAT ENERGY AND FUELS position of the ash has to be considered, as a coal rich in sulphur or phosphor is detrimental for certain uses. TABLE LXXX. ANALYSES OF BITUMINOUS COALS. Locality. Gas. Coke. Composition of coal in Per cent. "si il _! H 5497 7098 6420 7296 8392 7069 7465 Yield in Per cent. C H N H 2 O Ash. Sulphur Per cent. I E a a Austria: Kladus 59.48 75.09 68.80 77.21 73.20 72.38 89.32 85.62 85.90 79.82 84.54 74.46 78.93 3.55 4.51 3.99 4.00 4.93 4.46 3.80 4.65 4.56 4.96 4.77 5.10 4.90 8.89 8.41 8.23 8.32 19.11 15.05 2.71 5.93 4.77 4.79 4.59 8.25 7.24 1.16 8.41 1.36 1.39 1.71 1.56 1.25 0.84 1.52 1.57 7.90 6.08 5.65 2.41 3^00 1.25 6.07 4.36 19.02 5.31 11.97 6.07 2.76 8.11 4.17 2.09 3.21 5.36 4.00 4.08 1.96 0^82 0.49 1.04 0^90 0.68 Pilsen Karwin Maehr. Ostrau Germany : Upper Silesia. Saarbriicken . . Aachen 70.5 Essen Bochum Westphalia. . . France: St. Etienne . . . England : Tyldesley Bickershaw. .. 19.75 32.08 29.81 69^9 79.0 57.75 63.87 By dressing and washing, the ash-content can be considerably decreased. Of technical importance is the decomposition of coal in the atmosphere by absorption of oxygen, which takes place in two stages; at first the available hydrogen and some carbon are oxidized to water and carbon dioxide ; in the second stage oxygen is absorbed by the coal, but no carbon dioxide nor water escapes, so that an increase in weight takes place, sometimes as much as 4 per cent. Thereby not only the thermal value, but also the property of caking and the yield of coke is decreased. By this absorption of oxygen and oxidation the coal is heated, sometimes to such a high temperature that not only the included gases escape (causing decrease in weight) but also spontaneous combustion can take place. This spontaneous combustion is facilitated by the oxidation of pyrite, which is present in the BITUMINOUS AND ANTHRACITE COALS 185 coal. The gases included in bituminous coals vary in composi- tion as follows: Methane per cent to 90 per cent. Carbon dioxide 0.2 per cent to 54 per cent. Oxygen trace to 17 per cent. Nitrogen 10 per cent to 90 per cent. The quantity varies between 18 and 190 cu. cm. in 100 g. of coal. TABLE LXXXI. ANALYSES OF BITUMINOUS COALS. (G. Arth.) BITUMINOUS COAL FROM THE FRANKENHOLZ MINE WITH 8 . 1 PER CENT OXYGEN. C Per H 2 Per Ash. Per C Per H Per O Per cent. cent. cent. cent. cent. cent. of Organic Compounds. Fresh mined 2.08 81.69 5.79 8.15 83.42 5.91 After 12 months: In running water 1.75 82.24 5.70 7.88 83.70 5.80 In stagnant water 1.82 82.15 5.62 7.94 83.67 5.72 Exposed to the weather 1.96 81.45 5.58 8.80 83.08 5.49 . BITUMINOUS COAL FROM DROCOURT (PAS DE CALAIS) WITH 3.7 PER CENT OXYGEN. Fresh mined 4.08 85.06 5.20 3.68 88.68 5.42 After 12 months: In running water 4.33 85.70 5.26 2.71 89.58 5.49 In stagnant water 4.78 84.67 4.87 3.74 88.92 5.11 Exposed to the weather 5.77 82.78 5.00 4.54 87.84 5.30 BITUMINOUS COAL FROM AISEAU-PRELE (CHARLEROI) WITH 1.6 PER CENT OXYGEN. Fresh mined 2 86 89 83 3 88 1 59 92 41 3 99 After 12 months: In running water 2 64 89 30 3 79 2 61 91 70 3 89 In stagnant water 3 31 89 01 3 84 2 05 92 05 3 97 Exposed to the weather 3.19 88.77 3.99 2.38 91.69 4.05 186 HEAT ENERGY AND FUELS B. ANTHRACITE. Anthracite is the last stage of carbonaceous decay. It is black, very hard and strong, has generally conchoidal fracture (some- times it is very slaty), and has a specific gravity of 1.40 to 1.80. Anthracite burns without smoke, with a short, weak, reddish flame. By distillation an extremely small quantity of volatile matter is obtained. The composition of the organic component is: C 93 to 95 per cent H 4 to 2 per cent + N 3 per cent 100 per cent. TABLE LXXXII. ANALYSES OF ANTHRACITES. 1 Coke *J "cd Gas C C H O N H 2 Ash C OJ > Occurrence. Per Ppr Per Per Per Per Per Per IS ~ : Observer. cent. xcjr cent. cent. cent. cent. cent. cent. cent . f co la a H Denver, Ruby Mine, U.S.A. 87.56 3.11 2.69 0. 13 0.72 4.15 0.89 Denver, An- thracite Mine, Fischer. U.S.A ..... 89.49 3.33 1.19 0.66 0.59 4.00 0.78 Pennsylvania, V Wilkesbarre. . . 86.91 2.80 3.89 5.97 0.43 Schultze. Do 2.75 87.90 86 . 456 1.995 1 . 449 0. 75 3.45 5.90 7484 P. Mahler. Tonking, Kebao 4.56 85. 19 85.746 2.733 2.671 0.60 2.80 5.45 7828 Do. Turacher-Alpe Styria 84. 14 2.55 4.18 4.31 4.82 7339 R. Schoffel. Werchzirm- Alpe, Styria . 75.48 2.05 3.88 2.56 16.03 6560 Do. The distillation yields: Powdered coke 90 to 92 per cent Gas 10 to 8 per cent 100 per cent. The anthracites are of the greatest importance in America, where they occur in immense deposits. They are of no impor- tance in Europe. BITUMINOUS AND ANTHRACITE COALS 187 Suggestions for Lessons. Examination of various solid fuels. Elementary and interme- diate analysis, fuel tests, ash analysis. Determination of the density and of the weight of 1 cu. m. Examination of green and seasoned fuels. Determination of the quantity and composition of the included gases. CHAPTER XIV. ARTIFICIAL SOLID FUELS. FOR certain purposes it is advantageous to use fuels richer in carbon than the ones occurring in nature. Such fuels are pre- pared by destructive distillation of the natural solid fuels, whereby the following products of decomposition are formed: (1) gases; (2) tar; (3) tar water, and (4) residuum rich in carbon. The quality and quantity of the products of decomposition depend on the nature of the raw material, temperature of decom- position and other circumstances. With increasing temperature the output of gas increases both as to weight and volume, but simultaneously the quantity of heavy hydrocarbons in the gas decreases, and therefore also the illuminating power of the gas. The pressure under which the distillation is carried out is also of importance relative to the products formed. The advantages of producing carbonized (coked) fuels are: 1. A fuel of higher thermal value is obtained. (a) As the carbon-content of the coked fuel is higher than that of the natural fuel. (b) As the volatile substances in spite of their combustibility, require for their gasification a considerable amount of heat, which is at our disposal when we use coked fuels. Thereby the cost of transportation per heat unit is decreased. 2. Combustion of coked fuels is smokeless. 3. Coked fuel does not bake. 4. Coked fuel contains less sulphur than does raw fuel. 5. Under certain conditions valuable by-products can be collected. On the other hand coking has the following disad- vantages : 1. The carbonizing (coking) of the natural fuels requires a certain amount of heat, fuel, wages and machinery. 188 ARTIFICIAL SOLID FUELS 189 2. Coked fuel burns with a short flame, while for certain operations a long flame is essential. 3. The ash-content is increased by coking. Heat of formation of 1 kg. of a fuel is the number of calories which were set free by the formation of such fuel from its ele- ments, and which naturally have to be added again for the decomposition into the elements. Heat of decomposition is obtained by deducting the directly observed heat of combus- tion of the fuel from the sum of the heats of combustion of the elementary components. Schwackhofer found for Ostrau (Austria) nut coal: C 73.55 per cent H 2 4.54 per cent 11.38 per cent N 0.46 per cent. Hygr. H 2 2.44 per cent Ash 5.63 per cent Combustible sulphur 0.60 per cent Thermal value 7433 cal. The heat of combustion of the elementary components of this coal are: C 0.7355 X 8080 = 5942.84 cal. H 2 0.0454 X 29,600 - 1343.84 cal. S 0.0060 X 2500 - 15.00 cal. Total 6301.68 cal. Thermal value of coal deduct 7433.00 Heat of formation of 1 kg. coal - 1131.32 cal. For coal from Leoben (Styria) Schwackhofer found: C 60.91 per cent H 2 4.22 per cent 17.99 per cent N 0.71 per cent Hygr. H 2 9.92 per cent Ash 6.25 per cent Combustible sulphur 0.52 per cent Thermal value. . . 6013 cal. 190 HEAT ENERGY AND FUELS The heat of combustion for the elementary components is : C 0.6091 X 8080 - 4921.53 cal. H 0.0422 X 29,600 = 1249.12 cal. S 0.0052 X 2500 - 13.00 cal. Total 6183.65 cal. Thermal value of coal deduct 6013 . 00 cal. Heat of formation of 1 kg. coal + 170 . 65 cal. The heat necessary for gasifying coal depends on the nature of the gasification, i.e. the nature of the products of decomposition. If the gasification is effected by destructive distillation, the heat necessary equals the difference of the heat of formation of the coal and the heat of formation of the distillation products (from the elements). The heat necessary for gasifying can also be calculated by deducting the thermal value of the distilla- tion-products (calorimeter) from the thermal value of the coal. Therefore the heat required for the destructive distillation of 1 kg. of this coal is 254.792 cal. According to the nature of the raw material, the coked mate- rials are named: 1. Charcoal. 2. Peat-coal. 3. Coke; to the class of artificial fuels belong also the 4. Briquettes. TABLE LXXXIII. COMPOSITION AND PRODUCTS OF DESTRUCTIVE DISTILLATION OF COAL. (P. Mahler.) Substance. Percentage of Elementary Compo- sition. Ther- mal Value in Cal. Yield in Kg. from 100 Kg. of Coal. Thermal Value of Products in Cal. C H 2 O N Ash HaO Bitum. coal of Corn- men try 75.182 5.176 8.202 0.94 7.05 3.45 7423.2 100 742326.0 Coke Tar from hydraulic main Tar from tar collector. Tar from cooler Tar from condenser . . . Gas... Ammonia water 85.773 90.186 89 910 87.222 85.183 55.086 0.414 4.848 4.945 5.499 5.599 21.460 2.043 s *, 4. 5. 7. 9 23. 0.62 966 145 279 218 454 17g 10.27 . perl 0.88 ter " 7019.4 8887.0 8942.8 8831.0 8538.4 11111.0 65.66 3.59 0.87 1.46 1.89 17 09 9.36 460893.8 31904.3 7780.2 10243.9 16137.6 189887.0 Total Heat lost in destruc- tive distillation Coke used as fuel 7019^ 99.62 716846.8 2K09 25479.2 148053.2 CHAPTER XV. CHARCOAL. THE dry distillation of wood yields (a) Hygroscopic water. (6) Illuminating gas, consisting mainly of Acetylene, C 2 H 2 . Ethylene, C 2 H 4 . Benzol, C 6 H 6 . Naphthalene, C 10 H 8 . Carbon Monoxide, CO. Carbon Dioxide, C0 2 . Methane, CH 4 . Hydrogen, H 2 . (c) Tar, consisting of Benzol, C 6 H 6 . Naphthalene, C 10 H 8 . Paraffin, C 20 H 42 to C 22 H 46 . Retene, C 18 H 18 . Phenol, C 6 H 6 0. Oxyphenic Acid, C 6 H 6 2 . Kresylic Acid, C 7 H 8 0. Phlorylic Acid, C 8 H 10 O. fC 7 H 8 2 . Creosote -] C 8 H 10 2 . (C 9 H 12 2 . Resins (d) Pyroligneous acid, consisting of Acetic Acid, C 2 H 4 2 . Propionic, Acid, C 3 H 6 2 . Acetone, C 3 H 6 0. Wood Alcohol, CH 4 0. (e) Charcoal. 191 192 HEAT ENERGY AND FUELS Charcoal contains, besides carbon, H, and ash, and generally also hygroscopic water. The average composition of air-dry charcoal is C (including H and O) 85 per cent Hygroscopic H 2 12 per cent Ash 3 per cent 100 per cent. Tamm takes the average composition of charcoal as follows : Air-Dry Perfectly Dry 83.0) 90 . per cent 13 . 2 [ 98 . 9 per cent 2.7) 1.1 100.0 100.0 According to the researches of Violette on charring wood, the wood remains unchanged up to a temperature of 200 C; at 232 C. it gets brown; between 270 and 350 C. red coal and at 400 C. black coal is formed. The so-called red wood, which stands between red and black coal, has the following composition (Fresenius) : C 52.66 percent H 5 . 78 per cent 36.64 percent . Ash . 43 per cent H 2 0. : 4. 49 per cent 100. 00 per cent. Violette 's researches comprise the following series: 1. Coals made at different charring temperatures (150 to over 1500 C.) from one kind of wood (Rhamnus frangula). 2. Coals from the same wood produced at different tem- peratures in entirely closed vessels. 3. Coals from those kinds of wood which are mainly used in France for gunpowder manufacture. 4. Coals made at 300 C. from 72 different varieties of wood. CHARCOAL 193 PQ B PS o e of Cha onds to enta P -qO The M Poin 001 1 g jj . mills S^OQ pa H oooooooooo'oopooo'o'oooo* "*' 'o' ir\ if\ un m m vDsDiXu^'^Trrv' r- (Nl OO O ^ Csl * -i ON OQ i ^^^^49^Trc^f^S(Nr5cscgcscNcsS( 6 194 HEAT ENERGY AND FUELS For these experiments the wood was cut into cylindrical pieces of 1 cm. diameter and dried in a current of steam at 150 C. The charring (except in the second series) was effected up to 350 C. with superheated steam, at higher temperature in a crucible at the melting point of antimony, copper, silver, gold, steel, iron, and platinum. The results of the first series are given in the table on page 193. TABLE LXXXV. YIELD OF COAL BY CHARRING. (Karsten.) Kind of Wood. Rapid Distillation. Slow Distillation. Karsten. Karsten. Stolze. Winkler. Oak wood, young Oak wood old 16.54 15.91 14.87 14.15 13.11 13.65 14.45 15.30 13.05 12'20 12.15 14.25 14.05 16.22 15.35 15.52 13.75 13.30 25.60 25.71 25.87 26.15 25.22 26.45 25.65 25.65 25.05 24.70 25.10 25.25 25.00 27.72 24.75 26.07 25.95 24.60 | 26.1 | 24.6 | 23.8 24.4 28.8 24.4 | 23.4 j 21.5 | 23.7 22.8 21.1 22.2 22.8 17.8 17.6 17.7 17.6 20.6 20.1 16.2 19.4 15.0 Red beech, young Red beech, old White beech, young White beech, old Alder, young Alder, old Birchwood, young Poplar. . . . Birchwood, old Birchwood, well preserved. . . . Red pine, young Red pine, old Fir wood young Fir wood, old . Pine, young. ... Pine, old Linden Ash Willow. 13.40 17.00 '24!e6' 27.95 Rye straw Fern The tests show that quick coking yields only about half as much charcoal as slow coking. Violette obtained by charging wood into a preheated (432 degrees) charring vessel about 8.96 per cent coal, while he obtained 18.87 per cent by heating the same kind of wood for six hours gradually up to 432 degrees. In the second series of Violette's experiments the wood pieces (Rhamnus frangula) were weighed, dried at 150 C. and were kept in closed glass tubes at constant temperature with super- heated steam. The results were : CHARCOAL 195 PN >H x S H I O I G cS 0) c g i 8 g 1 Jj | 0) 1 1 I *5 "O _J2 _G B CD r . a | T5 t O 3 b >* . S g S i 1 0) ^3 t) G I S W cS i "S 1 1 |t 03 I a a s came brown a B 6 lary structur " ordinary ap; 1 -1 -S 15 2 ^S 1 >>^ > S3" 2 ti mass withoi ant, entirely soft coal. milar to moll JS 1 ss, IT i o k coal o - -S O O D "o i ^ 03 stance si 0) T3 o3 "3 & 3 a c fe S^ X H PH 6~ 5 (fi 3 02 * T 1 I 1 III 1 1 00 cj 1. ^S ^S S ,1 S P: g WOO J. 4> .. .. . . . . 2 O t, g 31 1 M- . 88 88 88 88 88 88 88 88 88 88 a"S I* G n d d d d d d d d d d ni 1 1 1 1 III 1 S c 2 - N * * * 00 196 HEAT ENERGY AND FUELS The third series of experiments with coals made from different kinds of wood showed the variable composition of the charcoal obtained. Violette found in the interior part of the apparatus coal with 85 per cent carbon, on the walls with 70 per cent of carbon. In the fourth series of experiments 72 kinds of wood were dried for two hours with steam of 150 C. and then charred for three hours with steam of 300 C. The results were as follows : TABLE LXXXVII. YIELD OF COAL BY CHARRING. No. Kind of Wood dried at 150 Degrees, Charred at 300 Degrees. Yield of Coal, Per cent. No. Kind of Wood dried at 150 Degrees, Charred at 300 Degrees. Yield of Coal Pei- cent. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Cork wood 62.80 54.30 52.00 52.17 49.69 46.99 46.09 46.06 44.89 44.25 43.75 43.07 41.86 41.48 40.95 40.90 40.75 40.64 40.44 40.35 40.31 39.49 39.44 39.22 38.83 38.46 37.93 37.41 37.31 37.27 37.21 36.96 36.60 36.53 36.06 36.01 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 Currant bush Medlar tree Cherry bush American aspen Hooded milfoil 35.66 35.57 35.53 34.87 34.85 34.75 34. 7C 34.69 34.69 34.59 34.44 34.40 34.28 34.24 34.17 34.06 33.76 33.75 33.74 33.61 33.42 33.36 33.33 33.28 33.28 32.79 32.70 32.21 32.05 32.03 31.88 31.85 31.84 31.33 31.12 30.86 Ebony Satinwood Willow (foul) Wood from Herculaneum . Wheat straw Oak Yew tree Mahogany Ivy Hawthorn Plane-tree Apple-tree Elm-tree . . . Beech Ironwood Juniper Pockwood Moor pine Poplar (leaves) Poplar (root) Fir Fungus growing on willows Box Hornbeam . Alder-tree Barberry Furze Birch-tree Plum-tree Sycamore Maple Willow Alder buckthorn . . . Virginian acacia Flowery dogwood .... Broom Ash-tree Quince-tree Hazel-tree Bird cherrv Holly-tree*. Alaternus Guelder-rose Pear-tree Linden Lote-tree Bird cherry Palm-tree Thuja, Canadian Hemp stalk Virgin's bower Rush .... Cocoanut-tree Carded cotton Elder-tree Varnish-tree Rose-tree (wild) Honeysuckle Spindle-tree Lilac Begonia Poplar Vine Chestnut Bean trefoil Horse-chestnut CHARCOAL 197 The conclusions that can be drawn from Violette's experi- ments are : 1. Wood yields less coal the higher the temperature. For the same kind of fuel the yield for instance is : At 250 C 50 per cent weight, At 300 C 33 per cent weight, At 400 C 20 per cent weight, At 1500 C 15 per cent weight. 2. From woods treated at the same temperature the yield of coal is proportional to the time of distillation. With slow dis- tillation the yield is twice as great as with quick distillation. 3. The carbon content of the coal is proportional to the tem- perature of distillation ; the coal contains for instance : At 250 C 65 per cent, At 300 C 73 per cent, At 400 C 80 per cent, At 1500 C 96 per cent. 4. By distillation in perfectly closed vessels very little carbon is gasified, as most of the carbon is retained in the coal in solid form on account of the increased pressure. This explains the higher yield in retorts as compared to pile-charring. 5. The charring of wood in perfectly closed vessels yields at 280 C. 80 per cent of red coal, while by means of superheated steam only 40 per cent can be obtained. This is due to the increased pressure, which changes the equilibrium towards a smaller volume. 6. In perfectly closed vessels wood melts at from 300 to 400 C. under formation of a black, brilliant mass, without any organic structure, similar to melted pitch-coal. 7. Coals produced in cylinders or iron pots are of variable composition (70 to 84 per cent C.), while with superheated steam - according to temperature coal of any constant composition can be made. The red coal used in gunpowder manufacture is nothing but half-charred wood of red-brown or brown-black color. It burns with a long illuminant flame and therefore contains less carbon and more hydrogen than charcoal proper (black coal). 198 HEAT ENERGY AND FUELS Good charcoal is black in color with a steel-blue lustre. It has a distinct wood structure, conchoidal fracture, low specific gravity (0.17 to 0.24), is fairly strong, easily ignited, and burns with a very short, blue, smokeless flame. By lying in the atmosphere charcoal absorbs about 10 per cent of water; if moistened directly with water, 50 per cent is absorbed. WEIGHT OF CHARCOALS (Petraschek). Charcoal. 100 Liters Weigh, Kg. From soft wood, average From hard wood, average.. . . 17 24 Hard and soft wood mixed. . . 21 The loss of volume of charcoal during transportation, etc., by breakage and friction is, according to Wessely : Decrease in Volume. Per cent. Carting. Sleighing. Hours road. 1 according to quality of Limits. Average. 3-8 5 Limits. Average. 3-6 5 2 IlQl 9i 11_Q 94 3 . 1-3 2 1 24 ll 4... 1-2 H 1-1 4- U One volume of charcoal from boxwood absorbs the following quantities of gas (Saussure) : NH 3 90vol. I HC1 85vol. ' S0 2 65vol. H 2 S 55vol. N0 2 40vol. C 2 H 4 35vol. CO, 35 vol. CO 9.42 vol. O 9.25vol. N 7.50vol. CH 4 5.00vol. H 2 1.75 vol. 0.59 g. of different kinds of coal absorb the quantities of dif- ferent gases (in cu. cm.) given in Table LXXXVIII. CHARCOAL 199 TABLE LXXXVIII. ABSORBING CAPACITY OF COALS. Gases. Charcoal. Peat. Bone Black. NH 98 5 96 43 5 HC1 TT 45.0 30 60.0 28.5 9.0 COo 14.0 10.0 5.0 o 0.8 0.6 0.5 SO 2 32.5 27.5 17.5 The temperature of ignition depends on the temperature of distillation as shown in Table LXXXIX. TABLE LXXXIX. TEMPERATURE OF IGNITION OF CHARCOAL (Violette). Temperature of Charring. Temperature of Ignition. 300 G. 360-380 C. 260-280 C. 340-360 C. 290-350 C. 360-370 C. 432 C. 400 C. 1000-1500 C. 600-800 C. Melting point of plati- 1250C. num. We can classify as follows the different methods of producing charcoal. A. Charring in the woods or carbon- izing under mov- able cover (with changeable volume of the charring ap- paratus). B. Charring in ap- paratus with con- stant volume of the charring space. (a) Without re- covery of by- products. (6) With recov- ery of by-prod- ucts. (a) Pile-charring (the heat re- quired is gen- erated in the interior of the coking space). (6) The heat for charring is fur- n i s h e d from outside. (a) in pits. (a) in pits. (^) in piles. (a) The heat necessary for char- ring is furnished by partly burning the wood to be charred (piles with admission of air to the interior). (/?) The heat necessary for char- ring is furnished by combustion by gases free of oxygen (piles with admission of combustion gases free of oxygen to the interior). (7) The heat is furnished by superheated steam. 200 HEAT ENERGY AND FUELS A. Charring in the woods, (a) Charring without recovery of by-products, (a) Charring in pits. The pits are about 1 m. deep, 2 m. wide at the top, somewhat narrower at the bottom. The fire is started with brushwood, then the wood is piled up and cov- ered with earth. The coal is light and unequally burned. (/?J Charring in round piles. These piles have generally the form of a paraboloid, and their cubic content is calculated according to the formula d 2 n h d 2 hn T' 2~~T or, as on the finished pile, the circumference can be figured more easily than the diameter: u 2 7i h u 2 h u 2 h 7?' 4'2 = 8~x = 25.31 ' As, however, the shape of the piles is not exactly like a para- boloid, from 4 to 6 per cent is deducted from the volume calcu- lated according to above formula. The following varieties of wood are mainly used for charring in piles: of coniferous trees: pine, fir, red pine, and larch; of leaved wood: oak, red beech, white beech, ash, elm, alder, and birch. The most favorable age of trees for charring is given in Table XC. TABLE XC. PROPER AGE OF TREES FOR CHARRING. (Scheerer.) Wood. Age of most Per- fect Development. Age at which Tree can be cut. Pine 140 80 to 100 Red pine Fir 150 80 to 100 70 to 80 60 Larch . . 80 to 90 50 Oak . 200 to 250 50 to 60 Red beech White beech Elm | 120 to 140 80 120 20 to 30 Alder... 18 to 20 Birch 40 20 CHARCOAL 201 In winter time the wood contains less moisture than in sum- mer; winter is therefore the most favorable time for cutting the wood. For the erection of piles, locations are selected that are protected from wind, and a ground not too dry and not too wet. A dry ground will break and crack, allowing too much air to enter into the pile. A wet ground generates steam, which, with the glowing coal, is decomposed into hydrogen and carbon dioxide. In both cases a loss of coal results. The foundation ground of the pile, which is a little inclined towards the center, is first of all covered with a layer of culm coal, In the center a strong, straight post (center pole) is driven into the ground (Slavic piles, Figs. 32 and 33), or three posts of even length are driven in, forming an equilateral triangle, the length of the sides being about 20 cm. These three posts form the center shaft (Italian piles, Fig. 34). Logs are now laid around the center of the charcoal kiln (pile), either vertical as in Fig. 34, or horizontal, or both ways combined, as shown in Fig. 33. Depending on the size of the pile, one, two, or more layers of logs are put together, the upper layer always being less steep than the lower. Small logs are used to fill the spaces between the large logs. The upper layer is covered with small logs and small pieces of wood, for rounding the shape of the pile (peak of the pile). In piles with center shafts the logs are always vertical, except the dome, which consists of horizontal logs. In these piles the center shaft is used for starting the fire, while in piles with a center post a channel is left open for this purpose on one side of the bottom part, extending to the center. The pile is then covered on the outside with branch wood, then with leaves and grass (smoke cover), and at last with earth, sand, and coal culm (earth cover). This cover does not reach to the ground (Fig. 32, C, D), but is supported by timber. For starting the fire some kindling wood is put in on the bottom at the center. The fire is started by inserting glowing coal in the kindling wood through the center shaft or through the above-mentioned channel. Then the shaft is filled with small pieces of wood and covered. The fire now extends upwards and to the sides; the hygroscopic water is evaporated and condenses again on the sur- face of the pile (the pile sweats) . Then acid gases and later com- bustible gases escape, and wherever they get mixed with air an explosion takes place, throwing off parts of the cover or parts of 202 HEAT ENERGY AND FUELS D D FIG. 32. Slavic Pile. FIG. 33. Slavic Pile. FIG. 34. Italian Pile. CHARCOAL 203 the pile. Such damage to the pile has to be repaired instantly. This first period of charring lasts from 18 to 24 hours. Meanwhile the center shaft is burned out and pieces of wood have to be filled in again and again until the period of sweating is over. The bottom of the pile is now also covered, and by mak- ing openings into the cover (driving the pile) the fire is drawn gradually to the lowest parts. The upper openings are closed as soon as blue smoke starts to escape, the lower as soon as the flame shoots through. The " drawing" of the coal is performed by removing the cover on one side and cooling the hot coal with cold water. The coal is marketed in the following sizes : (1) Lump coal; (2) blacksmith coal; (3) small size; (4) culm; (5) half-charred wood. According to the size of the pile (120 to 300 cu. m.) the process of charring requires from 15 to 20 days. Probably the largest pile kilns are operated at Neuberg (Styria, Austria). They are built up to 400 to 430 cu. m. capacity, the 500 cu. m. size having been abandoned on account of difficulty of regulation. Red pine and red beech are charred at Neuberg in separate piles. The following data, gathered from these plants might be of interest: 1 cu. m. hard wood half dry weighs 550 kg. 1 cu. m. soft wood half dry weighs 400 kg. 1 cu. m. (cord wood) hard wood green weighs 900 kg. 1 cu. m. (cord wood) hard wood half dry weighs 700 kg. 1 cu. m. (cord wood) hard wood dry weighs 580 kg. 1 cu. m. (cord wood) soft wood green weighs 800 kg. 1 cu. m. (cord wood) soft wood half dry weighs 600 kg. 1 cu. m. (cord wood) soft wood dry weighs 400 kg. 100 liters hard coal weighs 23 kg. 100 liters soft coal weighs 14 kg. The piles have a diameter of 14 m., a height of 4.7 m., and a cubic content of 400 cu. m. of wood. They are built with five layers of log wood of 1 m. height. The yield of such a pile is Piece coal (large pieces) . . . 2000 hectoliters ) 60 per cent volume Piece coal (small pieces) . . 400 hectoliters J of the wood, Culm 1 per cent, Half-charred wood 1 per cent. 204 HEAT ENERGY AND FUELS TABLE XCI. COMPOSITION OF KILN GASES. (Ebelmen.) Composition in Per Cent. No. Hours after Starting. Appearance of Gas. (Volume.) C0 2 CO K, N 2 , 48 white opaque 25.57 8.68 9.13 56.62 2 72 white opaque 26.68 9.25 10.97 53.40 3 96 white opaque 27.23 7.67 11.64 53.46 4 66 white transparent 23.51 5.00 4.89 66.60 5 71 fairly transparent 23.28 5.88 13.53 57.31 6 95 bluish and transparent 23.08 6.04 14.11 55.77 The time required is : Erection of pile 4 days, Starting fire. \ hour, Charring process 18-28 days, Removing charcoal 4 days. In working shifts : Erection 4 days per 10 men 40 shifts, Covering with branch wood 1 day per 2 men 2 shifts, Covering with leaves 2 shifts, Covering with earth 1 day per 12 men 12 shifts, Charring, average 8 shifts, Removing charcoal 4 days per 8 men 32 shifts, Preparing ground 2 shifts, Night-watch (average) 2 shifts, 100 shifts. The temperature of the escaping gas right below the cover was from 230 to 260 C. One liter of same showed the following content of condensable products (tar, water, etc.) : 1. White and opaque 0.987 g. 2. Similar to A 1.068 g. 3. Bluish and transparent 0.531 g. (/?,) Charring in rectangular piles. CHARCOAL 205 The horizontal piles are not circular but oblong, generally having a length of from 9.5 m. to 12.5 m. and a width of from 2 to 3 m. (Fig. 35). They are surrounded by posts which are connected by timbers. The logs are put in perpendicular to the FIG. 35. Rectangular Pile. longitudinal axis of the pile. The hollow spaces are filled out with branch wood. The height in front is about 0.6 and increases towards the back part at an angle of from 15 to 20 degrees. The fire is started in the front and goes slowly through the entire length of the pile. (6) Charring in the woods with recovery of by-products. (a) When charring in pits a vessel covered with a grate is put on the bottom for collecting the tar. (/?) In pile-charring (for recovering by-products) iron pipes are put into the cover, leading to a condensing chamber. This is done 24-36 hours after starting the fire, as in the first period almost nothing but steam escapes. Fig. 36 shows a French pile with a channel leading to a tar- collecting vessel. About 20 per cent of tar is obtained. B. Charring in apparatus with constant volume of the charring space. (a) Pile-charring. (a) The heat necessary for charring is furnished by partly burning the wood to be charred (piles with admission of air to the interior). 206 HEAT ENERGY AND FUELS As an example we will describe the round pile oven (kiln), Fig. 37, which has a grate on the bottom for the admission of air, the quantity of the latter being regulated by means of the ash- FIG. 36. French Pile. door. The wood is charged first through the main door, then through the upper charging-chute. After starting the fire the main door is closed with bricks and mortar and as soon as steam . . FIG. 37. Round Pile Oven. and tar begin to escape, the upper charging-chute is also closed, so that the escaping gases have to go through the pipe shown at one side of the cover (dome) to the condensing vessels. When the oven is sufficiently heated, the ash-door is closed. When CHARCOAL. 207 the charring is finished, the oven is allowed to cool and the coal removed through the main door. (/?) Charring in pile-oven with admission of combustion gases free of oxygen to the interior. Such an oven was built by Grill for the iron works in Dalfors (Sweden), Figs. 38 and 39. It is rectangular and provided with Stack FIGS. 38 and 39. Grill's Pile Oven. charging openings on both short sides. The gases of combustion rise from a fireplace below the oven, pass vertically through the center of the oven and escape in four directions through side- flues. The volatile products of distillation escape through two 208 HEAT ENERGY AND FUELS channels arranged in opposite corners, and pass through iron- pipes to a tar-collecting vessel, the stack being arranged above this vessel. After getting- the fire up, the oven is closed tight. A charge consists of 172.26 cu. m. of wood; 37.58 cu. m. of wood are used for heating; the yield is 147.31 cu. m. charcoal. The wages per cu. m. of charcoal at this plant are 6.25 cents. The Schwartz oven is of similar construction, Figs. 40 and 41. It is provided with two fireplaces in the middle of its length, and Fireplace FIGS. 40 and 41. Schwartz Oven. with two flues in the middle of the short sides, whereby a more uniform heat is obtained. (?-) Heating by means of superheated steam (Fig. 42). This process, which was introduced by Violette for the manu- facture of red coal (gunpowder coal), yields about 36 J per cent of red coal and no black coal, and is therefore very much superior to the old process by which 14.18 per cent red coal and 17.81 per cent black coal (total 31.99 per cent) is obtained. Fig. 42 shows a longitudinal section. Steam from a boiler is led through a coil located in the oven. By the direct fire the steam in the coil is CHARCOAL 209 superheated. The fire gases play around the retort and escape through the flue. The superheated steam from the coil enters the sheet-iron cylinder (retort), which is closed in front with a wrought-iron cover, and then passes into the inner cylinder, which is charged with the wood to be charred. Steam and FIG. 42. Charring with Superheated Steam. FIG. 43. Section through French Oven heated from the Outside. products ' of distillation escape through a pipe into the atmos- phere or into a suitable condensing apparatus. Opposite the entrance of steam a baffle-plate is provided for distributing the steam. (6) Charring by heat supplied from the outside. 210 HEAT ENERGY AND FUEL FIGS. 44-47. Pile Retort Oven. FIGS. 48-52. Ovens with Horizontal Retorts. CHARCOAL 211 Charring is performed in retorts or large cylindrical vessels. In Russia, vertical sheet-iron cylinders are used, having a cubic content of about 8 cu. m. : a special fireplace is provided for heat- FIG. 53. Longitudinal Section of a Modern Charring Plant with Vertical Retorts. ing the vertical shell. For quickly preheating the wood to 100 degrees, steam is admitted at the bottom of the cylinder. The tar flows through a pipe arranged at the bottom, to a collecting FIG. 54. Cross-section of a Modern Charring Plant with Vertical Retorts. vessel, while the vapors leave through a pipe on the top, and go to a condensing apparatus, from which the condensed tar passes to the above-mentioned collecting vessel. The products of dis- 212 HEAT ENERGY AND FUEL tillation pass through a cooled pipe, while the combustible gases are lead back into the fire. FIG. 55. Plan of a Modern Charring Plant with Vertical Retorts. Fig. 43 shows a vertical section through a French oven of simi- lar type. Vertical, horizontal and inclined retorts are used with equal success for charring wood. At present pile ovens are used only for certain purposes, as, for instance, for charring pine wood, where the recovery of the valuable Swedish tar and pine oil more than pays for the loss of wood-alcohol and acetate of lime. Modern pile ovens are built of sheet iron for avoiding the loss through brickwork. Such a modern pile-retort oven is shown in Figs. 44 to 47. In the fireplace the grate e (Fig. 46) and the arch dd (Fig. 44) can be seen. Through the arch the fire gases go into the pipes /, while another part of the fire gases goes upwards near the arch and enters the pipes, e. YIG. 56. Modern Charring Plant with Vertical Retorts. FIG. 7. Oven with Stationary Permanent Retorts. All these vertical pipes go CHARCOAL 213 through the interior of the pile-retort. The doors bb are used for discharging. Similar ovens with horizontal retorts are shown in Figs. 48 to 52. Figs. 53 to 56 show a modern charring plant with verti- cal retorts. The retorts a can be lifted out of the furnace by a crane g, and can be brought to a suitable place for charging or discharging. Fig. 57 shows an oven where the retorts remain in permanently; they are discharged into small cars that can be moved right under the retorts. To the rotary retort, however, belongs the future of the char- coal industry. The increase of the charcoal industry is shown by the following figures, which relate to this industry in Austria-Hungary: About 30 years ago the output of charcoal was about 10,000 cu. m., ten years later 120,000 cu. m., and today it is 350-400,000 cu. m. per year. For the prosperity of forestry this industry is of the greatest importance, as only hereby are we enabled thoroughly to utilize widely distributed forests (by the utilization of refuse wood). CHAPTER XVI. PEAT-COAL, COKE AND BRIQUETTES. THE destructive distillation of peat, lignite or coal yields : (1) gases, (2) tar, (3) tar water, and (4) a solid residue very high in carbon, which, depending on the raw material used, is called peat coal or coke. For conveying an idea of the process of destructive distillation, we give below tables for the two extreme cases (peat and bitu- minous coal). DESTRUCTIVE DISTILLATION OF PEAT. (H. Vohl.) 100 parts of peat of a Swiss bog yielded by destructive dis- tillation : r Heavy Hydrocarbons, CnH 2 n I Methan, CH 4 I Hydrogen, H 2 I Carbon Monoxide, CO [Tar 0.820 sp. g. 1 Heavy Oil 0.855 sp. g. I Paraffin Ammonia Methylamin Picolin Lutidin Anilin Caespidin "C0 2 H 2 S CyH Acetic Acid Propionic Acid Butyric Acid Valerianic Acid Phenol 17. 625 gas 5. 375 tar 25. 00 tar water bases acids - . water 25.00 peat coal 214 PEAT-COAL, COKE AND BRIQUETTES 215 % DESTRUCTIVE DISTILLATION OF BITUMINOUS COAL. (R. Wagner.) 100 parts gas coal of the following composition : C 78.0 per cent Disposable H 2 4.0 per cent N 1.5 per cent S 0.8 per cent H 2 chemic combined 5.7 per cent H 2 hygroscopic 5.0 per cent Ash 5.0 per cent 100.0 per cent. Products of dry distillation : 1. 70-75 parts of coke j !f^ n T^-T g ^^ ' I Fe 7 S 8 and earthy matters, 10- 5% 2. Tar water (ammonia water) containing (a) Main components (water, carbonate of ammonia and sulphide of ammonia). (ft) Additional components (chloride, cyanide and sulfo- cyanide of ammonia). 3. Tar, containing: (a) Liquid hydrocarbons (Benzol, Tolnol, Pseudocumol, Cyanol, Propyl, Butyl, etc.). (ft) Solid hydrocarbons (Naphthalin, Acetylnaphthalin, An- thracen, Reten, Chrysen, Pyren). (?) Substances containing oxygen (Phenol, Kresol, Phlorol, Rosolic Acid, Oxyphenolic Acid, Creosote, Pyridin, Anilin, Picolin, Lutidin, Collidin, Leukolin, Iridolin, Akridin). (d) Asphaltic substances (Anthracen, Resins, Coal). 4. Illuminating Gas : {Gases : Acetylen, Ethylen, Propylen, Bu- Tr tylen ' -D i Vapors: Benzol, Styrol, Naphthalin, Acetylnaphthalin, Propyl, Butyl. 216 HEAT ENERGY AND FUELS (/?) Diluting parts (Hydrogen, Methane, Carbon Monoxide). (7-) Impurities (Carbon dioxide, Ammonia, Cyanogen, Rho- dan, Sulfuretted Hydrogen, Sulfuretted Hydrocarbons, Bisulphide of Carbon, Nitrogen). The manner in which the distillation proceeds and the quantity and composition of the various products are distinctly affected by other factors than the character of the raw mate- rials. The most important of these factors is the gasifying temperature. L. T. Wright has distilled at different temperatures a coal of the following composition: C 75 . 71 per cent, H 2 6 . 27 per cent, S 1 . 72 per cent, N 1.72 percent, 11 . 59 per cent, Ash 2 . 99 per cent, 100. 00 per cent. The yield of 100 kg. of coal at a gasifying temperature of 800 C. is given in Table XCII. TABLE XCII. ANALYSIS OF DESTRUCTIVE DISTILLATION PRODUCTS. 100 Kg. Coal C H 2 S N O Ash. Yielded. K ?. Coke Tar . . . 57.38 6 11 1.24 46 1.05 05 1.06 06 1.28 60 2.96 64.97 7 28 e!43 Gas water Gas 0.08 7 56 1.06 2.85 0.12 trace 0.22 0.36 8.30 1.46 9.78 12.23 9.78 21140.0 In purifying mass 0.22 0.02 0.39 0.56 0.56 1.20 Total 71.35 5.63 1.61 1.71 12.20 2.96 95.46 PEAT-COAL, COKE AND BRIQUETTES 217 The yield obtained at a temperature of 1100 C. is given in Table XCIII. TABLE XCIII. ANALYSIS OF DESTRUCTIVE DISTILLATION PRODUCTS. 100 Kg. Coal Yielded. H 2 Ash. Kg. Total. Liters. Coke Tar Gas water Gas In purifying mass Total . . 57.95 4.78 0.08 8.53 0.38 71.73 0.70 0.38 1.06 3.42 0.04 5.61 0.77 0.06 0.13 trace 0.74 1.70 0.47 0.05 0.21 0.86 0.02 1.61 1.24 1.18 8.30 2.30 0.93 13.95 2.97 64.10 6.47 9.78 15.11 2.11 5.37 9.66 31200.0 2.97 97.57 At 800 C. At 1100 C. There was further Soot in tar Specific gravity of gas water Illuminating power of gas at an hourly use of 150 liters 15 per cent 1.0 18 candles 25-30 per cent 1.2 15.3 candles A further comparison shows: At 800 C. At 1100C. Coke Tar Gas water, Gas. . 64.75 kg. 6.43 1. 9.78 1. 21.14cu. m. 64.16 kg. 5.371. 9.961. 31.20cu. m. With increasing temperature the gas quantity (volume), the specific gravity of the tar, and its content of soot, increase, while the crude naphtha and, especially on light tar oil, content of tar considerably decrease. With increasing temperature the creosote and anthracen oil content decreases, while the pitch content increases. The sulphur content of the gas other than that in the form of H 2 S is three times as great at the high as at the low temperature. The ammonia content is small at low temperature, is a maximum at medium and decreases with temperature rise at high temperature. 218 HEAT ENERGY AND FUELS The course of distillation is different at the beginning and at the end. In the Paris gas plant at a temperature of 1000 C. there is obtained : Time of distillation, hrs.O 1 2 3 456 Volume of gas 17 30 27 20 6 Ilium, power per 1051... 1.15 0.90 0.30 0.10 0.4 C. G. Miller divides the time of distillation into two periods: In the first the period of distillation proper at the com- paratively low temperature of 500-600 C. strongly illuminant gases, steam and tar are generated while the coal is coked. In the second period (bright red glow) the coke, decreasing in volume, yields gases (about one-third of the total gas volume) which are free of tar and of low illuminating power. The coke remaining at the end of the first period is probably a mixture of very stable carbon-compounds having the average composition C 16 H 4 0. This substance is further decomposed in the second period at high temperature. But even at the highest practical heat it is impossible to remove the traces of oxygen, hydrogen and nitrogen. If large quantities of coal are put into highly heated retorts, both processes take place simultaneously. The two, however (coal decomposition and coke decomposition), could be separated by using two furnaces, one for heating the material to 600 degrees and removing the tar, the other to decompose the coke. Such a separation might be practicable under certain conditions. The experiments made by Mueller on a small scale confirm the well-known fact that only one-fifth of the nitrogen of the coal is present in the form of ammonia compounds ; further, that the ammonia is formed in the first part of the decomposition of coke. The ammonia yield was Test. In the First Period. In the Second Period. No. 1 0.065 0.267 2 0.059 0.144 3 0.108 0.145 4 0.120 0.178 5 0.063 0.183 6 0.056 0.242 Average 0.0785 0.1931 PEAT-COAL, COKE AND BRIQUETTES 219 How the composition of the products changes by using dif- ferent qualities of gas-coal is shown in Table XCIV. TABLE XCIV. CHANGE IN COMPOSITION OF PRODUCTS WITH QUALITY OF COAL. Bituminous Coal from Pas de Calais. Eng- land. Comen- try. Blanzy. 1 H 2 O, hygroscopic Ash 2.17 9.04 2.70 7.06 3.31 7.21 4.34 8.8 6.17 10.73 fl a. o 5.56 6.66 7 71 10.10 11 70 1 - H 5 06 5 36 5 40 5 53 5 64 C 88 38 86 97 85 89 83 37 81 66 N 1 1 1 1 1 02 _ * h Gas Tar 13.70 3.90 15.08 4.65 15.81 5 08 16.95 5 48 17 5 59 -n T Ammonia water 4.59 5.57 6.80 8.61 9 86 $2:* Coke 71.48 57 63 64 90 60 88 58 - Coal dust 6.33 7.07 7.41 8.08 9.36 "5 Volume, cu.m Illuminating power, Carcell .... 30.13 131c 31.01 112c 30.64 104c 29.73 102. Ic 27.44 101. 8c ^3 'o CO... CO 1.47 6.68 1.58 7.17 1.72 8 21 2.79 9 86 3.13 11 93 > H 9 54.21 52.79 50 10 45 45 42 26 9 CH 4 34.37 34.43 35.03 36.42 37 14 c CH 79 99 96 1 04 88 CH 2 48 3 02 3 98 4 44 4 76 The influence of the mineral substances on the course of dis- tillation is remarkable, as is seen from Knoblauch's researches. He mixed with his coal 2.5, 5, and 10 per cent of lime, and 5 per cent silica respectively. The table on following page shows the differences of yield with these mixtures (from 1000 kg ? of coal). We see that the quantity of products of distillation is not changing in proportion to the quantity of the addition. The gas yield, however, seems to be an exception, as it increases in proportion to the addition. The yield in ammonia increases very slowly as the lime is added, so that with a certain quantity of lime a maximum is reached, above which even a large addition of lime has no effect. There is no relation between silica and ammonia and H 2 S, since no reaction takes place. The small differences shown in the above table are caused by variations in 220 HEAT ENERGY AND FUELS the decomposition of the coal, since the quantity of coke increases with additions more rapidly than the quantity of tar decreases, and since at the same time gas quantity increases the carbon content and therefore the illuminating power of the gas is necessarily decreased, which decrease is not sufficiently counterbalanced by the increased yield of gas. TABLE XCV. EFFECT OF ADMIXTURE OF LIME AND SILICA IN DISTILLATION PRODUCTS. 1000 Kg. Coal. Addition of Lime. Addition of Silica, 5 Per cent. 2.5 Per cent. 5 Per cent. 10 Per cent. Gas cu rn incr68.se 14.7 16.8 5.2 0.483 2.02 1.42 0.93 21.3 59.7 20.1 18.2 7.9 0.608 2.53 1.58 1.03 26.7 66.2 35.3 17.5 9.0 0.929 3.88 1.81 1.19 40.9 76.2 21.5 27.4 11.8 0.15 0.67 0.21 0.138 0.7 8.8 Coke kg increase Tar kg. decrease . Ammonia, kg. increase Sulphate, kg. increase H 2 S kg decrease H 2 S, cu. m., decrease Ammonia ) in per cent ( increase H 2 S J of yield ( decrease For coals of approximately the same composition as the test- coal we can estimate the effect of adding 2.5 per cent of lime as follows : 1. The yield of gas is increased 5 per cent, the illuminating power decreased 5 per cent. 2. The yield of coke is 4 per cent higher, of which 2.5 per cent is lime, so that the actual increase of coke-output is 1.5 per cent. This increase is not accompanied by an increase in thermal value, on account of the higher ash content. 3. The quantity of tar is decreased 10 per cent and its quality deteriorated. 4. The ammonia output is increased 20 per cent. 5. The H 2 S output is decreased at the rate of 1.4 per 1000 kg. coal. 6. The C0 2 of the crude gas is increased 10 per cent. 7. The formation of cyan is somewhat decreased, but the quantity of ferrocyan is not changed. PEAT-COAL, COKE AND BRIQUETTES 221 This point, however, and also the question as to what extent the higher sulphur content of the coke (in the above case about 0.2 per cent) appears as combustible sulphur, have to be further considered. W. Jicinski made experiments with Moravian (Austria) coal from Ostrau of 5 mines ; the composition is given in Table XCV, and the yield from destructive distillation is given in Table XCVI. TABLE XCV. COMPOSITION OF MORAVIAN COALS. (Jicinski.) Percentage of Air-dried Coking Coal from Quality. C H N Ash. Johann .... 81.74 5.53 6.18 1.31 5.24 Good Gas coal Adolf 81 80 5 23 8 31 1 76 2 89 Very good Gas coal Giinther . . . Franziska.. Juliana.. . . 80.54 83.35 86.76 5.09 4.66 4.06 7.66 5.06 3.51 1.43 1.52 1.30 5.27 5.37 4.73 Very good Excellent Fair Coking coal Coking coal Anthracite coal S Content : . 50 to 1 . 05 per cent. P Content : . 004 to . 108 per cent. TABLE XCVI. YIELD FROM DESTRUCTIVE DISTILLATION OF COALS GIVEN IN TABLE XCV. Mine. Per 1 Kg. of Coal Cu. M. of Gas. Coke Residuum. Per Cent. Johann 30.86 67.00 Adolf 30.02 76.00 Giinther . . 29.96 75.00 Franziska 28.60 81.38 Juliana 27.12 86.62 The ammonia output is not in proportion to the nitrogen content of the coal. Ammonia seems to separate from some coals easier than from others. As an average about 0.75 of the total nitrogen of the coal remains in the coke; this is the so-called 22< HEAT ENERGY AND FUE1LS coal-nitrogen, which is only gasified by the complete combustion of the coal. About 0.25 of the total nitrogen the ammonia nitrogen takes part in the formation of ammonia. But even from this, one part escapes as cyan or as free nitrogen, so that the quantity of nitrogen actually available for the ammonia formation is only 0.188 to 0.089 of the total nitrogen. The table below shows the available quantity of ammonia nitrogen in some coals. The tar from coke ovens contains generally Benzene 0.9 -1.06 per cent, Naphthalene 4.26-5.27 per cent, Anthracen 0.57-0.64 per cent, Pitch. 50 per cent, Other residuum 40 per cent. TABLE XCVII. AVAILABLE QUANTITY OF AMMONIA IN COALS. Mine. rotal N in Per Cent of Air- Dry Coal. Available for NH 3 . ! c ^ ll , Available Tar in Per Cent. 6* o3 $8-; P-t +a S| m * rfl *d 13 v% Kaiserstul: Pluto Wilhelmin Johann Adolf Giinther Franziska Juliana Upper Sile Friedenshc Karl, Ge und Vik England, a ill [ Westphalia ej Austria sia, average 1.39 1.45 .77 .31 .76 .43 .52 .30 2.49 Un- known 1.40 0.144 0.146 0.142 0.140 0.126 0.120 0.089 0.134 0.188 Un- known 0.167 0.200 0.212 0.252 0.184 0.222 0.172 0.135 0.175 0.296 0.168 0.148 0.235 0.244 0.258 0.306 0.244 0.270 0.210 0.165 0.213 0.360 0.204 0.180 0.286 0.94 1.00 1.18 0.94 1.04 0.81 0.64 0.82 1.40 0.79 1.69 1.11 ) 1.7 1.7 1.3 2.6 1.8 3.6 3.0 2.5 3.12 >ffnung] org [Lower Silesia tor J verage The average tar output on a large scale is from 2 to 3 per cent of the coal. The difference between coke oven gas and gas house gas is given in Table XCVIII. PEAT-COAL, COKE AND BRIQUETTES 223 TABLE XCVIII. ANALYSIS OF COKE OVEN AND ILLUMINATING GAS. Components. Coke Oven Gas. Per Cent. From Gas House Per Cent. Benzole vapor Ethylene 0.61 1 63 1.54 * 1 19 HS 0.43 CO, 1 41 0.87 CO 6 49 5.40 H 2 CH 4 53.32 36.11 55.00 36.00 Sum 100.00 100.00 The experiments relative to the yield of carbonizing (coking) peat made by Sir Robert Kane and Professor Sullivan have given the following results : TABLE XCIX. ANALYSIS OF COKE OVEN GAS. From Alfre- From an Oven at From ton Coal, Seraing (Ebelmen). Gas- Distilled Products Obtained by Coking forth Coal (Bunsen). 2 7| 14 Aver- (Bun- For- Back- Hours after Starting. age. sen). ward. ward. Methane 1 44 1.66 0.40 1 17 7 6.6 6.2 Carbon monoxide. . . ..... 4.17 3.91 2.19 3.42 1.1 1.6 6.3 Carbon dioxide 10.13 9.60 13.06 10.93 1.1 1.1 2.3 Olefine gas 0.7 0.5 1.6 H 2 S 0.5 0.2 0.2 H 6 28 3 67 1 10 3 68 5 4 1 4 NH 3 :... 0.2 0.2 0.3 N 77 98 81 16 83 25 80 80 03 HO 7 5 12 4 Tar 12 23 9 7 16.6 Coke 68.92 67.2 65.1 Volatile components 30.8 to 32. 7% Combustible gases 19.2 to 22. 3% 100 pounds of peat of different quality was coked in retorts similar to illuminating gas retorts. The volatile matters were 224 HEAT ENERGY AND FUELS condensed in a number of Woulf-bottles and in a cooled coil. The gases were also collected (Table C). TABLE C. PRODUCTS OF PEAT DISTILLATION. Origin. Water. Tar. Coal. Gas. Even mixture of Light peat Dense peat light and heavy peat of Mount Lu- cas Bog near Phil- 23.600 2.000 37.500 36.900 lipstown. Light peat from Wood of Allen .... 32.273 3.577 39.132 25.018 Heavy peat from Wood of Allen . . . 38.102 2.767 32.642 26.489 Upper layer of Ticknevin 38.628 2.916 31.110 32.346 Upper layer of Ticknevin, distilled at red glow 32.098 2.344 23.437 42.121 Upper layer of Shannon 38.127 4.417 21.873 35.693 Dense peat 21.189 1.462 18.973 57.746 Averag e 31.378 2.787 29.222 36.606 TABLE CI. PRODUCTS FROM DISTILLATION OF PEAT. Origin. Tar Water. Tar. Ammonia. Acetic Acid _. "o 5} cT 1 d *j h w cf a dJ ^ S _o nd * B fc &f d 1 |a 1 1 3 Even mix- tures of Light light and peat heavy peat 0.302 1.171 0.076 0.111 0.092 0.024 0.684 0.469 Dense of Mount peat Lucas Bog, near Phil- lipstown Light peat from Wood of Allen . . . 0.187 0.725 0.206 0.302 0.171 0.179 0.721 0.760 Heavy peat from Wood of Allen .... 0.393 1.524 0.286 0.419 0.197 0.075 0.571 q.565 Upper layer of Tick- nevin 0.210 0.814 0.196 0.287 0.147 0.170 0.262 0.617 Upper layer of Tick- nevin , distilled at red glow 0.195 0.756 0.208 0.305 0.161 0.196 0.816 0.493 Upper layer of Shan- non 0.404 1.576 0.205 0.299 0.132 0.181 0.829 0.680 Dense p >eat 0.181 0.702 0.161 0.236 0.119 0.112 0.647 0.266 Average 0.268 1.037 0.191 0.280 0.146 0.134 0.790 0.550 PEAT-COAL, COKE AND BRIQUETTES 225 The analysis of the tar water and tar showed for the qualities given in Table CI. Table CII gives the results of another series of experiments in which a part of the peat was burned by means of a blower. TABLE CII. PEAT DISTILLATION. Origin. Water. Tar. Ash. Gases. Light peat from Wood of Allen .... Heavy peat from Wood of Allen . . . Upper layer of Shannon 30.678 30.663 29 818 2.510 2.395 2 270 2.493 7.226 2 871 63.319 59.716 65 041 For further comparison the figures given in Table CIII, taken from both series of experiments, will be interesting : TABLE CIII. PEAT DISTILLATION. Origin. Tar Water. Tar. NH 3 . Acetic Acid. Alcohol CH 4 Paraf- fin. Oil. Light peat from Wood of Allen Heavy peat from Wood of Allen Upper layer of Shannon Average 0.322 0.344 0.194 0.179 0.268 0.174 0.158 0.156 0.106 0.169 0.086 0.119 1.220 0.946 1.012 0.287 0.207 0.140 0.125 1.059 These tables also give an idea of the valuable products obtained by distilling peat. Table CIV from Muspratt's Chemistry gives the yields from Irish peat. TABLE CIV. DESTRUCTIVE DISTILLATION OF PEAT. Products of Destructive In Closed With Admission Distillation. Vessels. of Air. Ammonia 0.268 0.287 or sulphate of ammonia 1.037 1.110 Acetic acid 0.192 0.207 or acetate of lime 0.280 0.305 Wood alcohol 0.146 0.140 Oils 1.340 1.059 Paraffin 0.134 0.125 226 HEAT ENERGY AND FUELS TABLE CV. DESTRUCTIVE DISTILLATION OF PEAT. Yield in Per Cent. Kane and Sullivan, Per Cent. Hodges, Per Cent. Prospectus of Irish Peat Company, Per Cent. Sulphate of ammonia 1.110 1.000 1 000 Acetic acid or acetate of lime Wood alcohol 0.207 0.305 140 0.328 232 0^700 185 Tar - 2 390 4 440 Paraffin Oils 0.125 1.059 0.104 0.701 The average composition of perfectly dry peat-coal is C 75 to 85 per cent H 2 2 to 4 per cent , 10 to 15 per cent Ash 5 to 10 per cent. The per cent of ash can be as high or higher than 60 per cent. Air-dry peat-coal contains at least 10 per cent of hygroscopic water. The sulphur and phosphorus content of the ash is some- times considerable. TABLE CVI. DESTRUCTIVE DISTILLATION OF PEAT. Products of Distillation. Peat from Neumarkt (Wagenmann.) Peat from Oldenburg, (Vohl). A. T> Per Cent. Water in peat Ash in peat 33.58 6.76 36.26 5.49 air dry Coke Amn Amn Tar Gase Vapc T lonia water 27.70 50.01 0.32 0.435 1.103 1.943 K105 0.304. | 17.400 -^ 25.77 58.03 0.25 0.380^ 1.124 2.389 o'ees 0.634. jll.ll O5 10 35.3120 40.0000 1.7633* 1.7715 1 . 5582 0.3005 3.6695 15.6250 CO CO O lonia in same li^ht oil heavy oil paraffin matter , asphalt paraffin creosote carbonaceous residuum loss s >rs otal 100.32 100.10 100.0000 * This tar-output is, according to Stohmann, entirely too high, probably on account of some water being present. PEAT-COAL, COKE AND BRIQUETTES 227 Peat-coal is very porous and light, has a specific gravity of 0.23 to 0.38, absorbs dyes and odoriferous substances, and is therefore used for removing fusel oil from brandy, as disinfectant, and as fertilizer. It is easily ignited and continues to burn even with very weak draught. The calorific value varies from 6500 to 7000 cal. Brown coal (lignite) coke. Earthy brown coal disintegrates in the heat and therefore cannot be coked. Of this class of fuels lignite and pitch coal are almost the only ones that can be used for this purpose, and lignite furnishes a coke similar to charcoal. The destructive distillation of lignite yields 40 to 50 per cent Coke 12 to 20 per cent Tar water 14 to 35 per cent Tar 12 to 25 per cent Gases. Coke from bituminous coal is generally dark gray, sometimes silver gray, light gray or black. The light coke is melted, the dark generally baked. Coke-oven coke is generally less dense than gas-retort coke, which explains the advantage of the former in metallurgical operations and firing. According to Muck the specific gravity varies from 1.2 to 1.9. In practice the strength, and composition of the coke is of importance, the former for blast furnaces on account of the great weight of the charge, the latter on account of deleterious effects of certain substances. Director Jugnet has found the following data relating to strength of coke: Carve's oven 70 cm 66.4 kg. per sq. cm. Carve's oven 66 cm 79.72 kg. per sq. cm. Carve's oven 50 cm 92.32 kg. per sq. cm. Beehive oven 50 cm 43.92 kg. per sq. cm. Smet oven 50 cm 42.12 kg. per sq. cm. Coppee oven 50 cm '.' . . . 80.50 kg. per sq. cm. Relative to the composition, the quantity of sulphur and phosphor is of technical importance. Coke is hard to ignite, burns with a short, blue flame, and 228 HEAT ENERGY AND FUELS requires a strong air draught. The calorific value is from 7000 to 7800 cal. A hair-like formation, called coke-hair, is sometimes formed on the surface of the coke. This coke-hair is free of ash and is the coked residuum of tarry products of distillation. The composition (dried at 110 C.), according to V. Platz, is C 95.729 per cent H 2 0.384 per cent O 3.887 per cent Ash 100.000 per cent We will now discuss in a few words pressed coal, or briquettes. In order to utilize the culm coal it has been attempted (with or without suitable binding materials) to combine the small pieces into larger pieces called briquettes, and we have : Peat briquettes or pressed peat, which is made and used in the vicinity of peat deposits. Soft coal briquettes, in which tar, pitch, asphalt, starch, molasses, clay, gypsum, alum, lime or soluble glass, etc., is used as binder. The coal dust is mixed with the binder and pressed into bricks. They have frequently the disadvantage of develop- ing smoke of disagreeable odor or containing too much ash. Charcoal or coke briquettes are made in the same way. Lignite briquettes. Here the resinous and other organic matters of the coal serve as a binder. The coals are dried until they contain about 15 per cent of water and are then pressed hot (at 1000-1500 atm. pressure). The content of water is necessary for preventing the decomposition of the organic substances. The manufacture of such lignite is steadily increasing in Germany and Austria. In 1901 120,000 carloads of briquettes were sold for domestic use in Berlin, and only 5000 carloads of soft coal. The combustion of these briquettes is peculiar, as for a good utilization of the fuel a very weak draught has to be used, where- by the lignite is burned very slowly, giving most of its heat off to the stove. With a strong draught the briquettes are burned quickly, and the largest part of the heat is lost through the chimney. The analysis given in Table CVII is taken from the Zeitschrift des Vereines deutscher Ingenieure (1887, page 91). PEAT-COAL, COKE AND BRIQUETTES 229 TABLE CVII. COMPOSITION OF LIGNITE BRIQUETTES. Ash Water Volatile matter. Fixed carbon. . . Calorific value. . 5.83 19.81 24.53 ( 74 Q 48.83f 74 ' 3 3203 Cal. 5.59 18.67 24.93 50.79 3215 Cal. 75.72 5.93 21.10 28.52 44.83 3159 Cal. 72.85 5.95 22.46 16.74 54.74 2784 Cal 71.48 I and II are good, III and IV inferior briquettes. Briquettes from Schallthal (Styria) contain: C 48.21 per cent, H 2 3.99 per cent, 19.92 per cent, S 1.35 per cent, H 2 (hygroscopic) 15.63 per cent, Ash 10.91 per cent. Thermal value 4280 cal. The analysis of the so-called Clara briquettes shows : Elementary analysis : C 48.72 per cent, H 2 5.80 per cent, and N 22.93 per cent, Ash 12.62 per cent, H 2 (hygroscopic) 10.93 per cent. Intermediate analysis : H 2 (hygroscopic) 10.93 per cent, Volatile matters 44.21 per cent, Fixed carbon. . : 32.24 per cent, Ash 12.62 per cent. Calorific value (determined in calori- meter) 4656 cal. Effective thermal value (H 2 formed calculated as steam) 4349 cal. Calorific value of the coal free of ash and H 2 5688 cal. CHAPTER XVII. COKING APPARATUS. THE apparatus for manufacturing coke (and peat-coal) from raw fuels can be classified as follows: A. Coking in piles. (a) The piles are built with coal lumps exclusively and covered with earth. The pile has a shaft opening in the center and draught holes (Fig. 58). (ft) The pile has a brick' shaft in the center (Fig. 59). (7-) A channel on the bottom of the pile and a movable pis- ton in the shaft serves for saving the products of distilla- tion: Dudley's coke pile. FIGS. 58 and 59. Coke Piles. B. In heaps. (a) Analogous to the heaps used for charring wood. (/?) Heaps temporarily surrounded with boards (like Fou- cault's charring system). The heaps are made either rec- tangular or circular. 280 COKING APPARATUS, 231 C. In closed piles (kilns) with brick walls on the sides. Gen- erally rectangular and provided with charging doors in the center of both short sides. Vertical and horizontal air channels, which Charging Door 1 D D 1 i P Q I I P P l : P n 1 1 D n i n n n D FIGS. 60 and 61. Closed Piles (for coking). FIGS. 62 and 63. Riesa Oven. FIGS. 64 and 65. Bee Hive Oven. can be partly or entirely closed with bricks, etc., transverse the walls and serve for regulating the air admitted. The pile is covered with coke culm (Figs. 60 and 61). The Schaum- . burger coke ovens belong to this class. 232 HEAT ENERGY AND FUELS D. Coking in closed ovens. (a) Ovens with admission of air to the interior, the heat for coking being furnished by partly burning the coal to be coked. To this class belong the older construction of Riesa (Figs. 62 and 63), and the beehive ovens (Figs. 64 and 65). The latter are largely used in America and England. FIG. 66. Section of Francois-Rexroth Coke Oven. FIG 67. Section of Francois-Rexroth Coke Oven. The composition of the gases from these ovens was given in the last chapter (Table XCIX). Since these gases contain a large amount of combustible matter at a high temperature, their util- ization for heating purposes was suggested. This purpose is frequently accomplished (in connection with the beehive type) by heating boilers with the gases; in this case the boilers are COKING APPARATUS 233 built on top of the oven, this heat are : Some of the other methods of utilizing (6) Coke ovens without admission of air to the interior, which are heated by the gases generated during the coking process. The coking is performed in chambers of prismatic form, which are classified as (a) Horizontal ovens: 1. Without condensing plant for the gas. 2. With condensing plant for the gas. (/?) Vertical ovens: 1. Without condensing plant for the gas. 2. With condensing plant for the gas. (f) With inclined axis (system Powel and Dubo- chet) has not come into practical use. FIG. 68. Coke Oven, System Smet (elevation). The horizontal ovens are constructed in different styles accord- ing to the path of the gas through the furnace. The most im- portant types are: Frangois-Rexroth coke oven (Fig. 66 cross-section, Fig. 67 longitudinal section through chamber). 234 HE A T ENERGY AND FUELS FIG. 69. Coke Oven, System Smet (plan). FIGS. 70 and 71. Coke Oven, System Smet (details of doors). j, ....235G... ....?. ... FIG. 72. Coke Oven, Francois (cross-section). COKIXG APPARATUS 235 The gases leave the chambers at the sides, pass through two horizontal channels (in the side walls) then through two horizon- tal channels in the bottom into the flue. Smet coke oven (Fig. 68, front view and section; Fig. 69, section through chambers and channels in the bottom ; Figs. 70, 71, details of doors). The gases go as in the previous type through horizontal chan- I ! ilLMMiffiJlli i-; JjjWS , ,, ,,. .;''^3 FIG. 73. Coke Oven, Francois (longitudinal section). nels near one of the side-walls and under the floor of the chamber. The gases leave the chamber at the highest point. Frangois coke oven (Fig. 72, cross-section ; Fig. 73, longitudinal section). The gases of distillation leave at the side, the same as in the Frangois-Rexroth system; the gases are carried parallel to the wall of the chamber in vertical channels downward, under the floor of the chamber (however, in horizontal channels) into the flue. Similar are the systems of Coppee (Figs. 74, 75, 76, 77, and 78), and Dr. Otto. The main difference between these and the former types is the greater height, and length and smaller width of the chambers, whereby an increase in the heating surface is effected. Vertical coke ovens without condensation belong to the oldest types (Appolt system, 1854). They have an exceedingly large heating surface and were at one time held in high esteem. They are, however, very much more expensive to build and 236 HEAT ENERGY AND FUELS FIGS. 74-78. Copp6e's Coke Oven. COKING APPARATUS 237 operate than the horizontal ovens, so that they are only of historical interest. In the destructive distillation of coal, besides coke, a number of by-products, as tar, gas water, etc., are obtained, the recovery of which in many cases is desirable on account of their content of valuable substances (ammonia, benzol, etc.), notwithstanding the loss of heat by cooling and the decrease in calorific value by removal of the products of condensation. As the by-product recovery in the coke industry is coming more and more into use, we want to show the changes in oven construction caused by the introduction of this process, taking as an example the bottom-fire oven of Dr. Otto (Figs. 79, 80, 81). The gases pass up through two pipes provided with valves and connected to the highest point of every chamber into the receivers a, which extend across the entire battery of ovens, analogous to the hydraulic main in a gas plant. In the receiver a part of the tar is condensed, and the gas goes through condensing and puri- fying apparatus, from here returning to the ovens. It passes through gas pipes b (one for every two ovens) to the burners of the combustion chambers. The air of combustion enters around every burner. The combustion gases go through the center of the combustion chamber downward, through slots into a side flue (below every coking chamber), which conducts to the main flue. In the more modern ovens the combustion air is preheated in regenerators before entering the ovens. The coke obtained in such an oven is removed red hot and cooled with water, for preventing combustion in the atmosphere. For making peat-coal (coke) we have, besides the above apparatus, E. Ovens heated exclusively from outside: (a) With a special fireplace (Lottmann's oven; Crony retort oven). (6) With superheated steam (Vignoles' oven), (c) With combustion gases Crane's oven, using solid or gaseous fuel. Finally we want to say a few words about coking of lignite (brown coal), which is carried on mainly in Saxony and Thuringia, where coals rich in paraffin are mined. Rolle's plate oven is almost exclusively used for this purpose. Such an oven can coke 238 HEAT ENERGY AND FUELS COKIXG APPARATUS 239 240 HEAT ENERGY AND FUELS 2500 kg. of lignite in 24 hours, with a coal consumption of 25 to 30 per cent and at a temperature of 800 to 900 C. The yield is Tar 10 per cent, Water 50 per cent, Coke 32 per cent. The specific gravity of the tar at 35 C. is 0.82-0.95. Suggestions for Lessons. Examination of different artificial solid fuels; elementary analysis, calorific value, determination of the ash, sulphur and phosphorus content, ash analysis; determination of specific gravity, strength and porosity. Yield by destructive distillation of carbonized fuel, gas, tar and tar water, also ammonia, acetic acid, etc. Herein the influ- ence of the temperature of distillation, slow or quick heating, of admixtures, etc., has to be studied. CHAPTER XVIII. LIQUID FUELS. To this class belong oil (petroleum), tar from destructive dis- tillation of coal and wood, schist-oil, and to a small extent certain vegetable oils, alcohol, turpentine, benzine, etc. The liquid fuels have the advantage of burning up without residuum. Such a residuum as remains of solid fuels might obstruct the grate, cause uneven air supply and incomplete com- bustion. The utilization however, of liquid fuels presents some serious difficulties and makes the construction of well designed' and carefully tested burners imperative. The main difficulty is the atomization, otherwise carbon is deposited, which will cause stoppages and block the flow of the liquid. A general use of liquid fuel is prevented by high cost. How- ever, under certain local conditions it can be used economically. The experiments for introducing alcohol as fuel on a large scale have so far not been successful. Table CVIII contains some data relating to the use of liquid fuels. TABLE CVIII. COMPOSITION OF LIQUID FUELS. Kind of Fuel. Composition in Per cent. Calorific Value in Kg-cal. C. H. o. Ash. American crud.6 oil 83.0 85.0 85.5 90.0 87.0 86.7 14.0 11.5 14.2 5.0 13.0 13.0 3.0 3.5 0.3 5.0 0.3 11100 10300 11046 8900 10900 10805 8830 8830 9620 Caucasian crud.6 oil Refined American oil Coal tar Heavy oil from American petroleum Heavy oil from Caucasian petroleum Schist oil Tar oil '77 '.2 ii'7 11.1 Rape oil . 241 242 HEAT ENERGY AXD FUELS The source of oxygen in petroleum is dissolved water; in coal tar the oxygen is partly chemically combined, partly from water. TABLE CIX. COMPOSITION OF LIQUID FUELS. Liquid Fuel. Burnt to Calorific Kg-ca Value in 1. I XT 1 Kg. 1 Mol. Benzole Hexane Hexane CO 2 and H 2 O liquid ' ' vapor 9997 11525 10636 779800 991200 914800 Heptane Alcohol liquid 11375 7054 1137500 324500 Glycerine Butter Animal fat average ...... lit iC 4316 9231 9500 397100 The residuum of the first distillation of crude oil is sold in Russia under the name of Masut. When heated to 150 degrees it generates combustible gases, can be ignited at 215 degrees, ignites itself at 300 degrees, and its specific gravity is 0.91. The calorific value is 11,000 cal. In practice 62 kg. Masut replace 100 kg. good bituminous coal. 1000 liters of air are necessary to burn 1 kg. Masut completely. Table CX shows comparative data (Wright) which, however, change according to the construction of the fire-place. TABLE CX. THERMAL EFFICIENCY OF FUELS. Calculated Actual Thermal Evaporation, Evaporation, Efficiency, Lb. English. Lb. English. Per Cent. Nottingham cannel coal 12.27 8.78 71.56 Gas coal 14 24 10.01 70.30 Cannel coal 12.23 9.91 81.03 Gas-house coke 13.83 11.15 80.62 Tar : 15.06 12.71 84.40 Creosote. . J 16.78 13.35 79.56 CHAPTER XIX. GASEOUS FUELS. THE gaseous fuels have, like the liquid fuels, the advantages of burning up without residue, of easy transportation to the place of combustion, and of convenient regulation of tempera- ture. Furthermore, the length of the flame can be varied within certain limits, and for complete combustion a considerably smaller excess of air is required than with solid and liquid fuels. The gaseous fuels, therefore, have a higher temperature of com- bustion, and generate a smaller quantity of gaseous products of combustion than other fuels of the same composition, whereby a better utilization of the generated heat can be secured. Another advantage is that in this case not only the air for com- bustion but also the gas can be preheated. Such gaseous fuel occurs in nature and is then called natural gas. The average composition of Pennsylvania natural gas is Methane 67 per cent, Hydrogen. . 22 per cent, Nitrogen 3 per cent, Ethane 5 per cent, Ethylene 1 per cent, Carbon dioxide 0.6 per cent, Carbon monoxide 0.6 per cent. As the occurrence of natural gas is limited, similar gases are artificially produced for industrial use by the following methods : 1. Dry distillation of substances containing carbon, as coal, lignite, peat, wood, fat, etc., whereby gases of distillation (illu- minating gas) are obtained. According to the raw material used the manufactured gas is called coal gas, peat gas, wood gas, fat gas, oil gas, etc. 2. Incomplete combustion of coal with insufficient amount of air, whereby generator gas, also called producer gas or air gas, is obtained. 243 244 HEAT ENERGY AND FUELS 3. Decomposition of water (steam) by glowing coal or com- bustion of coal by means of steam, whereby water gas is obtained. In special cases other methods are used for producing fuel gases, as for instance : 4. Incomplete combustion of coal by simultaneous action of air and oxides, the latter thereby being reduced. This reaction takes place in iron blast furnaces and furnishes a gas of high fuel value, low in nitrogen and high in carbon monoxide, which is called blast-furnace gas. If water is used as oxide, semi-water gas or Dowson gas is obtained. 5. For getting high temperatures or high luminant power, acetylene C 2 H 2 is sometimes used, which is obtained by reaction of calcium carbide and water: CaC 2 + 2 H 2 = Ca (OH) 2 + C 2 H 2 . We therefore have the following summary of methods for the PRODUCTION OF FUEL GASES. 1. By dry distillation : From coal, coal gas, From peat, peat gas, From wood, wood gas, From fat, fat gas, From oil residue, oil gas. 2. By incomplete combustion of coal : (a) With air alone, producer gas (air gas). (6) With air and oxides of metals Fe 2 3 , etc., blast-furnace gas. (c) Air and steam, Dowson gas. (d) Air and carbon dioxide, regenerated combustion gases. 3. By decomposing carbides with water: Mainly calcium carbide, acetylene. Leaving aside the acetylene and the blast-furnace gas, which are only of local importance, the following industrial gases have to be mainly considered: (1) Gases of distillation, obtained by dry distillation of car- bonaceous substances. (a) Illuminating gas made in retorts. It is used for illum- inating, heating and for internal combustion engines. GASEOUS FUELS 245 As an example, the composition of French illuminating gas is given below, which is identical all over France : Weight of cubic meter = 0.523 kg. Thermal value of 1 cubic meter = 5600 cal. Weight of 22.42 liters = 2 grams. Thermal value of 2 grams = 125 cal. Analysis in per cent by weight : Carbon, 43.2 per cent, Hydrogen, 21.3 per cent, Oxygen and nitrogen, 25.5 per cent. Analysis in per cent by volume : 51.0 per cent H 2 33.0 per cent CH 4 8.8 per cent CO 1.8 per cent CO 2 1.0 per cent 2 + N 2 1.1 per cent C 6 H 6 3.3 per cent absorbable CnH 2 n 100.0 .(b) Gases of distillation, produced as by-product in the coking or charring of fuels, mainly coke-oven gas. (2) Generator gas, air gas, or producer gas is properly the name of such gas only, which is made from carbon (charcoal or coke) ; i.e., from a coal free from hydrogen and oxygen, and using dry air for the incomplete combustion. In practice, however, we comprise under the classification " generator gas" any gas generated in certain apparatus (gas producers) by leading air without steam through a glowing layer of fuel of sufficient height. The air never being dry, we get in practice always a mixture of generator gas and water gas, and also gases of distillation if crude, uncoked fuel is used. (3) Water gas is used for illuminating and fuel purposes. (4) Semi-water gas or Dowson gas is used for fuel and power purposes, and is prepared by leading a mixture of air and steam through a coal layer in a producer. CHAPTER XX. PRODUCER GAS. IF air is led at moderate speed through a layer of pure carbon (in practice charcoal or coke), incomplete combustion takes place; i.e. by the reaction of oxygen on the glowing coal, formation of carbon monoxide occurs : C + i 2 = CO. Supposing the air to contain 4 mols nitrogen to 1 mol oxygen, which is probably correct, we can write the reaction : C + } 2 + 2 N 2 = CO + 2 N 2 , and we get a gas which theoretically contains 2 mols N 2 to 1 mol CO, and should have the composition : CO 33 . 3 per cent by volume. N 66.7 per cent by volume. This gas ought to yield per 22.42 liters if burned at constant vol- ume 0.333 X 67.9 = 22.61 cal. If burned at constant pressure 22.61 + 0.5 X 0.54 = 22.88 cal. The thermal value of the same at constant pressure would be per cubic meter 1020.5 cal. The thermal value of 1 gram of gas is calculated as follows: According to the equation the gas has for every gram atom of carbon 12 grams carbon j 2 n monoxide _ 16 grams oxygen ) 56 grams nitrogen. Sum 84 grams. As 84 grams of gas contain 3 mols (CO + 2 N 2 ), 22.42 liters of the same at C. and 760 mm. are equal to 28 grams, and there- fore 1 gram of gas generates 817 cal. This reaction, however, only takes place at very high tempera - 246 PRODUCER GAS 247 tures. At lower temperatures a second reaction occurs simul- taneously, and the extent to which it occurs increases with decreasing temperature. This reaction is C + 2 = C0 2 , / or, if the air is used instead of oxygen, C + 2 + 4 N 2 = C0 2 + 4 N 2 , Between these two reactions there exists a certain equilibrium for every temperature and pressure. If we subtract the equation C + 2 = C0 2 from 2 C + 2 = 2 CO, we get 2 CO = C0 2 + 0, which reaction actually takes place at fairly high temperatures, and determines the proportion of the two first reactions. It is reversible : 2 CO < C0 2 + C. That is, while pure CO within certain temperatures is decom- posed into C0 2 and C, we find that under similar conditions CO is produced by reduction of C0 2 by means of C. Therefore, there exists necessarily an equilibrium between CO, C0 2 and C, which depends on the temperature and concentration (gas pressure). Since out of two volumes CO only one volume C0 2 is formed, and since the reaction, according to our equation (from left to right), takes place without decrease of volume, it is clear that an increase of pressure facilitates the formation of C0 2 , while a decrease of pressure favors the formation of CO. Therefore, the primary air (wind) in a gas producer should be of low pressure if a gas high in CO is desired. The influence of temperature on the equilibrium is shown by the balance of the reaction heats : C + 2 = C0 2 + 97,600 cal. 2 (C + 0) = 2 CO + 57,800 cal. 2 CO = C0 2 + C + 39,800 cal. 248 HEAT ENERGY AND FUELS i.e., the decomposition of 2 CO into C0 2 and C takes place under generation of heat. Therefore an increase of temperature facili- tates the formation, a decrease of temperature the decomposition of CO. Thence it is clear that the gas will be the richer in CO with higher temperature. All these observations are of importance for the state of equi- librium. Whether this is reached in practice or not depends on Vol.% Vol.% CO, ^ 10 I ^^ 1 I I I I ^f 1 1 ^^ I 1 l^^kn. I 1 500 600 700 800 900 10CO 1100 12001300 500 600 700 800 900 1000 1100 1200 130C FIG. 82. Ideal Composition of Gener- ator Gas from Pure Oxygen. FIG. 83. Ideal Composition of Gener- ator Gas from Dry Air. the height of the coal, porosity of same, velocity of wind, etc. It is, however, of the greatest importance for the theory of the gas producers as well as for the practice, to know the equilibrium for all the different conditions, since the only way to judge the PRODUCER GAS 249 quality of a gas producer process is to compare the results obtained in practice with those corresponding to the theoretical equilibrium. We therefore give in Tables CXI, CXII, and CXIII the ideal composition of generator gas at different temperatures and pressures. Table CXI gives the ideal composition of producer gas, pro- duced with pure oxygen. Fig. 82 shows the content of this table graphically. TABLE CXI. IDEAL COMPOSITION OF PRODUCER GAS (GENERATOR GAS) PRODUCED WITH PURE OXYGEN. Air Pressure. 1 Atmosphere. 2 Atmospheres. Volumetric Composition at a Temperature of CO C0 2 CO C0 2 227 C. . 500 abs. 0.004 99.996 0.0028 99.9972 327 600 0.123 99.877 0.087 99.913 427 700 1.427 98.573 1.011 98.989 527 800 8.794 91.206 6.303 93.697 627 900 32.542 67.458 24.809 79.191 727 1000 70.35 29.65 58.105 42.259 827 1100 92.75 7.25 87.198 12.802 927 1200 98.445 1.555 97.00 3.00 1027 1300 99.50 0.50 99.00 1.00 Air Pressure. 3 Atmospheres. 4 Atmospheres. Volumetric Composition at a Temperature of CO CO_, CO C0 2 227 C. 500 abs. 0.0023 99.9977 0.002 99.998 327 600 0.0711 99.9289 0.061 99.939 427 700 0.826 99.174 0.716 99.284 527 800 5.177 94.823 4.499 95.591 627 900 20.408 79.592 17.945 82.055 727 1000 51.788 48.212 47.017 52.983 827 1100 -82.72 17.28 78.987 21.013 927 1200 95.65 4.35 94.315 5.685 1027 1300 98.97 1.03 98.67 1.33 Table CXII gives the ideal composition of producer gas, pro- duced with dry atmospheric air. The data of this table are graphically shown in Fig. 83. 250 HEAT EX ERG Y AND FUELS TABLE CXII. IDEAL COMPOSITION OF PRODUCER GAS (GENERATOR GAS) PRODUCED WITH DRY ATMOSPHERIC AIR. Air Pressure = 1 Atmosphere. Partial Gasifying Temperature. Pressure of Composition in Per Cent by Volume. CO+C0 2 . C. T abs. In Atm. C0 2 . CO. N 2 . 227 500 0.21 21.00 79.00 327 600 0.21 21.00 79.00 427 700 0.2145 20.31 1.14 78.55 527 800 0.24 16.40 7.60 76.00 627 900 0.29 8.75 20.25 71.00 727 1000 0.334 ' 2.14 31.26 66.60 827 1100 0.344 0.47 33.93 65.60 927 1200 0.346 0.14 34.46 65.40 1027 1300 0.3465 0.01 34.65 65.35 Air Pressure = 2 Atmospheres. 227 500 0.42 21.00 79.00 327 600 0.42 21.00 79.00 427 700 0.4228 20.39x 1.01 78.60 527 800 0.466 18.14 5.82 76.70 627 900 0.555 11.94 17.09 72.25 727 1000 0.6535 4.31 29.56 67.32 827 1100 0.6865 0.83 33.74 65.67 927 1200 0.692 0.21 34.44 65.40 1027 1300 0.693 0.10 34.56 65.35 Air Pressure = 3 Atmospheres. 227 500 0.63 21.00 79.00 327 600 0.63 21.00 79.00 427 700 0.6395 20.51 0.81 78.68 527 800 0.686 18.14 4.76 77.00 627 900 0.8075 11.94 14.98 73.08 727 1000 0.957 4.31 27.59 68.10 827 1100 1.625 0.83 33.37 65.80 927 1200 1.0365 0.21 34.34 65.45 1027 1300 1.04 0.10 34.56 65.34 PRODUCER GAS 251 TABLE CXII. Continued Air Pressure = 4 Atmospheres. Partial Gasifying Temperature. Pressure of Composition in Per Cent by Volume. CO + C0 2 . C. T abs. In Atm. C0 2 . CO. N 2 . 227 500 0.84 21.00 79.00 327 600 0.84 21.00 79.00 427 700 0.851 20.59 0.71 78.70 527 800 0.905 18.52 4.11 77.37 627 900 1.056 12.73 13.67 73.60 727 1000 1.258 5.00 26.46 68.55 827 1100 1.359 1.13 32.85 66.02 927 1200 1.381 0.28 34.25 65.47 1027 1300 1.385 0.13 34.50 65.37 TABLE CXIII. IDEAL COMPOSITION OF PRODUCER GAS (GENERATOR GAS) PRODUCED WITH 50 PER CENT OXYGEN. Air Pressure = 1 Atmosphere. Partial n Gasifying Temperature. Pressure of Composition in Per Cent by Volume. CO+C0 2 . CL T abs. In Atm. CO 2 . CO. N 2 . 227 500 0.50 50.00 50.00 327 600 0.50 50.00 50.00 427 700 0.502 49.40 '0.80 49.80 527 800 0.522 43.40 8.80 47.80 627 900 0.568 29.60 27.20 43.20 727 1000 0.633 10.10 53.20 36.70 827 1100 0.66 2.00 64.00 34.00 927 1200 0.663 1.10 65.20 33.70 1027 1300 0.6655 0.35 66.20 33.45 Air Pressure = 2 Atmospheres. 227 500 I. 49.56 50.00 327 600 1. 45.65 50.00 427 700 ' 1.0035 34.03 6.61 49.83 527 800 1.0295 15.50 5.83 48.52 627 900 1.1065 34.03 21.30 44.67 727 1000 1.23 15.50 46.00 38.50 827 1100 1.308 3.80 61.60 34.60 927 1200 1.326 1.10 65.20 33.70 1027 1300 1 . 3305 0.43 66.10 33.47 252 HEAT ENERGY AND FUELS TABLE CXIII. Continued Air Pressure = 3 Atmospheres. Partial Gasifying Temperature Pressure of Composition in Per Cent by Volume. CO + CO 2 . C. T abs. In Atm. C0 2 . CO. N 2 . 227 500 1.5 50.00 50.00 327 600 1.5 50.00 50.00 427 700 1 . 5045 49.55 0.60 49.85 527 800 1.538 46.20 5.07 48 . 73 627 900 1 . 6345 36.55 17.93 45.52 727 1000 1.814 18.60 41.87 39.53 827 1100 1.9455 5.45 59.40 35.15 927 1200 1.986 1.40 64.80 33.80 1027 1300 1 . 9955 0.45 66.07 33.48 Air Pressure = 4 Atmospheres. 227 p 500 2. 50.00 50.00 327 600 2. 50.00 50.00 427 700 2.0053 49.60 0.54 49.86 527 800 2.0443 46.68 4.43 48.89 627 900 2.1615 37.89 16.15 45.96 727 1000 2.384 21.20 38.40 40.40 827 1100 2.588 5.90 58.80 35.30 927 1200 2.6435 1.74 64.35 33.91 1027 1300 2.6605 0.46 66.05 33.49 Since it is not improbable that in future a mixture of 50 per cent oxygen and 50 per cent nitrogen may be used in gas pro- ducers, the data for this case are given in Table CXIII. Fig. 84 gives the results graphically. The following important general conclusions may be drawn from these tables and diagrams : 1. In all cases the C0 2 content of the ideal generator gas at low temperature is a maximum, which is practically constant up to 400 C. 2. With increasing temperature the C0 2 content is decreasing; between 800 and 1000 C. no C0 2 is present. 3. No CO is found up to about 400 C. 4. With increasing temperature the CO content is increasing and is reaching a maximum at 800 to 1000 C. 5. At constant temperature the C0 2 content is increasing with PRODUCER GAS 253 the pressure, and therefore also with the oxygen content of the primary air. 6. CO shows the opposite property. 7. At low temperatures the absolute C0 2 content is increasing with the oxygen content of the primary air. 8. At high temperatures the absolute content of the gas in CO is increasing with the oxygen content of the primary air. Vol.% 700 800 900 1000 1100 1200 1300 FIG. 84. Ideal Composition of Generator Gas from 50 per cent Oxygen. Therefore the following facts have to be considered for getting a generator gas of the highest possible thermal value and also rich in CO. 1. The oxygen content of the primary air being the same, the gasifying temperature has to be high. In practice a temperature of 700 to 900 C. is sufficient, as at this temperature the maxi- mum CO content is practically reached. 2. At high gasifying temperatures the quality of generator gas, i.e., the content of CO, is increasing with the oxygen content of the primary air. 3. High air (wind) pressures are unfavorable, as thereby, under otherwise constant conditions, the C0 2 content is increased. If, 254 HEAT ENERGY AND FUELS however, it is desired to generate the largest possible quantity of C0 2 in the producer, which is sometimes the case in the hot blow- ing period of the water-gas process for the purpose of rapidly increasing the temperature, a very low temperature has to be kept during the process if the equilibrium is to be reached. This is easily understood, as with increasing temperature the quantity of the CO formed is rapidly increasing, and the quantity of C0 2 is decreasing. If in the producer the equilibrium is reached, the temperature of the producer must not get high if it is the inten- tion to get a high yield of C0 2 . These conditions are not changed by increasing the oxygen content of the primary air. From the above facts we can calculate the volume proportions of C0 2 to CO, of C0 2 to CO + C0 2 and of CO to CO + C0 2 , also the quantity of carbon gasified by a certain volume of air, the quantity of air necessary for gasifying a certain quantity of car- bon, and also the quantity of carbon and air required for generating a certain volume of ideal generator gas. We have so far treated the ideal generator gas, i.e., a gas which is produced by the action of dry primary air on glowing coal, under the supposition that in the process of combustion the state of equilibrium is reached. We now have to consider the case in which equilibrium is not reached, this case occurring very frequently in practice. Every single layer of coke consists of pieces of coke and air spaces between. The larger the pieces of coke the larger the air spaces. With coke of fist size, the air spaces amount to one- quarter to one-fifth of the total volume, and these spaces allow the air to pass through the producer. Every piece of coal, therefore, is surrounded by a layer of air varying in thickness from a few millimeters to a few centimeters. The reaction between the oxygen of the air and the coal takes place only on their contact points, and the question arises which reaction will occur first. The law of the gradual reactions states that wherever several reactions might take place, the first reac- tion is that one which corresponds to the least stable state, then the next stable, and at last the most stable. In our case we have but two possible reactions : The formation of C0 2 and CO, and we have to find out which one of the two is more stable. We, therefore, have to consider the free energies of formation of the two compounds. PRODUCER GAS 255 Under the supposition that the concentration of the free oxygen is one atmosphere, we find that the curves of the two energies of formation go through the same point at a little below 1000 abs. (about 700 C.), and that at lower temperatures the free energy of formation of the C0 2 is the larger one, at higher temperatures, that of CO. We find the same relation in the stability of the two compounds, and, therefore, at the beginning of the reaction at low temperatures first of all CO, at higher temperatures first of all C0 2 , will be formed. In rising upwards the gases will further react with the upper layers of coal and with the air contained in the interior part of the gas current. The reaction of the outer part of the gas current with coal con- sists either in combustion of coal by means of C0 2 or in formation of carbon from carbon monoxide (2 CO = CO 2 + C). Since at low temperatures first of all CO, is formed, the most plausible reaction under such condition is the decomposition of the CO and formation of C. The reaction, however, between the inner and outer parts of the gas current counteracts this decomposition, since the of the inner part would burn any C which was depos- ited from the CO. The velocity of diffusion and mixture between the inner and outer parts of the gas current being sufficiently large, no C will be deposited ; on the contrary, the CO formed will be burned to C0 2 , and the oxygen going to the outer part will oxidize some more carbon. Therefore the average composition of the gas will approach more and more the equilibrium. At higher temperatures at first C0 2 is formed, and this will, by contact with the higher layers of coal, oxidize some C to CO. On the other hand, the oxygen of the inner part will tend to oxidize the CO present to C0 2 . In both cases we have two effects counteracting each other. At low temperatures the reaction between coal and the outer layer of gas tends to prevent the reaching of equilibrium, while the reaction between outer and inner layers favors the approach to the equilibrium. At high temperatures, however, we find that the reaction between gas and coal favors the equilibrium, and the reaction in the gas current works against it. The conditions become still more complicated if we consider that the actual velocity of the gas current at different points of the generator varies according to the unequal dimensions of the air spaces, and that also the temperature throughout the genera- 256 HEAT ENERGY AND FUELS tor is not at all uniform. If the generator is working with the fire on top (maximum temperature in the upper parts of the charge), the state of equilibrium of the rising gas current is getting more and more favorable to the formation of CO. The reverse is true with the maximum temperature in the lower parts of the producer. The location of the maximum tem- perature of the producer, however, changes during the operation. In starting the fire the upper layers of the generator will be cold, and will allow the formation of C0 2 . They are gradually heated up by radiation of heat from the combustion gases to the coal, and the hot zone will therefore extend from the bottom further upwards. After continued blowing we can imagine a coke col- umn which has the combustion temperature of the hot carbon in cold air. As will be seen from the above considerations the research of the generator process is extremely difficult, and we have but a few scientific investigations on this subject. One of the best is by 0. Boudouard, even this being not free from objectionable points. He passed air at different speeds through a tube filled with char- coal and analyzed the gases obtained. He found at 800 C. the results given in Table CXIV : TABLE CXIV. ANALYSIS OF PRODUCER GAS. (Per Cent by Volume.) Gas. Flow in Liters per Minute. 0.10 0.27 1.30 1.4655 3.20 COo 18.2 5.2 18.43 3.8 0.47 77.30 18.92 1.88 0.94 78.26 19.9 1.83 78~27 19.4 0.93 0.93 78.74 CO" o N 2 (difference) 76.6 The analysis corresponding to the equilibrium at this tempera- ture is C0 2 . 92 per cent by volume, CO 34 . 32 per cent by volume, N 74 . 76 per cent by volume. PRODUCER GAS 257 It will be noticed that the gases from Boudouard's experiments are very high in C0 2 and very low in CO. In three cases they also contain free oxygen. This is in accordance with the fact that at 800 C., C0 2 is less stable than CO, so that, therefore, C0 2 must be formed first and the gas composition is approaching the equi- librium but gradually. To better understand these conditions we are going to decom- pose the gases into the elementary components. We have in 22.42 liters of gas the amounts given in Table CXV. TABLE CXV. ELEMENTARY COMPONENTS OF PRODUCER GAS. Flow in Gram-atoms C. in Mol. Oxygen in Prim- Liters per CO.. Total. ary Minute. C0 2 . CO. Total. CO. Free. gen. Air. 0. 0.92 34.32 35.24 0.92 17.62 18.54 64.76 83.30 0.0 18.2 5.2 23.4 18.2 2.6 20.8 76.6 97.4 0.27 18.43 3.8 22.23 18.43 1.9 0.47 20.8 77.30 98.1 1.30 18.92 1.88 20.80 18.92 0.94 0.94 20.8 78.26 99.06 1.465 19.9 1.83 21.73 18.9 0.92 20.18 78.27 98.45 3.20 19.4 0.93 20.33 19.4 0.47 0.93 21.20 78.74 99.94 According to the law of gradual reaction in the beginning, a thin layer of C0 2 is formed, which then oxidizes the coal layer through which it passes. It will, therefore, be pretty nearly correct to suppose that the outer layer (surface) of the gas cur- rent will have, shortly after its entrance into the tube, the com- position which corresponds to the equilibrium. In this case the ratio of C0 2 to C0 2 + CO must be equal to 0.0261, and there must have been formed the amounts given in Table CXVI : TABLE CXVI. Flow in Liters per Minute. Vol. CO 2 . Vol. CO. Oxygen in Same. Corresponding Amount of Air. 0.10 0.61 22.79 12.01 57.19 0.27 0.58 21 65 11.41 54.33 1.30 0.54 20.26 10.67 50.81 1.465 0.54 20.19 10.64 50.67. 3.20 0.53 - 19.80 10.43 49.67 258 HEAT ENERGY AND FUELS If we deduct the air volume actually used for the original com- bustion from the volume of primary air, we get the surplus quan- tity of air from which we can figure by a simple way the surplus air given in Table CXVII and Fig. 85. -5- 012 8 Velocity FIG. 85. Curve of Surplus Air. TABLE CXVII. SURPLUS AIR FOR COMBUSTION. In 100 Volumes Generator Of 100 Volumes Gas Volumes of Primary Air. Flow in Liters per Minute. N Times Surplus Air. Primary Air. Air for Original Combus- Surplus Quantity For Original Combus- Surplus Air. tion. tion. 0.10 97.40 57.19 40.21 58.72 41.28 0.737 0.27 98.10 54.33 43.77 55.38 44.62 0.805 1.30 99.06 50.81 48.25 51.29 48.71 0.949 1.465 98.45 50.67 47.78 51.46 48.54 0.943 3.20 99.94 49.67 50.27 49.70 50.30 1.012 The following consideration will be still more useful for the practical regulation of this process: PRODUCER GAS 259 We suppose again that in the first moment the least stable gas is formed, but that in a short time on the surface area the equilibrium corresponding to the actual gasifying temperature will be reached. In the further course of the process this equi- librium will, however, be disturbed by the gradual mixture of the outer gas layer with the inner air volume, by the fall in tem- perature resulting therefrom, and by the combustion of a part of the original CO to C0 2 , due to the surplus oxygen. Referring again to Boudouard's experiments at 800 C., we can calculate from the free oxygen content of the gases the corresponding amount of air, deduct the latter from the com- position of the gas, calculate the temperature of equilibrium corresponding to the gas mixture obtained, and compare the temperature of equilibrium with the actual gasifying temper- ature (800 C. - 1073 abs.). We obtain thereby the results given in Table CXVIII. TABLE CXVIII. IDEAL GASIFYING TEMPERATURE, ETC. Flow in Liters per Minute. 0.10 0.27 1.30 1.465 3.9 Free oxygen, per cent by vol.... 0.47 0.94 0.93 Corresponding amount of air, per cent by volume 2.24 4.48 4.43 Composition of the gasfCO 2 .... 0^92 18^2 18.85 19.81 19.9 20.20 free from air, per cent-ICO 34.32 5.2 3.89 1.98 1.83 0.97 by volume |N 2 64.76 76.6 77.26 78.21 78.27 78.74 Gasifying temperature (absol.), corresponding to the com- position 1073 763 749 732 729 700 Difference between the latter and the actual gasifying tem- perature, which is higher by . . 307 324 341 344 373 As may be seen from Table CXVIII and from Fig. 86, the " ideal" (or apparent) gasifying temperature corresponding to the actual composition of the gas is clearly below the actual, and the curve of this difference of temperatures consists of two prac- tically straight branches, which are connected with each other 260 HEAT ENERGY AND FUELS by a short, sharply bent curve. In the one branch, which is practically vertical, the velocity of reaction is the main factor, while in the inclined branch the velocity of the wind is of main importance. Naturally, the position and shape of this curve depends, not only on the gasifying temperature, but also on the size of coal used, and on the height of the fuel layer. Under conditions, however, which can be compared with each other, these additional factors will have the same character and the position of the bending point of the curve seems a very suitable characteristic point for the conditions. With increasing gasifying tem- perature, the velocity of reaction increases, and the bending point of the curve will move to the right. Increase of the fuel height and decrease of the coal size will have a similar effect. In the latter cases, however, some other influences have to be considered, such as friction FIG. 86. Difference of Temperature between Actual and Apparent Gasi- fying Temperature. between gas current and coal pieces, heating of the upper layers by the rising gas, location of the maximum temperature in the generator, etc. The following figures are given as practical results of genera- tors that were charged with carbonized fuel. Ebelman gasified at Audincourt small-sized charcoal in a pressure producer, which had the shape of a small blast furnace, and he obtained a gas of the following composition (per cent by weight) : CO 34.1 percent C0 2 0.8 per cent N 64 . 9 per cent H 2 0.2 percent 100.0 per cent. PRODUCER GAS 261 In a gas producer at Pous 1'Eveque, which was charged with coke, he obtained a gas of the following composition : CO 33. 8 per cent C0 2 1.3 percent N 64 . 8 per cent H 2 0.1 per cent 100 . per cent. MIXED DISTILLATION AND COMBUSTION GASES. If we subject natural uncarbonized fuel in proper apparatus (gas generators, also called gas producers) to incomplete com- bustion, mixed distillation and combustion gases are formed. In the upper layers of the producer the hygroscopic water is removed. In further going downwards the fuel (material to be gasified) is subjected to dry distillation, coke being the result of this process. The coke is burned incompletely in the lowest part of the producer, whereby, besides the heat necessary for evaporation and dry distillation, CO is also generated. The water which is introduced as moisture with the atmospheric air is also decomposed. A clear idea of these processes is given in the table below, without, however, taking into account the formation of tar, which is inconsiderable. Composition of the coal used (bituminous coal of Ostrau, Moravia) mixed with lignite of Leoben (Styria). C = 64.92 H 2 = 2.50 N - 0.50 Chemically combined water 14.22 Hygroscopic water 12.42 Ash 5.44 100.00 Combustible sulphur 0.52 Calorific value 6374 calories. (a) Process in the upper part of the generator (drying of coal) : 100 kg. coal yield 12.42 water (steam), and 87.58 kg. dry coal. (b) Process in the middle part of the generator (dry distilla- tion of coal). 262 HEAT ENERGY AXD FUELS TABLE CXIX. ELEMENTARY ANALYSIS OF COAL AND PRODUCTS OF DISTILLATION. 87 . 58 Kg. Dry Coal Contain. Yield. Coke. Kg. Gases of Distillation Kg. KO. CO. CH 4 . H,. NH 3 . H 2 S. Ash . 4.92 64.92 0.50 0.52 4.08 12.64 87.58 4.92 58.73 0.12 0.635 5.08 5^67 7^56 0^52 0.17 3.14 0.50 o.n 0.40 0.025 C N S H, or::...:...:..:.: Sum 63.77 5.715 13.23 0.69 3.14 0.61 0.425 TABLE CXX. ELEMENTARY ANALYSIS OF COAL AND PRODUCTS OF COMBUSTION. Components in Kg. Coke. Air. Sum. Yields. Losses thr'h Grate Open- ings. Gases. CO.. CO. H 2 0. N. Ash.. 4.92 58.73 211.63 0.25 64.49 276.37 4.92 58.73 211.63 0.12 0.25 64.49 4.92 15.67 6^57 36*49 0.25 211^63 c N. S H * lo*.:::::::: Sum 0.12 0.12 0.25 17.51 48.65 63.77 340.14 20.96 24.08 85.14 0.25 211.63 We suppose that the coke contains nothing but carbon, besides the ash, and that the gases of dry distillation contain no oxygen except as CO and H 2 (the latter supposition is not quite, but sufficiently correct, since the gases contain CC^ and other oxygen compounds). The formation of tar is not taken into consideration. Since only a small amount of N is present, we calculate the entire amount as NH 3 ; actually, however, but one-fifth of the nitrogen of coal is transformed into NH 3 . PRODUCER GAS 263 (c) Process on and just above the grate (incomplete com- bustion of the coke formed). The coal analysis shows 5.44 per cent ash, while the table shows only 4.92 per cent, which is explained by oxidation, mainly formation of sulphates from Fe 2 S. The composition of gas shown in the last table results from the average composition of generator gas and the composition of the gases of distillation, which is given in Table CXIX. The distribution of heat in the generator is shown in the heat balance, Table CXXI. TABLE CXXI. HEAT DISTRIBUTION IN GENERATOR. Production of Heat and Non-Produced Heat. Single. Combined. Cal. Per Cent. Cal. Per Cent. I. Production of heat: 1. Heat produced in generator by chemical processes 2. Heat introduced by coal and air (by their temperature) II. Non-produced heat: 1. Unburned coal falling through the grate . . 179666.4 3337.9 26.67 0.49 183004.3 490641 . 6 183004.3 126613.6 27.16 72.84 27.16 18.79 126613.6 364028.0 18.79 54.05 2. Heat capacity of generator gases III. Heat losses: 1. By fuel and ash falling through grate 2. By heat carried away by the gas produced 3. Loss by moisture of gas 4. By decomposition of water. . . . 5. (a) Radiation (b) Heat necessary for gasify- ing coal . . . 2316.1 28282.0 12346.3 8615.5 94890.7 36553.5 0.34 4.20 1.83 1.28 14.09 5.42 IV. Non-produced heat: By unburned coal falling through grate Heat gained 309617.9 364028.0 45.95 54.05 673645.9 100.00 264 HEAT ENERGY AND FUELS It is understood that the composition of generator gas depends, besides the quality of fuel, on the size of same, height of fuel layer, construction of generator, and also temperature and air pressure during the operation. Table CXXI was prepared by Richard Akerman. TABLE CXXII. GENERATOR GAS FROM WOOD OF FIR TREES. Trunks Kind of Fuel. and Roots. Brush- wood. Logwood. Sawmill Refuse. ( Thickness m.m. 20-35 35-150 20-200 Size. ] maximum maximum maximum ( Length m.m. 500-750 200 890 340 Contents: Hygroscopic water, per cent . . . 12. 16. 27. 60. Ash, per cent 0.9 Q.6 0.5 0.3 Wood substance, per cent 87.1 83.4 72.5 39.7 Composition of wood substance: C, per cent 53.0 ? 51.0 ? Hi per cent 7.1 *j> 6 1 9 O, per cent 39.8 ? \ 294 \ ? N, per cent 0.1 ? \ 4 i ? Grate area, square meter, of gen. 0.0 0.81 1.72 1.37 Cubic content, cubic meters, of generator 26.7 1.9 24.2 7.4 Consumption of fuel per dav : Ccu m 8. 1 23.8 14.4 Per sq. meter grate area < i ' 1654 8891 7909 Per generator j c g m> 65.2 14866 6.6 1340 41.0 15293 19.7 10835 Number of charges per 24 hours.. 2.8 5.6 4.1 6.6 Length of time of presence of fuel in generator (hours) 8.6 4.3 5.9 3.6 Temperature of gas leaving gen- erator, degrees C 180 505 147 125 Kg. tar in 24 hours ? ? 444 ? Composition of tar: C, per cent 75.5 H. 2 per cent 7.4 O. per cent 16.6 N.per cent 0.5 Volume composition of gases free of moisture and air: CO,. 3.8 6.2 6.0 11.3 CO. 29.8 26.0 29.8 19.6 CJL. 0.6 0.3 0.9 CH 4 4.2 5.1 6.9 4.3 H 6.4 4.3 6.5 7.4 55.2 58.4 50.5 56.5 2 PRODUCER GAS 265 TABLE CXXIII. GENERATOR GAS FROM PEAT. Origin. Quantity of Peat. Munkfors Good Fibrous Peat. Lotorp Good Fibrous Peat. Hygroscopic water, per cent 25.0 36.0 ^ -2 -| Gases, noncombustible 8.3 17.6 ^ ^ ? Gases, combustible. 39.0 16.9 * 5 1 Fixed carbon, per cent 24.9 24.0 Ash, per cent 2.8 5.5 ,C, per cent . . 57.8 61.0 Composition of peat substance JQ 2 ' PJ, ^l^t ' 6.8 34.0 6.3 30.6 IN, per cent.. 1.4 2.1 Grate area, square meters ( , pnprator Cubic content, cubic meters. . . \ ol gen 0.0 22.8 1.6 21.9 * g per sq. meter grate area j <* bio meter ; 12.8 5279 & iflPer generator j^^; 20.6 6262 40.2 8446 Number of charges per 24 hours 1.3 1.1 Length of time for which fuel remains in gener- ator in hours 18.5 21.8 Temperature of gas leaving producer, deg. C . . . 86-100 75-105 Kg tar in 24 hours 152 173 rC 79.6 79.8 f H 9.3 I "- 1 { 9.2 9.6 1.4 Composition of tar \ ^. 2 " IN CO,, vol. per cent . 6.6 6.8 - 7.4 co" : 29.6 27.6 -26.2 Composition of gas free of C 2 H 4 0.7 4.0 0.4 - 0.4 3.75- 3.70 air and water . . ..... 1 CH 4 H 2 5.3 12.3 -13.5 N 2 53.8 49.15-48.8 TABLE CXXIV. GENERATOR GAS FROM BITUMINOUS COAL. Intermediate analysis. Hygroscopic water, per cent Gases, non-combustible, per cent Gases, combustible, per cent Coked coal, per cent Ash /C, per cent . . Composition of coal substance j^ 2 ' ^ |* ' \N, per cent . . 7.6 9.1 13.6 64.6 5.1 79.0 5.9 13.7 1.4 266 HEAT ENERGY AND FUELS TABLE CXXIV. Continued. Limestone addition, per cent Residue in ash-pit eight in per cent of coal C, per cent. ...*... H 9 , per cent. . . Composition O 2 + N 2 , per cent Ash . Grate area, square meters, of generator .................... Cubic content, cubic meters, of generator .................. Daily consumption of coal per Sq. m. grate area j -^ m " Generator. . ( Cu. m. ... I Kg ..... Number of charges per 24 hours ........................... Length of time for which fuel remains in generator ......... Temperature of gas leaving generator, deg. C .............. CO 2 , vol. per cent Composition of gases free of air and water .... CO 2 H 4 'H 4 3.4 12.1 40.2 1.0 1.2 57.6 2.0 4.0 1.7 1251 3.4 2502 1.2 20 500 1.8 27.3 0.4 4.2 6.2 60.1 TABLE CXXV. GENERATOR GAS FROM LIGNITE. Below are given results with a lignite generator: Number of generators 3 Grate area per generator. 2.5 square meters Duration of test 12 hours 45 minutes Coal charged 3600 kg. Leoben (Styria) coal Composition of coal Calorific value C.. Volatile H 2 , N H 2 O chemically combined . H 2 O hygroscopic 9 . 34 61.72 per cent 1.85 per cent 0.22 per cent 20.09 Ash Combustible S , 6.78 0.37 5446 kg. cal. Losses through grate . . . 936.7 kg. Composition of losses < A ' i ' ' ( Asn 73.94 per cent. 26. 06 per cent. Aver- 1 2 3 4 age. CO 2 , vol. per cent 5.3 5.4 4.2 4.4 4.64 2 , 0.3 0.8 0.6 0.8 0.65 Composition of dry generator gas . . . CO, CH 4 , 25.19 0.29 25.05 0.15 25.39 0.51 26.50 0.40 25.59 0.38 ^2> 10.29 10.65 11.29 11.60 11.11 N 9 58.63 57.95 58.01 56.30 57.63 PRODUCER GAS 267 TABLE CXXVI. QUANTITY GASIFIED PER HOUR AND SQUARE METER GRATE AREA. Logwood and sawdust mixed 45- 50 kg. Sawmill waste 200-330 Logwood 370 Loose peat (bad quality) 75-120 Good fibrous peat 200-250 Lignite 40-50 Bituminous coal 60-250 SUGGESTIONS FOR LESSONS. Air (generator) gas has to be made in a small experimental producer using different grades of fuel, varying height of fuel layer and air of different pressures. Gas and fuel is to be analyzed, the quantity of the fuel consumed and of the gas generated to be found and the balance of the process to be put up. The results are to be compared with the ideal process. On a small scale (in glass and porcelain tubes) experiments can be made for demonstrating the influence of the length of the tube (fuel height) and velocity of the wind. CHAPTER XXI. WATER GAS. INSTEAD of producing fuel gases by the action of the oxygen in the air on glowing coal, we can use for this purpose the oxygen of water in place of the oxygen in the air. If steam is led over glowing coal, two different reactions will take place depending on the temperature. At very high tem- peratures the reaction takes place according to the equation C + H 2 = CO + H 2 , while with decreasing temperature a second reaction becomes more and more prevalent according to equation C + 2 H 2 = C0 2 + 2 H 2 . The first equation is furnishing a mixture of equal volumes of CO and H 2 , CO 50 per cent by volume and H 2 50 per cent by volume, while the second reaction, if taking place exclusively, furnishes a gas containing two volumes H 2 for every one volume of C0 2 , hence C0 2 33.33 per cent by volume and H 2 66.67 per cent by volume. The thermal value of the first gas per 22.42 liters is 68 cal., of the second gas, 45.4 cal. A comparison of the generator (air) gas process with the two -water gas processes shows : TABLE CXXVII. PRODUCER AND WATER GAS PROCESSES. Volume Per Cent. H 2 . CO. C0 2 . N 2 . Thermal Value of 1 Volume. Cal. Of Mix- ture at Constant Pressure. Cal. lC+i(O 2 )-2N 2 =CO-f2N 33 66$ 22.6 22.9 2C+2H 2 O=CO 2 X2H 2 66 33 45.4 46.5 3 C+H 2 O=CO+H 2 50 50 68.0 68.5 268 WATER GAS 269 The figures of thermal value refer to the same gas volume in each case, and are well adapted for comparing the qualities of the gases. In case, however, we want to consider the utilization of fuel, we have to refer the thermal values to equal quantities of carbon (equal volumes of CO and C0 2 ) , and we obtain : 12 Grams C. Yield Liters of Gas. Value of the Gas at Constant Volume. Pressure. 2 3 67.26 67.26 44.84 67. Seal. 113.3cal. 125.8 cal. 68. 7 cal. 116.1 cal. 126.8 cal. We see that water gas even under the most unfavorable cir- cumstances yields more heat (thermal value) than the ideal air (generator) gas, besides the fact that it contains less non-com- bustible gases. For making a perfect comparison we have to calculate at least if not the pyrometric heating effect the quantity of air theoretically required for combustion. We have for each 22.42 liters of gas : TABLE CXXVIII. COMPOSITION OF PRODUCER AND WATER GASES. Composition of Gas in Per Cent by Volume. Theoretical Amount of Air Combus- tible In- Products of Combustion. different H 2 . CO. C0 2 . N 2 . 2 . N 2 . Gases. H 2 O. C0 2 . N 2 . 1 33$ 66* 16* 64^ 33$ 131$ 33$ 66 2 66 33$ 33$ 133$ 66 166 66 33$ 133$ 3 50 50 50 200 100 200 50 50 200 As the decomposition of water requires more heat than is furnished by the formation of CO, and even CO 2 , both water gas processes are taking place only with the assistance of external heat. We have C + i (0 2 ) = CO + 28,900 cal. C + 2 H 2 = C0 2 + 2 H 2 + 97,600 - 116,120 = CO 2 + 2 H 2 - 18.5 cal. C + H 2 = CO 4- H 2 + 28,900 - 58,060 = CO + H 2 - 29.2 cal. 270 HEAT ENERGY AND FUELS Considering the external heat we have: Thermal Value of Gas per 12 Grams C. External Heat to be Supplied. Gain in Heat. C+*(0 2 ) + 2N 2 =CO+N., 68. 7 cal. -28. 9 cal. 97.6 C + 2H 2 O=CO,+ 2H 2 C+H 2 O=CO+H 2 116.1 cal. 126.8 cal. + 18.5 cal. + 29. 2 cal. 97.6 97.6 The advantage of water gas, therefore, does not consist in a gain in heat, but exclusively in the higher thermal value of this gas, which allows a better utilization in the combustion. As can be seen from the above statements, the reaction, C -h H 2 = CO + H 2 , will take place if steam is led through a layer of sufficiently hot coal.. As heat is absorbed by this reac- tion, the coal will cool off, and besides the above reaction, the process C + 2 H 2 = C0 2 + 2 H 2 will take place. As the cool- ing continues the second process will begin to outweigh the first, and finally, since the second reaction also absorbs heat, the coal will be so cold that the reaction will stop, and thus the steam will go through the fuel undecomposed. This necessitates reheating the coal in the generator. This is done by shutting off the steam and blowing air through the generator until the coal is sufficiently hot. During this period air (generator) gas is produced which can be utilized independent of the water gas. This period is called "hot-blowing." As soon as the coal is hot again, the air blast is stopped and the steam valve opened, and water gas is made until the cooling off of the fire again prevents the rational production of water gas. We have here, therefore, an intermittent process, which not only requires careful supervision but also the erection of double the number of generators in places where a continuous stream of water gas is required, and where a large gas holder is objec- tionable. As we have seen, the two water gas reactions are taking place in parallel. Since, however, the one furnishes a superior gas with better utilization of coal than the other, it is of importance to know the conditions which determine to which extent each of the two reactions will take place. For this purpose we have to study the state of equilibrium between the two reactions. WATER GAS 271 To find the equilibrium of the gas phase, we have to consider the reactions that are taking place. If we deduct C + H 2 = CO + H 2 from C + 2 H 2 = C0 2 + 2 H 2 , we get C0 2 + H 2 <= CO + H 2 0. This is a reversible reaction in which two volumes (CO + H 2 0) are formed from two volumes (C0 2 + H 2 ). It is, therefore, independent of pressure at all temperatures above the boiling point of water. One might now conclude that the composition of water gas at a given temperature is independent of the pressure ; this, however, is not correct. From the last equation we get for the isothermic equilibrium Ceo, . CH,O Ceo Cn 2 or x 4 Cco 2 . Cn 2 Cco 2 1 Cn 2 o We therefore see that at a given temperature there is corre- PO TT spending to every - - a different r -pr . To reach definite CO 2 H 2 O results we have to look for a reaction which determines the equi- librium between the gas phase (in our case consisting of C0 2 , CO, H 2 and H 2 0) and the solid phase (C), and as such we are going to use the equation mentioned already in the generator gas process : C0 2 4- C^2CO; from this equation we have Ceo And now the conditions are given for calculating the isothermic equilibrium. As the last-mentioned reaction depends on the pressure, we must necessarily conclude that the composition of water gas also depends on the pressure. We are going to discuss now the theory of the water gas process in a few words. If we express the steam pressure by P and the gasifying temperature (in degrees C.), by t, the ideal composi- tion of the water gas (i.e., the composition corresponding to the equilibrium reached) is as follows: 272 HEAT ENERGY AND FUELS TABLE CXXIX. EFFECT OF STEAM PRESSURE AND TEMPERATURE ON COMPOSITION OF GAS. Vol. Per Cent. 0.1 0.25 0.5 Steam Pressure, P, in Atmospheres. 0.75 1.0 1.5 2.0 2.5 3^0 4.0 5.0 10.0 CO.. 0.24 0.12 0.06 0.04 t = 400C. 0.03 0.02 0.02 0.01 0.01 0.01 0.01 0.00 CO 2 10.88 7.86 5.97 5.04 4.46 3.73 3.27 2.97 2.73 2.40 2.15 1 55 H 2 ?.... H 2 O .... 21.99 66 88 15.84 76.18 11 99 81.98 10.12 84.80 8.94 7.48 86.57 88.77 6.56 90.15 5.94 91.08 5.47 91 .79 4.82 92.77 4.31 93.53 3.11 95.34 t = 600C. CO... CO 2 .... 26.66 12 84 18.87 16 06 14 65 17 15 11.56 17 79 10.03 8.14 17 86 17 67 6.99 17 41 6.20 17 12 5.61 16 84 4.78 16 32 4.22 15 88 2.87 14 32 H 2 H 2 0.... .. 52.34 .... 8.16 50.89 14.18 48.95 19.25 47.14 23.51 45.75 43.48 26.36 30.71 41.81 33.79 40 44 36.24 39.29 38.26 37.42 41.48 35: 99 43.91 3K5I 51.30 t = 800C. CO C0 2 .... H 2 H 2 0.... .. 49.04 .... 0.50 .... 50.03 .... 0.43 47.81 1.13 50.07 0.99 46.04 2.02 50.03 1.86 44.46 2.80 50.06 2.68 43.05 40.56 3.48 4.66 50.02 49.88 3.44 4.90 38.53 5.59 49.71 6.17 36.83 6.34 49.51 7.32 35.41 6.95 49.21 8.43 32.81 8.02 48.85 10.32 30.69 8.88 48.45 11.08 24.38 11.05 46.48 18.09 t~ioooc. CO C0 2 .... H 2 H 2 O .... 50.00 :::: 56:60' 50.00 56:66 50.00 56:66 50.00 50.66 50.00 49.42 0.25 50.00 49.92 ... 0.41 49.42 0.25 49.92 0.41 49.00 0.45 49.90 0.65 48.57 0.61 49.79 1.03 48.35 0.71 49.77 1.17 47.98 0.87 49.72 1.43 46.24 1.59 49.42 2.75 CO 50 00 50.00 50.00 50.00 t=1200C. 50.00 50.00 50.00 50.00 50.00 49 32 49 31 49 31 C02.... H 2 H 2 O :::: 56:06 56:66 50:06 50:66 56:66 56:66 50:66 56:66 56:66 0^5 49.82 0.61 0^5 49.80 0.64 0^5 49.80 0.64 t=!400C. CO CO 2 .... H 2 H 2 0.. .... 50.00 50.00 50:06 50.00 56:06 50.00 56:06 50.00 50.00 56:66 56:66 50.00 56:66 50.00 50:66 50.00 56:06 50.00 50:06 50.00 50:66 50.00 50:00 Figs. 87 and 88 show the ideal composition of water gas at a steam pressure of one and four atmospheres. We see from the diagrams that with increasing pressure the curves are moving towards higher temperatures. We also see that the quantity of undecomposed steam present is rapidly decreasing from a certain temperature on, while the quantity of CO and H 2 is rapidly increasing in the same manner. The curves of CO and H 2 are in their middle part practically parallel, but the upward move- ment of the H-curve is beginning 200 C. below the bend of the CO curve. The C0 2 curve starts to rise together with the H-curve (but more slowly), until it crosses the steam curve and falls with the latter. The result of this discussion for practice is that the most favorable gasifying temperature is between temperature limits of about 200, and increases with the steam pressure. WATER GAS 273 8 &P ot e s 9 s 11 .3 I L S3 o o 274 HEAT ENERGY AXD FUELS Vol.% 200 300 400 500 600 700 800 900 1000 1100 1200 Temperature in cleg. cent. FIG. 89. Combustible Gases Present in Water Gas. WATER GAS 275 This becomes clearer when we calculate the quantity of com- bustible gases (CO and H 2 ) present in water gas (Fig. 89). TABLE CXXX. QUANTITY OF COMBUSTIBLE GASES PRESENT IN IDEAL WATER GAS. Steam Pressure in Atm. Gasifying Temperature in Degrees Cent. 400 600 800 1000 1200 1400 0.1 0.25 0.5 0.75 1.0 1.5 2.0 2.5 3 22.23 15.96 12.05 10.16 8.97 7.50 6.58 5.95 5.48 4.83 4.32 3.11 79.00 69.76 63.60 58.70 55.78 51.62 48.80 46.64 44.90 42.20 40.21 34.38 99.07 97.88 96.12 94.52 93.08 90.44 88.24 86.34 84.62 81.66 79.14 70.86 100.00 100.00 100.00 100.00 100.00 99.34 99.34 98.90 98.36 98.12 97.70 95.66 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 99.14 99.11 99.11 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 4.0 5.0 10.0 As the combustion of one mol CO yields 68,600 cal., the com- bustion of one mol H 2 to liquid water 68,400 cal., which is prac- tically the same amount of heat, we can use the above table for comparing the thermal value of the different gases. As one mol of every gas at and 760 min. pressure occupies a space of 22.42 liters, we can calculate the thermal value of 1 cubic meter of the above gases in large calories by multiplying their content of com- bustible gases with 1000 X 68.5 _ 100 X 22.42 THERMAL VALUE OF TABLE CXXXI. CUBIC METER OF IDEAL WATER GAS IN KG. CAL. Gasifying Temperature in Degrees Cent. Steam Pressure in Atm. 400 600 800 1000 1200 1400 0.1 680 2417 3032 3060 3060 3060 0.25 590 2135 2995 3060 3060 3060 0.5 369 1946 2941 3060 3060 3060 0.75 311 1715 2892 3060 3060 3060 1.0 274 1707 2848 3060 3060 3060 1.5 230 1580 2767 3040 3060 3060 2.0 201 1493 2700 3040 3060 3060 2.5 182 1427 2642 3026 3060 3060 3.0 168 1374 2589 3010 3060 3060 4.0 148 1353 2499 2002 3034 3060 5.0 132 1230 2422 2990 3033 3060 10.0 95 1052 2168 2927 3030 3060 276 HEAT ENERGY AXD FUELS This table shows more clearly that the thermal value of the ideal water gas increases with increasing temperature and decreases with increasing pressure. Vol-% 100 90 40 30 20 "200 300 400 500 600 700 800 90 000 1100 1200 Temperature in deg. cent. FIG. 90. Undecomposed Steam in Water Gas. At a steam pressure of 1 to 2 atmospheres the most favorable gasifying temperature is between 800 and 1000 C., and at 10 atmospheres pressure between 1000 and 1300 C. It is, there- fore, not advisable to use steam of too high pressure. WATER GAS 277 The quality of the water gas is deteriorated by its content of undecomposed steam and of C0 2 . We, therefore, will consider the influence of pressure and temperature on the quantity of H 2 and C0 2 present in the gas. The quantity of undecomposed steam in the ideal water gas decreases rapidly (Fig. 90) with increasing gasifying tempera- ture and slowly increases with the pressure. As thereby the 600 700 800 900 Temperature in deg. cent, FIG. 91. CO, in Water Gas. looo uoo 1200 inflammability of the gas is decreased, the gasifying temperature should not be below 700 to 800 C., with a steam pressure of 1 to 10 atmospheres, since otherwise the quantity of undecomposed steam will be considerably above 10 per cent by volume. The content of C0 2 (Fig. 91) is injurious, as it causes an unfa- vorable utilization of the carbon. Moreover, it deteriorates the gas, increasing the quantity of non-combustibles and lowering the temperature of combustion. As the C0 2 amounts only to a few per cent at 600 to 700 C., it does not have to be considered in the production of generator gas. 278 HEAT ENERGY AXD FUELS In practice, however, it is of importance to know the quantities of carbon and steam which are required for the formation of 1 cubic meter of water gas. This information is given in the following tables: TABLE CXXXII. QUANTITY OF STEAM IN CU. M. REQUIRED FOR THE FORMATION OF 1 CU. M. OF IDEAL WATER GAS. Steam Pressure in Atm. Gasifying Temperature in Degrees Ce.it. 400 600 800 1000 1200 1400 0.1 0.25 0.5 0.8887 0.9202 0.9397 0.9492 0.9551 0.9625 0.9671 0.9702 0.9726 0.9759 0.9784 0.9845 0.6050 0.6057 0.6820 0.7065 0.7211 0.7419 0.7560 0.7668 0.7755 0.7890 0.7990 0.8280 0.5046 0.5106 0.5194 0.5274 0.5346 0.5478 0.5588 0.5683 0.5764 0.5917 0.6043 0.6457 0.5000 0.5000 0.5000 0.5000 0.5000 0.5033 0.5033 0.5505 0.5092 0.5094 0.5115 0.5217 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5043 0.5044 0.5044 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.5000 0.75 1.0 1.5 2.0 2.5 3.0 4 5 10.0 TABLE CXXXIII. THEREFORE ONE CUBIC METER OF STEAM FURNISHES THE FOLLOWING NUMBERS OF CUBIC METERS OF IDEAL GAS. Steam Pressure in Atm. Gasifying Temperature in Degrees Cent. 400 600 800 1000 1200 1400 0.1 0.25 0.5 1.125 1.087 1.068 1.053 1.047 1.039 1.034 1.031 1.028 1.024 1.022 1.015 1.653 1.537 1.466 1.415 1.386 1.348 1.323 1.304 1.289 1.269 1.251 1.208 .981 .958 .925 .896 .871 .825 1.789 1.759 1.735 1.690 1.655 1.548 2.000 2.000 2.000 2.000 2.000 1.986 1.986 1.978 1.963 1.963 1.955 1.916 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 1.983 1.982 1.982 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 0.75 1.0 1.5 2.0 2 5 3 4.0 . 5.0 10.0 WATER GAS 279 The last table is specially valuable for this practice, since it permits an easy control of the operation of the generator and allows the determination of the ideal gasifying temperature, which corresponds to the process. The content of one component of the gas, for instance C0 2 (which can be easily determined with an Ados or Strache apparatus) being known, the complete analy- sis of the gas can be found. TABLE CXXXIV. ONE CUBIC METER OF WATER GAS CONTAINS GRAMS OF C. Steam Pressure in Atm. Gasifying Temperature in Degrees Cent. 400 600 800 1000 1200 1400 0.1 0.25 0.5 0.75 1.0 1.5 2.0 59.51 42.71 32.27 27.19 24.03 20.07 17.61 17.05 14.66 12.90 11.56 8.30 211.40 186.95 170.19 157.08 149.27 138.14 130.59 124.81 120.15 112.93 107.58 91.96 265.14 261.23 257.22 252.94 249.08 242.07 236.13 231.05 226.71 218.52 211.78 189.62 267.60 267.60 267.60 267.60 267.60 265.83 268.83 264.66 263.21 262.57 261.45 255.99 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 265.30 265.25 265.25 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 267.60 2.5 3.0 4.0 5.0 10.0 TABLE CXXXV. ONE CUBIC METER OF STEAM GASIFIES GRAMS OF C. (Fig. 92). Steam Pressure in Atm. Gasifying Temperature in Degrees Cent. 400 600 800 1000 1200 1400 0.1. . 0.25 0.5 0.75 1.0 1.5 2.0 2.5 3.0 66.96 46.41 34.81 28.64 25.16 20.85 18.21 17.57 15.07 13.22 11.81 8.43 349.44 287.30 249.54 222.34 207.00 186.19 172.74 162.77 154.93 143.13 134.64 115.06 525.44 511.61 495.23 479.59 465.92 441.89 420.77 406.54 393.32 369.31 350.45 293.67 535.20 535.20 535.20 535.20 535.20 528.17 528.17 523.56 516.91 511.52 511.14 490.68 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 526.17 525.87 525.87 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 535.20 4.0 5.0. 10.0 280 HE AT ENERGY AND FUELS If the steam of the gas condenses which frequently happens in practice the composition and thermal value of the gas changes accordingly. The calculation of the gas composition from the C0 2 content is very simple. The C0 2 of the dry gas being c per cent by volume, the content of Q CO = 50 - - c per cent by volume, H 2 = 50 + - c per cent by volume. ,200 300 400 500 600 700 800 900 1000 1100 .1200 1300 Temperature of gas_in_deg. cent FIG. 92. Gasification of Carbon by Steam. For example, we take a gas made at 800 C. and 2.5 atmospheres steam pressure. The C0 2 content having been found as 6.84 per cent by volume, the content of CO = 50 - 1.5 X 6.84 = 39.74 per cent by volume, H 2 = 50 + 0.5 X 6.84 = 53.42 per cent by volume. The following two tables contain the most important data on dry water gas. Compared with the wet gases, in which at con- stant pressure the C0 2 content at first increases with the tem- perature up to a maximum and then decreases, the dry gases have far more regular properties. The C0 2 content at constant pressure decreases with increasing temperature, while CO and H 2 increase simultaneously. On the other hand C0 2 increases at constant temperature with decrease simultaneously. the pressure, while H 2 and CO WATER GAS 281 TABLE CXXXVI. QUANTITY OF DRY GAS PRODUCED FROM ONE CUBIC METER OF STEAM. Steam Pressure in Atm. One Cubic Meter of Steam is Yielding, at the Temperatures Stated Below, Cubic Meters Dry Water Gas. 400 C. 600 C. 800 C. 1000 C. 1200 C. 1400C. 0.1 0.25 0.5 0.373 0.259 0.192 0.160 0.141 0.117 0.102 0.092 0.084 0.074 0.066 0.047 1.518 1.304 1.184 1.082 1.021 0.934 0.876 0.831 0.796 0.743 0.702 0.588 1.972 .939 .889 .845 .807 .736 .679 .630 1.589 1.516 1.457 1.268 2.000 2.000 2.000 2.000 2.000 .978 .978 .965 .943 .940 .927 .863 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 1.971 1.969 1.969 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000 0.75 1.0 1.5 2.0 2.5 3.0 4.0 5.0 10.0 The most favorable conditions for producing the dry water gas are therefore the same as for the wet gas. We have so far discussed the case in which the state of equilibrium is actually reached in the producer. We are now going to consider the case which is very common in practice, that the equilibrium is not reached. If steam is blown through a layer of glowing coal the reaction will undoubtedly take place completely on the contact points of steam and coal, i.e., the state of equilibrium will soon be reached here. On its further way the gas current will undergo a change in two respects. Partly by diffusion, partly by mechanical mixture, a reaction will take place between the outer part of the current and the inner part, which is richer in steam ; on the other hand, the equilibrium of the outer layer will be disturbed by the contact of same with other parts of the coal. If the gas passes from the cold to the hot coal layers ("Ge- genstrom"), a gas rich in C0 2 will be formed at first in the outer layer; then, by coming in contact with hot coal, it is enabled to oxidize new quantities of coal, getting thereby richer in CO. If, however, the steam passes from the hot to the cold coal layers ("Parallelstrom"), a gas rich in CO will be formed at first in the outer layer, and by passing further it will get richer in C0 2 and poorer in CO. 282 HEAT ENERGY AXD FUELS Rg 8 g:^ g O N I vC i IX ri O ^' O vO oOQO'^-f'Ofv] 00 GO "*T 8 :88.| > O^ f^i O -O O < \O* iA iA O 8S88 xr 8 :88f 8 :88] fCj o O O r^ O *OO< iA iA O *A iA O t^ m v cs m - O 00--i-< I I t _ IA s - < _c S o 1 >SS;g~ r5Q2S ( m o in o o ' f> O O O m O ( 8 :S: ?gg^ S :S8^ S 8 :88 8 :88 8 2 * oo -5 N <^ 5r S J^ o oo i-^ | t~ J[_ o ; 8 8 g ^ 8 o o vo ^, o 8 o > g ^ 2 o 8 :88 8 :88 8 8 ;88| 8 ;88| 8 :88| RSffilj Rfiisl. r" , RRtf Dombustibh 3 fe' 1 1' - - -C O- H > . . * jfl P WATER GAS 283 We will now consider again the reaction between the outer gas layer and the inner steam current. In working according to the "Gegenstrom principle," the steam of the inner surface can react with the outer gas layer, so that CO is oxidized to C0 2 and H 2 is liberated. Supposing the temperature remains constant or decreases, the thermal value of the gas remains unchanged. If, however, the average temperature of the gas current rises - which is probable, since the gas comes into the hotter parts of the producer this reaction decreases and the actually occurring improvement in the quality of the gas cannot be explained but by oxidation of glowing coal by means of the C0 2 and the steam of the outer layer and also by the outward diffusion of the steam. If we work according to the " Parallelstrom principle" the hot outer layer formed in the start will react vigorously on the steam (on account of the higher temperature both the diffusion and velocity of reaction will be greater) and the gas without practical change in thermal value will get richer in H 2 and poorer in CO. Hereby the quality of the gas is improved, just the same as above, by the reaction of the outwardly diffusing steam with the glowing coal. On the other hand, the gas quality is deteriorated as the steam gradually comes in contact with cooler coal, whereby the quantity of C0 2 is increased. Undoubtedly the first mentioned way of gasifying is more advantageous, the more so as in this case the gas and steam current is also preheated gradually. If we consider the average composition of water gas, in case the state of equilibrium is not reached, we always find this relation between C0 2 , CO, and H 2 , that the volume of H 2 is equal to the sum of the CO volume and double the C0 2 volume. Besides this some steam is also present. The composition of the wet water gas as well as of the dry gas will, therefore, under all con- ditions correspond to one equilibrium, which, however, at the same steam pressure corresponds to another (the ideal) gasify- ing temperature, the latter being lower than the actual gasifying temperature. Dr. Hugo Strache and R. Jahoda have studied the influence of height of fuel and air and steam velocity on this process, both during hot-blowing and gas making, and have found : In the beginning of the hot-blowing period (when the tem- perature of the fuel is rather low) C0 2 is formed almost exclusively 284 HEAT ENERGY A\D FUELS without any CO, while with increasing temperature the forma- tion of CO increases. We have here again the equilibrium which was mentioned before : 2 CO + C0 2 -j- C. As less C is absorbed by a certain volume of air for the forma- tion of C0 2 than for the formation of CO, the fuel consumption is considerably less in the first stages of hot-blowing than in the later stage, while the quantity of heat developed per minute is very much greater at the start than in the later stages. The loss of heat by the hot gas leaving the producer increases with the temperature. The heat accumulated in the producer is evidently equal to the difference of generated and lost heat. The ratio of accumulated heat and carbon used is called by Strache "the efficiency in hot-blowing." This ratio is high in the beginning (at low temperature) and decreases with increas- ing temperature and fuel consumption. Content of C0 2 and efficiency in hot-blowing are as follows at Efficiency. Per cent. C0 2 . Per cent. 625 C 80 18 672 C . . . 70 16 929 C 1300 C 40 30 7.6 4 6 The total efficiency for a certain blowing period decreases rapidly between 650 and 900 degrees; it is therefore advan- tageous not to raise the temperature of the producer above 900 degrees. The losses of heat during the hot-blowing period can be utilized to a large extent for preheating the steam (in the manu- facture of pure water gas). The losses during gas making depend on the velocity of steam and the temperature of the producer. Too low velocity yields a rather small quantity of gas and causes comparatively great loss of heat by radiation; too great velocity is disadvantageous on account of the steam going through undecomposed ; in this case large quantities of heat leave the producer without being utilized on account of the high specific heat of steam. WATER GAS 285 The results of these researches are : 1. The quantity of undecomposed steam and the C0 2 content of the gas increase at constant temperature with the increasing velocity of the steam in about the same proportion. 2. The content of steam and C0 2 of the crude gas at constant velocity of steam decreases with increasing temperature. 3. Even at low temperature the content of C0 2 and steam can be reduced to a minimum by decreasing the velocity of steam. 700 800 900 1000 1100 1200 1300 1400 1500 1600 1703 FIG. 93. Efficiency of Water Gas Making Referred to Velocity of Steam. The efficiency in gas making is calculated from the carbon consumption during gas making, loss of heat in the producer, and the thermal value of the water gas produced. The total heat loss is made up of the heat of formation, heat of the gas pro- duced and of the undecomposed steam, and the radiation of heat from the producer. For every temperature there is a certain velocity of steam, with which a maximum efficiency is reached (87 to 93 per cent). 286 HEAT ENERGY AND FUELS The total efficiency for any given velocity of steam can be calculated from the carbon consumption during blowing and gas making and from the loss of heat during blowing and gas making. Fig. 93 shows a diagram of these conditions. The total efficiencies also show a maximum at a certain velocity of steam. At 780 C 72.5 per cent, At 860 a C 77 per cent. SUGGESTIONS FOR LESSONS. Experiments analogous to those under generator (air) gas can be made. CHAPTER XXII. DOWSON GAS, BLAST-FURNACE GAS, AND REGENERATED COMBUSTION GASES. THE production of pure water gas has the advantage of fur- nishing a gas of high absolute and pyro metric efficiency, which is of importance for certain purposes. Besides the fact that this gas cannot be generated except by employing external energy (for decomposing steam) and by using an expensive boiler plant, the producer gas which is herein obtained as by-product with a high percentage of carbon dioxide can be used mostly for auxiliary purposes only. Furthermore this process has two disadvantages : 1. It is an intermittent process (two stage), comparatively difficult, complicated, and expensive. 2. It requires a plant of double the size of that of a continuous process. The idea presented itself of having the two processes of hot- blowing and gas making take place in parallel and simultaneously in one producer, whereby Dowson gas or semi-water gas (some- times also called producer gas) is obtained. The purpose of this process being the generation of gas of the highest possible heating value, the amount of carbon dioxide has to be kept as low as possible. Since with decreasing carbon dioxide the nitrogen content considerably increases, the thermal value of the gas decreasing at the same time, this point deserves serious consideration. We will now consider the ideal conditions. The reaction C + H 2 = CO + H 2 takes place with the consumption of 42,900 cal. for every 12 g. of carbon gasified, while in the reaction C + i (O a ) = CO 21,100 cal. are liberated for every 12 g. of carbon. Therefore in order to keep the temperature of the producer constant, we have to get as much heat from the second process as is consumed by the first process (not considering the losses of 287 288 HEAT ENERGY AND FUELS heat). We therefore have to gasify two atoms of carbon with air for every atom of carbon gasified with steam. The ideal equation for this process is 3 C + H 2 + 2 + 4 N 2 = 3 CO + H 2 + 4 N 2> which is equivalent to a Dowson gas of the following composition : CO 37.5 H 2 12.5 N.. . 50.0 100.00 In the reaction C + 2 H 2 = C0 2 + 2 H 2 , on the other hand, for every 12 g. of carbon 40,400 cal. have to be furnished by gasifying with air. This is also one atom of carbon gasified with steam to two atoms of carbon gasified with air. The ideal equation is 3 C + 2 H 2 + 2 + 4 N 2 =-C0 2 + 2 H 2 + 4 N 2 + 2 CO, the analysis of the gas : C0 2 11.1 CO 22.2 H 2 22.2 N 2 45.5 101.0 In working with coal instead of with carbon, volatile matters enter this reaction, whereby the nitrogen content is further decreased. In practice on account of unavoidable losses more than two atoms of carbon have to be gasified with air for every atom gasified with steam. The equilibrium CO + H 2 <= C0 2 + H 2 causes the formation of steam, which can considerably deteriorate the quality of the gas. The principle of this process is the oxidation of carbon partly GASES 289 by oxygen of the air and partly by oxygen of an oxide (water). A similar reaction takes place in the blast furnace, where, besides the oxygen of the air, the oxygen of the iron oxide is used for oxidizing the carbon mainly according to 3 C + Fe 2 3 = 2 Fe + 3 CO, and to a small extent according to 3 C + Fe 2 3 = 4 Fe + 3 C0 2 . The ordinary composition of blast-furnace gas is Average C0 2 5-16 12 CO 20-32 24 H 0.1-4.5 2 CH 4 0.2-2.5 2 N 2 56-63 60 Blast-furnace gas has a fairly high thermal value. The source of the hydrogen in this gas is the air moisture, which acts on the carbon; the methane content is very probably caused by direct synthesis. Since a considerable part of the oxygen of the blast- furnace gas is derived from the ore instead of the atmosphere, the quantity of nitrogen in furnace gas is lower than in producer gas generated by an exclusive oxidation by means of air. The content of carbon dioxide is partly explained by conditions of equilibrium (in the cooler part of the furnace some of the carbon monoxide is decomposed according to 2 CO = C0 2 + C) and partly by the reduction process (3 CO + Fe 2 3 = 3 C0 3 + 2 Fe). Instead of using the oxygen of water or oxides of metals for partly oxidizing carbon, the oxygen of carbon dioxide can be used: C + C0 2 = 2 CO. This can be done by passing gases rich in carbon dioxide through a glowing layer of coal, which process is called regenera- tion. Such " regenerable " gases are for instance combustion gases and gases from lime kilns or blast furnaces. The last named gas seems to be especially adapted on account of the small amount of nitrogen present. If we should succeed in converting by this process the total carbon dioxide of a blast-furnace gas of the above average 290 HEAT EX ERG Y AND FUELS analysis into carbon monoxide, a gas of the following composition would be obtained: 60 N = = 53 . 58 per cent, CO = 24 * 2 * 12 = 42.86 per cent, _L . \.2i CH 4 = = 1 . 78 per cent, 2 H = - = 1 . 78 per cent, the thermal value of which would be considerably higher than that of the original gas. The heat consumption for this process is as follows : The reaction C0 2 + C = 2 CO absorbs 97,600-2 X 26,100 - 45,400 cal. If we want to reclaim this amount of heat (as with Dowson gas) by the reaction C + = CO + 21,100 cal., we have to transform for every mol of carbon dioxide contained 45 4 in the gas '-- or about 2 atoms of carbon into air-producer gas. We get about the same conditions as with water gas, and in prac- tice we will have to burn, instead of 2 mols carbon, from 3 to 5 mols to carbon monoxide. Supposing we should get 2 mols of carbon monoxide by direct combustion, for every mol of carbon dioxide, we would have the following theoretical composition for the regenerated blast-furnace gas: 1 .81 _ 58.06 per cent, 94. 4- 4 V 1 9 CO = \ * = 39 . 74 per cent, 1 .81 CH 4 = = 1 . 10 per cent, 1 .81 2 H 2 = = 1.10 per cent. 1 . 81 As above stated a larger part of the carbon will have to be burned in practice on account of unavoidable losses in heat. GASES 291 Supposing we take 3 gram-atoms of carbon for every mol of dioxide to be reduced, we get a gas of the following theoretical composition : N^ 6 t!!- 71 -59.21 per cent, 2.1o CO = ^ +3+ ^ = 38 ' 93 CH 4 = ~= 0.93 per cent, Zi . It) H 2 = -2 = 0.93 per cent. . J.O In practice this result could be obtained only by applying a sufficiently high gasifying temperature, as otherwise the reaction would be incomplete. So far this method is not in practical use. SUGGESTIONS FOR LESSONS. Production of Dowson gas, same as in the two former lessons. Effect of air and carbon dioxide upon a layer of glowing coal. CHAPTER XXIII. APPARATUS FOR THE PRODUCTION OF FUEL GASES. (GENERATOR OR PRODUCER GAS PLANTS.) THE apparatus which are used in practice for manufacturing fuel gases are called gas-generators or gas-producers. These are, generally speaking, chambers lined with firebrick. These chambers are charged with coal, wood or peat respectively, and the air of combustion or steam or a mixture of steam and air is passed through, generally upward. If air (generator) gas is produced the gas in the producer is moved either by draft (chimney) alone or by pressure (blower). Accordingly we have a classification in draft and pressure- producers. The latter have to be closed tight at the bottom. FIG. 94. Boetius Gas Generator. We shall consider first the air-gas generators, which were built originally right near the furnace, which was to be heated (Siemens gas or half-gas). Their development is shown by the following types : FUEL GASES 293 Fig. 94. Boetius producer. The producer compartment, G, is separated from the combustion chamber of the furnace by a vertical wall and from the outside atmosphere by an inclined wall upon which the charged coal slides down. The opening, a, for the charge can be closed by means of the slide, ss. The inclined wall is supported by the iron bar, 6, which contains an FIGS. 95 and 96. Boetius Double Generator. opening for poking and air-admission. At the bottom the producer compartment, G, is separated from the ashpit, A, by the inclined grate, r. The channels, c, in the back wall allow a preheating of the air of combustion. Figs. 95 and 96. Boetius double producer, developed from the former type by combining two producers (right and left) FIGS. 97 and 98. Bicheroux Generators. and leaving out the back walls. Thereby less brickwork is required and loss by radiation from the back wall avoided (at the same time doing away with the preheating of air). We find here the air-channels in the side walls. The inclined grate is supplanted by a plane-grate. R is the grate, c the air-channels. Larger than these are the Bicheroux producers (Figs. 97 and 98) which are provided either with step-grate, T, and inclined 294 HEAT ENERGY AXD FUELS grate, R, or with a plane-grate, r. f is the charging opening. These producers are also built right near the fireplace. Largely used are the shaft producers of William and Friedrich Siemens. They are built independent of the furnace to be IV III FIGS. 99 and 100. Siemens Generator. heated. In order to avoid as far as possible losses of heat and to save brickwork they are frequently built below the floor level in rows or in squares. Figs. 99 and 100 show a plant of the latter kind in elevation and ground plan. Fig. 99 shows two producers with one common wall. These producers are provided with step-grates, T, and inclined grate, R. The ground plan shows four producers I, II, III and IV, arranged in the form of a square. FUEL GASES 295 There are two charging chutes for each producer; the holes, s, are for poking the fire. The gas leaves all four producers through one gas main. The back wall of these producers is inclined, for preventing the air from passing along the vertical wall (least resistance). A charging hopper is shown in Fig. 101. Same is provided with a valve operated by a counterweight and a cover which Cover FIG. 101. Charging Hopper. closes gas-tight by means of a sand or tar seal. For charging coal the cover is removed, coal filled in, the cover put on and then the valve opened. Thereby losses of gas are prevented. In order to increase the fuel height, (7, which is to be measured in the direction of the arrows, in some cases the charging hopper FIG. 102. Siemens Generator of Neuberg. has been moved more toward the center (Fig. 102). For dis- connecting one producer of a producer system, valves, V, are provided. Below the ash-pit there is an excavation filled with water, the latter being evaporated by the ash and fuel falling through the grate, whereby the quality of the gas is improved (Dowson gas). If we omit one of the two separating walls in a square of 206 HEAT ENERGY AXD FUELS FIG. 103. Siemens Double Generator. FIGS. 104 and 105. Old Shaft Generator of Donawitz. FIG. 106. Generator of FIG. 107. Bituminous Coal Generator Kolsva. of Odelstjerna. FUEL GASES 297 four Siemens producers, we arrive at double producers (Fig. 103) which can be built singly or in rows. Shaft producers (old Donawitz type) for lignite and brown coal are shown in Figs. 104 and 105. The inclined step, a, in the brick lining is necessary for preventing the rising of the air alongside the walls. Other types of shaft producers are : The producer of Kolsva in Sweden (Fig. 106) in which Parry's hopper, p, is used for charging. The different types of producers of Odelstjerna are : (a) For bituminous coal (Fig. 107). This producer is wider at the bottom to facilitate the downward movement of the coal. For preventing the rising of the air alongside the wall an offset is arranged at the bottom of the shaft. (b) For peat, wood and shavings (Fig. 108). For these fuels the shaft has to be considerably wider and the fuel-height FIG. 108. Odelstjerna 's Generator for Peat, Wood and Shavings. FIG. 109. Generator of Tholander. greater than for coal. A plane or step-grate is used in these pro- ducers, which are generally arranged for blast and provided with air-tight doors, T. The soft coal producer of Tholander (Fig. 109), which is of peculiar shape, is arranged for air blast at the bottom. In this construction the active height of fuel (i.e. the way along which the primary air comes in contact with glowing coal, ab) is kept constant at all periods. The fuel rests on a solid base, cd. F is the charging hopper, ww is the blast-channel, G the 298 HEAT ENERGY AND FUELS producer-shaft, ss are the poke-holes and TT the ash-cloors. As seen from the above descriptions the cross-sections of producers are made both square and circular. In single (isolated) pro- Li 11 I FIG. 110. Funnel-Shaped Grate. FIG. 111. Conical Grate. ducers the circular cross-section is of advantage on account of more uniform operation and smaller loss of heat by radiation. They are provided either with a plane-grate (as in the Odelstjerna FIG. 112. Conical Grate. FIG. 113. Bottom of Generator with Step and Plane Grate. type for peat, wood, etc.), or with a funnel-shaped or conical grate (Figs. 110, 111 and 112). Less advantageous is the combined use of two step-grates and one plane-grate (Fig. 113). FUEL GASES 299 Plane-grates can be used only for large-size fuels as fuel of small grain would fall through the grate-bars. Step-grates have to be used for the latter fuel. In many cases the Lichtenfel's construction of plane and step-grates is convenient, which com- bines the good points of plane and step-grates (Fig. 114). The FIG. 114. Lichtenfel's Plane Step Grate. trouble of cleaning the grate is reduced to a minimum if the grate- bars 1, 3 and 5 are arranged unmovable while 2 and 4 are kept in motion at a right angle to the elevation of the producer, as thereby most of the ash falls through automatically. FIGS. 115 and 116. Turnable Eccen- tric Cone-Grate. FIG. 117. A. Sailler's Pressure Pro- ducer with Slag Openings. The same effect is reached by revolving conical-grates, espe- cially if the axis of rotation and axis of the cone are not the same (Figs. 115, 116). Such an eccentric cone-grate can be mounted upon a circular base-plate, which moves in a channel. 300 HEAT ENERGY AND FUELS If the plate is provided with teeth around the edge it can be driven by a simple worm gear. On the other hand some rather complicated stirring-arrange- ments have been put on circular producers. In pressure producers a grate is not an absolute necessity, as we have seen on Tholander's producer. It is of advantage to work without grate, if badly clinking and coking fuel is used, in which case it is frequently advantageous to add a flux to the fuel for forming an easily fusible slag, which is let off from time to time. Saillers' producer (Fig. 117) shows such a construction. FIG. 118. Steam Jet-Blower for Dowson Gas Generator /is the charging arrangement, ss are the poke-holes, WW the blast channel, aa slag openings. A convenient device for preventing the escape of gas during poking was designed by Hofmann and Stache. A steam coil of pipe perforated on the side toward the center of the coil is arranged around the poke-hole. If one of the holes is opened a steam valve is opened automatically and steam blown through the perforations, which prevents the escape of gas. The disadvantages caused by putting green fuel into the pro- ducer from time to time, namely non-uniform temperature of the producer and uniform composition of the gas, was the rea- son for experiments to separate the process of distillation from the process of gasification. Such suggestions were made by Minary, Brook and Wilson, Kleeman, C. Neese, Groebe-Luhr- mann, Wilhelm Schmidhammer, Fr. Toldt, etc. All these pro- ducers are rather complicated and better result can be obtained more conveniently by combining a number of producers. The manufacture of Dowson gas in draft-producers is effected FUEL GASES 301 by arranging a water-basin below the grate. By the radiating heat of the grate-bars and the hot ash falling through, water is evaporated and with the air carried through the producer. In pressure producers air and steam are either led under the grate separately (which allows independent regulation of air and gas) or a steam jet-blower is used, which draws in the air (Fig. 118). The condensation of the products of distillation in the producer gas by cooling and washing is, under ordinary conditions, unec- onomical, as both by cooling and condensation considerable quantities of heat are lost. The apparatus for producing pure water-gas will be considered later. SUGGESTIONS FOR LESSONS. A producer gas plant is to be designed for a certain amount of heat required per hour and a fuel of known composition and gas- yield. Herein secondary circumstances can also be considered (plan of the floor space at disposal, convenient transportation of coal to the producers, reserve-producers, coal storage, etc.). An existing draft-producer plant is to be changed into pressure- producers or into a Dowson-gas plant. An existing producer plant is to be enlarged, so as to yield double the amount of gas. INDEX Absorbing capacity of coals, 199. Air, surplus, for combustion, 258. Alloys melting points of, 54. Princep's, 53. Ammonia available in coals, 222. Analysis of anthracites, 186. ash, 151. bituminous coal, 184, 185. brown coal, 173. brown coal- ash, 177. peat, 168, 171. producer gas, 256. products of destructive distilla- tion, 216, 217. Anthracites, analysis of, 186. Arth's formula, 115. Artificial fuels gaseous, 243. solid, 143, 188. Ash- analyses, 151. content of peat, 169. of wood, 149, 150. Berthier's method, 111. Bessemer converter, temperature in, 72. Bituminous coal analysis, 184, 185. classification, 178. destructive distillation, 215. generating gas from, 265. Blast furnace gas, 287. temperature in, 72. Boiling and melting points, 51. Briquettes, 228. composition of lignite, 229. Brown coal analysis, 173. ash, 177. classification, 174. Calculation of thermal values, 110. Calibrating pyrometers, 83. Calorimeter Fischer, 64, 93. Mahler, 94. Parr, 100, 104. Weinhold, 61. Carbon dioxide, dissociation of, 120. Carbonaceous decomposition, 156. Charcoal, 191. absorbing capacity, 199. classification, 199. composition, 192. temperature of ignition, 199. weight, 198. Charring, 193. with steam, 208. yield of, 194-196. Classification charcoal, 199. coal, 174, 178, 180. fuel, 141. peat, 166. wood, 145. Coal- ammonia available, 222. yield from destructive distillation of, 221. Coke oven Coppee, 235. Francois, 235. Frangois-Rexroth, 233. Dr. Otto, 235. gas, 223. Smet, 233. tar, 222. 303 304 INDEX Coking apparatus, 231. Combustion data, 130. gases, regenerated, 287. heat, 91, 105, 108. incomplete, 117. of producer gas, 139. products of, 262. surplus air for, 258. temperature of coal, 136. of producer gas, 138. Composition of coals, 221. of fuels, 142, 157, 160.' of Kiln gases, 204. of peat, 169. of products of destructive distilla- tion, 190. of wood, 148. Cones composition of, 57, 58. melting points of, 56. Seger, 55. Content of wood, actual, 147. Coppee oven, 235. Crony oven, 237. Data on charring, 193. Decomposition, carbonaceous, 156. Depression of glass, 38. Destructive distillation analysis, 216, 217. effect of admixtures, 220. of coal, composition of products of, 190. of coal, yield from, 221. of bituminous coal, 215. of peat, 214, 224, 225, 226. Determination of thermal value, 92. Dissociation of carbon dioxide, 120. Distillation, products of, 262. Distribution of heat, 263. Dowson gas, 287. Economy of operation, 8. Elementary composition of coal and products of combustion, 262. distillation, 262. Elementary composition of producer gas, 257. Emissive power of substances, 73. Energy changes of, 12. chemical, change of, 26. distance, 14. electric, 27. forms of, 13. of reaction, 24. radiant, 30. radiation of, 78. surface, 16. volume, 25. Errors in the measurement of temper- atures, 38. Evaporating power of wood, 153. Explosives, 124. External work, 132. Fery's thermoelectric telescope, 79. Fischer calorimeter, 64, 93. Formula Arth, 115. Gmelin, 112. Goutal, 116. Frangois oven, 235. Frangois-Rexorth oven, 233. Fuels artificial solid, 143. classification of, 141. composition of, 142, 157, 160. . formation heat of, 161. liquid, 241. composition of, 241, 242. natural solid, 142. thermal efficiency of, 242. Fuel gases production of, 244. value of wood, 153. Furnace, ideal, 128. Gas, producer, 246. analysis, 256. elementary components, 257. influence of temperature in the manufacture of, 247. ideal composition of, 249, 250, 251. INDEX 305 Gases combustion temperature, 135. mixed distillation and combustion, 261. specific heat, 129. Gasifying temperature, 259. Generator gas from bituminous coal, 265. lignite, 266. peat, 265. wood, 264. gas plants, 292. heat distribution in, 263. Glass, standard thermometer, 39. Glow colors temperatures corresponding to, 69. of silver, 71. Gmelin's method, 112. GoutaPs formula, 116. Grates for producers, 297, 298. Lichtenfels', 298. Hartmann and Braun's pyrometer, 81. Heat capacities, 66. combustion, 91. distribution, 263. of combustion products, 138. Ideal furnace, 128. Illuminating flames, 123. Illuminating gas, 223. Incomplete combustion, 117. Increase of value of a substance, 7. Kiln gases, composition of, 204. Klinghammer's thalpotasimeter, 52. Law Joule's, 30. Ohm's, 29. Lichtenfels' grate, 298. Light, intensities of, 74. Lignite briquettes, composition of, 229. Liquid fuels, 241. composition of, 241, 242. Lottmann oven, 237. Mahler's calorimeter, 94. Measurements pyrometrical, 80, 81. with thermoelements, 82. Melting point of alloys, 54. of metals, 60. Mixed distillation and combustion gases, 261. Moisture in wood, 150, 151. Natural gas, composition, 243. Natural solid fuels, 142. Odelstjerna producer, 297. Optical methods of measuring tem- peratures, 68. Otto oven, 235. Oven, pile retort, 212. Parr, calorimeter, 100, 104. Peat analysis, 168, 171. ash content, 169. classification, 166. coke ovens, 237. composition, 169. destructive distillation, 214, 224, 225, 226. generator gas, 265. thermal value, 170. Pile oven, 206. Piles, 202. Poking producers, 300. Potential, chemical, 22. Princep's alloys, 53. Producers grates, 297, 298. Odelstjerna, 297. poking, 300. Siemens, 294. Tholander, 297. Producer gas, 246. analysis, 256, 269. elementary components, 257. ideal composition of, 249, 250, 251. influence of temperature in the manufacture of, 247. plants, 292. 306 INDEX Production of fuel gases, 244. Pyrometer calibrating, 83. of Cornu Le Chatelier, 73. of Hartmann and Braun, 81. of Mesure and Nouel. 68. of Wanner, 75. of Weinhold, 61. polariscopic, 71. water (Siemens), 67. Pyrometrical measurements, 80, 81. Pyroscopes, composition, 57, 58. Resin content of wood, 149. Seasoning of wood, 152. Seger cones, 55. composition of, 57, 58. melting points of, 56. Siemens' producer, 294. water pyrometer, 67. Smelting furnace, 123. Smet oven, 233. Solid substances, combustion tem- perature of, 135. Specific gravity of woods, 145, 146. Specific neat of gases, 129. Superheated steam for charring, 208. Tar from coke ovens, 222. Temperatures corresponding to glow colors, 69. determination, 75, 77, 86. gasifying, 259. measurement of high, 37. of ignition of charcoal, 199. optical methods of measuring, 68. Thalpotasimeter, 52. Thermal value Berthier's method for determining, 111. calculation, 110. direct determination, 92. Gmelin's method, 112. of peat, 170. of wood, 152. Thermodynamic laws, 19. Thermoelectric telescope, 7:). Thermoelements, 85. measurements with, 82. Thermometers, 37. correction factors, 40. gas or air, 43. reading of, 39. Thermophone, 87. Tholander's producer, 297. Vignoles' oven, 237. Wanner pyrometer, 75. Water gas, 268. carbon content, 279. combustible gases in, 275. composition of, 269. effect of steam pressure and tem- perature, 272, 282. equilibrium, 271. quantity of steam required for formation of, 278, 281. theory of, 283. thermal value of, 275. Weight of wood, 148. Weinhold ; s pyrometer, 61. Wiborgh's thermophone, 87. Wood, 145. actual content of, 147. ash content of, 149, 150. classification of, 145. composition of, 148. distillation of, 191. evaporating power of, 153. generator gas from, 264. moisture in, 150, 151. resin content of, 149. seasoning, 152. specific gravity of, 145, 146. thermal value, 152, 153. weight of, 148. Work, external, 132. Yield from destructive distillation of coals, 221. OF THE ( UNIVERSITY | The Mechan ical Appl iances OF THE Chemical and Metallurgical Industries BY OSKAR NAGEL, PH.D. A Detailed Description of all Machines, Appli- ances and Apparatus Used in the Chemical and Metallurgical Industries. THE ONLY AMERICAN BOOK ON THIS SUBJECT CONTENTS I. General. II. Steam and Water Power. III. Gas Power. IV. Electric Power. V. Transportation of Solids. VI. Transportation of Liquids. VII. Trans- portation of Gases. VIII. Grinding Machinery. IX. Mixing Machines. X. Firing and Furnaces. XI. Separating Machines. XII. Purification of Gases. XIII. Evaporating, Distilling and Condens- ing. XIV. Drying. 300 Pages 8vo. 292 Illustrations Price, $2.00 Sent Anywhere on Receipt of Price OSKAR NAGEL P. O. Box 385 NEW YORK