OIL FUEL FOR STEAM BOILEES THE POWER HANDBOOKS The best library for the engineer and the man who hopes to be one. This book is one of them. They are all good and they cost $ 1.00 postpaid per volume. (English price 4/2 postpaid.) SOLD SEPARATELT OR IN SETS BY PROF. AUGUSTUS H. GILL Or THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY ENGINE ROOM CHEMISTRY BY HUBERT E. COLLINS BOILERS KNOCKS AND KINKS SHAFT GOVERNORS PUMPS ERECTING WORK SHAFTING, PULLEYS AND PIPES AND PIPING BELTING BY CHARLES J. MASON ARITHMETIC OF THE STEAM BOILER BY RUFUS T. STROHM OIL FUEL FOR STEAM BOILERS McGRAW-HILL BOOK COMPANY, INC. 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. OIL FUEL FOR STEAM BOILERS BY RUFUS T. STROHM ENGINEERING TEXTBOOK WRITER INTERNATIONAL CORRESPONDENCE SCHOOLS FIRST EDITION McGRAW-HILL BOOK COMPANY, INC. 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. 1914 -ff < o COPYRIGHT, 1914, BY THE McGRAW-HiLL BOOK COMPANY, INC. THE. MAPLE. PRESS. YORK. PA s 'V PREFACE The purpose of this volume is to describe, in clear and simple language, the principles that underlie the use of oil as a fuel in steam-boiler practice; the form and action of various types of burners; the arrangement of furnaces for burning oil under different kinds of boilers; the opera- tion of such accessories as pumps, heaters, and clean- ing devices; the methods of storing oil; and such other matters as might naturally arise in connection with the purchase and use of oil fuel. No attempt has been made to describe the use of oil in locomqtive or marine practice, or in heating, tempering and hardening furnaces, because these applications are so extensive as to deserve individual treatment. In- stead, this volume is confined to the burning of oil in the furnaces of stationary steam boilers, and the endeavor has been to cover the ground fully and thoroughly. No claim for originality is made, except in the manner of arranging and presenting the facts. The material is a compilation of the available information on the sub- ject of oil burning, and was obtained from catalogs and from various technical publications issued during the past ten years. The greater part of the contents of this volume appeared as a series of articles in the Electrical World during 1913 and 1914. v VI PREFACE The author takes this opportunity to thank the various manufacturers who furnished catalogs and other valu- able information and to acknowledge his indebtedness to the publishers of the Electrical World for granting permission to reprint the series of articles in book form. RUFUS T. STROHM. SCRANTON, PA., May, 1914. CONTENTS PAGE PREFACE v LIST OF ILLUSTRATIONS ix CHAPTER I. PROPERTIES OF OIL FUEL i II. REQUIREMENTS FOR EFFICIENT BURNING OF OIL FUEL 15 III. METHODS OF SPRAYING OIL FUEL 20 IV. BURNERS FOR OIL FUEL 27 V. CLEANING OF OIL FUEL 44 VI. PUMPING AND HEATING OF OIL FUEL 54 VII. OIL-BURNING FURNACES 65 VIII. INSTALLATION OF OIL BURNERS 80 IX. STORAGE OF OIL FUEL 89 X. COMBUSTION OF OIL FUEL 102 XI. MANAGEMENT OF OIL-BURNING PLANTS 108 XII. PURCHASE OF OIL FUEL 117 XIII. ADVANTAGES AND DISADVANTAGES OF OIL FUEL. . . 129 XIV. PERFORMANCES OF OIL-BURNING BOILERS 136 INDEX 141 Vll ILLUSTRATIONS FIG. PAGE 1 Hydrometer for determining density of oil 6 2 Curve showing relation of specific gravity and density 8 3 Flame of wax candle 16 4 Atomizing by pressure and centrifugal force combined. ... 22 5-6 Principle of outside-mixing burners 24 7-8 Principle of projector burner and inside-mixing burner. . 24 9 Principle of injector burner 25 10 Regular Gem oil burner 28 1 1 Improved Gem oil burner 29 1 2 Parson oil burner 29 13 Booth oil burner with pipe connections 30 14 Best oil burner : 32 1 5 Hammel oil burner 34 1 6 Piping for Hammel burner 35 17 Regular Kirkwood oil burner 36 18 Piping for Kirkwood burner >37 19 Koerting centrifugal spray nozzle 38 20 Kirkwood burner with fixed steam-to-oil ratio 40 21 Slot oil burner with renewable disk 41 22 Inside-mixing slot oil burner 42 23-24 Simple oil strainer and piping for strainer 46 25-26 Suction-pipe strainer and T-fitting used for strainer 48 27-28 Perforated metal strainer and basket strainer for quick cleaning 49 29 Koerting type of oil strainer 50 30-31 Two views of oil strainer arranged for cleaning without removal 52 32-33 Standpipe used to obtain steady oil pressure and safety device for draining standpipe 55 34 Oil-pressure pump with heater 58 35-36-37 Forms of oil heaters 61 ix X ILLUSTRATIONS Fia. PAGE 38 Corrugated counterflow oil heater 62 39 Thermometer for finding temperature of oil in pipe 64 40 Return- tubular boiler with slot oil burner 66 41 Return-tubular boiler with Kirkwood oil burner 67 42 Return-tubular boiler with Best oil burner 68 43 Babcock & Wilcox boiler with burner at front 69 44 Babcock & Wilcox boiler with burner at bridge wall 71 45 Heine boiler with preheating of ak supply 73 46 Stirling boiler with auxiliary air duct 74 47 Stirling boiler with burner at back of furnace 75 48 Stirling boiler with burner set high at front 76 49 Coal-burning boiler with oil used for banking and peak loads 78 50 Piping for Gem oil burner 80 51 Piping and oil-regulating cock for Best burner 81 52 Oil-regulating cock 82 53-54 Oil-regulating valve and arrangement for finding amount of steam used by burners 84 55 Oil-storage tank with connections 90 56-57-58 Arrangement for emptying tank car; simple form of vent pipe; vent pipe and telltale 93 59 Indicator for oil-storage tank 96 60 Section of oil tester 120 61 Lamp of tester for flash point of oil 121 62 Sampling pipe 126 63 Sampling bottle on rod 126 OIL FUEL FOR STEAM BOILERS CHAPTER I PROPERTIES OF OIL FUEL At the rate at which oil fuel is being produced at the present time, there is no danger that it will supplant coal as a boiler fuel, except in a few localities. For if all the oil produced throughout the world in a year were used for the purpose of steam generation, it would furnish an amount of power equal to only about one-thirtieth of that annually required by the power and manufacturing plants of the globe. Therefore, unless far greater oil fields are discovered and the yearly yield of the wells is enormously increased, there is no danger that oil will become a general competitor of solid fuel in steam-boiler plants. Nevertheless, there are localities in which oil forms a useful, economical and desirable fuel, and in which it is used to the exclusion of coal. Such localities are the regions in which the oil is produced. Yet there are oil fields in which little oil is used for steam-boiler fuel, be- cause of the fact that the oil is more valuable for other purposes. Consequently, the factors that determine whether oil shall be used for fuel in preference to coal are as follows: 1 2 OIL FUEL FOR, STEAM BOILERS The price of the oil must be low enough to enable it to compete with coal in that particular neighborhood; the supply must be continuous and ample, so as to prevent shut-downs; and it must be of a quality that can be used without unusual difficulties in the furnace. In the United States the greatest oil fields are located in three regions. The first of these embraces western Pennsylvania, Ohio and West Virginia. The second includes portions of Texas, Louisiana and Oklahoma. The third is in southern California. The oil that is produced in the first of these regions, however, is not used to any great extent as a fuel for steam boilers, for the simple reason that it is of such quality and composi- tion that it is more valuable for refining. Also, this same region contains great deposits of bituminous coal, so that it is more economical to use this solid fuel for power plants. The oil produced in the second and third fields named above is also used in refineries, but a moderate proportion is employed for fuel in boiler furnaces. The reason lies in the fact that coal is scarce in either of these fields. That is, all coal used in these districts must be brought by rail or water from some distant point or points, with the natural result that the cost per ton is greatly in- creased. Because of this fact, it is far cheaper to use oil as the fuel, as it is found in the immediate vicinity and does not need to be transported over such great distances. The oils that are used for fuel are forms of petroleum, which is the term that includes all the mineral oils derived from the earth. The characteristics of petroleum, such as color, density and odor, vary according to the region PROPERTIES OF OIL FUEL 3 in which the oil is obtained. In some parts of the world petroleum is clear and without color, like water, and in other parts of the world it is black. The petroleum found in the United States is brown or reddish brown in color, as a rule, when in a tank or other vessel. But if a sample is poured into a glass or a bottle and is then held up so that the light can pass through it, the oil will appear to have a dark green color. In spite of the differences in color and other character- istics, however, all petroleums are very much alike in composition; that is, they are all liquid hydrocarbons. The principal elements of which they are composed, and which make them valuable as fuel, are about the same as those in coal, namely, carbon and hydrogen; also, like coal, petroleum contains oxygen, nitrogen and moisture. The relative percentages of these constituents vary some- what according to the locality from which the oil is de- rived. For example, an average Texas petroleum has 84.6 per cent, of carbon, 10.9 per cent, of hydrogen, 1.6 per cent, of sulphur and 2.9 per cent, of oxygen. A sample of California petroleum, on the other hand, contains 85 per cent, of carbon, 12 per cent, of hydrogen, 0.8 per cent, of sulphur, i per cent, of oxygen, 0.2 per cent, of nitrogen and i per cent, of moisture. Thus, petroleum may be taken as having from 83 to 87 per cent, of carbon, from 10 to 16 per cent, of hydrogen, and trifling percentages of sulphur, oxygen and nitrogen. Those oils that contain sulphur usually have a disagreeable smell, due to the presence of the sulphur. Although all oil used for fuel is derived primarily from petroleum, it may be obtained commercially in either of - 4 . OIL FUEL FOR STEAM BOILERS two forms, namely, crude oil and fuel oil. Crude oil is simply raw petroleum, in the condition in which it is obtained from the oil well, and is not subjected to any treatment. Fuel oil, on the other hand, is a residue; that is, it is the oil that remains when petroleum is sub- jected to a partial distillation. The distillation process just referred to drives off the lighter oils contained in petroleum and leaves the heavier ones. The crude oil is put in closed tanks called stills and is slowly heated. Now, the crude oil consists of a mix- ture of a large number of liquid hydrocarbons having different densities and boiling points. Consequently, as the temperature in the still rises, these various oils are brought to the boiling point, one after another, and escape from the still in the form of vapor. The vapor is led through pipe coils and is chilled, whereupon it condenses and becomes liquid again. At first, while the temperature rises from about 100 deg. Fahr. to 160 deg. Fahr., petroleum ether will be boiled off, this being a very light oil. From a temperature of 1 60 deg. Fahr. to about 175 deg. Fahr. gasoline will be distilled. Naphtha will be driven off while the tempera- ture changes from about 175 deg. Fahr. to about 300 deg. Fahr., and from 300 deg. Fahr. to 570 deg. Fahr. the oil driven off will be what is commercially known as kero- sene. The oil that remains in the still after the tempera- ture has reached 570 deg. Fahr. consists of lubricating oils, paraffin and coke or asphalt. The crude oils found in the region of western Pennsylvania have a coke base, whereas those from Texas and California have an asphalt base. PROPERTIES OF OIL FUEL 5 The residue, or oil remaining in the still after the petroleum ether, gasoline, benzine and kerosene have been distilled, is what is frequently used as fuel for steam boilers and sold under the name of fuel oil. It is simply the oil remaining after the lighter oils have been driven off from the crude petroleum. The effect of the heating and driving off of the lighter constituents is to leave a residue that weighs more per cubic foot than the original petroleum ; in other words, the density of fuel oil is greater than that of the crude oil from which it is obtained. Moreover, the distilling process causes a change in the composition of the oil. The percentages of carbon and sulphur are decreased slightly and those of hydrogen and oxygen are increased. As the constituents of liquid fuel are the same as those of coal, the same formula may be used to calculate the heat values, or calorific values, of the two kinds of fuel; that is, Q = 14,600 C+ 62,000 ( H j + 4,000 S in which Q = calorific value, in heat -units per pound; C = percentage of carbon, expressed decimally; H = percentage of hydrogen, expressed deci- mally ; O = percentage of oxygen, expressed decimally; 5 = percentage of sulphur, expressed decimally. Thus, if a fuel oil has 83.3 per cent, of carbon, 12.5 per cent, of hydrogen, 0.5 per cent, of sulphur and 3.7 per cent, of oxygen its theoretical calorific value is Q = 14,600 X 0.833 + 62,000(0.125 -/ ) + 4,000 X \ o / 0.005 = T Qj645 heat units. 6 OIL FUEL FOR STEAM BOILERS This, it must be remembered, is but the approximate heat value, based on the chemical composition of the oil. A more reliable estimate of the heat value may be ob- tained by making a calorimetric test of a sample of the fuel oil. The calorific values of oils vary according to the locali- ties from which they are derived and range from about 17,000 to 21,000 heat units per pound. The Texas and California crude oils used in power-plant work seem to have a calorific value averaging about 18,600 heat units per pound. Fuel oil and crude oil are usually not quite so heavy as water, bulk for bulk; that is, the specific gravity of oil is ordi- narily less than that of water. As a general rule, however, in the purchase and sale of oil fuel the specific gravity is not directly mentioned; instead, it is implied by stat- ing the density in degrees Baume, or the reading of a Baume hydrometer allowed to float in the oil. The method of determining the density of an oil by means of the Lydrometer is shown in Fig. i. A sample of the oil is put into the deep glass a, and the hydrometer is lowered into the oil, in which it will float and soon come to rest. The hydrometer consists of a glass tube b, at the lower end of which are the chamber c and the bulb d. The large part c is filled with air, and the bulb d is filled with quicksilver. The former causes the FIG. i. H y d r o m eter for determin- ing density of oil. PROPERTIES OF OIL FUEL 7 hydrometer to float, and the latter keeps it in an upright position. The stem b is graduated with a series of divisions, the lowest one being marked 10. When the hydrometer is put in a vessel of pure distilled water, it sinks until the graduation marked 10 is even with the surface of the water. In other words, 10 deg. Baume, or 10 deg. B., as it is usually abbreviated, corresponds to a specific gravity of i, or the specific gravity of pure water. When the hydrometer is put into a vessel containing oil that is lighter than water, it sinks farther than it did in water, and some other graduation greater than 10 comes even with the surface of the oil. The number of this graduation then indicates the density of that particular oil, in degrees Baume. For example, if the graduation marked 26 came level with the surface of the oil, the density of the oil would be 26 deg. Baume. If the density of an oil lighter than water is given in degrees Baume, the corresponding specific gravity may be found by using the formula 140 in which G = specific gravity of oil; B = density, in degrees Baume. For instance, if an oil has a density of 20 deg. Baume its specific gravity is ~ 140 To enable the specific gravity for any Baume reading to be found quickly, without any calculations, the curve OIL FUEL FOR STEAM BOILERS CO O C\J r*. ex) oq AJ.IAVUO OIJI03ds PROPERTIES OF OIL FUEL 9 shown in Fig. 2 is given. For example, suppose that it is desired to find the specific gravity of an oil having a density of 19 deg. Baume. On the horizontal scale locate the division corresponding to 19, which is the first vertical line to the left of that marked 20. From the point where this vertical line meets the curve follow horizontally to the scale at the left-hand edge of the diagram. It will meet the scale at a point that corresponds to 0.94. This is the desired specific gravity. In other words, a Baume reading of 19 deg. corresponds to a specific gravity of 0.94. The same diagram may be used to find a Baume read- ing corresponding to a given specific gravity, by reversing the foregoing method. Suppose that it is desired to find the Baume reading of an oil having a specific gravity of 0.91. Having located the point corresponding to 0.91, midway between 0.90 and 0.92 on the left-hand scale, follow horizontally to the curve and then down to the bottom scale. The point thus reached will be at the first division to the left of 25, corresponding to 24. Hence, a specific gravity of 0.91 corresponds to a Baume reading of 24 deg. If possible, the density of oil should be determined at a temperature of 60 deg. Fahr., as the formula and the curve will give the correct equivalent specific gravity only under this condition; however, it may not be con- venient to do this in all cases. If the temperature of the oil sample is greater or less than 60 deg. Fahr., it should be noted, so that the specific gravity correspond- ing to the Baume reading may be corrected for the differ- ence in temperature. A higher temperature than the standard, 60 deg. 10 OIL FUEL FOR STEAM BOILERS Fahr., causes the oil to expand, and the specific gravity calculated from the Baume reading will therefore be too low. A lower temperature than 60 deg. Fahr. will cause the oil to become more dense, so that the specific gravity corresponding to the Baume reading will be too high. The correction amounts to 0.0004 f r each degree Fahrenheit. That is, if the temperature is less than 60 deg. Fahr., the observed specific gravity must be reduced by an amount equal to 0.0004 times the difference be- tween the observed temperature and 60 deg. Fahr.; and if the temperature is above 60 deg. Fahr., the observed specific gravity must be increased by an amount equal to 0.0004 times the difference between the observed tem- perature and 60 deg. Fahr. To illustrate, suppose that a sample of oil is tested at a temperature of 46 deg. Fahr. and found to have a den- sity of 30 deg. Baume. The specific gravity corresponding to this reading is 0.875 with oil at 60 deg. Fahr. But in this case the oil has a temperature 14 deg. lower than the standard. Hence, the observed specific gravity, 0.875, must be reduced by 0.0004 X 14 = 0.0056, and the corrected specific gravity then becomes 0.875 ~~ 0.0056 = 0.8694, which is the true specific gravity of the oil. Again, suppose that at a temperature of 80 deg. Fahr. an oil showed a density of 25 deg. Baume, equivalent to a specific gravity of 0.9032. As the temperature of the sample is 20 deg. in excess of the standard, the observed specific gravity must be increased by 0.0004X20 = 0.0080, giving a corrected value of 0.9032 + 0.0080 = 0.9112. PROPERTIES OF OIL FUEL 11 Particulars as to the flash point, firing point, specific gravity, and calorific value of various American oils are given in Table I. These values are taken from a table published in the Iowa Engineer of October, 1905, and cover the main oil fieMs of the United States, with the exception of Ohio. The calorific values were obtained by tests made with a Parr calorimeter. It may be noted that the calorific values of crude oils from any particular district vary but little. The reduced oils, or those from which some of the lighter constituents were removed, gained in specific gravity and did not lose in calorific value; also, the flash point was raised considerably. In a number of cases, double sets of values are given. These are the results of tests on samples obtained from different companies in the same field. Table II is given because it is a summary of a large number of tests made on the petroleums of the San Joaquin Valley, California, by the Government Bureau of Mines. The detailed report of the tests is contained in Bulletin 19. The composite samples referred to in the table were made up by taking equal weights of all the samples from a given locality and mixing them. For example, the composite sample of Kern River oil was made up of 30 grams from each of the 40 samples previ- ously tested. 12 OIL FUEL FOR STEAM BOILERS IU M o 8 N O o" ^> CO vO t'O o U be gj ON o- ON ON 00 00 CO ON ON C/3 c3 6 6 6 6 6 s hJ M .s ^ o $ 10 00 O M ^^ 9 ON fa bo . M > 3 1 C ol ^ t^ LOUISIANA Calcasieu county. . , Calcasieu county. . . i^, u 8 j 1 M 1 ^ ^i d to .5 c/T * 1 rt o c/) d ^3 S s S II 3 i > *3 d o i > PROPERTIES OF OIL FUEL 13 L O O O *O co O O O <*O *O O^ O t"^ cs tn Os O O O\ O^ O\ OO OO O^ O^ O^ OO s * O O^ n >> ^ f og> Or^o OMt^.-^-oiovoM Is oo ON 00 IO oo * 00 bO al Composite O O C CU Composite [cKittrick Average of Composite 'o bo I! Composite unset Average of Composite M u f^ ^ C/2 CHAPTER II REQUIREMENTS FOR EFFICIENT BURNING OF OIL FUEL The first essential for the successful burning of crude oil or fuel oil is that it must be atomized or broken up into a fine spray or mist; next, it must be thoroughly mixed with a sufficient amount of air to insure its complete combus- tion; and, finally, the combustion must take place in a furnace of suitable size and shape. These three require- ments must be met in every power plant in which liquid fuel is to be used. When crude oil was first tried as a fuel for steam boilers, attempts were made to burn it by running it into shallow pans and igniting its surface. This was simply following the old methods applied in the case of coal. For, as the coal was spread out in the form of a bed of fairly uniform thickness on the grates, so was the oil spread out in a shallow sheet. This method, however, was wholly un- satisfactory and unsuccessful and was soon abandoned. The reason for its failure was that oil differs so greatly from coal. With coal the effect of the heat is to drive off the vola- tile matter in the form of gases, which, mixing with the air passing through the bed of fuel, burn and generate suffi- cient heat to ignite the solid carbon remaining on the grates. This bed of burning carbon then furnishes the heat required to ignite succeeding charges of fresh fuel. 15 16 OIL FUEL FOR STEAM BOILERS With oil, there is no incandescent bed of fuel. The oil does not burn in the liquid form. Before it can burn it must be changed to a vapor, or volatilized, and this is done by the action of heat. The action may be illustrated by the burning of a common wax candle, as shown in Fig. 3- When the wick of a candle is lighted the heat due to the burning melts some of the wax just below the flame, and the melted wax is at once carried up the wick by capillary action. As it comes closer to the flame it grows hotter and hotter, until at length it reaches the boil- ing point and passes into vapor. This vapor mixes with the air and thus forms a combustible mixture, which burns above the tip of the wick. Part of the heat due to its burning is used to melt and vaporize more of the wax, and the burning is thus rendered a continuous process. It will be observed that the flame of a candle varies in color. Just around the tip of the wick there is nothing to be seen. This transparent section a is the vaporized wax, before it has had a chance to mix with air and burn. Around this is another transparent section b that has a bluish tinge. Here the vapor has mixed with some air and is being partly burned. Farther up, there is more opportunity for the mixing of a sufficient quantity of air, and the flame there becomes yellow or yellowish white. That part of the flame that is tinged with blue indicates FIG. 3. Flame of wax candle. EFFICIENT BURNING OF OIL FUEL 17 incomplete combustion, because the supply of oxygen in the air that mixes with the vapor is not sufficient to burn the carbon to dioxide. This portion of the flame does not have so high a temperature as the yellowish portion where the combustion is complete. As a further experiment to show that the crude oil will not burn in the liquid form, a live coal or a blazing stick may be dropped or thrust into a vessel containing the oil. Instead of firing the oil, the live coal will.be quenched or the flame of the stick will be extinguished by the oil, for the simple reason that the oil is vaporized so slowly that the inflammable gas produced is not sufficient to support continuous combustion. The object of atomizing the oil, or dividing it into a fine mist or spray, can now be understood. By separating the body of oil into a great number of fine particles, each par^ ticle will have its surface exposed to the heat and will be more readily vaporized than a large bulk of oil. The finer the mist or spray, the more easily will the vaporizing occur. This can be shown by a very simple example. If oil is broken up into a series of drops each o.i in. in diameter, the ratio of the surface area to the volume of each drop is sixty to one. But if the drops are o.oi in. in diameter, the ratio of area to volume is 600 to i. That is, a drop of oil o.oi in. in diameter will expose ten times as much sur- face per unit volume as a drop o.i in. in diameter. The finer the particles, therefore, the greater will be the amount of external surface per unit volume exposed to the action of the heat and the more rapidly will the oil turn to vapor. When the oil has been properly vaporized, it must be 18 OIL FUEL FOR STEAM BOILERS thoroughly mixed with air in the correct proportions to produce complete combustion. This may be done by allowing the air to enter the furnace through openings in the floor or the ashpit, somewhat after the manner in which it is admitted to the furnace of a coal-burning boiler. Again, it may be admitted through the same openings as those through which the burners are intro- duced, in which case the air sweeps over the burners. But it is more than probable that both methods will be used at one time, so that part of the necessary air will be admitted by each. The third requirement for the efficient use of oil fuel is a furnace of suitable design and construction in which the combustion may take place. The common furnace used for solid fuel will not ordinarily answer the purpose with- out alterations. The coal-burning furnace can be fired intermittently, for there is always a bed of incandescent fuel on the grates so that when the fresh coal is added the incandes- cent portion will fire the green fuel. But the injection of the liquid fuel is continuous, and the conversion of the freshly admitted oil from the liquid to the gaseous state must be accomplished by a part of the heat of the oil that was burned just before. As there is no fuel bed, the heat must be stored in the lining of the furnace. In other words, the furnace is lined with firebrick, which becomes highly heated and acts as a heat reservoir and equalizer. The chamber in which the combustion of the liquid fuel takes place should not be bounded by cold metal surfaces. For if the partly burned gases strike such surfaces they will be chilled, combustion will be checked, and there will EFFICIENT BURNING OF OIL FUEL 19 be a loss of heat and probably the formation of smoke. By having the combustion occur in a firebrick furnace, however, the chilling is prevented, and when the gases have been burned completely they may be led against the boiler tubes and surfaces without danger of producing smoke. CHAPTER III METHODS or SPRAYING OIL FUEL The atomizing of liquid fuel, or the breaking up of the oil into a spray or mist, so as to enable the air to mix thoroughly with it, may be accomplished in a number of different ways. The most common method is that in which a current of steam or a blast of air is directed into or across the flow of the oil so as to divide it into fine particles. Another way is to subject the oil to a high pressure and then to allow it to escape through small orifices. These orifices are so shaped and placed that the escaping oil is expanded, scattered and properly atomized. A third method involves the use of centrifugal force. A whirling motion is given to the oil, and the centrifugal force set up causes the oil particles to fly off in the form of spray. The principles involved in all of these methods are used in modern liquid-fuel burners, but centrifugal force alone is not relied upon to produce the desired atomization. In the lengthy and exhaustive tests made by the Bureau of Steam Engineering of the United States Navy several attempts were made to use an atomizer consisting of a steel disk that was rotated at a high speed and over which the oil was allowed to flow. The earlier con- structions warped under the effect of the heat or were wrecked by the centrifugal force developed, but by 20 METHODS OF SPRAYING OIL FUEL 21 altering the construction in accordance with the ex- perience gained from these initial experiments a centrifu- gal apparatus was eventually produced. It consisted of a circular disk of saw steel riveted to a hollow pivot that was held solidly in vertical bearings. Buckets or vanes were attached in a circle to the under side of the disk, and a jet of steam from a single nozzle was directed on this series of vanes, thus rotating the disk at a high speed. The oil to be sprayed was forced up through the hollow pivot under a small pressure and over- flowed on to the disk at the center. Under the action of the centrifugal force set up by the very rapid rotation, it was flung off at the outer edge, and when ignited by a torch it burned in a ring of flame from 4 ft. to 5 ft. in diameter. In spite of the fact that a mechanical rotary atomizer had thus been developed, this type has not been adopted in commercial installations using oil fuel. The reason is that the spraying force is derived from the jet of steam, and it is simpler to use the steam directly for spraying, without the introduction of the rotating disk. Also, it is probable, from the results of the experiments referred to, that trouble would arise through warping of the disk and wearing of the pivot. It is true that the flow of the oil across the face of the disk has a tendency to cool it some- what and thus reduce the warping effect, but the fact remains that the purely centrifugal sprayer has not met with favor. In connection with pressure spraying from an orifice, however, the centrifugal principle has been used success- fully. This combination may be illustrated by the simple 22 OIL FUEL FOR STEAM BOILERS sketch shown in Fig. 4. At the end of the pipe a that con- veys the oil, the oil passage b is tapered down to the open- ing c through which the oil is discharged. The series of slanting vanes d on the rod e deflect the oil and break it up into a number of currents, each of which has a whirling motion as it enters the space / around the end g of the rod. These separate currents are intermingled in the space /, and on emerging from the ori- fice c they spread as shown by the diverging lines. The oil is forced into the pipe a under fairly high pressure, and thus the atomizing is due to both the twisting motion given by the vanes and the expansion following the escape at high velocity from the orifice. Though the principle just described could be applied in any installation, it would doubtless be most advantageous in the case of a plant in a district where suitable water is scarce or hard to obtain. For the steam that is used to atomize the oil by direct action goes along v.ith the prod- ucts of combustion and escapes at the top of the chimney. It is thus lost absolutely, so far as the chances of recover- ing it are concerned; whereas by using a device similar to that shown in Fig. 4 there is no waste of steam. It is true that steam would be required to run the pressure pumps, but it could afterward be led to some form of condenser and thus recovered for boiler feed-water. FIG. 4. Atomizing by pressure and centrifugal force combined. METHODS OF SPRAYING OIL FUEL 23 A disadvantage of the system of spraying oil by pres- sure lies in the fact that the openings through which the oil is forced must not be much greater than 1/16 in. in diameter. An opening of this small size can very easily become clogged by a bit of dirt or a grain of sand; there- fore, a strainer should always be inserted in the oil system. The holes in the strainer, of course, must be small enough to catch and retain all dirt of sufficient size to clog the burner. Usually they are made about half the size of the hole or holes through which the oil is sprayed. By far the greater number of oil-fuel plants use steam or air as the atomizing agent. If steam is used, it is obtained from the boiler being fired or from another boiler in the plant, and if air is used, it is obtained by means of a positive blower or an air compressor. No matter which agent is used, it is led in a sheet or a jet against the oil to be atomized. The mixing of the oil and the steam or the air may take place inside the atomizing device or outside it, but in either case the spraying is due to the expansion that occurs when the steam or air under pressure escapes from the orifice and mingles with the oil. The device that accomplishes the atomization of the oil is called the burner, though it has nothing to do directly with the combustion. There are two main classes of burners, namely, outside mixers and inside mixers. A common form of outside-mixing burner is shown diagram- matically in Fig. 5. The oil to be atomized is led through the passage a and is allowed to flow out and down at the orifice b. The steam or air is conducted through the passage c and allowed to escape through the narrow ori- fice d just below the oil orifice. The oil that oozes or 24 OIL FUEL FOR STEAM BOILERS drools out is thus caught by the rapidly escaping and expanding steam or air and is thoroughly sprayed. This type is ordinarily termed the drooling burner. Another form of outside-mixing burner is shown in Fig. 6. It differs from the other only in that the oil passage is turned downward at the outlet end, and the steam or FIGS. 5 and 6. Principle of outside-mixing burners. air issuing from the orifice a sweeps directly across the face of the oil orifice b. This type is called the atomizer burner. The type shown in Fig. 7 is called the projector burner and also belongs to the outside-mixing class. In this case, however, the orifices a through which the steam or air FIGS. 7 and 8.- -Principle of projector burner and inside-mixing burner. escapes are at some distance from the oil orifices b, so that the steam or air has expanded considerably by the time it meets the oil. One form of inside-mixing burner is shown in Fig. 8. The oil flows into the chamber a surrounding the nozzle b through which the steam or air is led, and the latter meets METHODS OF SPRAYING OIL FUEL 25 and mingles with the oil in the chamber, after which both are discharged at c. This form of burner is termed a chamber burner. The diagram in Fig. 9 illustrates the principle of the in- jector burner. The steam or air flows from the orifice a into the passage b containing the oil, and the mixture is carried forward with increasing velocity toward the nar- rowest part c of the burner. Beyond this throat the mouth is flared, and the rapid expansion atomizes the oil. \a b FIG. 9. Principle of injector burner. The various types of burners employed in steam plants involve the use of one or more of the foregoing principles. Air is used only in special instances as the atomizing agent, steam being the most common. So far as economy is con- cerned, there is little to choose between the two, for the reason that the amount of steam required for direct atom- izing is about the same as that required to run an air compressor to furnish a sufficient supply 'of air at the necessary pressure. On the other hand, the addition of a compressor means increased cost for installation over that for a plant using steam directly; also, the amount of piping and apparatus is increased by the use of a compres- sor, with the natural result that accidents are more likely to happen and so cause partial or complete shut-downs. The amount of steam used to atomize i Ib. of oil, whether directly or indirectly, may be taken as about 0.5 26 OIL FUEL FOR STEAM BOILERS lb. for average cases. There are plants in which only about 0.3 lb. of steam per pound of oil is used for atomiza- tion, and in the tests made by the Bureau of Steam Engi- neering some burners used as low as 0.15 lb. of steam per pound of oil. This last was an exceptionally good per- formance and was unusual. The average plant may con- sider that its economy is fair if its steam consumption for atomization only amounts to from 0.3 lb. to 0.5 lb. per lb. of oil. In addition to the steam required for atomizing the oil, there is the steam required for running the pumps by which the oil is supplied under pressure and the steam used in some cases for heating the oil. The amount of steam used for atomization is roughly 2 per cent, of the total amount generated by the boiler; that is, out of every 100 lb. of steam formed, 2 lb. are taken to spray the oil. The oil-pressure pumps and the oil heater require about 2 per cent, more, so that the total steam consumption of the oil system is in the neighborhood of 4 per cent, of the steam generated. CHAPTER IV BURNERS FOR OIL FUEL The purpose of the burner is to spray the oil fuel into the furnace; consequently the first requisite of a good burner is that it shall atomize the fuel satisfactorily. As oils are of different densities and viscosities, and as different rates of feed must be used to accommodate the rate of com- bustion to the load on the boiler, it follows that the burner must be fitted with suitable valves in order that its action may be regulated closely. This regulation applies not only to the oil but to the atomizing medium as well. A second important feature of a good burner is accessi- bility for cleaning and repair. It is almost impossible, even after taking the precaution of cleaning and strain- ing, to prevent dirt from being carried along with the oil. As a result, clogging of the oil orifices may occur, and it then becomes necessary to clean the burner. To do this easily and quickly, the burner must be designed so that it may be taken apart readily and without undue labor. In some types of burners the oil and steam currents cause erosion, and in such forms it is necessary to make provi- sion for removing and renewing the worn parts without loss of time. A form of Gem burner designed particularly for use in small furnaces is shown in Fig. 10. Its body a is of cast iron and contains two inlets b and c, the former for the oil 27 28 OIL FUEL FOR STEAM BOILERS and the latter for the steam that is used as the spraying agent. The oil flows along the central pipe d and escapes at the tip of the burner. The steam passes along the pipe e surrounding the oil pipe and is given a whirling motion by the vanes of the whorl / near the tip. It then escapes past the conical end of the oil pipe, through an annular opening g, sweeping the oil into the furnace. FIG. 10. Regular Gem oil burner. As the oil pipe a is surrounded by live steam throughout its entire length, the oil becomes well heated in flowing through the burner, and the effect of this heating is to make it more fluid and easy to atomize. The regulation of the flow of oil and steam is accomplished by valves in the pipes attached at b and c respectively, since there are no moving parts in the burner itself. Should the oil pipe become clogged with dirt, the cap at the back may be unscrewed and a rod may be inserted to remove the obstruction. An improved form of this burner is shown in Fig. n. It differs from the form shown in Fig. 10 mainly in that BURNERS FOR OIL FUEL 29 it has a needle valve included in the burner to enable the oil flow to be regulated more closely. The stem a, Fig. 1 1, of the needle valve is threaded near its inner end and passes through a stuffing-box b at its outer end; thus any FIG. ii. Improved Gem oil burner. expansion of the stem due to increase of temperature does not alter the adjustment of the valve, as it would do if the stem were threaded at the stuffing-box end. The oil sur- rounds the stem inside the pipe c and flows to the nozzle through grooves cut in the side of the stem. The atomi- FIG. 12. Parson oil burner. zation is effected in the same way as in the simpler type. Each of these burners may easily be unscrewed and taken apart for cleaning. The Parson burner illustrated in Fig. 12 is similar in 30 OIL FUEL FOR STEAM BOILERS principle to that shown in Fig. n. The tip a of the Parson burner has a passage b for the steam, which is admitted through the connection c. The oil enters at d' and flows into the chamber e, from which it is allowed to pass into the nozzle / past the regulating valve g. This valve has a very slight taper, and consequently the flow f"l 9 9 FIG. 13. Booth oil burner with pipe connections. of oil can be adjusted with great precision. The nozzle projects through the center of the steam passage in the tip, and the oil is thus heated on its way to the furnace. The valve stem h is furnished with a stuffing-box i to prevent the leakage of oil. The Booth burner, shown in Fig. 13, is one that has been used extensively in stationary-boiler practice. The body BURNERS FOR OIL FUEL 31 of the burner consists of a box-shaped casting a that is set horizontally. It contains two passages b and c, oil being admitted to the former through the pipe d and steam to the latter through the pipe e. The oil flows outward through the wide, shallow slot / at the tip of the burner and drools downward across the end. An adjustable steel plate g is bolted across the steam orifice. This plate has a long notch cut in the top edge, forming the outlet h for the steam, and on the inside it is beveled or chamfered so as to direct the steam upward toward the orifice. The escaping steam sweeps along the under side of the burner tip and in expanding sprays the oil that runs down from the upper slot. The bolts that hold the plate g in place pass through long vertical slots in the plate, and this con- struction allows the plate to be moved up or down to give the desired depth of slot h. This adjustment, of course, is made when the burner is disconnected and not in use. The arrangement of the piping to the Booth burner is simple. The supply of steam is brought to the burner through the pipe , the flow being regulated by the valve i. In the same way a valve j in the oil line d is used to con- trol the rate of flow of the oil. Between the oil pipe and the steam pipe is inserted a short connection fitted with a valve k. This serves as a by-pass to admit steam to the oil passage when it becomes necessary to clean out the passage. The oil valve j and the steam valve i are first closed and then the by-pass valve k is opened. The steam rushes through the oil passage, and its heat and its cutting action together scour the passage clean. The steam passage may be cleaned by removing the plate g completely and allowing steam to blow through at full 32 OIL FUEL FOR STEAM BOILERS pressure. The passages in the burner are straight and fairly large, and there is little danger of their becoming clogged frequently. A form of externally atomizing burner known as the Best burner is shown in Fig. 14. The tip by which the atomizing is accomplished is supported by two pipes a and b that convey the steam and the oil, and these pipes are made of such length that they will extend through the a FIG. 14. Best oil burner. boiler front and bring the burner just within the front of the furnace. The tip is of cast iron and contains a steam passage c and an oil passage d connecting with the oil pipe b. The oil passage is curved upward, so that the escaping steam sweeps across the face of the orifice e at right angles to the direction of flow of the oil, thus insuring excellent atomization. Moreover, it is stated that this arrange- ment of the two orifices causes the steam to have a sort of ejector action on the oil, with the result that the oil is BURNERS FOR OIL FUEL 33 drawn toward the orifice e and only a low pressure is necessary in the oil system. The steam orifice / is a long, shallow slot in the under face of a hinged lip g that during the normal working of the burner is held down firmly against the body of the tip. A fork h is pinned to the lip and has fastened to it a rod i that is threaded at its outer end and fitted with two ad- justing nuts j and k on opposite sides of the bracket /. When the steam passage becomes clogged or choked, these nuts are turned so as to force the rod i inward and swing the lip upward. Full steam pressure is then turned on to blow out the obstruction, after which the lip is drawn down on its seat. This may be done from the front of the boiler without disturbing the setting of the burner. The flow of oil is regulated by a cock m and the steam supply by a valve n in the steam pipe. A by-pass valve o is inserted between the steam and oil pipes, to enable the oil side of the burner to be cleaned out readily, as explained before. The construction of the Best burner is such that there is little or no wear, and the absence of needle adjusting valves and constricted passages reduces the likelihood of clogging. If desired, this burner may be operated with tar as fuel, and it is equally serviceable with heavy oils. The flame produced is fan-shaped and spreads to about the width of the boiler furnace. The Hammel burner, shown in perspective and in sec- tion in Fig. 15, belongs to the inside-mixing type. It con- sists of three main parts a, b, and c, held together by bolts d and e. The lower part a contains the passage/ through which steam is admitted to the burner, and the upper 34 OIL FUEL FOR STEAM BOILERS section b has the oil connection g from which a duct h leads downward to a mixing chamber i formed by a recess in the under side of the section c. The steam flows up from the passage / into the chamber j, from which three slanting ducts k, I and m lead to the mixing chamber. These ducts are inclined in different directions, and their lower ends are grouped about the end of the oil duct h in FIG. 15. Hammel oil burner. such a way that the escaping steam will mingle thoroughly with the oil in the mixing chamber. From the mixing chamber a flaring opening n extends outward to the tip of the burner, and as the steam flows at high velocity and escapes from the wide orifice o, it spreads the oil and causes the burner to produce a fan-shaped flame. Experience with steam turbines has shown that steam traveling at high speed has an erosive effect on pipe BURNERS FOR OIL FUEL 35 fittings, valves, vanes and other parts that deflect its motion. This cutting action is present likewise in oil burners that use steam as the atomizing agent, and in the Hammel burner the erosion is greatest in the divergent mouth n. The wear is due to the cutting action of wet steam and to the presence of particles of dirt and grit in the oil. As a consequence, the upper and lower faces of the opening n are lined with steel plates p and q that take FIG. 1 6. Piping for Hammel burner. all the wear and that may be renewed at small cost when they become greatly eroded. To insert new plates, the bolts d are unscrewed and the section c is removed, thus uncovering the plates. The set screw r serves to hold the upper plate p firmly in place when the burner is put together. The Hammel burner is attached to the ends of tfre steam and oil pipes, as shown in Fig. 16, and these pipes are made of suitable lengths to allow the burner to project into the furnace through the front of the boiler setting. 36 OIL FUEL FOR STEAM BOILERS The valve a regulates the flow of oil and the valve b the flow of steam. The valve c acts as a by-pass for use in cleaning out the burner in case it becomes choked with grit or carbonized oil. A perspective view of the Kirkwood burner is given in Fig. 17, and in Fig. 18 is a longitudinal section of the burner, together with the arrangement of the piping. FIG. 17. Regular Kirkwood oil burner. The same reference letter is used to designate correspond- ing parts that appear in both views. The main part of the burner is a hollow casting a into which the steam supply pipe b is screwed. A plug c is inserted at one end and at the other is a stuffing-box d through which the pipe e extends into the chamber /. At its outer end the pipe e is threaded and passes through a threaded collar g that may be rotated in the bracket h by mecins of the handle i. At the inner end the pipe is closed by a plug j containing an orifice k that may be closed by screwing the long stem / inward until it seats against the plug. A handle m is fastened to the outer end of the stem and carries a pointer n that moves over the dial on the end of the flange o on the elbow p. The supply of oil is admitted from the pipe q through the elbow p to the pipe e, and it BURNERS FOR OIL FUEL 37 escapes past the regulating stem / through the orifice k, where it is picked up by the steam flowing into the cham- ber / and carried through the opening r into the furnace. The handle i carries a pointer s that moves over a dial on the face of the bracket h. Movement of the handle i FIG. 1 8, Piping for Kirkwood burner. governs the position of the plug j with respect to the plug c and so determines the amount of steam used for atomiz- ing the oil. The position of the stem / is regulated by the handle m, thus governing the rate of flow of oil. The two dials enable the fireman or the boiler attendant to adjust the flow of steam and oil very accurately after he has 38 OIL FUEL FOR STEAM BOILERS once determined the relative proportions that give the best results. By having the regulating valves very close to the point where the steam and oil mingle, as in this burner, the full pressure of each is maintained up to the moment of its escape. The valve / is a by-pass valve through which steam may be admitted to the oil pipe to clean it. A slip joint is sometimes inserted in the hori- zontal section u of the by-pass pipe to allow easy sliding when the oil pipe e is moved in or out by the handle i. FIG. 19. Koerting centrifugal spray nozzle. The setting or adjustment of the oil-regulating stem is not affected by the movement of the pipe e because the latter is fixed rigidly to the elbow p through which the stem passes, so that any movement of the pipe carries the stem along without changing its distance from the plug k. The construction of the Koerting centrifugal spray nozzle is shown by the section in Fig. 19. The burner consists of a casting a that is inserted in a suitable opening in the boiler front and that in turn has an opening b through which the tips c of the spray nozzles may project. There are two of these nozzles held in the casting d that BURNERS FOR OIL FUEL 39 contains the oil passages and strainers. The tip c has at its end a small orifice that is expanded inward to form a chamber to contain the screw e, which is carried by a stem / that fits in the plug g, and is held in position by the pressure of the spring h. The oil enters through the pipe i and passes through the strainer j on its way to the spray nozzle, thus being cleaned. The cage k that carries the strainer is screwed into the casting d and may be taken out for cleaning by first removing the cap /. The oil is sprayed by the whirling set up by the screw in the tip of the nozzle, in combination with the pressure maintained in the oil system. The air required for combustion is admitted through registers around the outside of the casting a. The stems/ are held by springs so that, when heated, they may expand freely. If they were held down by the direct pressure of the plugs g, any expansion due to heating would cause them to buckle. The screws e may be removed for cleaning by taking out the plugs g. In all of the types of burners heretofore described the relative proportions of the atomizing agent and the oil are under the control of the operator. The Kirkwood burner shown in section in Fig. 20 belongs to that class in which the relative sizes of the openings for oil and steam or air are fixed during the construction or assembling of the burner. The oil and the steam enter through the pipes a and b, respectively, which are connected to opposite sides of the body casting c. The regulation of the flow of oil and steam is accomplished by turning the single handle d, which is threaded on the boss e and carries the stem /. This stem is hollow and is drilled with lateral holes g that connect with the oil supply. At its inner end it is tapered 40 OIL FUEL FOR STEAM BOILERS to fit a seat in the plug h. A tapered stem i is fixed cen- trally in this plug and projects into the hollow stem /. When the handle d is turned to the right as far as it will go, the stem i closes the duct j and at the same time the tapered end of the stem / comes against its seat in the plug h and shuts off the flow of steam to the tip k of the FIG. 20. Kirkwood burner with fixed steam-to-oil ratio. burner. In this way the burner is shut down. By turning the handle in the opposite direction, both steam and oil are admitted to the mixing chamber /, the relative proportions being governed by the taper of the stems / and i. The position of the stem is fixed by the manu- facturer and cannot easily be changed by the operator. This removes the danger of having an unskilled operator BURNERS FOR OIL FUEL 41 affect the efficiency of the burner by changing the relative amounts of oil and steam. The outside-mixing burner in Fig. 21 illustrates a type that is made in a number of forms differing only slightly in detail. The steam pipe a and the oil pipe b are made FIG. 21. Slot oil burner with renewable disk. of such length as to bring the tip of the burner to the proper point in the furnace. The burner consists of two cup-shaped castings c andd separated by a narrow disk e. The three pieces are of the same diameter and are held together firmly by the central bolt /. As shown in the sepa- 42 OIL FUEL FOR STEAM BOILERS rate views, the disk ghas its rim cut away on both sides for about one-third of its circumference. Thus, when it is bolted between the castings c and d, two slots g and h are formed, extending about one-third of the way around the burner. The oil flows through the upper casting c and drools over the edge of the disk e from the slot g. The steam flows through the lower casting d and escapes through the slot h, meeting the oil and spraying it so as to produce a wide fan-shaped flame. The greater part of FIG. 22. Inside-mixing slot oil burner. the wear due to erosion comes on the disk e, which can be renewed when badly worn. The arrangement of the regu- lating valves for oil and steam and of the by-pass for cleaning is similar to that already described. Another form of inside-mixing slot burner differing considerably from the Hammel burner is shown in section in Fig. 22. The steam enters at a and flows out through the holes in the conical tip of the section b into the narrow passage c. The oil enters at d and flows around the sec- tion b, being heated in so d$ing. Under its own pressure, BURNERS FOR OIL FUEL 43 and aided by the suction produced by the escaping steam, it flows past the conical tip, where it is caught by the steam, broken up, and carried along the pipe c. Further mixing of the steam and oil takes place in the chamber and the spray escapes through the slot e into the furnace. The spread of the flame may be changed by using slots of different proportions. CHAPTER V CLEANING or OIL FUEL The greater number of burners for oil fuel are con- structed with small orifices through which the oil is sprayed. It therefore becomes necessary to take proper precautions to prevent the burners from becoming clogged by particles of sand or other foreign matter. The dirt found in the oil may be in the crude oil as it comes from the well, or it may find its way in during the subsequent transportation and handling of the oil. Oil wells are driven through strata of various earthy materials to pierce the oil-bearing sands, and as a consequence the crude oil issuing from a well contains more or less sand. If the crude oil is used directly as a boiler fuel, it must be strained; otherwise the particles of sand will clog the burners and render them erratic in their operation. The heavier and more viscous the oil, the more easily will it hold and carry with it particles of sand and dirt. A common method of separating dirt held in suspen- sion in liquids of smaller specific gravity is that of sedi- mentation or settling. Thus, if oil fuel containing dirt is run into storage reservoirs or settling tanks and there allowed to remain undisturbed for some time, much of the heavier sediment will fall to the bottom by reason of its own greater density. The cleaned oil may then be drawn off at the top. However, this method involves storage of 44 CLEANING OF OIL FUEL 45 the oil for a time, with the consequent expense of tanks and pumping machinery; moreover, if the oil is very heavy and viscous, it is by no means certain that the settling method will result in thorough cleaning. It is therefore a wise precaution to use strainers in the piping system that conveys the oil to the burners. Even the heat treatment or partial distillation that re- sults in the formation of fuel oil cannot be relied on to pro- duce a clean oil ; so, where fuel oil is used, strainers should be installed. They not only prevent clogging, but they also lessen the wear on the burner tips due to the erosive effect of grit. The material of which the strainer is made may be wire netting, gauze or perforated metal. In any case, the meshes or openings should be only about half as wide as the smallest passage or orifice in the burner. Brass wire gauze is the material commonly used, although good strong mosquito netting may be bent into shape to form a strainer. On account of the comparatively large open- ings in mosquito netting, it should be used only in connec- tion with burners that have no minute orifices, as, for example, the Best burner. The simplest form of strainer, shown in Fig. 23, con- sists of a circular piece of wire gauze a held between a pair of pipe flanges b and c\ but the simplicity and cheap- ness of this form are its only commendable features. The oil flowing from the pipe d to the pipe e on its way to the burners will deposit the sand and dirt on the gauze, and sooner or later the latter will become choked, because it has so small an area. In this condition it will seriously obstruct the flow of oil; therefore, a strainer of this kind 46 OIL FUEL FOR STEAM BOILERS would have to be cleaned frequently. Each cleaning would necessitate opening up the joint at the flanges, so that the gauze could be taken out, and before this could be done it would be necessary to shut off the flow of oil. This type of strainer, therefore, is to be avoided in the simple form shown. The arrangement of piping shown in Fig. 24 does away with the objectionable feature of breaking the joint to FUGS. 23 and 24. Simple oil strainer and piping for strainer. clean the strainer. The oil from the pump flows through the pipe a and the valve b and passes upward through the wire gauze held between the flanges at c, continuing on its way to the burners through the valve d and the pipe e. The steam line / to the burners has a branch g that is joined by the T h to the oil line and is fitted with a valve i. Below the strainer the oil pipe is extended and fitted with a valve/. When the burners are working, the valves i and/ are closed and the valves b and d are open. When CLEANING OF OIL FUEL 47 the strainer becomes clogged and requires cleaning, the valves b and d are closed and a bucket is placed under the valve jj which is then opened. Finally, .the valve i is slowly opened, admitting live steam above the strainer, and this steam, rushing downward through the gauze, will clean it and blow out all the dirt collected beneath it. The valves are then set again for normal working. The valve 2' must be tight or condensed steam will leak into the oil and cause the burners to sputter. The nipple k should be fairly long, to form a trap for water and dirt. A pressure gage, shown at /, may be attached to the oil pipe on the pump side of the strainer. An abnormal rise of pressure shown on it will indicate that the strainer is clogged and in need of cleaning. The requirements of a good oil strainer are that it shall stop and hold the solid foreign matter entrained with the oil, that it shall have ample straining surface, so that cleaning may not be required too frequently, and that it shall be constructed and installed so that the cleaning may be quickly and easily done. The strainer shown in Fig. 25 is made of wire gauze bent into the form of a conical frustum, with the large end a open and the small end b closed. This form is inserted in the open end of the suction pipe c leading to the oil pump and provides a large area through which the oil may pass on its way to the pump. An advantage of having the strainer at this point is that it removes much of the grit that would otherwise cause wear of the pump barrel and plunger. The large end a is made slightly larger than the diameter of the suction pipe. The strainer is simply pressed into place in the pipe and is 48 OIL FUEL FOR STEAM BOILERS held there by friction and by the suction effect of the pump. A bail or loop d is fastened to the large end so that the strainer may easily be withdrawn when it must be cleaned. The tapering form allows ample space around the strainer, as at e, for the oil after it has passed through the gauze. FIGS. 25 and 26. Suction-pipe strainer and T-fitting used for strainer. A T-fitting may be used to form a simple and inexpen- sive strainer, as shown in Fig. 26. The fitting a is in- serted at a right-angled turn in the oil piping, and the oil, entering through the pipe ft, passes through the strainer c and flows away through the pipe d. The strainer is cylindrical in shape and hangs in the pipe d, being CLEANING OF OIL FUEL 49 supported by a ring e that rests on the upper end of the pipe. When the strainer requires cleaning, the plug/ is removed and the strainer is lifted out by the bail g. The type of strainer shown in Fig. 27 consists of a special casting a that is installed in the oil line and that contains the perforated metal cylinder b by which the actual straining is done. The oil enters at c and flows out at d. The cylinder b may easily be removed FIGS. 27 and 28. Perforated metal strainer and basket strainer for quick cleaning. after the plug e is unscrewed; but, as in the case of the strainers previously shown, the flow of oil must be shut off during the cleaning operation. In order to reduce the period of stoppage to a minimum, it is advisable to have more than one perforated cylinder, so that a clean one can be inserted as soon as the dirty one is removed. Any dirt that passes through the strainer and settles in the bottom of the chamber / may be taken out through the hole closed by the plug g. 50 OIL FUEL FOR STEAM BOILERS Rapidity in cleaning is the chief feature of the basket strainer shown in Fig. 28. The device is installed in a horizontal section of the oil-pipe line, and the oil flows through from a to b, being thus forced to pass through the strainer c, which consists of a metal basket closed at the bottom, perforated on the sides with large holes, and lined with closely fitting wire gauze d. The gauze does the straining and the metal basket simply holds the gauze and prevents it from being torn. If the gauze were not supported and it be- came clogged, the resist- ance it would offer to the passage of the oil might cause it to be torn. The basket has a rim that rests on the seat e and the in- clined ribs / on the rim are locked firmly under the lugs g by giving the basket a part of a turn. The screw- down cover h has a pair of handles i by which it may be unscrewed quickly and lifted off, after which the basket is given a twist to unlock it and is then removed. Packing under the flange of the cover prevents leakage of oil. Sometimes the strainer is located in the same casting with the burner, as in the Koerting type, shown in Fig. 29. The casting 0, of which only a part is shown, contains a pair of burners, each of which is supplied with oil from an FIG. 29. Koerting type of oil strainer. CLEANING OF OIL FUEL 51 oil inlet b through a perforated metal strainer c. The strainer is cylindrical and fits snugly over a cylindrical hollow cage d that has several long slots e in the sides. The cage is screwed into the casting a, being inserted through the opening made by removing the plug /. The oil from the inlet b surrounds the strainer, passes through it and the slots to the interior of the cage, and then flows through the opening g to the chamber h, which leads to the burner. As each strainer serves its own burner and the two are separate, it is possible to shut down one burner and remove its strainer without affecting the operation of the other burner. On restarting after inserting a clean strainer, the burner that remained working will ignite the fresh spray of fuel from the other burner. This arrangement enables the strainers to be cleaned without completely interrupting the operation of the burners. Of course, the same object could be accomplished by installing a pair of strainers of any type, with the valves and piping so arranged that while one was out of service for cleaning or repair, the oil could be sent through the other. A special type of strainer is illustrated in Figs. 30 and 31, which show two different positions of the same device. Corresponding parts in both views are therefore marked with the same reference letters. The important feature of this strainer is that it can be cleaned without taking it apart and without interrupting the flow of oil. Fig. 30 shows a section of the strainer in its normal working posi- tion. The oil flows in at a and is directed downward by the curved passage b into the interior of the conical per- forated strainer c. The passage b is formed in a tapering 52 OIL FUEL FOR STEAM BOILERS plug d that fits closely in the body e of the device, and this plug may be rotated by means of the handle /. The strainer c is held down firmly by the collar g on the lower end of the plug. The oil, after passing through the cone into the surrounding chamber h, flows upward and out at i. The plug is held in place by the pressure of the k FIGS. 30 and 31. Two views of oil strainer arranged for cleaning without removal. plate j bolted to the body e, and packing is inserted at the joint to prevent leakage of oil. The handle / has on its under side a lug that comes against one or the other of the lugs k and I set 90 deg. apart on the plate j. These limit the rotation of the handle, and consequently of the plug, to a quarter- turn. CLEANING OF OIL FUEL 53 When the strainer becomes so dirty as to require clean- ing, the handle /is given a quarter- turn, which brings the plug into the position shown in Fig. 3 1 . There is a second passage m at right angles to the passage b, and when the plug is turned the oil flows directly from the inlet to the outlet, without passing through the strainer. Next, the blow-out valve n at the bottom of the chamber o is opened, after a bucket is set under it. Then the valve p is opened, admitting live steam to the chamber h from the supply pipe q. The steam rushes through the cone in a direction opposite to that in which the oil flows and loosens the dirt, which falls to the bottom of the chamber o. It is then blown out through the valve. By the use of this strainer there is no interruption of the oil supply and unstrained oil is sent to the burners only during the brief time required to blow out the dirt. The handle / is then swung back to its first position and the strainer resumes its normal working. CHAPTER VI PUMPING AND HEATING OF OIL FUEL In every oil-fuel installation there must be pumps to draw the oil from the storage tanks and deliver it to the burners under pressure. The storage tanks are invariably located underground and therefore at a lower level than the burners. The primary purpose of the pumps, conse- quently, is to lift the oil from the tanks. The heavy oils employed for fuel are usually too viscous and sluggish to flow freely of their own accord, and so the pumps fulfil the second object of supplying the oil under pressure. In this way the maximum amount of oil supplied may be regulated to suit the demand, regardless of the condition or quality of the oil. One of the simplest methods of insuring a steady pres- sure of oil at the burners is to use a standpipe, as shown in Fig. 32. The oil is drawn from the storage tank through the suction pipe a by the pump b and is dis- charged through the pipe c into the standpipe d. This is made of 4-in. pipe and is of sufficient height to give the desired pressure of oil at the burners. An overflow pipe e one or two sizes larger than the discharge pipe c is connected near the top and is carried back to the storage tank. The speed of the pump is regulated so that the amount of oil delivered is somewhat in excess of that used by the burners. As a result, the standpipe is 54 PUMPING AND HEATING OF OIL FUEL 55 constantly kept full to the level of the overflow. The excess of oil simply flows back to the storage tank through the pipe e, and as the height of the oil column in the standpipe remains unchanged, the pressure in the oil main /, leading to the burners, remains constant. The FIGS. 32 and 33. Standpipe used to obtain steady oil pressure and safety device for draining standpipe. pipe g is an extension of the standpipe that serves as a trap for water and sediment contained in the oil. These impurities, being heavier than the oil, fall to the bottom of the pipe g and may be blown out at intervals through the pipe h. A vent cock i is added at the top of the 56 OIL FUEL FOR STEAM BOILERS standpipe to allow the release of gas that enters with the oil and collects above the column. The object of maintaining a uniform pressure of oil is to insure proper working of the burners and econon> ical combustion. If the pressure were allowed to vary rapidly, the rate of flow of the oil would be changed and the burners would work erratically. Not only that, but the ratio of air to oil would be altered continually and inefficient combustion would result. There seems to be no fixed value for the pressure at which the oil is delivered to the burners. In an extended series of tests made by the Bureau of Steam Engineering of the United States Navy, the pressure varied from 9 Ib. to 160 Ib. per sq. in., depending on the type of burner, the quality of the oil and the nature of the installation. In the greater number of cases, however, the pressure lies within the limits of 10 Ib. and 50 Ib. per sq. in. The required height of the column of oil in the stand- pipe to produce a desired pressure may easily be calcu- lated, if the specific gravity of the oil is known, by the use of the formula p 2.304 in which H = height of oil column, in feet; P = required oil pressure, in pounds per square inch; G = specific gravity of oil used. The height H of the oil column thus found is the ver- tical distance between the level of the burner orifices and the level of the overflow at the top of the standpipe. PUMPING AND HEATING OF OIL FUEL 57 For example, if a pressure of 15 Ib. per sq. in. is required and the oil has a specific gravity of 0.96, the height of the oil column must be # = 2.304X15-;- 0.96 = 36 ft. With the standpipe arrangement, a considerable quantity is stored at a point above the level of the burner outlets; consequently, if a burner should inad- vertently be left open when out of service, the furnace would be flooded with oil. Because of this, some in- surance companies refuse to insure plants in which oil is fed by gravity. The danger of flooding with oil may be overcome by using a safety device, so that when there is no steam pressure for atomizing, the oil in the standpipe will be rpturned to the storage tank. An arrangement of this kind is shown in Fig. 33. The pipe a, leading from the standpipe b to the burners, has a branch c, in which is fitted a cock d that is opened when the weighted lever e is allowed to fall. This lever is connected by a chain / to the piston rod g of a small piston in the cylinder h. A steam pipe from the boiler is attached at i and a pipe j leads to the oil pump, so that the steam supply to the pump must pass through the cylinder h. The pressure of the steam forces the piston to the upper end of the cylinder and holds it there, thus keeping the cock d closed as long as there is sufficient pressure in the boiler. But when the steam pressure falls below that required to run the pump and atomize the oil, the lever e drops and opens the cock d, thus allowing all the oil in the standpipe to run back into the storage tank. 58 OIL FUEL FOR STEAM BOILERS Another way of maintaining a uniform pressure of oil is to employ a duplex feed-pump and to put on the dis- charge pipe a relief valve set to open when the desired pressure is exceeded. A side view of such an apparatus is shown in Fig. 34 in connection with a longitudinal FIG. 34. Oil-pressure pump with heater. section of an oil heater. The duplex pump a has a suc- tion pipe b that leads direct from the storage tank. The discharge from both sides of the pump is led through the pipe c to the heater d. The air chamber e and the relief valve / are in communication with the discharge pipe PUMPING AND HEATING OF OIL FUEL 59 through the croSs g. The air chamber cushions the in- termittent discharges of oil and prevents shocks. The relief valve, which is merely a spring-loaded valve, is set to the pressure desired at the oil burners. As soon as the pump supplies too much oil, and this pressure is exceeded, the valve rises and the excess of oil is returned to the storage tank by a pipe connected at h. Two small pipes lead from the tops of the discharge chambers to the overflow pipe and are fitted with valves i to allow any gas collecting in those chambers to be removed. The speed of the pump is regulated automatically by a governor j on the steam line k to the pump. The governor consists of a flexible diaphragm directly con- nected to a throttle valve in the steam line. One side of the diaphragm is acted on by the pressure of the oil, which is transmitted through the small pipe /, and on the other side by a spring that can be adjusted as desired. When the oil pressure rises too high, the pressure of oil on the diaphragm overcomes the spring pressure and closes the throttle valve somewhat. This reduces the steam supply to the pump and lessens its speed. The oil pressure then decreases and the spring forces the diaphragm back again, opening the valve and admitting more steam. By adjusting the tension of the spring, a very uniform speed of the pump may be obtained. The exhaust from the steam ends of the pump is led through the pipe m to the heater, where it is used to heat the oil. A pressure gage is attached at n to show the pressure of the oil on the discharge side of the pump. The object of the heater is to increase the temperature of the oil and thereby decrease its viscosity. The heavy 60 OIL FUEL FOR STEAM BOILERS crude oils are very sluggish, and in this condition they are not easily atomized. If their temperature is low, their rate of flow is still further reduced. Therefore, a heater is inserted in the oil system to render the oil more fluid and easy to break up into a spray. In the illustration the heater is placed between the discharge of the pump and the burners. It consists of a cylindrical outer shell d into which the exhaust steam is conducted by the pipe m. The head o of the heater has two compartments, and into it are screwed two sets of tubes. The larger tubes are closed at one end and fit over the smaller ones, which are open at both ends. The oil from the pump flows into the inner compartment in the head, thence into the larger tubes, around the smaller ones, and finally back through the inside tubes to the outer compartment, from which it passes to the burners through the strainer p. t The water and uncondensed steam are drawn out of the shell at q. The form of heater shown in Fig. 34 is efficient, be- cause the oil is divided into a number of thin films that pass between the outer and inner tubes while the heat is transmitted through the outer tubes. A much simpler form, and one that is less expensive, is shown in Fig. 35. It consists of two cast-iron cylinders a and b, one inside the other. The narrow space c between the inner and outer shells is filled with the oil to be heated, which flows in at d and out at e. Steam is led into the inside cylinder through a pipe/, and the water and waste steam are removed atg. This form is not extremely efficient, because the cast-iron walls are thick and the oil is not divided into very thin sheets. PUMPING AND HEATING OF OIL FUEL 61 Another way of arranging the coils in the heater is shown in Fig. 36. The oil flows into the heater shell a through the pipe b and surrounds the pipe coils c, which are made up of straight pipes joined by return bends. Steam is admitted into the top coil through the connec- tion at d, and the water is drained out at e. The oil flows through the heater from b to/. The heater shown in Fig. 36 is more efficient than that in Fig. 35, but the one shown in Fig. 37 gives better heating than either, because the coil a that carries the steam has a greater amount of heating surface exposed to the oil. It is made in a continuous coil that fits closely inside the shell b. Steam enters at c and the condensation escapes at d. The oil enters at e and is discharged at/. The corrugated film heater shown in Fig. 38 is designed with a view to obtaining a very high efficiency. It consists of two spirally corrugated copper tubes a and b. These fit very closely, leaving only a thin space between them, and oil is led into this space through the inlet c. It flows upward between the two corrugated tubes and passes out at d. Steam is admitted through the pipe e and flows directly to the interior / of the tube b. At the same time a branch pipe g admits steam to the cham- FIGS. 35, 36 and 37. Forms of oil heaters. 62 OH, FUEL FOR STEAM BOILERS FIG. 38. Corrugated coun- terflow oil heater. her h surrounding the outer tube and formed by the in- closing cylindrical shell i. The oil film is thus heated by the transmission of heat inward through the outer tube and outward through the inner tube. The steam and oil flow in opposite directions, so that the warmest oil meets the steam entering the heater. This counter-current adds to the efficiency of operation. The drain pipe j serves to remove all condensation from the steam chambers, and the shell is pro- tected by a non-conducting covering k that reduces the loss of heat to the surrounding air. The tubes may be removed for cleaning; or the plugs / and m may be taken out and live steam may be blown through between the tubes. This will quickly and thoroughly clean out all sediment and tarry de- posits. As the heater is placed be- tween the pump and the burners, it is subjected to the full pressure of the oil, and it PUMPING AND HEATING OF OIL FUEL 63 should be tested to see that it is capable of withstand- ing the maximum pressure that may be put upon it. Some makers guarantee their heaters for a pressure of 200 Ib. per sq. in., which is well above the point that will be reached in ordinary work. The joints of the steam coils or of the tubes fitted in the head of the heater should be absolutely tight, so that no water can leak into the oil supply. Also, the pipes and tubes should be arranged so that they can expand and contract freely, without springing joints open and causing leaks. Heating of the oil between the pump and the burners is done to make atomization easier. In some cases, however, it is necessary to heat the oil in the storage tank so that it will flow readily to the pump. This is particularly true of installations in cold climates. There are crude oils that at temperatures of from 30 to 40 deg. Fahr. become so sluggish that they cannot be drawn to the pump, and they must be heated sufficiently to cause them to flow. It is neither necessary nor advisable to heat the entire bulk of oil in the storage tank. A steam coil can be located around the lower end of the suction pipe. This will heat the oil in the immediate neighbor- hood of the entrance to the pipe and enable it to be drawn up. In any case, the heating must not be carried to a point at which the oil will begin to decompose, that is, break up into its constituent hydrocarbons. The tem- perature at which decomposition occurs varies for oils of different qualities and from different localities, but usually it does not exceed 180 deg. Fahr. The temperature of the oil may be observed by a thermometer placed in a mercury cup in the oil line 64 OIL FUEL FOR STEAM BOILERS leading to the burners, as shown in Fig. 39. The pipe a conveys the oil to the burners, and into it is screwed a fitting b that carries the ther- mometer tube c and the scale d. At the bottom is a long cup e filled with mercury, in which the lower end of the tube c rests. The heat of the oil flowing through the pipe is thus transmitted to the tube and the temperature is regis- tered on the scale. If the plant is of such character that even a brief shutdown would entail great loss or inconvenience, the oil pump should be duplicated, so that one set of pumps will be in reserve in case the other set fails. This can be arranged by FIG. 39. Thermom- using a system of cross-overs in eter for finding temper- the p i p i n g. Also, it is an excellent 1 in pipe ' plan to have the entire system of oil pipes connected so that live steam may be blown through it to clean it of dirt and tarry matter ad- hering to it. CHAPTER VII OIL-BURNING FURNACES The arrangement of the furnace of a boiler that is to be fired with oil fuel varies according to the type of boiler and the location of the burner; also, it makes con- siderable difference whether the boiler setting is orig- inally planned for the use of oil fuel or whether it is altered from the coal-burning type. Details of the arrangements will differ because of the manner in which the air supply is allowed to enter. In view of these facts, it would manifestly be impossible to illustrate all of the many styles of furnaces, but several of them will be given to show their distinctive features. A form of oil-burning furnace for a return- tubular boiler is shown in section and in plan in Fig. 40. There is a single fan-tailed burner a installed in the center of the fire-door. It projects well through the front wall and is surrounded by a short firebrick sleeve or arch b. The grates c are retained, and on them is laid a closely fitted layer d of firebrick that prevents air from rising through the grates except at the extreme rear end. On this layer of brick are placed a number of blocks that support another layer e, and this top layer forms a con- tinuous floor from the arch b to the top of the bridge wall /. The air supply is admitted through the door g to the space beneath the grates, whence it flows to the 5 65 66 OIL FUEL FOR STEAM BOILERS rear, up through the grates, forward between the fire- brick layers d and e, and then past the burner into the FIG. 40. Return-tubular boiler with slot oil burner. combustion chamber, as indicated by the small arrows. The arch b and the layer e of firebrick are kept at the point of incandescence by the flame from the burner, OIL-BURNING FURNACES 67 and the air in flowing along in contact with the hot brickwork becomes heated to a high temperature be- fore it reaches the tip of the burner. This preheating of the air supply adds to the efficiency of the combus- tion. All joints or openings around the burner are care- fully closed, so that no cold air can leak into the furnace. The entire air supply must therefore pass under the heated slabs e. FIG. 41. Return-tubular boiler with Kirk wood oil burner. A return-tubular boiler arranged to use a Kirkwood burner is shown in section in Fig. 41. In this case the grate bars are retained but are covered with a closely laid floor a of firebrick that has a single slot b for the admis- sion of air to the furnace from the ashpit. The burner c is set in firebrick in the fire-door opening and the slot it is just in front of it. The air on meeting the oil spray unites with it and the flames are thrown toward the rear, where they strike the firebrick pier d built on the grates. 68 OIL FUEL FOR STEAM BOILERS This pier is not solid, but forms a sort of checkerwork by which the burning gases are thoroughly diffused and mixed so as to prevent the possibility of incomplete combustion, beyond the bridge wall the floor e is brought level with the top of the bridge wall, so that the hot products of combustion are kept in close contact with the boiler shell. With this arrangement the FIG. 42. Return-tubular boiler with Best oil burner. flames are directed against the firebrick on the grates and that forming the pier, but not against the boiler shell. The arrangement suggested for a return-tubular boiler fitted with a Best burner is shown in Fig. 42. The bridge wall is torn down until its top is level with the surface of the grates. On this surface firebrick is laid flat, with air spaces about 1/2 in. wide in the part on the grates. The burner is inserted in an opening in the front wall of the setting, on the center line of the furnace. Its tip is OIL-BURNING FURNACES 69 about 8 in. above the firebrick on the grates and about 2 in. inside the front wall. The flame is thrown out parallel to the grate surface and to the full width of the furnace. The air supply passes up through the openings in the brickwork covering the grates and mixes with the vaporized oil at all parts of the furnace. FIG. 43. Babcock & Wilcox boiler with burner at front. The furnace arrangement shown in Fig. 43 is for a Babcock & Wilcox water-tube boiler. The grates are covered with a single layer of firebrick a laid close to- gether except at the front, where a series of openings b are left. The burner c, which throws a fan-shaped flame, projects through the fire-door and its tip is just inside the front wall. Thus the flame from the burner is directly 70 OIL FUEL FOR STEAM BOILERS above the openings b in the brickwork. The air supply in this case is not preheated to any great extent, because it flows into the ashpit through the door d and passes immediately to the combustion chamber through the openings in the grates. The slot in the end of the burner is horizontal, and the sheet of flame thus produced is practically parallel to the surface of the grates. The arrangement shown in Fig. 44 is also for a Babcock & Wilcox boiler. It differs markedly from that pre- viously illustrated in that the burners are located at the back of the furnace, against the bridge wall, instead of at the front. The grates are removed completely and a firebrick floor a is built to cover the entire area from the front wall to the bridge wall. As may be seen in the plan view, this floor is carried by the side walls of the furnace and by the three sets of bearing bars b that rest on the side walls and on two longitudinal piers. The burners c are set in recesses in the front face of the bridge wall, just above the level of the floor, and are of the Hammel type. They direct fan-shaped flames forward over the flat floor a. The three passages formed beneath the bearing bars contain the oil and steam pipes leading to the burners and also serve as air ducts by which the air supply is led to the burners. Inasmuch as the floor a is kept incandescent, the air flowing along beneath it is heated hignly before being allowed to flow upward past the burner into the furnace. The three transverse rows of firebrick just in front of the burners are not laid end to end, but small spaces are left, in order that some of the air may rise directly through these openings and mingle with the oil vapor OIL-BURNING FURNACES 71 above the floor. This is done to prevent carbon from being deposited on the brickwork just below the tips of the burners. To the remainder of the floor a a coating of FIG. 44. Babcock & Wilcox boiler with burner at bridge wall. fireclay wash is given to fill up all joints and prevent air from flowing up through except as provided by the slots. The passage for each burner is separate from the others, 72 OIL FUEL FOR STEAM BOILERS and the air supply to each burner can therefore be regu- lated by the ashpit door, independently of the others. The object to be gained by placing the burners at the bridge wall and directing the flames forward is a better utilization of the combustion space. When the air and the gasified fuel unite and burn, the heat generated causes the temperature of the gases to rise, and they ex- pand in volume as a consequence. By having them projected toward the front of the furnace, where the area of vertical cross-section is greater because of the upward slant of the tubes, the increased volume of the gases is accommodated by the increased space and the rate of flow of the products of combustion is thus rendered more nearly uniform. It will be observed that the front wall of the furnace is protected from the heat of the flames by a firebrick lining. A form of furnace construction used in connection with a Heine water- tube boiler is shown in Fig. 45. The bridge wall is torn out completely and the whole floor is brought to the level of the bottom of the ashpit. On this surface two layers of firebrick are placed, as at a and b, separated by bricks c laid on edge and so supported as to leave an air passage d underneath the lower layer. The air supply enters through the ashpit doors, flows to the back end of the boiler through the passage d, then for- ward between the layers a and b, and escapes, highly heated, into the furnace just beneath the burner e. The burner is of the slot type and throws a fan-shaped flame that spreads to the sides of the furnace. The inclination of the burner is such that the flame is about parallel to the rows of tubes. OIL-BURNING FURNACES 73 The Stirling water- tube boiler arranged for burning oil with a Best burner is shown in section in Fig. 46. The grates are removed and the sloping floor of the furnace is covered with firebrick laid flat in rows 9 in. from center to center. On top of this firebricks are laid on edge and 9 in. from center to center. The top layer of firebrick is laid flat, with i/4-in. air spaces; thus the air supply is ad- FIG. 45. Heine boiler with preheating of air supply. mitted over the whole bottom of the furnace after being heated by contact with the brickwork. The burner a is inserted through the front wall about 8 in. above the grate and parallel thereto, the tip extending into the furnace about 2 in. Over the tip is constructed a firebrick arch b forming an igniting chamber. The arch is brought to in- candescence by the heat of the flame, and in case the ac- tion of the burner is momentarily interrupted, as by a slug 74 OIL FUEL FOR STEAM BOILERS of water carried over with the oil, the spray will be reig- nited by the hot brickwork when the burner continues its operation. The bridge wall is constructed with a fire- brick facing and a flared top, so that the flames striking FIG. 46. Stirling boiler with auxiliary air duct. into the pocket thus formed are turned back on them- selves. This is done to prevent the flames from striking directly against the tubes. An auxiliary air "duct c is formed in the bridge wall. It connects with the passages OIL-BURNING FURNACES 75 beneath the furnace floor and admits air to the upper part of the flame when the fires are being forced. At such a time there is a tendency to form carbon monoxide at the top of the flame, and the air admitted through the duct c supplies the oxygen required to convert this to dioxide. The arch d is retained and serves to deflect the gases to- ward the front bank of tubes. If desired, the burner can be put at the rear end of the furnace, as in Fig. 47. The arrangement in this case is FIG. 47. Stirling boiler with burner at back of furnace. like that for the Babcock & Wilcox boiler fired from the rear. The air ducts are formed beneath the floor, there being one for each burner, and the burners are protected somewhat by being set in recesses in the bridge wall. The arch over the furnace is omitted, and the front wall is heavily protected with firebrick. One way of altering the usual furnace construction of the Stirling boiler so as to adapt it to the use of oil fuel is shown in Fig. 48. The rear half of the grate is removed and a brick pier a is substituted. A firebrick floor b is 76 OIL FUEL FOR STEAM BOILERS built over the top of the pier and the remainder of the grate surface, and air spaces from 1/4 in. to 1/2 in. wide are left between the bricks on the grates. The arch usually found inside the furnace, above the fire-door, is removed entirely, because the burner c is installed at about the height of the top of this arch. The burner is of the slot type and is inclined so as to project the flames downward into the angle or pocket formed by the firebrick floor b $$%$$$'/- , FIG. 48. Stirling boiler with burner set high at front. and the bridge wall d. The flames thus are given a re- bound before they enter the first pass among the tubes. The air enters through the space below the grates and flows up through the space in the brickwork into the furnace. From an examination of the settings that have thus far been described the following conclusions may be drawn: The furnace of an oil-fired boiler, particularly in those parts against which the flames strike, must be lined with a good quality of firebrick so as to protect the outer walls and the boiler and to resist the high temperatures pro- OIL-BURNING FURNACES 77 duced. There should be a combustion chamber of ample size, in which the gases and the air may meet and commingle thoroughly, so that combustion may be com- plete before the resulting products of combustion are brought against the comparatively cool boiler surfaces. If combustion is not completed before the gases strike the metal parts of the boiler, the consequent chilling will pre- vent further combustion and cause smoke to be formed. If it seems likely that the flames will strike the boiler, baffles or arches should be set up to prevent direct con- tact. This is particularly necessary in the case of the blow-off pipe of a return-tubular boiler, when the blow- off is carried straight down through the gas passage at the rear end of the boiler. It is advisable to preheat the air supply before admitting it to the furnace. Oil fuel is used as an auxiliary to coal in some cases. In one electric power station oil burners are installed with the idea of helping out on peak loads and for the purpose of banking the boilers. The arrangement of the furnace of one of the boilers is shown in Fig. 49. At the front there are the usual grates a on which coal fires are carried for the normal operation of the boilers. Behind the bridge wall b the burners are installed, as shown at c. The combustion chamber for the oil is formed by the baffle d, the floor e, the wall /, and the side walls of the setting. After combustion, the hot gases from the oil burner pass forward over the bridge wall and travel along with the gases rising from the grates. The air supply to each burner is admitted through the passage g that contains the steam and oil pipes. 78 OIL FUEL FOR STEAM BOILERS By this arrangement it is possible to fire the boiler at both ends, using coal and oil at the same time. The result is the same as would be obtained by increasing the rate of combustion with coal alone; that is, the steaming FIG. 49. Coal-burning boiler with oil used for banking and peak loads. capacity of the boiler is greatly increased. Of course, the oil burners are used to supply the additional steam demanded by a peak load. Under normal load the coal fires only are used; but as soon as a sudden increase of OIL-BURNING FURNACES 79 load comes on, the oil burners are put in action, and in a very short time the capacity is equal to the increased demand. This rapidity of response to sudden changes of load forms one of the strongest advantages of oil fuel. By adopting the scheme here outlined the boiler horse- power may be increased two-thirds, without increasing the number of boilers. During periods when the load is light oil is used to bank the boilers. There are four burners to each boiler, and one of these is connected so that it can be operated independently of the others when the boilers are to be b anked. At this particular plant the oil costs more per heat unit than the coal; yet it is found more economical to use oil for banking, because the combustion is more efficient with the oil than with the slow coal fire. CHAPTER VIII INSTALLATION or OIL BURNERS When installing oil burners the piping should be pro- vided with unions near the burners, to facilitate the work of taking them down when they must be repaired. This point is very clearly illustrated in Fig. 50, which shows the piping for a Gem burner a. The oil flows to the burner through the valve b and the connecting pipes, FIG. 50. Piping for Gem oil burner. and the steam for atomizing is admitted through the valve c and the branch to which it is fitted. The unions d and e enable the burner to be detached from the sys- tem very easily and quickly. The plug/, when removed, allows the connection to be cleaned out. The valve b is closed, and a cap is placed over the end of the burner 80 INSTALLATION OF OIL BURNERS 81 so that the steam will back up in the burner and blow back through the oil connection, cleaning it. The pipe connections for a Best burner are shown in Fig. 51 in a diagrammatic way. The burner is located at a and the oil and steam lines are attached on opposite sides. There are unions b and c to facilitate the re- moval of the burner and stop valves d and e for oil and steam respectively. In addition, there is an oil-regulat- ing cock / between the stop valve d and the burner, to enable the flow of oil to be regulated with great precision. FIG. 51. Piping and oil-regulating cock for Best burner. An end view and a vertical section of the regulating cock are shown in Fig. 52. It consists of a conical plug a that fits a conical seat in the body b of the cock and that is held snugly in place by the upward pressure of the spring c. The spring is kept in position by the ex- tension d on the bottom of the plug and by the cap e. The latter can be unscrewed so as to allow the plug and the spring to be removed from .the body of the cock. The oil flows through a triangular opening / in the plug. The opening is made triangular in form so as to insure close regulation of the oil. The opening g in the body of the cock on the outlet side of the plug is rectangular in shape and the outline of this opening is dotted around the opening in the plug. By turning the plug slowly, 82 OIL FUEL FOR STEAM BOILERS the amount by which the triangular opening overlaps the edge of the rectangular outlet can be varied very gradually, thus giving close adjustment of the oil supply to the burner. The packing h around the stem of the plug is compressed under the screw cap i and prevents leakage of oil around the stem. The cock is opened fully or closed completely by giving the handle j a quarter-turn. There is a lug k on the handle, and it comes against a stop / cast on the body of FIG. 52. Oil-regulating cock. the cock when the plug is turned to the closed position- Also, there is a knurled screw m in a bracket n fastened to the body of the cock. When the plug is turned to open the cock, the lug o comes against the point of the screw and the handle can be turned no farther. The screw can be adjusted to give any desired amount of opening of the cock, and the cock can be opened and set instantly to this position. The bracket n is hinged, and if the cock is to be opened to its full extent, the bracket is INSTALLATION OF OIL BURNERS 83 simply swung upward and backward, taking the stop screw m out of the way of the lug o. A form of valve for regulating the flow of oil with extreme nicety is shown partly in section in Fig. 53. The inner end of the valve stem carries a hollow cylinder a that fits snugly in a circular hole in the seat b. In the side of the cylinder is cut a triangular opening c, so that, when the stem is screwed out, the point of the triangular opening rises above the face d of the seat and allows the oil to pass through. The higher the stem is drawn, the greater is the amount of opening. Owing to the penetrative nature of oil fuel, the piping should be carefully put together and all joints should be tight. In making up the connections the pipe threads should be perfect and should be cut in oil, so as to be smooth and free from cracks. If the threaded end is made too long the pipe will screw into the fitting too easily and leakage may result. It is better to cut the threads so that it will require a considerable force on the pipe wrench to put the pipes together, as this will be more apt to give tight joints. The pipes leading to and from the storage tank are usually permanent and are not likely to be taken apart, so the joints may be made up with a cement of litharge and glycerine to insure tightness. If it is possible to do so, elbows should be avoided in installing the oil piping, as the foreign matter in the oil will collect at these fittings and eventually clog the pipes. It is preferable to em- ploy bends of long radius instead of elbows. It will be found advisable to arrange the piping in such a way that the oil can be turned off and live steam sent through the 84 OIL FUEL FOR STEAM BOILERS oil lines to loosen the deposits of asphalt or tarry matter and blow them out of the pipes. The proportions of the furnace and the style of oil burner to be used will govern the number of burners that must be supplied in a given installation. To illustrate, if a furnace is long and narrow, a single burner giving a long, conical flame will be sufficient; but if the furnace is short and narrow, a single fan-tailed burner will give FIGS. 53 and 54. Oil-regulating valve and arrangement for finding amount of steam used by burners. the desired results. In case the furnace is wide, two or more burners may have to be installed. Some makes of burners are so constructed that they can be made to throw a long, narrow flame or a short, wide one. It may be said that, as a rule, one burner for each 6 ft. or 7 ft. of width of furnace will be required. The capacity of the burner must also be taken into account. One INSTALLATION OF OIL BURNERS 85 manufacturer guarantees a capacity of from 5 to 350 boiler-hp. with a single size and type of burner. Another rates his burners at from 75 to 100 boiler-hp. each. Still others manufacture different sizes of burners of the same type, each size corresponding to a certain capacity. The location of the burner is a matter that cannot well be considered apart from the furnace arrangement. In the case of the return-tubular boiler, it is common to find a burner in the center of each fire-door; but if sufficient capacity can be obtained by the use of a single burner it may be inserted through an opening between the fire- doors, cut through the boiler front and the front wall of the furnace. Whatever the location of the burner or burners, the furnace space should be utilized as far as possible. This is one reason why it is found advisable in some in- stances to locate the burners at the rear end of the fur- nace in inclined-tube water-tube boilers. The importance of supplying dry steam for atomizing cannot be overestimated. A steady white flame is pro- duced if the steam is dry; but if water is carried along with the steam the burner sputters and combustion is re- tarded. The presence of water in the steam may be due to priming of the boiler or to condensation in the pipe line leading to the burner. One way of avoiding such mois- ture is to superheat the steam, which can be done very easily by running the steam pipe from the boiler to the burner through the furnace or the boiler breeching. Such an arrangement, however, is not always convenient. It is advisable, then, to put a steam separator on the steam line near the burner, in which the steam will be freed of its moisture. This is accomplished by an 86 OIL FUEL FOR STEAM BOILERS abrupt change in the direction of flow of the steam, by centrifugal force set up during a whirling motion caused by spiral guides or vanes, or by the separating action of baffle plates. The moisture collecting in the bottom of the separator may be removed through a drip or by an automatic trap. The economy of a burner is measured by the amount of steam it uses to atomize a pound of oil. There are sev- eral ways of determining this, but the simplest way is to condense the steam that issues from the burner in a given time, weigh it, and compare it with the amount of oil used in an equal period. A tank of cold water is set on scales and weighed accurately. Then the burner, with the same piping and connections as are used in ordinary operation, is submerged in the tank. The steam valve is then opened to the same extent as during the normal working of the burner and is left open for a definite time, say, a quarter of an hour. The steam escaping from the burner will condense in the water in the tank, increasing the amount of water and the temperature. At the end of the given time the burner is removed and the tank and its contents are weighed again. The increase of weight represents the amount of steam used in the observed time. The accuracy of the test may be checked by taking the initial and final temperatures of the water in the tank and calculating how much steam at the usual working pressure would be required to produce the observed rise of temperature in the known weight of water. This result should agree fairly well with the in- crease of weight of the water in the tank. The amount of oil used in the same length of time can be calculated from INSTALLATION OF OIL BURNERS 87 the readings of the telltale on the tank, or from the read- ings of the meter on the oil line, if there is one installed. This method is very simple and the apparatus is com- monly available; but there is the disadvantage that during the test the burner does not operate under the same condi- tions as in service. When the burner is atomizing oil the issuing steam meets the resistance of the viscous oil in the mixing chamber or at the orifice, whereas in the test- ing tank the resistance is due to the water. These resist- ances differ more or less, and the greater the difference the greater the error in basing the economy of the bur- ner on the results of the test. It is probable that the water will offer less resistance than the oil, so that the test will show the burner less economical in steam than it really is. A more nearly accurate test may be made by using the apparatus shown in Fig. 54. The vertical pipe a leads to the burners and conveys the steam for atomizing. Be- tween the two flanges b on this pipe is a thin plate in the center of which a hole 3/8 in. in diameter is drilled. The steam flows through this orifice in the plate on its way to the burners. On opposite sides of the flanges the pipes c and d are connected, leading to the steam-pressure gages e and/. The gages register the steam pressures on opposite sides of the orifice in the plate, and these pressures vary according to the amount of opening of the steam valve, and hence according to the rate of flow of steam. A series of tests are made with different openings of the steam-regulating valve, observing the pressures on the gages and catching and condensing the steam in a weighing tank filled with cold water. In this way a 88 OIL FUEL FOR STEAM BOILERS table is made up showing the amount of steam flowing through the plate in a given time for each different com- bination of pressures. After such a table is once com- piled the steam consumption of the burners at any time may be found quickly by observing the pressures regis- tered by the gages and then noting the corresponding steam rate in the table. CHAPTER IX STORAGE OF OIL FUEL The method of storing the supply of oil for an oil- burning boiler plant is a matter to which careful con- sideration should be given. The objects that should be kept in mind while planning the storage system are safety and capacity. For the average boiler plant of small or medium size the oil supply is usually stored in cylindrical steel tanks like that shown in Fig. 55. The tank is built up of steel plates, has dished ends and is usually buried in the ground at such a level that its top is below the level of the tips of the burners. The object of this arrangement is to prevent flooding of the furnaces or of the boiler room with oil in case a burner valve is accidentally left open; for with the tanks below the level of the burners the oil will flow back by gravity if a valve is left open at the burners. As the tank is usually covered with earth, it should have a good coat of tar or some protective paint to enable it to resist the effects of dampness. The common sizes of oil tanks for boiler installations are 8 ft. in diameter by 28 ft. long and 9 ft. in diameter by 33 ft. long. The former has a capacity of about 10,500 U. S. gallons and the latter a capacity of approxi- mately 15,700 U. S. gallons. In either case, a good 89 90 OIL FUEL FOR STEAM BOILERS quality of steel plate 5/16 in. thick should be used, and the heads should be made of 3/8-in. plate. There should be no openings in the bottom, sides or ends of the storage tank. Such openings as are required should be at the top. The largest opening required is that for the manhole, as at a, Fig. 55, and this should be fitted with a screw-down cover. There must be a flange b for connecting the suction pipe c that leads to the pump, and another d for the overflow pipe e, leading back from the standpipe or from the pressure pumps. d b FIG. 55. Oil-storage tank with connections. The filling pipe /, by which the oil is run into the tank from the tank car, may be attached by a T to the over- flow pipe and both connected with the tank through the nipple g and the flange d. Again, there must be a flange h to which a ventilating pipe can be connected. If the oil around the end of the suction pipe must be heated, so that it will flow readily to the pumps, then it will be necessary to add two more flanges for the pipes that convey the live steam and carry off the condensation. The work of designing and constructing the tank STORAGE OF OIL FUEL 91 should be put in the hands of a manufacturer familiar with the requirements of steam-boiler construction, be- cause the tank must be absolutely oil-tight. All petro- leum oils are very penetrative in their character, and if there is any suspicion of looseness at the seams or around the rivets, the oil will find its way through. For this reason the rivet holes should be drilled, or else punched and reamed, and the seams should be thoroughly calked. The capacity of the tank or tanks installed depends on the size of the plant and the frequency with which shipments of fuel may be delivered. If the plant lies fairly close to the oil fields, so that there is little delay in obtaining fresh shipments, it is unnecessary to carry a large supply in storage, and the tank or tanks may be made of such size as to hold oil enough to run the plant for a week. A tank 9 ft. in diameter and 33 ft. in length will contain one week's supply of oil for a plant of 500 boiler-hp. operating ten hours a day at an average effi- ciency of 75 per cent. If the plant is so located that shipments of oil may be delayed and cannot be relied on to arrive with regularity, it may be necessary to provide storage capacity for a month or more of continuous working, so as to make reasonable provision against the possibility of a complete shut-down. The location of the storage tanks must be carefully considered, in order to conform to the requirements of the underwriters. For example, if the tank is placed above the ground level, it must be situated at least 200 ft. from inflammable property, so as to minimize the danger to that property in case the oil should catch fire. 92 OIL FUEL FOR STEAM BOILERS In the case of a plant located in a town or a city, this requirement would be hard to meet, owing either to the difficulty of finding available storage space or to the high cost of such space. On this account, storage tanks are usually placed underground. The require- ments for an underground tank are that it must be at least 30 ft. from the nearest building and that it must be at least 2 ft. below the surface of the ground. In either form of installation the top of the tank must be below the level of the lowest pipe in the oil system, so that the plant cannot be flooded with oil. For ease in filling, the storage tank should be near the railway siding on which the tank cars are run, and at a lower level, so that the oil may be run from the tank cars into the storage tank'by gravity. This is the least expensive method of making the transfer. If the tank is not at a low enough level to allow this method of filling to be used, the oil may be pumped out of the tank car into the tank, the suction pipe extending into the tank car and the discharge pipe being connected to the filling pipe of the storage tank. Air pressure has been used as a substitute for pumping in some instances. The method by which it is employed is shown in Fig. 56, in which a represents the central part of the tank car. Two pipes b and c are connected to the dome d. The former is short and extends only a little distance into the dome. The other is long enough to reach to the bottom of the tank car and is connected to the filling pipe of the storage tank. All ether outlets from the tank car are kept closed, and compressed air is admitted through the pipe b. The pressure of the air STORAGE OF OIL FUEL 93 VOTS uo u crv- FIGS. 56, 57, and 58. Arrangement for emptying tank car; simple form of vent pipe; vent pipe and telltale. 94 OIL FUEL FOR STEAM BOILERS on the surface of the oil forces the oil up the pipe c and over into the storage tank. It is stated that tank cars are tested under a pressure of 40 Ib. per sq. in., but it is wise to use a compressed-air pressure of not more than 10 Ib. per sq. in. A pressure of 10 Ib. per sq. in. will balance an oil column approxi- mately 24 ft. high, and it is doubtful whether the storage tank will ever exceed this height above the bottom of the tank car. The use of air pressure in this way is strongly condemned by some of the tank-car lines, and placards are attached to their cars warning users not to employ this method of emptying the cars. Of course, compressed air is not available in a great many plants, as most of them use steam to atomize the oil. Steam pressure would force the oil out of the tank car just as well as air pressure, but the steam would con- dense, and the water would settle to the bottom of the car and be forced out with the oil into the storage tank. As a result, steam is not used in this way. While the storage tank is being filled with oil, the air originally contained in it is being displaced and driven out. To afford a means of escape for this air, a vent pipe is attached to one of the flanges at the top of the tank. This pipe serves another purpose, also, in that it allows the escape of gases rising from the oil. At the ordinary temperatures at which the oil is kept in the storage tanks, there is a certain amount of evaporation, the lighter and more volatile constituents changing to the gaseous form. The vent pipe, open to the outer air, affords easy escape for these gases and prevents the rise of pressure that would result if there were no outlet. STORAGE OF OIL FUEL 95 One of the simplest forms of vent pipe is shown in Fig. 57. It consists of a straight piece of pipe a about 3 ft. long, screwed into the flange b on top of the tank c. On its upper end a return bend d is screwed, and over the opening e, which faces downward, a piece of wire gauze / is firmly bound. The downward curve of the return bend prevents any sparks from dropping into the vent pipe and igniting the gases arising from the oil, and the gauze prevents the flame from traveling back into the tank even if the gases are ignited at the opening e, outside the gauze. Another form of vent pipe is shown in Fig. 58. It is a straight pipe a, somewhat longer than the diameter of the storage tank b, and is screwed into a flange at the top of the tank. At the top of the pipe is a cap c that has a number of openings in its under side. These openings allow the escape of air or gases from the tank and are covered with wire gauze to prevent a flare-back. This particular form of vent pipe serves also as a tell- tale, that is, as an indicator to show the amount of oil in t the tank at any specified time. Inside the cap c is a small pulley over which a wire passes. To one end of the wire is attached a float d, which falls or rises as the level of the oil in the tank changes. To the other end of the wire is attached a pointer , and as the float falls or rises the pointer rises or falls an equal distance. On the vent pipe, just behind the pointer, a scale is marked, divided into feet and inches, the total length of the scale being equal to the inside diameter of the tank. The position of the pointer then indicates the depth of oil in the tank, in feet and inches. A table may easily be compiled show- 96 OIL FUEL FOR STEAM BOILERS ing the amount of oil in the tank at each inch of depth. Then, when the depth of oil is noted on the telltale, the amount of oil corresponding to that depth can quickly be found. If compressed air is used as the atomizing agent in the plant, or is otherwise available, the form of indicator illustrated in Fig. 59 may be used. A glass tube a of \ . Jc i 1 FIG. 59. Indicator for oil- storage tank. U, shape is fastened to a board b that in turn is fastened to the wall or to some other convenient support. The tube is partly filled with mercury and the leg c is left open to the air. The other leg d is connected by a rubber tube to a pipe e that is screwed into the T-fitting /. Two other pipes are connected to the T. That at g leads to the compressed-air system and is fitted with a valve h. The other pipe I leads to the bottom of the oil- STORAGE OF OIL FUEL 97 storage tank j. All of this piping may be of i/8-in. wrought-iron pipe. The action of the indicator is simple. The valve h is opened very slightly, so that air leaks past it into the leg d of the U-tube and into the pipe i. As the air continues to flow into the pipe i, the pressure therein grows greater, and this pressure acts on the mercury and on the oil with equal intensity. The result is that the oil in the pipe k is forced down until finally it is all driven out at the lower end, and air escapes into the tank. At the same time the increasing pressure of the air forces the mercury down in the leg d of the tube and up in the leg c. Behind the leg d is a graduated scale /, and the position of the top of the mercury column in the leg d is read on the scale. The deeper the oil in the storage tank, the greater is the pressure required to force the oil down out of the pipe k, and consequently the lower will the mercury be forced in the leg d. Every reading of the mercury level on the scale I therefore corresponds to a certain depth of oil in the storage tank, and hence to a certain definite quantity of oil. A table is compiled showing the amount of oil in the tank corresponding to each division on the scale. By comparing the reading at any time with the table the corresponding quantity of oil can be found. The ac- curacy of this device is based on the assumption that practically the same grade of oil is used continuously. If the oil varies in specific gravity from time to time, the scale will not correctly indicate the amount of oil in the tank. With proper care there is little danger that the oil in the storage tank will catch fire; however, in some installa- 7 98 OIL FUEL FOR STEAM BOILERS tions a steam pipe is connected to the top of the storage tank, so that live steam may be run direct from the boiler into the tank to smother any fire that may start. Reference has been made to tables from which the quantity of oil on hand can be determined when the depth of oil in the tank is known. Two such tables are given herewith. Table III shows the amount of oil at each inch of depth in a cylindrical tank 8 ft. in diameter and 28 ft. long, lying in a horizontal position. Table IV shows the amount of oil at each inch of depth in a similar tank 9 ft. in diameter and 33 ft. long, placed in the same position. The values representing the amounts of oil are given in United States gallons and are only ap- proximate, being calculated to the nearest 5 gal.; how- ever, the device used to indicate the depth of oil is likely to introduce slight errors, so that these values are suffi- ciently accurate for all practical purposes. The method of using the tables is easy to understand. In the first column are given the depths of oil in inches, or fractions of a foot, and at the heads of the remaining columns are placed the depths in feet, ranging from zero to a value that is i ft. less than the full diameter of the tank. To find the amount of oil corresponding to a given depth of oil in the tank, the column headed by the number of feet of depth is first located. Then, in the first column, the number denoting the depth in inches is located. The number that lies on the same horizontal line with this depth in inches, and in the column headed by the depth in feet, is the quantity of oil in gallons. Suppose that it is desired to find the amount of oil STORAGE OF OIL FUEL 99 in a tank 8 ft. in diameter and 28 ft. long when the indi- cator shows a depth of 3 ft. 8 in. In Table III the col- umn headed 3 is located, and in this column, on the same line with 8 in the first column, is the value 4,705; there- fore, the amount of oil at this depth is 4,705 gal. Again, suppose that the depth of oil in the same tank is exactly 6 ft., that is, 6 ft. o in., and the quantity of oil is to be found. There is no zero in the first column to represent o in.; but 6 ft. is the same as 5 ft. 12 in. Then, the quantity of oil at a depth of 5 ft. 12 in., or 6 ft., is found in the column headed 5, on the same line with 12, and is 8,470 gal. In the same way, the amount of oil at a depth of 4 ft., or 3 ft. 12 in., is 5,265 gal., and at a depth of 8 ft., or 7 ft. 12 in., the tank is full and con- tains 10,530 gal. If the depth of oil is not more than i ft., or 12 in., the quantity is found in the second column, headed o. For instance, if the depth of oil is 9 in., which is o ft. 9 in., the amount is 500 gal., because 500 is in the column headed o and on the same line as 9 in the first column. The values for the larger size of tank are found from Table IV by the same methods as those described in connection with Table III. 100 OIL FUEL FOR STEAM BOILERS +-> 0) a c^3 Q OOOOiooOOO*ooo OO O O n H cs co co ^t* Th 10 *o O M cs r}- oo" 00" CioH^O>OJ>-O>Oc -^- 00 OO H I \c- ^ _ - l>^ t^ t^ t^ 00^ oo" oo" oo" oo" oo' o 4^ d rt O to O O O to O to to *o to O to to to O O to to CN \O CN O\ VO "^" H M YB 15440 302931 UNIVERSITY OF CALIFORNIA LIBRARY