, . //; ,. AND ITS W.H. BOOTH LIQUID FUEL AND ITS APPARATUS LIQUID FUEL AND ITS APPARATUS By WM. H. BOOTH, F.G.S. MEMBER OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS ; FORMERLY OF THE NEW SOUTH WALES GOVERNMENT RAILWAYS AND TRAMWAYS, OF THE MANCHESTER STEAM USERS' ASSOCIATION, OF THE BRITISH ELECTRIC TRACTION COMPANY, ETC. SECOND EDITION NEW YORK E. P. BUTTON AND COMPANY PUBLISHERS Printed in Great Britain ly BUTLER & TANNER, Frame and London O' TABLE OF CONTENTS PART I THEORY AND PRINCIPLES. PAGE Preface . . . . . . . . .13 INTRODUCTION Historical Notes ; Advantages of Liquid Fuel ; Petroleum ; General Notes ; Economies possible by the use of Liquid Fuel 21 CHAPTER I The Geology of Petroleum ; Petroleum Drilling ; Pumping . 28 CHAPTER II The Economy of Liquid Fuel ; The Dangers of Petroleum ; Air necessary for Combustion ; General Principles of Liquid Fuel Combustion ; Flame Analysis ; Refractory Furnace Linings ; The Weir Boiler ; Liquid Fuels ; The necessity for Atomizing ; Vapourizing ; Varieties of Liquid Fuel ; Ameri- can Petroleum ; Russian Petroleum ; Creosote Oils ; Tar Distillates ; Blast Furnace and Shale Oils ... 35 CHAPTER III Texas Oil ; Analysis of Oil ; Physical Properties ; Russian Oil ; Calorific Capacity of Oils ; Advantages of Liquid Fuel ; The Use of Oil on Locomotives ; The World's Oil Production ; The Limits of Liquid Fuel ; Equivalence of Oil and Coal ; Tests of Texas Oil 48 CHAPTER IV Chemical and other Properties of Petroleum ; Water in Oil ; Petroleums suitable for Fuel; Physical Properties of Petro- leum ; Specific Gravity of Petroleum ; Materials ; Cast Iron ; Steel ; Firebricks ; Fireclay ; Clay Analysis ; Special Forms of Bricks ; Classification of Clay Goods . 62 5 492179 6 TABLE OF CONTENTS CHAPTER V PAGE, Combustibles and Supporters of Combustion." Carbon : its Forms and Origin ; its Calorific Properties ; its Combustion and Chemistry. Hydrogen : its Physical and other Pro- perties ; its Compounds with Carbon ; its Combustion ; Air ; The Atmosphere ; Properties of Air. Oxygen : its Compounds with Carbon ; its Properties ; Water ; its Properties ; Origin and Sources of Water Impurities ; Solu- bility of Salts ; Sea Water ; Useful Data . . .78 CHAPTER VI Calorific and other Units ; Thermo Chemistry ; Heat ; Tem- perature ; Thermometers ; Specific Heat ; Latent Heat ; Dissociation ; Units of Heat ; Units of Work ; Units of Weight ; Gravity ; Compound Units ; Calorific Power of Fuels ; Calculation of Temperatures ; Effects of Dissocia- tion and of Variation of Specific Heat ; Relative Volumes produced by Combustion ; Evaporative Power of Fuel ; Temperatures due to Combustion ; Calculation of Calorific Capacity of Fuels ; Smoke and Combustion ; Varieties of Smoke ; Its Prevention ; Influence of Refractory Furnaces ; The Combustion of Bituminous Fuels ; Carbon Vapour ; Liquid Fuels ; Furnace Temperatures ; Theoretical Flame Temperature ; Total Heat generated ; Air Supply ; The Heat Properties of Carbon ; The Process of Coal Combus- tion ; Effect of Vaporizing Solid Fuels ; Flame Analysis ; The Principles of Combustion ; The Necessity of Tem- perature ; Smoke due to Loss of Heat of Burning Gases ; The Use of Coloured Glass for Flame Inspection ; The Weir Boiler ; Ringelmann's Smoke Chart .... 90 PART II PRACTICE. CHAPTER VII Oil Storage on Ships ; Example of Improvised Tank Steamer ; Example of Cargo Steamer ; Example of New Tank Steamer ; Use of Liquid Fuel at Sea ; Supply of Oil at Ports ; Safety and Flash Point ; Advantages for War Ships ; Economic Advantages of Liquid Fuel . . . .127 CHAPTER VIII Marine Furnace Gear ; Arrangement of Shell Line Steamers ; Interchange of Coal and Oil ; The Flannery-Boyd System ; The Orde System ; Results of Use of Liquid Fuel at Sea ; Wallsend Slipway Company's Arrangement ; The Lanca- shire Boiler with Orde's System ; Korting System ; Howden System .133 TABLE OF CONTENTS 7 CHAPTER IX PAGE Liquid Fuel Application to Locomotives ; The Holden System ; Advantage of Oil ; Method of Working ; Management of Fire ; Particulars of Oil Burning Locomotive ; Regulation of Oil Supply ; The Atomizer ; Life of Fire Boxes ; Heating the Oil ; Air Heater 154 CHAPTER X "Application of Liquid Fuel to Stationary and other Boilers ; The Lancashire Boiler ; Cornish Boiler ; Water Tube Boiler ; Locomotive Boiler ; Level of Atomizer in Mixed System ; Management of Fire ; United States Navy Tests ; The Meyer System ; The Mixed System of Coal and Liquid Fuel Combustion : its use in the Italian Navy ; M. Bertin's Calculations ....... .167 CHAPTER XI Russian and American Locomotive Practice ; The Baldwin Com- pany's System ; The Equivalence of Coal and Oil ; Compari- sons of Cost of Liquid Fuel ; The Danger of Crude Oil ; The Urquhart System ; General Arrangements ; Management of Furnace ; Firebox Designs ; Smoke Results on Grazi and Tsaritsin Railway . . . . . . . .178 CHAPTER XII American Stationary Practice with Liquid Fuel ; The Billow System ; Fuel Oil Pumping Systems ; Double Pumping Systems ; Furnace Construction ; Operating a Fuel Oil Plant ; Examples of Boilers with Liquid Fuel Furnaces . . 195 CHAPTER XIII English Stationary Practice with Liquid Fuel ; The Kermode System ; Analysis of Borneo Oil ; Tests of Borneo Oil ; The Hydroleum System ; Tests ; The Sprayer ; Air Supply . 208 CHAPTER XIV The Combustion of Vaporized Liquids ; The Clarkson-Capel Burner: its Various Applications; Starting Devices . .218 CHAPTER XV Comparison of Air and Steam Atomization ; The Ellis and Eaves System ; Steam Atomization ; Air Atomization ; Tests . 222 8 TABLE OP CONTENTS CHAPTER XVI PAGE The Storage and Distribution of Liquid Fuel ; Tanks ; Piping ; Ventilation ; Great Eastern Railway System ; Grazi and Tsaritsin Railway System ; Oil Pumps ; Flue Gas Analysis ; Calculation of Volumes ; The Orsat Apparatus ; CO 2 Recorders ; Calorimetry and Draught ; Calorimetric Deter- minations ; Draught ; Gauges ; Difference of Solid and Liquid Fuel in Relation to Draught . . . .228 CHAPTER XVII Compressed Air ; Air Compressors ; Principles of Compression ; Weight of Air necessary for Liquid Fuel Atomization ; Adia- batic Calculation of Air ; Compound Air Compression ; Volumetric Efficiency ; Power to Compress Air ; Outflow of Air . . 242 CHAPTER XVIII Atomizing Liquid Fuels ; Various Atomizers ; Elementary Forms ; Vaporizers ; The Symon-House Burner ; Atomizing Agents ; French Trials ; Air Compression ; Certain Advantages of Steam ; d'Allest Atomizer ; Fvardofski System ; Russian Atomizers ; Object of Atomizing ; American Practice . . 250 CHAPTER XIX Application of Liquid Fuel to Metallurgy ; The Hoveler System . 266 CHAPTER XX The Oil Engine ; The Diesel and other systems . . .270 PART III Tables and Data . 281 INDEX TO ILLUSTRATIONS FIG. PAGE 0. Hypothetical Section of Oil-bearing Strata ... 30 1. Kiln Furnace ........ 74 2. Form of Baffle 74 3. Brick Fire Arch 75 4. Shaped Bricks 76 5. Shaped Bricks 76 6. Unshaped Arch Bricks . . . . . . .76 7. Weir Boiler 121 8. Ringelmann Smoke Chart 122 9. Furnaces, s.s. Murex ....... 134 10. Furnace Brickwork, s.s. Murex . . . . .135 11. Furnace, s.s. Trocas 136 12. Service Tank, Flannery-Boyd System . . . .137 13 and 13a. s.s. New York 138 14. Water Tube Boiler, Orde's System . . . .141 14a. Fuel Bunker, Draw-off Pipe 142 15. Orde's Atomizer ........ 144 16. Detail Arrangement for Lancashire Boiler, Orde's System . 145 17 and 17a. Design for Oil Furnace, Wallsend System . 146 18. Wallsend Pressure Burner . .148 19. Diagrammatic Arrangement, Wallsend System . .150 19a. Detail Arrangement, Wallsend System . . . .150 20. Water Tube Boiler, Wallsend System . . . .151 21. Furnace, s.s. F. C. Laeisz . 152 22. Atomizer, Korting System . . . . . .153 22o. Atomizer, Korting System . . . . . .153 23. Great Eastern Locomotive, Atomizer, Holden's System . 158 24. Atomizer, Form (1911), Holden's System . . .159 25. Atomizer, Locomotive Type, Holden's System . .160 26. Great Eastern Locomotive, Holden's System, Firedoor . 161 27. American Locomotive Firebox for Liquid Fuel . .163 28. Great Eastern Locomotive . . . . . .165 29. Lancashire Boiler, Holden's System . . . .168 30. Water Tube Boiler without Grate, Holden's System . 169 31. MacAllan Variable Blast Pipe Cap . . 170 32. Locomotive Boiler, Southern Pacific R.R. . . .171 33. Meyer System 173 34. Atomizer, Baldwin System . . . . . .179 35. Oil Regulator, Baldwin System 179 36. Locomotive Firebox, Baldwin System, Old . . .180 37. Locomotive Firebox, Baldwin System, New . . .181 10 INDEX TO ILLUSTRATIONS FIG. PAGE 38. Goods Locomotive, Urquhart System . . . .188 39. Goods tender, Urquhart System . . . . .190 40. Firebox, Urquhart System . . . . .191 41. Locomotive Firebox, Urquhart System . . . .192 42. Atomizer, Urquhart System . 193 43. Locomotive Performance Chart, Urquhart System . .194 44. Atomizer, Billow System . . 196 45. Double Pumping System, Billow . . . 198 46. Tuyere, Billow System 199 47. Tuyere Block, Air Regulator, etc., Billow System . . 200 48. Tank Car Hose Connection ... .201 49. General Furnace Mouthpiece Arrangement, Billow System 202 50. Underfired Boiler, BiUow System 205 51. Water Tube Boiler, Billow System . . . .206 5 la. General Arrangement, Billow System .... 207 52. Liquid Fuel Furnace, Kermode's System . . . 209 52a. Enlarged Details, Kermode's System . . . .210 53. Furnace Arrangement, Kermode's System . . .211 54. Furnace Arrangement, Kermode's System, Babcock Boiler 213 55. Furnace Arrangement, Hydroleum System . . .215 56. Furnace Arrangement, Hydroleum System . . .216 57. Clarkson-Capel Burner for Fire Float . . . .219 58. Clarkson-Capel Burner for Automobile .... 220 59. Air Heater, Ellis and Eaves System .... 223 60. Ellis and Eaves Furnace Door 223 61. Oil Supply Tank 231 62. Weir Pump . . . .232 63. Diagram of Adiabatic Compression. .... 244 64. Diagram of Compound Compression with Intercooling . 244 65. Atomizer, Hoveler System ...... 267 66. Atomizer, Rusden-Eeles 251 67. Atomizer, Aerated Fuel Process ..... 252 68. Atomizer, Kermode's Pressure System . . . .253 69. Atomizer, Kermode's Hot-Air System .... 254 70. Atomizer, Kermode's Steam System .... 255 71. Atomizer, Hydroleum System ..... 255 72. Atomizer, Elementary Form ...... 256 73. Atomizer, Swensson . . . . . . .256 74. Symon-House Vaporizer . . . . . .257 75. Atomizer, Guyot ........ 258 76. Atomizer, Nozzle Incorrect Form ..... 259 77. Atomizer, Nozzle Correct Form . . . . .259 78. Furnace of French Torpedo Boat No. 22 ... 260 79. Atomizer, d'Allest 261 80. Atomizer, Double, d'Allest 262 81. Atomizer, Soliani . . . . . . . 263 82. Torpedo Boiler tried at Cherbourg .... 264 82a. Assembly of Gregory's Fuel Oil Burner .... 265s 83. Hornsby-Akroyd Engine . . . .272 84. Cross Section, Vaporizer, Hornsby-Akroyd . .273 85. Griffin Engine Vaporizer . . - .276 INDEX TO TABLES TABLE PAGE I Composition of Crude Oils 281 II Calorific Capacity of Liquid Fuel Oils . . .281 III Coefficient of Expansion of Crude Oil . .281 IV Calorific Capacity of Crude Oil .... 284 V Table of the Properties of Gases (Kempe) . . 282 VI Temperature Table 284 VII Specific Heat of Gases 284 VIII Equivalents, Various 285 IX Calorific Properties of Carbon .... 285 X Tension of Aqueous Vapour . . . . .286 XI Relative Economy Oil and Coal .... 286 XII Russian and Pennsylvanian Oils, Analysis of . . 286 XIII Comparative Trials of Petroleum Refuse . .287 XIV Conversion Table, Degrees Baume .... 288 XV Heat of Combustion (B. Th. U.) und Air per Pound of Fuel . . 288 XVI Theoretical Flame Temperatures . . . .289 XVII Weight and Volume of Gases . . . .289 XVIII Weight and Volume of Oxygen and Air for Combustion. Metric 290 XIX Weight and Volume of Oxygen and Air for Combustion. English 290 XX Theoretical Evaporative Value of Petroleum and Coal 291 XXI Ignition Temperature of Gases .... 292 XXII Conversion Tables for Evaporation and Combustion 292 XXIII Temperature Determination by Fusion of Metals . 293 XXIV Volume and Weight of Dry Air . .293 XXV B. Th. U. in Water . * , . .294 XXVI Saturated Steam Data ... . 294 XXVII Factors of Evaporation ... .295 XXVIII Heat Balance Table ... . 296 XXIX Heat Lost in Chimney Gases (Diagram) - 297 PREFACE TO LARGER EDITION OF 1903 subject of Liquid Fuel is one that has now been before X the public about twenty-five years, but little had been done in this country until about twelve years ago, when Mr. Holden, of the Great Eastern Railway, began to use the tar of his oil-gas process, and found many advantages in using this hitherto almost unsaleable product. The success of this tar led him on to the use of creosote and other hydrocarbon by-products, and now he is using Texas oil. In this book the Author has endeavoured to put together what has been done in the burning of liquid fuel, and at the risk of repetition has given descriptions of various systems and apparatus ; and while no statements have been accepted unconsidered, he has not hesitated to use descriptions and statements of manufacturers in some cases with little altera- tion where such statements were sound and reasonable. The Author is not only indebted to the many whose names appear in the text, but also to many others who have furnished him with information, particularly Professor W. B. Phillips, Ph.D., of the University of Texas, from whose bulletins the Author has drawn so copiously for information on Texas oil ; to Mr. Thomas Urquhart, of Dalny, who, as Locomotive Superin- tendent of the Grazi and Tsaritsin Railway, first placed liquid fuel burning on a sound basis in locomotive work, and whose papers on the subject may be found in the Proceedings of the Institution of Mechanical Engineers ; to his friend Mr. B. H. Thwaite, whose researches in combustion have been so extensive. The work of the United States Naval Department, under Rear-Admiral Melville, has been so valuable that special appendices have been devoted to a copious abstract of the coal and oil tests made by the Bureau of Steam Engineering upon a water-tube boiler as well as tests upon the s.s.Mariposa The Author has also drawn liberally upon the bulletins of the U.S. Geological Survey for information on petroleum production. 13 14 PREFACE TO LARGER EDITION OF 1903 To Mr. Alfred J. Allen acknowledgment is due for informa- tion on tar and creosote, and for tabular matter to Mr. Poole, whose excellent treatise on the Calorific Power of Fuels deals so exhaustively with coal. Appendices are added giving the Rules of the National Board of Fire Underwriters (U.S.), and also the Rules of Lloyd's Register of Shipping. Acknowledgments are due to the Electrical Review (London) for permission to reproduce portions of the Author's articles in that Journal on questions of combustion. To Mons. L. Bertin, of the French Navy, the Author is indebted for infor- mation as to the use of liquid fuel in the French Military Marine. The means for utilizing Liquid Fuel are very varied, yet all practically result in, or at least aim at, one end. It has been impossible within two covers to do more than select a number of such apparatus to illustrate the principles which have been followed in achieving success. The successful com- bustion of liquid hydrocarbon is but an extension of the prin- ciples necessary for bituminous or hydrocarbon coal. The difference is that coal is burned partly upon the grate, and air, to burn the hydrocarbon distillates, cannot well be introduced from below, as it can with liquid fuel which is burned in a floating condition, and can be fed with air from below very easily. The difference is but one of degree, but with liquid fuel the fact that all the fuel is floating, and would produce a specially foul black smoke under the conditions in which coal is burned, has compelled the adoption of means that ought to be adopted with coal-fired furnaces. The Author has endeavoured to connect the two practices, for in the present state of liquid fuel supply it is more than probable that its use will be parallel with the use of coal, especially hi dealing with the sudden and high load peaks of electric stations. Liquid fuel cannot be universal unless the supply increases to many times what it is at present, and this points to a good future for the mixed system of firing, oil and coal being burned together in the same furnace. It has been difficult to make a selection of apparatus to be described, but the Author trusts that he has selected a suffi- cient number of types practically to cover the ground and show the general trend of practice without unduly multiplying examples. Indeed the tendency seems to him to be in the direction of one general type. As regards special boilers, oil does not appear to require anything more than what is re- quired by coal, though coal is not treated to the necessary PREFACE TO LARGER EDITION OF 1903 15 appliances, and oil is so treated, and gains success where coal is allowed to fail. Much that perhaps ought to appear in such a book as this has been omitted, as it appears to the Author that the question of draught, for example, is not of the same importance with liquid fuel as it is with solid fuels. More might be said on the subject of flue-gas proportion, but this again has been so fully treated by other writers that it did not seem desirable at present to deal with it more fully. The most important detail of liquid fuel apparatus is the fur- nace and the provision of air, and of means to secure combus- tion and conserve temperature to enable combustion to be made perfect. Mr. Horace Allen kindly revised the section on gas analysis. Students of liquid fuel combustion will find enormous masses of information in the past volumes of the Engineer, Engineer- ing, and other technical papers. Much of this information is duplicated and historical, and the Author has found it necessary to eliminate almost all such matter and confine his space to systems now living or of recent use, or of a form recog- nized as useful to-day. Undoubtedly Aydon and the late Admiral Selwyn did much to urge the use of liquid fuel, but the latter injured the value of his best work by regarding steam as a combustible. The Author is also indebted to Messrs. Colonner and Lordier, the French engineers, for excellent information on liquid fuel, and indirectly no doubt to many others who are not directly traceable. Finally, his grateful acknowledgments are due to his Pub- lishers for the manner in which they have facilitated his labours throughout. WESTMINSTER. PREFACE THE object of this book is to present in a handy form the more immediate practical points of the Author's larger work on the same subject. 1 In that book the Author endeavoured to present not merely the subject of liquid fuel combustion but such side issues as water softening, and considerably more on the general theory of combustion and the physical properties of materials than can be found room for in this present work. The larger work is still available for those who may desire the fuller presentation of the subject, but it was written at a time when the popular idea of liquid fuel was very hazy, and when the world's production of petroleum was very much less than it is to-day. The ideas then presented by the Author have since received very general acceptance. Over parts of the world liquid fuel will continue to take the place of coal. In other parts it will be used because by its means things may be accomplished that would not be possible with coal. This was amply demonstrated during the naval manoeuvres a year or two ago, when the stokehold crew of one of the rival fleet divisions were worn out and unfit for further effort. Liquid fuel was then resorted to and the ships simply ran away from the " enemy " and ravaged the south coast. Much of what appears in the larger work is eliminated because of the foregoing reasons as well as the fact that the subject of liquid fuel is now quite removed from controversy and has entered more fully upon the commercial stage, for liquid fuel will now be used wherever it is cheaper than coal or possesses circumstantial advantages which outweigh expense. For the peak loads of electric light supply undertakings liquid fuel presents itself so favourably that only surprise can be felt that this particular field has so far been neglected. This book will therefore be fairly closely confined to the use of liquid fuel in steam raising and in direct power produc- tion in the internal combustion engine. This engine has in the last few years made great advances and bids fair soon to 1 Liquid Fuel and Its Combustion. Constable & Co., 1902. 17 B 18 PREFACE find itself employed as the motive power producer in ships of great size and tonnage. While bringing up to date the examples of apparatus these have been reduced in number. Tabular matter has been abridged in numbers and detail and much experimental record has had to be cut out in order to bring the book within its intended compass. Finally it may be added that since the issue of the Author's larger book, there has been little change in the methods or apparatus employed, though there is a steady extension, chiefly abroad, in the uses to which liquid fuel has been put. The Author trusts he has given sufficient examples of apparatus to enable any engineer to adapt liquid fuel to his own conditions. He wishes to make it clear that the examples and illustrations are chosen as examples and are not put forward as being other than typical. It is not possible to make a book into a complete catalogue of apparatus, and only a few can be selected as types. WM. H. BOOTH. 38, BROAD STREET AVENUE, E.G. Oct., 1911. There is still a big field for the use of systems of mixed solid and liquid fuel, as carried out notably with the Gregory burner described in Chapter XVIII. (June, 1921.) Part I THEORY AND PRINCIPLES INTRODUCTION THE first really practical and efficient employment of liquid fuel for steam-raising purposes appears to be due to Mr. Thomas Urquhart, of the Grazi and Tsaritzin Rail- way of Russia. Mr. Urquhart used the spraying system and obtained good results, and his paper of 1884 1 marks the beginning of the period of really useful work. The application of liquid fuel in the Caucasus owes its success to a combination of causes. Russian petroleum has less light oil in its composition, and therefore produces more astatki, i.e. mazut or residuum ; coal is dear in the district, and the man was present in Mr. Urquhart to render the application of liquid fuel successful, previous applications not having proved so. Urquhart placed the use of liquid fuel on a sound basis. The Chicago Exhibition in the early nineties gave great impetus to the use of liquid fuel in America, for all the boilers there were arranged with oil fuel only. In Great Britain the use of liquid fuel has not been extensive, but it has been marked by good practice, and only bids fair to become extensive since the introduction of mineral oil. Previously the tendency had been to use the products of distil- lation of coal or oil in the shape of tars or creosotes. To-day liquid fuel is well established and recognized as a fuel of extreme elasticity, and one that can be burned smokelessly. The days of experiment are past, and no serious difficulties remain to be overcome. Since 1902 liquid fuel has been adopted in the British Navy, and it is understood that very satisfactory results have been secured. At the same time the question must be considered from a conservative standpoint, because for years to come, if ever, the output of petroleum will not be sufficient to make it a serious rival of coal in every use. There is no certainty of extensive petroleum production in the future. Petroleum wells do not endure indefinitely. They are not like water wells, fed from 1 Institution of Mechanical Engineers, Minutes of Proceedings, 1884. 21 22 LIQUID FUEL AND ITS APPARATUS surface rainfall, and geology does not assure us that they are being fed from still deeper sources, nor is it decided whether petroleum is of mineral or of organic origin. The future of petroleum is thus uncertain. GENERAL CONSIDERATIONS A general idea of the liquid fuel problem should therefore be obtained before attempting to gauge its merits. There is a lack of the sense of proportion in many who discuss the question of liquid fuel. In Great Britain alone over 250 million tons of coal are raised each year. In the United States the amount is still greater. The present production of mineral oil is a mere fraction of the millions of tons of coal produced in the world. Liquid fuel has undoubted advantages in many cases, and probably nowhere could it be used to better advantage than in an electric light station. One of the principal advantages of oil is its high calorific value per pound. This, with the best oils, is double the capacity of the inferior coals, and 30 per cent, better than the best coal. The ease with which it can be stored and moved from point to point is an advantage. It can be fired mechani- cally, makes no ash or clinker, can be burned at maximum rate or entirely turned off in a moment. Further, a very large power of boilers requires very little labour in the stokehold. Petroleum consists of a very large variety of constituents, gaseous, liquid, or solid. The gas is marsh gas, CH 4 , and at once disappears ; the lighter liquids are very volatile, and finally there are solid bodies at the end of a long series of liquids of varying degrees of volatility and specific gravity. The chemical formulae which cover most of the constituents of petroleum are C n H 2n and C n H 2n 2. These formulae con- tinue throughout the whole range from marsh gas, CH 4 , onwards. Texas oil is used chiefly as it is found. Russian oil is used in the form of astatki, the residuum after distilling off the lighting and lubricating oils. Much of the American oil is also used in the form of residuum. The proportion of carbon in all the liquids used as fuel varies very little from 84 per cent., the hydrogen amounting to 16 per cent. There is little else, so that petroleum is practically all combustible. It is well established that there is at present only one way to burn liquid fuel for steam raising, and that is by atomizing the fuel in company with & sufficient amount of air around INTRODUCTION 23 each atom. In order that oil may atomize freely, it should be deprived of viscidity by heat. Heat also causes any water in the oil more easily to separate out, first, because heated oil, being more limpid offers less resistance to the freeing of the water ; and secondly, there is greater expansion of oil than of water due to the heat, and the water gains a relatively greater specific gravity. Warming is done by a steam coil, and may be merely local warming in the vicinity of the take-off valve in the tank. It is essential that water be fairly well separated, because if it comes through the burners in any quantity it may extinguish the fires, and the next following oil is apt lo ignite explosively. In storing oil there is always apt to be some vapour given off, and an empty tank ought not to be entered with a light. Though not nominally of double the calorific capacity of average fair coal, oil is found in practice to be worth double the price of coal, owing to the labour cost which it saves. This is as regards marine service, for the oil can be carried in ballast tanks, and paying cargo is carried in the coal bunker space. For land purposes, these latter considerations do not weigh, and the relative values must be based on the performance ratio of about 16 to 10, together with the economy of labour, cleaning, ash cartage, etc. Above and beyond all these things, however, is the power which liquid fuel gives of immensely increasing the steam- production of a boiler at short notice. In general practice a steam-boiler is designed with a given ratio of heating surface per unit of fuel burned. Any reduction of this ratio is accompanied by a poorer performance. Less steam is produced per pound of oil consumed. A reduction of the heating surface ratio does not, however, reduce the per- formance by anything like the same ratio. If a large demand for steam is made upon a boiler for a short fraction of its working hours, it may be cheaper to consume fuel at a high rate for a fraction of the time than to employ two or even three boilers at normal rates during a fraction of the day, the extra boilers remaining idle during the rest of the day ; albeit when the heavy load is past these extra boilers are retired hot and full of energy. The saving by the first method is very considerable in respect of space occupied, build- ings and capital cost generally, and if not carried too far it will outweigh the fuel cost of the short run at heavy output. For this system of working, coal can, of course, be employed. Coal, however, cannot be fired at abnormal rates with special 24 LIQUID FUEL AND ITS APPARATUS ease. A mechanical stoker does not readily increase its rate of working. The better forms of stoker on the coking prin- ciple cannot put their whole grate surface into the new and forced condition. The sprinkler class, again, do not work well at abnormal rates. Coal combustion is only to be regu- lated by draught intensity. With oil, the supply is instantly variable to suit the steam required, and a boiler can rapidly give its fullest output. With boilers of the smaller tube type especially, their small water contents enables the engineer to leave them standing cold to within a short time of maximum output. Oil is then turned on, and in a few minutes the boiler is in full work. When a boiler is already at work the mere turn of a handle puts it into its maximum steam-producing condition. So soon as the demand ceases the oil can be turned off, and the normal coal fire continued, or the boiler laid off entirely. By means of liquid fuel great elasticity is possible. In a lighting station the load factor is very usually about 12 per cent. That is to say, about one-eighth of the plant is, on the average, at work all the working hours. This excessive misproportion is remedied to any desired extent by means of accumulators, but it is not yet commercially economical to instal so high a proportion of battery power as to enable the power-plant to run at steady load all day. The peak of the load, however short in duration, cannot be sur- mounted without the aid of power, and it is to the height and small duration of the maximum load curve that the poor load factor of a lighting station is due. Accumulators for heavy output of short duration greatly improve the load factor, but, in any case, the number of boilers at work to tide over the peak is several times the mean number. If, by means of liquid fuel, boilers can be heavily pushed for two. three, or four hours, the capital outlay on boilers will be much reduced. When the various points are taken into account, the boiler scheme that will probably suggest itself will be, first, some boilers of the Lancashire type, economical and steady steamers ; secondly, large tube boilers with a moderate water contents and large grate area, and with efficient steam driers or superheaters. These boilers can be heavily forced with some sacrifice of economy, but the priming due to heavy forcing must be eliminated by a good superheater. This is essential to economy. Thirdly, small tube boilers of very small water capacity, capable of being heavily forced, delivering their steam preferably above water level in the steam drum. If all these boilers are fitted with oil sprayers, the maximum INTRODUCTION 26 demand for steam will be met with the minimum of capital outlay. It is a fallacy to suppose that boilers of small water capacity respond most readily to a sudden demand for steam. When a boiler is at work under full pressure, the whole of its water is at a temperature which corresponds with the pressure. Any addition to the furnace activity cannot add to the hea'o contents of the boiler, unless the pressure is allowed to rise ; obviously, therefrom, given the continuance of the same pres- sure, the boilers of large water contents will answer to an urged fire just as rapidly as a boiler of small water contents. When boilers are standing at rest, however, and cold, the boiler which contains the least water will, ceteris paribus, become most quickly hot. Such a boiler as the Solignac, which holds almost no water, can be made, by aid of oil fuel, to produce its maxi- mum power in a few minutes after lighting up. In this respect oil has a decided advantage over solid fuel. To secure a good fire with solid fuel there must be a thick bed of incandescent fuel on the grate, and this can only be built up with comparative slowness, and when its duty is over it remains a more or less wasted force. With oil, however, the maximum fire is instantaneous, and the only drawback is the cold brickwork of the setting, which must become hot before the maximum furnace duty is attained. For ordinary economical work the number of heat units that a boiler can absorb per square foot of heating surface will not be changed when liquid fuel is employed, except so far as liquid fuel can be burned without smoke more easily than can solid hydrocarbons, such as coal, and thereby the heating surface is maintained clean and free from dust and soot, and more efficient. Evaporative efficiency must not be allowed to out- weigh the overall, or commercial, efficiency. Exactly what governs the relation between evaporative and commercial efficiency cannot be stated positively. Indeed, commercial efficiency alone should be considered as the true basis of design. It may, however, be stated in general terms that plant which is on duty for long hours may be designed to work more economi- cally as regards fuel than plant intended to work very short hours. Let it be assumed that the boilers which are economical of fuel have an efficiency of 72 per cent., and that the small highly pushed boilers are run at 60 per cent, efficiency for three hours. Then, in course of a year, fuel is wasted which represents 12 per cent, difference of efficiency lost for three hours daily. To enable this loss to be avoided there would be so many 26 LIQUID FUEL AND ITS APPARATUS thousands of pounds extra capital cost in boilers, buildings, etc., and where oil is not employed, so much more labour cost as compared with oil. Properly equated at a suitable rate of interest and depreciation, the relative value of the alternative systems may be found after the manner of the Kelvin law applied to cable work. In many stations the extra labour for the heavy duty period is difficult to arrange satisfactorily. Men are employed more hours than they really work, and where it may be best to use coal for 10 hours, the labour cost may make it cheaper to use oil for 4 hours of a peak load, even if, in mere fuel cost per unit, the oil is more expensive. Trials with liquid fuel show that there is still much to be done in reducing the air supply. The air required to burn 1 unit weight of carbon is 11 J units. An ordinary oil fuel re- quires fully 15 units, with, of course, some additional excess as with solid fuel. But with oil fuel there ought to be better mixture of air and fuel, and therefore better combustion with less excess of air. If we regard air as the fuel and coal or oil as the sustainer of combustion, as we have a chemical right to do, we shall arrive at the conclusion that, approximately, the calorific value of a fuel in actual duty done will not differ much from the chemical ratio of air required in the combustion process. The large amount of air per pound of oil arises from the large percentage of hydrogen in the oil, and it is the large capacity for oxygen possessed by hydrogen which renders the theoretical tem- perature of combustion so nearly like that of carbon, in spite of the high calorific capacity of hydrogen. As regards the production of petroleum, that of the United States in the year 1901 was 69,389,194 barrels, valued at 66 J million dollars. If each barrel is assumed to contain 360 lb., or say 6 barrels per ton, the total tonnage will be 11,565,000, and the value, therefore, something under 23