«T— , V_ VVXV.V r t .t^>^.,^,». % ::^ CORNELL UNIVERSITY LIBRARY ENGINEERING CemaH Unlvaritty Library TP 32S.CS3 Coal; It* economical and amokeless combus 3 1924 004 686 873 DATE DUE CAVUOBO Cornell University Library The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004686873 COAL ITS ECONOMICAL AND SMOKELESS COMBUSTION BY JAMES F. COSGROVE Published by the Teohnieal-Book Publishing Company PHILADELPHIA, PA, p \ 9 CS3 c :? r,.„ Copyright, 1916, by JAMES FBANCIS COSGROVE. Copyright In Great Britain. All rights reserved. PREFACE This work was called forth by the lack of a thorough, comprehensive textbook on coal that would explain in clear, simple language just what must be known about the characteristics of the numerous varieties in order that coal may be purchased intel- ligently and burned economically and smokelessly. Fully ninety-eight per cent, of industrial plants use coal as a prime source of power, yet, owing to lack of knowledge of this subject, they seldom get the kind of coal best suited to their equipments. A large majority bum coal that can be burned neither economically nor smokelessly in their plants. In- stances are on record where selecting the coal best suited to a plant reduced the coal bills fully twenty per cent ; and it is safe to say that fully ten per cent can be saved in half the plants in operation simply by selecting the right coal for the furnace and draft. In many cases plants have been forced to re- strict their outputs or to increase their boiler capac- ity by an extra unit, when by simply selecting the right coal for their furnaces and by adjusting the draft to suit their conditions they would have gained the desired increase in capacity. With a given equipment and the right kind of coal, the capacity, economy, and smokeless operation of a locomotive or a power plant depends on the right manipulation of the fires. In this work, that phase of the subject is treated in an exhaustive man- ner, so that a person of average intelligence by studying the text can determine what is the best coal to purchase for his particular plant; what equipment is best suited to burn a particular kind of coal; what method of firing is best adapted to the coal and furnace ; and what the best method of pro- cedure is for the prevention of smoke. This applies with equal force to locomotive service, marine serv- ice, and stationary power service, and applying the information herein contained will effect wonders in economy, efficiency, and smokelessness of operation. To cope successfully with the smoke problem requires a special knowledge of the smoke-producing constituents of coal and of the types of furnaces best suited to the burning of coal smokelessly. All this is explained in detail and well illustrated, and, besides, the laws governing the production and prevention of smoke are thoroughly interpreted. The formation of clinker in a furnace not only is a source of great trouble to the fireman, but also is a cause of steam failures, with consequent delays and shutdowns. This subject received special con- sideration, particularly the cause and prevention of clinker, the methods of determining from the con- stituents of the ash whether an ash will clinker, and the best methods of handling clinkers once they have formed. The scope of this book is so broad, and the sub- jects are treated in so comprehensive a manner, that it is hoped the book will be of special benefit to mechanical engineers, electrical engineers, heat en- gineers, smoke inspectors, fuel inspectors, purchas- ing agents, power-plant owners, power plant super- intendents, superintendents of motive power, master mechanics, traveling engineers, traveling firemen, engineers, firemen, and in engineering class rooms. SCEANTON, Pa., Feb. 15, 1916. J. F. Cosgrove., TABLE OF CONTENTS Classification of Coals 1 Characteristics of Coal 8 Coal Classed AccoRniNG to Use 16 Composition of Coal 26 Effect of Size of Coal 49 Clinkering of Coal Ash 58 Prevention of Clinker 76 Geological History of Coal 81 The Coal Fields op America 91 Analysis op Coal 102 The Purchasing of Coal Ill Theory of Combustion 118 Combustion of Coal 137 Temperature op Combustion 148 Determining the Heat Value of Coal 162 Burning Bituminous Coal 167 Smoke and Its Prevention 172 Burning Coal Smokelessly 191 Draft Regulation 218 Hand-Fired Furnaces 225 Stoker Furnaces 238 LIST OF TABLES TABLE PAGE I. Fuels Grouped According to their Carbon and Oxygen Content 2 II. Coals Arranged According to Carbon and Hy- drogen Content 3 III. Classification of CoaJs According to Carbon- Hydrogen Ratios 5 IV. Grouping of Coals According to their Carbon- Hydrogen Ratios 7 V. Sizes of Anthracite 8 VI. Relative Values of Steam Coals 20 VII. Loss in Heat Value Due to Moisture 39 VIII. Ash from Different Sizes of Bituminous Coals 43 IX. Constituents of Coal and Lignite Ash 59 X. Fusing Temperatures of Oxides 61 XI. Formation Temperature of Silica-Iron-Lime Slags 62 XII. Seger Cones 72 XIII. Schedule of the Limits of the Divisions of the Rocks and Corresponding Divisions of Geological Time 84 XIV. Heat Value of Coals of Different Ages 109 XV. Cost, in Cents, for 1% Moisture, Sulphur and Ash in Coal 115 XVI. Atomic Weight of Elementary Substances Concerned in Combustion 121 XVII. Heat Value of 1 Pound of Hydrocarbon at 32° F. and Atmospheric Pressure 127 XVIII. Air Necessary for Combustion of Carbon, Hy- drocarbons, and Sulphur at 60° P 134 XIX. Density, Weight, and Volume of Gases at 32° F. and Atmospheric Pressure 135 XX. Igniting Temperatures of Fuels and Com- bustibles 140 XXI. Air Required for Combustion of Different Types of Coals 144 XXII. Heat Evolved by Different Combustibles 146 XXIII. Specific Heat of Gases, H,0 at 30° F.^1 149 XXIV. Theoretical Temperature of Combustion in Air 154 XXV. Effects of Insufficient Air Supply 155 XXVI. Cooling Effect of the Air Supply 156 XXVII. Weight of Vapor in Atmosphere 158 XXVIII. Heat Values of Unit Coal 165 XXIX. Air Required by Carbon and by Hydrocarbons 181 XXX. Relation of Height of Stack to Draft 198 XXXI. Thickness of Fire Carried in 64 Tests 211 XXXII. Draft-Gauge Pressures Corresponding to Vari- ous Heads of Water 222 Table A Appendix LIST OF ILLUSTRATIONS FIG. PAGE 1. Chart Showing Per Cent, of Fixed Carbon in Coal, Dry and Free from Ash 28 2. Chart Showing Gaseous Products of Coal 33 3. Chart Showing Illuminants and Hydrocarbons of Coal 34 4. Chart Showing Hydrogen in Coal 35 5. Chart Showing Smoky Constituents of Coal 36 6. Chart Showing Higher Hydrocarbons in Coal .... 37 7. Chart Showing Formation of Ferro-Calcic Silicates 63 Map of Coal Fields of America — opposite 91 8. Chart Showing Proportion of Smoke-Producing Compounds of Coals 185 9. Automatic Air- Admission Device 201 10. Arrangement of Steam Jets 202 11. Automatic Steam and Air Admission Device 202 12. Cross Section of Non - Automatic Air - Admission Furnace Showing Air Ducts 203 13. Water Draft Gauge 221 14. Recording Draft Gauge 223 15. Scale for Grading Smoke Density 223 16. Results of Tests Plotted for Density of Smoke 224 17. Plain Furnace, Babcock & Wilcox Boiler 226 18. Furnace Unsuitable for Bituminous Coal 227 19. Hand-Fired Dorrance Furnace, Babcock & Wilcox Boiler 228 20. Hand-Fired Wooley Furnace and Babcock & Wilcox Boiler 229 21. Wooley Furnace, Plan 229 22. Hawley Down-Draft Furnace, Heine Boiler 230 23. Hand-Fired Twin- Arch Furnace and Return Tubu- lar Boiler 231 24. Hand-Fired Twin-Arch Furnace, Plan 231 25. Chain-Grate Stoker, Babcock & Wilcox Boiler 239 26. Roney Front-Feed Stoker, Heine Boiler 242 27. Roney Double-Stoker Plant 244 28. Murphy Side-Feed Stoker, Return Tubular Boiler. 245 29. Murphy Side-Feed Stoker, Dutch Oven 246 30. Murphy Side-Feed Stoker, Heine Boiler 246 31. Detroit Side-Feed Stoker, Sterling Boiler 247 32. Jones Stoker and Heine Boiler 249 33. Jones Under-Feed Stoker, Cross Section 250 Coal and Its Combustion CHAPTER I Classification op Coals ' OAL is the carboniferous remains of pre- historic vegetable matter. In Amer- ica it is widely distributed throughout the United States, Canada, and Mex- ico, where it is found in various stages of carbonization. Wood fiber (cellulose) is the lowest group in the series, while the successive groups are known as peat, lignite, bituminous coal, semibituminous coal, semianthracite, anthracite, and graphite. In the lower groups, the coal is low in carbon and very high in oxygen. Each higher group is distinguished by an increase in carbon and a decrease in oxygen, as is shown in Table I. The hydrogen remains practically the same for all groups below the semibituminous, but decreases rapidly in the higher groups. Oxygen in coal is con- sidered an impurity, because it has the same effect on the heat value of the coal as a like amount of ash; hence, the lower groups have a much lower heat value than the higher groups. Each of the coal groups comprise a number of classes of coal that differ largely in physical char- acteristics rather than in chemical composition; consequently, it is hard to define each group accu- 1 COAL AND ITS COMBUSTION. TABLE I. Fuels Grouped According to Their Carton and Oxygen Content. Substance Per Cent. Carbon Per Cent. Oxygen 52.65 59.57 66.04. 42.10 34.47 28.69 73.18 7^.06 21.14 19.10 89.29 6.66 91.58 4.46 100.00 Per Cent. Hydrogen Wood fiber (cellulose) Peat [Lignite Bituminous coal Semibituminous coal . . Semianthracite Anthracite Graphite 5.25 5.96 5.27 5.58 5.84 5.05 3.56 rately. The anthracite, semianthracite, and semi- bituminous groups are fairly easy to define, but the term bituminous embraces such a wide variety of coals that it is of but little value in defining limits. The term lignite is even more loosely defined. In fact, no method of accurately defining the various classes of coals is generally accepted because of the difficulty of adapting a scheme of classification that will apply to lignites, as well as to bituminous coal and to anthracite. Various schemes of classification have been proposed from time to time, but none have been entirely satisfactory. One classification. Table II, is the Carbon-Hydrogen Ratio Classifica- tion proposed by Mr. M. R. Campbell and based on tests made by the U. S. Geological Survey and on the results of numerous government ultimate analy- sis of coals from all parts of the country. It is claimed that carbon and hydrogen are almost equally valuable fuel elements of coal ; hence, a classification to be satisfactory should take them both into account. COAL AND ITS COMBUSTION. TABLE II. Coals Arranged According to Carbon and Hydrogen Content. Pennsylvania, No. 3 . . Arkansas, No. 5 West Virginia, No. 11 Arkansas, No. 2 Arkansas, No. 1 West Virginia, No. 7. Arkansas, No. 3 West Virginia, No. 12 West Virginia, No. 10 West Virginia, No. 6. West Virginia, No. 4. West Virginia, No. 5. West Virginia, No. 9. Alabama, No. 2 Pennsylvania No. 4.. West Virginia, No. 3. Kentucky No. 4 West Virginia, No. 8. West Virginia, No. 1 . Illinois, No. 3 Kentucky, No. 1 Indian Territory, No. 3 Alabama, No. 1.. . . Indian Territory, No. 2 West Virginia, No. 2. Kansas, No. 5 Indian Territory,No. 1 Indian Territory, No. 4 Iowa, No. 1 Texas, No. 2 Kansas, No. 1 Illinois, No. 6 Montana, No. 1 North Dakota, No. 2 Kansas No. 2 Anthracite Spadra bed Pocahontas bed Huntington bed Huntington bed New River field Huntington bed Pocahontas field Pocahontas field New River field Upper Freeport bed Upper Freeport bed Kanawha field Warrior field Connellsville field Upper Freeport bed Western field Kanawha field Pittsburg bed Marion County Eastern field McAlester bed Warrior field Hartshorne bed Pittsburg bed Weir-Pittsburg bed Henryetta bed McAlester bed Wapello County Brown Lignite, Wood Co.. Weir-Pittsburg bed Montgomery County Red Lodge Brown Lignite, Williston'f. Weir-Pittsburg bed 3.39 4.36 4.58 4.65 4.66 4.67 4.68 4.72 4.83 4.99 5.35 5.38 5.46 5.54 5.54 5.54 5.62 5.62 5.67 5.68 5.68 5.70 5.73 5.74 5.75 5.81 5.86 5.86 5.88 5.90 5.95 6.04 6.04 6.05 6.06 90.73 90.11 89.95 90.18 88.16 87.95 87.89 90.55 90.63 88.72 86.26 85.97 85.86 80.10 87.10 85.95 82.38 85.86 84.45 77.67 83.03 80.17 83.29 82.07 84.01 S4.45 79.69 76.55 78.96 64.05 82.68 74.86 69.41 59.54 83.81 COAL AND ITS COMBUSTION. TABLE II — Continued. Name of Sample North Dakota, No. 1. Kentucky, No. 3 Kentucky, No. 2 Illinois, No. 4 Wyoming, No. 2 Colorado, No. 1 Illinois, No. 1 New Mexico, No. 1 . . . Indiana, No. 1 Iowa, No. 2 Indiana, No. 2 Missouri, No. 1 Iowa, No. 4 Iowa, No. 3 New Mexico, No. 2 . . . Kansas, No. 4 Missouri, No. 2 Iowa, No. 5 Wyoming, No. 1 Missouri, No. 4 Texas, No. 1 Name of Bed or Field Brown Lignite, Lehigh fd Western field Western field Belleville field Cambria field Black Lignite, Bolder field Belleville field Black Lignite, Gallup field. Sullivan County Marion County Warrick County Rich Hill field Appanoose County Polk County Black Lignite, Gallup field. Atchison field Bevier field Lucas County Black Lignite, Sheridan f d. Morgan County Brown Lignite, Houston Co. c bo « ) 70 80 50 /Oi9 Fig. 1. Per Cent. Fixed Carbon in Coal. Dry and Free from Asli. carbon at the beginning of the curve makes a large increase in the heating value of the coal. For ex- ample, increasing the fixed carbon from 51 per cent, to 52 per cent, increases the heat value per pound of combustible about 450 B. T. U. On the other hand, increasing the fixed carbon from 72 to 73 per cent, increases the heat value per pound of com- bustible only about 50 B. T. U. The curve shows, also, that, for steaming purposes, increasing the per- centage of fixed carbon above 80 per cent, causes a reduction in the heating value per pound of com- bustible, as already explained. The percentages of fixed carbon in more than 300 different coals are given in column 12 of Table A in the appendix. Hydrogen.— Hydrogen, though forming only a small percentage of the total combustible of coal. COAL AND ITS COMBUSTION. 29 is an important element of combustion, because, in burning, it produces nearly four and one-half times as many heat units per pound as carbon. It is found in the uncombined state in certain fuel gases, but in coal it is more commonly found combined with car- bon in the form of hydrocarbons, and with oxygen, in the form of water, as moisture. That part of the hydrogen which is combined as water is of no fuel value, and must be deducted from the total hydrogen in calculating the heat value of the hydrogen of a coal. The hydrogen that remains after deducting that which is combined with oxygen is capable of being burned, and is called the available hydrogen. If a fuel contains both oxygen and hydrogen, it is assumed that all the oxygen is combined with hydro- gen in the form of water. Water consists, by weight, of 8 parts of oxygen and 1 part of hydrogen. If, therefore, the oxygen in the coal is 8 times or more the weight of hydrogen, all the hydrogen will be combined with the oxygen and there will be no avail- able hydrogen ; if the oxygen is less than eight times the weight of the hydrogen, then the oxygen will combine with one-eighth its weight of hydrogen and the remaining hydrogen will be hydrogen in excess, or available hydrogen. The available hydro- gen, therefore is equal to the total hydrogen minus one-eighth the weight of the oxygen. Since oxygen in coal renders one-eighth its weight of hydrogen of no fuel value, it is plain to be seen why high-oxygen coals are of less heat value than coals of low-oxygen content. From an inspection of column 7, Table A, it will be seen that the variation in the amount of hydro- gen in any coal is not great, so that, from the stand- point of the heat value of the coal, the hydrogen 30 COAL AND ITS COMBUSTION. alone need not be given special consideration. It is the relation of the hydrogen to the oxygen that counts. The hydrogen is important in coals high in sulphur, because the general result of high-hydro- gen content is the neutralization of the bad sulphur effect. A high-hydrogen, low-oxygen content results in high available hydrogen. In coking coals, hydrogen is especially impor- tnat, because the adaptability of a coal to coking appears to be indicated by the ratio of the hydrogen to the oxygen contents, on the moisture-free basis. Practically all coals with H:0 ratios of 59 per cent, or more possess the quality of coking; the coking property seems to depend on the relative amount of hydrogen to oxygen on a moisture-free basis. With anthracite and semianthracite, the H:0 ratio does not always hold, as a relatively high carbon ele- ment in the volatile combustible of the coals with more than 79 per cent, of fixed carbon seems to be necessary in order to obtain the best coking results. Volatile Combustible Matter. — The combustible referred to in connection with the curve. Fig. 1, is the sum of the fixed carbon and the volatile com- bustible matter of the coal. A combustible contain- ing 52 per cent, of fixed carbon would, therefore, have 48 per cent, of volatile matter; one with 80 per cent, would contain 20 per cent, volatile matter; and so on for the other values of the curve. From the curve, therefore, 80 per cent, of fixed carbon and 20 per cent, of volatile matter appear to give the best results for coals used for steaming purposes. Reducing the volatile combustible matter from 20 per cent, to reduces the heating value of the com- bustible from 15,840 to 14,580 B. T. U. On the other hand, increasing the volatile combustible mat- COAL AND ITS COMBUSTION. 31 ter from 20 to 48 per cent, decreases the heating value of the combustible from 15,840 to 12,420 B. T. U. The reasons for this were given in the article on Fixed Carbon. As already mentioned, the results indicated in the curve. Fig. 1, are average results obtained from tests of seventy-eight different coals. As a matter of fact,i|the volatile content of different coals differs greatly in character. The volatile matter of the younger (Geologically) Western coals includes com- paratively large amounts of inert non-combustible material, such as carbon dioxide, and water and cor- respondingly small proportions of hydrocarbon gases and tarry vapors. Also, larger amounts of gas and tarry vapors are driven off quickly at moderate tem- peratures when the furnace temperature is low, and this greatly increases the amount of gas that escapes unburned.J It is very probable that the greatest heat loss through unburned gases occurs through the escape of the first gaseous products that are driven off, as at that time the furnace conditions are least favorable to the burning of gases. This loss due to inert volatile matter and to the escape of unburned gases explains the low efficiency usually obtained in burning high-volatile Western coals. The older bituminous coals of the Eastern type yield volatile matter that is low in inert non- combustible matter, but high in hydrocarbons and tarry vapors that are difficult to burn without smoke and without loss through unburned gases, due to lack of temperature, lack of combustion space, and lack of air properly mixed with the gases. These facts explain why a coal like Pittsburg coal is so difficult to burn without producing dense, black smoke. The presence of considerable light hydro- 32 COAL AND ITS COMBUSTION. carbon gas in the volatile matter of Pocahontas coal at low temperatures undoubtedly contributes to the smokelessness of that coal, because the burning of the hydrogen with its high-heat value assists greatly in producing the temperature necessary to the burn- ing of the smoke-producing content of the volatile. The inert non-combustible matter varies from 4 per cent, of the volatile in an Eastern coal hke Pocahontas to 42 per cent, in the subbituminous coals of Sheridan Field, Wyoming. Therefore, in designing a plant for steaming purposes that is to burn high-volatile coals, it is important that the furnace and draft be adapted to the kind of coal to be burned, and this necessitates a knowledge of the amount and the character of the volatile matter given off at different temperatures. Without this knowledge, the design will be only guesswork, as it is impossible to design a plant for the greatest efficiency without a thorough knowledge of the characteristics of the coal that is to be used. Gaseous Products at Various Temperatures. — The total quantities of different gases derived from 10 grams of air-dried coal and the quantities given off at the different temperatures is shown in Figs. 2, 3, and 4. The curves are plotted from data of Government tests reported by H. C. Porter and F. K. Ovitz of the U. S. Department of Interior, Bureau of Mines. Coal No. 1 is an lUinois coal from the No. 7 seam of the Ziegler, Franklin Co. mine. It represents the non-coking interior province coals and ranks high in volatile matter, in heating value, and as a steaming coal. Coal No. 3 is a Pennsylvania coal from Connells- COAL AND ITS COMBUSTION. 33 ville, Fayette Co., and is a representative steaming coal of the Pittsburg district. It is a coking coal, slightly lower in volatile matter and of higher heat- - -- ~ 1 - ' V J T 1 7 : t 2 2 ■$ « z R 5 - - " -v-Z! - A J ^^t ^ S2 ^^ z *s "S i h -/ ^^no ^ ?> ' ^ - ^ ^ •t. ,^ . «'',-' - : ^=' ^^ ^nn — ^ ^^ ;.^,-' ,«o^^' 1^^ ,^ -i,'^- 2 7 : ~ f,ti '"«■-' 7^ : ' Q."^ ■" '^ ^ K \s'~^^ — -'' -■^ tttt'^-'''^ f ^^''' J >c ^ C - "" ,^ --'' -I'- - rj-MiH-44tTM -___ S52 ///2 /^S^" /-#r.P /fiiKe /' s -it^y ^3^^ 3/d. G i ^^ \ ■ t -C^ « - JL 22 ■§^ ^ / S 1~ V % -,/ ,^ 1 Tt J \ -t -X ■5 jt 1 5 '^ / POoT-t-d , ttt Xit w ir P32 ///2 /?92 /^r^ /55? /5J2 Temperature In degrees Fahrenheit. Fig. 3. Illiiminants and Hydrocarbons in Coal. highest heating value of the bituminous coals, is low in volatile, and is one of the so-called smokeless coals. Coal No. 11 is a Wyoming coal from Dietz, Sheri- COAL AND ITS COMBUSTION. 35 dan Co. It is a low-grade, black lignite of low heat- ing value and high oxygen and moisture content; therefore, it gives a very low efficiency when used in 932 t/l2 JZ92 /4^7'2 /65P /SSZ Tt'uipcralurc in legrces Fabrcnlicit. Fig. 4. Hydrogen In Coal. steaming plants. It contains 30 per cent of moisture and slakes badly in weathering. From Fig. 2 it will be seen that, with the excep- 36 COAL AND ITS COMBUSTION. tion of coal No. 11, the volume of carbon dioxide plus carbon monoxide (CO^ + CO) given off is practically uniform throughout the range of temperature. The Illinois and Wyoming coals, however, give off much greater amounts than the Eastern coals. On the other hand, the Eastern coals, Figs. 3 and 4, give off considerably more hydro- carbons and more hydrogen than the Western coals. The heavy hydrocar- bons. Fig. 3, are given off much faster and in much greater volume from 982° F. to 1,292° F. than above that temperature, thus mak- ing them difficult to burn completely and without smoke, as the furnace con- ditions are not so favorable at the lower temperatures. All the hydrogen, on the other hand. Fig. 4, is prac- tically given off at temper- atures above 1,292° F.; therefore, furnace condi- tions are more favorable for the burning of hydro- gen. The smoky constitu- ents of the volatile matter consist of illuminants and heavy hydrocarbons, as well as tarry matter. Figs. 5 and 6 show the amounts ///? /eaa A^ri* /isa? Temperature of Furnace, Degrees Fahrenheit. Fig. 5. Smoliy Constituents of Coal. COAL AND ITS COMBUSTION. 37 of the smoky constituents in 10 grams of air-dried coal and the rates at which they are evolved as the temperature is increased from 1,112° F. to 1,652° F. Diagrams of two new coals, Nos. 10 and 18, are added in these figures. Coal No. 10 is a high- volatile West Virginia, Page, Fayette Co., gas coal; coal No. 18 is a "long-flame," high-grade, Wyoming steam coal from Diamondville, Juniata Co. The smoky constitu- ents, it will be noted, are greatest in the Connells- ville. West Virginia and Wyoming gas coals, the heavy hydrocarbons, espe- cially, being evolved quick- ly and in large volume during the early period of heating. The character and the volume of the volatile given off during the early period of heating have much more effect on fuel economy, on the pro- '~^5B duction of smoke, and on the general efficiency of the furnace than the vola- tiles produced at the later periods of heating, early periods of heating, neither the air supply nor the furnace temperature conditions are such as to iSo :. ~ i i^ _ -_p: ji -5^ •^ ' ~w 7 7 •~ ul I ' "s ^ 71 / s' X'^° ' htt-~- ^ ?/f ^ Lh b -,*«, ^ * /W '^ -„^9i?S'' ,» M olZ/'i -E5.^:-.r 2 > t 4 ^ zi-tJ . \ jtcz c^ xX < 4oM^ ^ . Temiiorature of Furnace. Degrees Fahrenheit. FiR. 6. Higher Hydrocarbons in Coal. This is due to the fact that, in 38 COAL AND ITS COMBUSTION. burn all the volatile gases completely. The per- centage of volatile matter in more than 300 kinds of coal are given in column 13 of Table A. Moisture. — ^Moisture in coal appears as surface moisture, or that which is on the exterior surface of the coal, and as hygroscopic moisture, or that which is held within the pores of the coal by capillary attraction. The surface moisture is readily absorbed by the atmosphere, whereas the hygroscopic mois- ture can be driven off only by heating the coal to a temperature of from 225)° to 250° F. The quantify of surface moisture that a coal will hold depends on the amount of surface exposed to the weather. Since breaking a lump will increase the surface exposed, it follows that small coal will hold more moisture than large lumps. When wet down or when rained upon, fine coal or slack may hold 10 per cent, of surface moisture. The capacity of coal to hold hygroscopic mois- ture varies greatly, even for coals of the same age and district and under apparently the same condi- tions as to progressive metamorphism. The capacity seems to depend largely on both the character of the original constituent organic matter and the condi- tions governing the first stages of coal formation. If a portion of the hygroscopic moisture be removed by heating the coal and the coal then exposed to the atmosphere, the coal will slowly reabsorb moisture until, finally, it will contain the original amount. -^^ Moisture exercises an anticalorific influence on coal, by which is meant an influence that reduces the power of the coal to produce heat. Moisture does this in three ways : By reducing the quantity of coal actually obtained by an amount equal to the weight of the moisture; by vaporizing the moisture in the COAL AND ITS COMBUSTION. 39 furnace at the expense of a portion of the heat of the | coal; and by then heating the vapor to a furnace temperature and cooling it to the temperature of the escaping gases of combustion, thus absorbing still more hea t, which is jwasted_thr""gh tViP stjirk The anticalorificlnfluence of moisture seems to increase slightly with the capacity of the coal to absorb moisture, as will be seen from Table VII, which is based on data obtained from seventy-nine Government tests of coal from the several localities given. TABLE VII. Loss in Heat Value Due to Moisture. Locality of Coals Arkansas. . . . Pennsylvania . Alabama West Vii'ginia Kansas Kentucky. . . . New Mexico. . Illinois Missouri Indiana Iowa Wyoming. . . . Colorado Per Cent, of Per Cent. Loss of Total Heating Value of Combustible Due to In Coal RInisture in Coal 1 Per Cent of Moisture in Coal 1.81 .17 .094 1.90. .18 .095 3.69 .40 .108 3.72 .24 .064 4.35 .45 .103 6.31 .66 .106 9.52 1.11 .116 11.31 1.37 .114 12.24 1.56 .127 12.48 1.43 .114 13.12 1.66 .126 16.46 2.20 .133 19.78 2.49 .126 From this table it will be seen that while 1 per cent, of moisture in Pennsylvania coal will cause a loss of only .095 per cent, of the total heating value of the combustible of the coal, 1 per cent, of mois- ture in Wyoming coal will cause a loss of .133 per 40 COAL AND ITS COMBUSTION. cent, of the heating value of the combustible of the coal. The first column of Table VII gives the per- centage of moisture in the coals ; the second column gives the loss due to the moisture expressed as a percentage of the total heat value of the combustible of the coal; and the third column is obtained by dividing the values in column 2 by the values in column 1, which gives the relative loss due to 1 per cent, moisture in the coal. It will be noted that the relative loss due to 1 per cent, of moisture increases according to the amount of moisture contained in the coal. The moisture not only reduces the heat value of the coal itself, but also reduces the actual amount of coal obtained per ton. For example, a ton of 2,000 pounds of Wyoming coal. Table VII, would contain 2,000 X 16.46 = 329.2, say 330, pounds of water, and only 1,670 pounds of coal. Thus, 380 pounds of water is purchased at coal rates, to which must be added the freight costs and the costs of hauling, handling, and storage. Also, in burning the coal, the moisture must be heated from normal temperature and vaporized in the furnace, and this requires about 1,100 units of heat per pound of water; the vapor thus formed must then be heated to the temperature of the gases of combustion in the uptake, which absorbs about 165 heat units from the fire, making a total of nearly 1,300 heat units loss per pound of moisture. The loss for 330 pounds of moisture would be 330 X 1,300 = 429,000 B. T. U. This represents a loss of 429,000 -^ 12,500 = 34 pounds of coal, so that the loss in coal due to the moisture equals 330 + 34 = 364 pounds per ton of coal. It is very probable that more heat is carried away with the moisture vapor and com- COAL AND ITS COMBUSTION. 41 bustible gases than is usually attributed to that loss, because the specific heat of the vapor and the gases of combustion probably increases with the tempera- ture. This may explain in part the losses unac- counted for in the heat balance of steaming tests. The loss would be especially high with the low-grade, high-moisture, high-oxygen coals. The percentages of moisture contained in over 300 coals are given in column II of Table A. Ash. — Earthy matter and other mineral impuri- ties in the coal that will not burn are classed as ash. Ash, in coal, not only includes the ash contained in the original plant and vegetable matter from which >. the coal was formed, but also includes silica and alumina in the form of sand, clay, shale, and slate, with varying amounts of ferric oxide, lime, mag- nesia, potash, and phosphoric acid. Also, it may con- tain fragments of the roof or floor of the mine or other impurities that become mechanically mixed with the coal in the process of mining or in transpor- tation. The clay, shale, and slaty material can, to some extent, be removed from the coal by hand pick- ing, or they can be removed quite thoroughly by crushing and washing the coal. Ash, like moisture, is anticalorific in that it reduces the heat value of the coal by taking the place of combustible matter. Therefore, it acts as a dilutent. Also, like moisture, it is bought at coal rates and, in the coal, costs money for hauling, hand- ling, and storage; besides, additional expense is incurred in cleaning the fires and ashpit and in the final disposition of the ash. The worst feature of ash, however, lies in the fact that it not only reduces the heating power of the coal on the grate, but also acts as an obstruction to the flow of air and distrib- 42 COAL AND ITS COMBUSTION. utes the air unevenly through the bed of fire, thus reducing the rate of combustion still more. In other words, for every 100 pounds of coal containing 15 per cent, of ash that is fired there would be less than 85 pounds of combustible burning; also, the 15 pounds of ash would block the air passages in the fire and make the combustible burn more slowly than it oth- erwise would, besides disturbing the uniform dis- tribution of air through the bed of coal in the fur- nace. The rate of combustion, therefore, is reduced in two ways by the action of the ash, and results in a reduced boiler capacity. With ordinary furnace equipment, there will be considerable loss in boiler capacity through a large percentage of ash, and with some of the poorer equipments there probably will be a drop in both boiler efficiency and boiler capacity. Besides the mineral non-volatile ash that all are familiar with, there is a portion of the ash that is volatile. This volatile portion is the water of hydra- tion or other volatile matter chemically combined with the mineral substance in such a manner that it is driven off when the ash is at a red heat. For example, the combined water in the shale, clay, slate, etc. is driven off and does not show up in the ash; lime in the ash, either as calcium carbonate or other- wise, loses carbon dioxide when heated; also, chlor- ine, as alumina combined as clayey matter, or in any other form, would be volatile. The quantity of lime in the ash is indicated by the amount of carbon dioxide in the volatile ; where- as, the quantity of alumina is indicated by the amount of chlorine. These volatile non-coal contents, in ordinary methods of coal analysis, are classed with the volatile combustible matter and do not show up COAL AND ITS COMBUSTION. 43 in the ash; consequently, coals high in these con- tents receive a higher heat rating than they deserve. From column 10, Table A, it will be seen that the ash in more than 300 coals ranges from 1.68 per cent, to more than 25 per cent., the higher values in the table being for screenings and slack. The ash in 204 other samples of coal arranged according to the sizes of the coal, is shown in Table VIII, which is compiled from data of Government tests. TABLE VIII. Ash Fiom Different Sizes of Bituminous Coals. Size of Coal Total No. of Sam])les Number of Samples Containing Ash, Between 2-5 % 5-8 % 8-10 1 10-13 13-15 % 1 % % 15-20 % 20-25 % 25-30 % Slack 49 4 4 7 8 17 7 2 Run-of-mine . 13 4 3 3 2 1 Nut 58 2 16 16 14 4 4 2 Pea 4 2 2 Lump 60 7 24 14 12 3 Total 204 13 47 39 35 15 24 9 2 It will be observed that the ash in slack is high in a majority of cases, varying from 10 to 25 per cent. The ash in the run-of-mine is fairly low, in most cases varying from 2 to 10 per cent. The nut and lump appear to run higher, most of the coal ranging from 5 to 13 per cent. The total quantity of ash in shipments of the same coal may vary considerably because of lack of care in removing the dirt, shale, rock, slate, etc. that accompanies the coal as it comes from the mines. The lumps of coal may average 5 per cent, of ash; whereas, the coal as shipped may average 15 per cent, owing to the dirt, etc. Usually, the per 44 COAL AND ITS COMBUSTION. cent, of ash in the smaller coals and in run-of-mine is larger than in the sized coals. Coals with less than 10 per cent, of ash is considered good, market- able coal. Rock, Slate, and Bone. — Anthracite, whether for domestic or for steam purposes, is allowed by the standard specifications to carry a certain percentage of rock, slate, or bone, according to the size of the coal. A piece of coal containing hardly any carbon is classed as rock; a piece containing less than 40 per cent, of carbon is classed as slate; a piece con- taining from 40 to 65 per cent, of carbon is classed as bone ; and a piece containing over 65 per cent, of carbon is classed as coal. Broken or grate coal is allowed 1 per cent, of slate or rock, and 2 per cent, of bone. Egg coal may contain 2 per cent, of slate or rock and 2 per cent, of bone. Also it must be free from mud or discoloration. Stove coal may contain 4 per cent, of slate or rock and 3 per cent, of bone. It must be free from mud and fairly free from discoloration. Chestnut or nut coal may contain 5 per cent, of slate or rock and 5 per cent, of bone. It must be free from mud or discoloration. Pea coal may contain 10 per cent, of slate or rock and not much more bone than slate. Its color must be fairly bright. Buckwheat No. 1 may contain 15 per cent, of slate or rock and not so much bone as to make the mass look dull in color. It must be washed free from mud. If it is washery coal, the ash is counted in with slate, and it must not contain more than 2 per cent, of ash. Rice coal may contain up to 20 per cent, of slate. COAL AND ITS COMBUSTION. 45 Barley coal must present a fairly bright appear- ance. A piece of coal free from bone, slate, or rock will burn to a fine ash unless the ash fuses and clinkers. Bone, slate, and rock maintain their form and appear in the ash in nearly their original size. An inspection of the ash, therefore, gives a good idea of the quantity of bone, slate, or rock in the coal. Commercially pure coal free from bone, slate, and rock will burn to a fine, white ash that is light in weight and small in bulk. If the coal contains iron pyrites, the ash will be of a reddish color, will be heavy, and will contain clinkers. If the coal con- tains bone, slate, or rock, the ash will indicate it by the pieces that are in the ash ; also, the ash will be heavy and of considerable bulk. Oxygen. — By reference to Table I, it will be seen that each step in the conversion of organic matter into coal is accompanied by the elimination of a part of the original oxygen of the organic matter that entered into the coal in its formation. Begin- ning with more than 40 per cent, of oxygen in the cellulose and lignose that comprises the bulk of the organic substance of coal, the amount reduces with each higher grade of coal until, in anthracite, it is only about 4 per cent. Each step in the elimination of the oxygen is accompanied by an increase in the per cent, of carbon, and, consequently, in the heat efficiency of the coal. Oxygen, therefore, is an original impurity in coal that detracts from the value of the coal, and its elimination results in increased heat value. A comparative study of numerous ultimate coal analyses of the U. S. Geological Survey by David White, supplemented by calorimeter tests, seems to 46 COAL AND ITS COMBUSTION. indicate that the anticalorific effect of oxygen in coal is nearly equal to that of the same weight of ash, the ash probably being slightly more injurious in most coals; that is, the calorimeter tests seem to show that if two coals have the same carbon con- tent, one having 15 per cent, of ash and 4 per cent, of oxygen and the other 15 per cent, of oxygen and 4 per cent of ash, their heat efficiency will be nearly the same. Furthermore, the negative value of the oxygen of moisture in the coal does not seem to differ much from that of the oxygen combined in the coal. In the lowest grades of bituminous coal, and for the grades of coal lower than that, it is probable that the oxygen is slightly more anti- calorific than the ash ; in the higher bituminous and the semibituminous coals, the ash has probably the higher anticalorific value. As oxygen and ash are approximately of equal anticalorific value, the efficiency of coals are found to conform fairly close to the order of the ratio of their carbon — to their ash plus their oxygen. From an inspection of column 14, Table A, it will be seen that among coals of all kinds those having the same ratio of C to + ash are found to have very nearly the same efficiency. Sulphur. — As a coal constituent, sulphur differs greatly both in quantity and in the condition in which it occurs. It is found in coal in four principal chemical conditions : As iron pyrite, or marcasite ; as sulphates of iron, lime, and alumina ; as organic sul- phur, that is, combined with carbon, hydrogen, and oxygen ; and, in rare instances, as free sulphur, that is, sulphur that is not in combination with other elements. '! In, some coal beds, pyrite is found in balls, bands, COAL AND ITS COMBUSTION. 47 and lenses. In other coal beds, it occurs throughout the lumps of coal in veinlets or as small particles. In weathered coal, sulphur is found combined as sulphates of iron, lime, and alumina. When exposed to the air, pyrite and marcasite tend to absorb oxygen and form sulphate of iron. We heat effect of the sulphur depends on the quantity, on the state of occurrence, and on the I available hydrogen present. Free sulphur is com- paratively harmless and may exert its full heat value. In the form of pyrite or marcasite, or other sul- phides, its heat value is lessened by combination, and differs with surrounding conditions. As a sul- phate, sulphur is of no fuel value. As the heat value of sulphur is very much less than that of car- bon, sulphur, even in its most favorable form, reduces the heat value of the coal, unless it is com- pensated by high available-hydrogen content. From a comparison of columns 7 and 9, Table A, it will be observed that, fortunately, coals high in sulphur are as a general rule also relatively high in hydrogen. The high hydrogen usually results in neutralizing the bad effect on the heat value of the coal of high sul- phur content. Aside from its effect on the heat value of the coal, high sulphur content in coal is injurious to the metal of the boiler, because the products of its com- bustion, sulphurous acid, attacks the metal of the boiler, particularly in the presence of moisture. The sulphurous acid is transformed into sulphuric acid under the action of the moisture, and attacks the iron, producing sulphate of iron. Nitrogen. — Nitrogen is an inert gas; hence, it acts as a dilutent in coal. By an inspection of col- umn 5, Table A, it will be seen that the percentage 48 COAL AND ITS COMBUSTION. of nitrogen in coal is quite low, averaging only 1.21 per cent, for the 319 samples in the table. It is quite uniform in amount for each kind of coal, but differs slightly for the different groups. It is highest in the peats and succeeding low grades of coals, and lowest in the anthracites and graphites. As it is present in such small quantities, and as it varies so little in amount in the same kinds of coals, it is of but relatively small importance in the study of fuels and in the purchases of coal. CHAPTER V Effect of Size op Coal I N GENERAL, it may be said that, other things being equal, the coal obtainable at the lowest price is the most eco- nomical, provided the furnace and the draft equipment are designed for the use of the kind and grade of coal selected. The size of coal to be used in a given plant, however, must be considered, because the size influences the capacity of any given equipment, owing to its effect on the draft. Coal of uniform size will give the best satis- faction, as it does not pack so closely as coal of dif- ferent sizes and will therefore burn more freely and will give greater boiler capacity for a given draft. With pea coal or with larger sizes, no difficulty should be experienced in developing the full capacity of a boiler, provided the plant is properly designed. However, with the finer sizes, much difficulty will be encountered in burning the coal so as to obtain full boiler capacity, unless, of course, the plant is very carefully designed for the purpose. The weight of air per pound of combustible con- sumed is much greater for the fine sizes than for the larger sizes of coal, and the excess air is nearly twice as great. Also, with fine sizes, the rate of combustion is limited by the rate of air supply that will lift the coal and disrupt the fuel bed so as to permit air to pass through the bed without coming into contact with the fuel. Just as soon as the fuel bed is dis- 49 50 COAL AND ITS COMBUSTION. rupted, the rate of combustion decreases and there rushes through an excess of air that results in a drop of the boiler capacity. The rate of combustion will increase as the draft is increased up to the point of disruption, after which increasing the draft will result in decreasing the boiler capacity. The great- est rate of combustion that can be obtained with a fine coal without disrupting the fuel bed is called the maximum rate of combustion for that size of coal, and the finer the coal the lower its maximum rate will be. As the maximum rate of combustion per square foot of grate area is limited for fine coal, sufficient grate area must be provided to burn the required amount of coal to develop the full capacity of the boiler. Large sizes of coal stand shipping and storing better than small sizes and are better adapted to a wider range of furnace conditions. Effects of Weathering Coal Loss of Calorific Value, — Storage of coal has become a necessity, in order that a sufficient reserve supply may be on hand to enable the industrial interests of the country to run without interruption in the event of labor troubles, car shortages, or other unforeseen circumstances that might temporarily prevent the delivery of coal. It has been commonly believed that coal in storage and exposed to the weather for a considerable time loses much of its heating value. Careful experiments, however, by Parr and Wheeler and others, seem to indicate that the loss is not nearly so great as has been imagined. Coal may be stored in the open air, in covered bins, and under water. The loss through storage may occur through change in weight, through loss COAL AND ITS COMBUSTION. 51 in calorific value, through disintegration, or through spontaneous combustion. Anthracite is practically unaffected by weather, except for the oxidation of the sulphur content, which is small. It is broken somewhat through handling, but is not subject to spontaneous combus- tion. There is practically no limit, therefore, to the size of the piles in which anthracite may be stored. The effect of weathering bituminous coals depends on the nature of the coal. The weight of the coal, in some cases, may be either increased or de- creased, depending on conditions. Atmospheric oxi- dation of the coal proceeds slowly, but continuously, under ordinary temperatures; usually, it does not produce any sensible increase in the temperature of the pile, owing to the radiation that is going on at the same time. However, it results in a decrease in weight and in the heat value of the coal. At higher temperatures, and with certain coals, the rate of oxidation is very much increased, and this tends still further to accumulate heat in the pile and may result in a temperature sufficient to ignite the coal. The coals most readily oxidized in the air are the ones that change most in weight and are more subject to spontaneous combustion. The higher the tempera- ture to which the pile is raised, the greater will be the resulting loss in weight and in heat value of the coal. As a general rule, however, very little change in weight occurs unless the coal heats considerably. Atmospheric oxidation may or may not result in a visible change in the coal, depending on the im- purities contained in the coal. If pyrite, marcasite, or some other inorganic impurity is present, visible changes will occur because of their oxidation. The iron sulphide of the coal will combine with the oxygen 52 COAL AND ITS COMBUSTION. of the air and form sulphate of iron and sulphuric acid. The sulphuric acid will then unite with the calcium and the magnesium of the coal and form, respectively, gypsum and magnesia sulphate. This change will result in an increase in the bulk of the pile and will cause disintegration of the coal; also, there will be a considerable increase in the weight of the coal unless the leaching action of the water compensates for the increase in weight. If the inorganic impurities are not present, no effect of the oxidation will be visible except that, in some coals, after long exposure, the color will be- come dull and of a brownish hue, similar to that of brown lignite. The loss in the calorific value of the coal is most rapid during the first few weeks after mining, after which this loss decreases at a constant rate ; also, the finer the coal, the greater the loss seems to be. The loss in screenings is larger than in nut coal, and so on. The loss for Illinois coal for 1 year was found to be 2.76 per cent, when exposed to the weather, 3.14 per cent, in covered bins, and 1.49 per cent, when stored under water. It is possible, therefore, that for the Illinois type of coal the calorific loss through storage will not exceed 3 per cent, in 1 year. The greatest loss occurs during the first 6 months. Disintegration. — Weathering disintegrates the lower grades of coal, causing them to slake or to break into fine pieces. Such disintegration greatly in- creases the loss in transportation and renders effi- ciency in burning the coal very difficult. The value of such coals, therefore, may be very greatly diminished by exposure to the weather, even though the calorific value may be practically unchanged. Disintegration might change a coal of a suitable size COAL AND ITS COMBUSTION. 53 to one of a smaller size that could not be burned economically in the plant for which it was originally purchased. Weathering also destroys the coking properties of coal. Coal stored out of doors disinte- grates more than coal protected from the elements. The disintegration is due to small cracks made by the shot that was fired at the time the coal was mined, to the action of frost, and to the breaking up of the lumps by the action of pyrite and marcasite in oxidizing. Probably the best way in which to prevent such disintegration is to store the coal under water, thus entirely overcoming the action of frost. Coal is much more frail after storage than when freshly mined, and breaks and crumbles more easily in handling. When coal is stored in piles subject to weather conditions, it is found that the weathering does not extend into a coal pile more than 12 to 18 inches, the depth depending on the length of time that the coal has been stored. The outer layers oxidize and slake and thus form a protective coat that serves to shield the inner coal from the effects of weathering. Spontaneous Ignition. — Most bituminous coals will ignite spontaneously if stored in large enough piles. Such ignition is due to the heat produced by the absorption of oxygen by unsaturated hydrocar- bons of the coal and by the oxidation or slow cumbus- tion of carbon, sulphur, and available hydrogen, in an air supply that is sufficient to support oxidation, but is not sufficient to remove entirely the heat that is produced in the process. This absorption and oxi- dation goes on continuously, and the resulting tem- perature of the pile depends on the rate of produc- tion of heat and the rate of radiation of the heat from the pile. Bituminous coal, especially when 54 COAL AND ITS COMBUSTION. freshly mined, has an affinity for oxygen which it absorbs with the evolution of heat. This heat tends to raise the temperature of the pile to the point where slow oxidation begins, after which the rise in tem- perature of the coal pile is comparatively rapid. The rate of oxidation depends on the porosity of the coal, on the amount of the surface of the coal exposed to the oxygen, and on the temperature of the interior of the pile. As porous and, fine coals expose more surface than is exposed by lump coal, they are much more liable to ignite spontaneously. The interior temperature of the pile depends on the rate of oxi- dation, on the amount of radiating surface of the pile as compared with the cubical contents, and on the circulation of air through the pile. Lump coal permits of a better circulation of air through the pile; therefore, it is easier to keep cool and is much less liable to ignite spontaneously. The radiating surface of the pile decreases with the size of the pile; hence, the interior of a shallow pile will be cooler than the interior of a deep pile. Oxidation generates heat, which, if not radiated, tends to increase the temperature and, thus, the rate of oxidation ; this tends further to increase the tem- perature, which, in turn, hastens the oxidation. This cycle is repeated until the pile assumes a natural temperature, depending on its size, contents, and radiating surface. The higher this temperature becomes, the greater is the danger of spontaneous combustion. Animal matter, vegetable matter or fats in the body of the pile greatly increase the dan- ger of ignition. The close proximity of an external source of heat, such as a steam pipe or a chimney flue, even though moderate in degree, may produce spontaneous combustion. Under favorable condi- COAL AND ITS COMBUSTION. 55 tions, the direct rays of the sun may be sufficient. Abnormal quantities of moisture, especially when the coal is alternately wet and dried through storms, etc., accelerate the process of absorption of oxygen and promote spontaneous combustion. The ground on which the pile rests should be dry when the coal is stored, because moisture from below is especially conducive to spontaneous combustion. Prevention of Spontaneous Combustion. — Spon- taneous combustion may be prevented by taking proper precautions. The coal should be screened so as not to contain a large amount of line coal, and care should be taken not to break the coal during handling and storing. If mixed lump and fine coal must be stored together, the various sizes- should be evenly distributed, so as to prevent the formation of air passages through segregated portions of the large sizes. When stored indoors, the pile should be in a fireproof bin 25 feet or more removed from the furnace, and there should be no steam pipe nor other source of heat near it. The height of a flat-top pile should be 6 feet or less for the lower grades of coal, and should not exceed 12 feet for the best grades. Where space permits, a good plan is to store the coal in piles in the form of long, narrow ridges separated by open spaces, to allow air cooling. In hot climates, where the coal would be subject to the heat of long, hot spells, the piles cannot be so high or so large as those in cooler climates. The coal should be mined at least 1 month before storing, and should not be loaded or stored in wet weather nor during hot weather. July and August, therefore, are not suit- able months for storing coal. High-volatile coals sustain greater weathering 56 COAL AND ITS COMBUSTION. losses and are more prone to spontaneous ignition than low-volatile coals. The coals from Texas and from parts of Arkansas are very liable to spon- taneous combustion, whereas Oklahoma, Missouri, Kansas, Illinois, and Northern Arkansas coals can be safely stored with proper precautions. Pennsyl- vania, West Virginia, Ohio, Kentucky, Alabama, and Tennessee coals when properly screened and piled are in very little danger of spontaneous combustion. Colorado, Wyoming, and New Mexico coals can safely be stored when proper precautions are observed. The conditions favorable to spontaneous igni- tion are porous or fine coal, the presence of moisture, a high sulphur content, occluded combustible gases, high temperature, alternate wetting and drying, and free access of air without ventilating effect. Temperature of Coal Pile. — The temperature of the pile at different points can be obtained as fol- lows: Screw a %-inch auger to an iron pipe of slightly smaller diameter, and place a maximum temperature thermometer within the pipe. Bore into the pile at the points deemed necessary, and let the pipe stand for 20 minutes so as to be sure to record the maximum temperature. The auger can be driven 8 to 10 feet per minute. In very large piles, permanent pipes into which the thermometer can be lowered are placed at points in the pile and records are kept of the temperature of the different points. When the temperature at any point reaches 140° F. to 150° F., action is at once taken to protect the pile, as oxidation increases very rapidly above that temperature. A trench of sufficient width and depth is dug to uncover the source of the high temperature. COAL AND ITS COMBUSTION. 57 Extinguishing a Coal-pile Fire. — To extinguish a coal-pile fire, the coal must be removed from around the burning part and spread out. Water can then be effectively used on the burning part. The fire is always in the interior of the pile, and a crust forms above it that prevents the water from reaching the seat of the trouble ; hence, the fire cannot be put out by drenching the pile. Where coal is to be stored in piles for 2 months or more, the interior temperature of the pile should be taken frequently, because ignition generally takes place within 90 days after storing. CHAPTER VI Clinkering of Coal Ash fORMATION OF CLINKER.— The for- mation of clinker is one of the worst troubles that has to be contended with in the combustion of coal. A knowl- edge of the degree of fusibihty pos- sessed by coal ash, therefore, is often of greater im- portance to the coal consumer than is the number of B. T. U. in a pound of the coal,, since, under certain conditions, a coal may clinker so badly as to be abso- lutely useless for furnace combustion. The seller of coal guarantees to deliver coal of a certain heat value, and he should be required to guarantee that the ash of the coal delivered shall not fuse below a certain desired temperature, depending on the fur- nace conditions and on the kind of service under which the coal is to be burned. Clinker affects both the capacity and the efficiency of a plant, as well as the cost of firing and the cost of repairs to the plant and its equipment; hence, a thorough knowledge of clinker formation is of the utmost importance to the consumer, as well as to those directly connected with the operation of a plant. Clinker is formed either by the chemical combi- nation of the constituents of the ash, thereby form- ing a slag, or by the fusing, or melting, of the ash of the coal. Every ash has a fusing temperature. Whether an ash may clinker through fusion will 58 COAL AND ITS COMBUSTION. 59 depend on whether the temperature to which the ash is subjected is above or below the fusing tem- perature of the ash. An ash having a fusing tem- perature of 2,700° F. or more will rarely give trouble from clinkering if the furnace is fired properly, since furnace temperatures seldom exceed that amount. If the fusing temperature of the ash is below 2,700° F., trouble will be ex- perienced, and the lower it is below that temperature the greater will be the trouble from clinker. Constituents of Ash. — Ash is a me- chanical mixture of sihcates, oxides, and sulphates, in which the percentages of the different constit- uents vary greatly. The siHca, however, predominates in most cases. Ash is com- posed largely of oxide of silica, SiO,; oxide of alumina, AI2O3 ; ox- ide of iron, either as ferrous oxide, FeO, or as ferric oxide, FeoO.; oxide of lime, CaO; and oxide of sulphur, SO,. Also, it contains 0. . 00000 1 rt* • 05 rH m ec rH z : r-! eg 10 • • rS U3 00 ?£) -^ m" : W N iH rH be M 00 «3 -^ e^ i> 4J IS iH ' '0 ' i-J a Ki tH rH u t- V 0" iH rH 0; •* 10 j4 (^ CO "H to ej < to IM rt » < to 1 in ■* i:g rH CTj n rH rH rH 06 rH ■<* a fl a 4) 3 4-1 0" CO o'o a '*j 00 00 00 TO 00 00 a EQ * rH m TO a — ' ^ to Tota Ash Per Cent eg in H* eg -^ S t^ t> l> 00 rH to rH rH rH « to . . _■ 3 . . .S CD . . 3 c B ., .;-i to to 3 •a acite itum Inou inou Biti A nthr smib: itum itum lack, ignit < M m m en h: 1 60 COAL AND ITS COMBUSTION. small percentages of oxide of magnesium, MgO; oxide of sodium, NaaO; and oxide of potash, K2O. It will be seen from Table IX that the composi- tion of ash varies greatly. However, the values in the tables are not given as limits to the range of variation, but merely as examples of variations in the composition of ash. Clinker is of two types, designated either as hard clinker or as soft clinker. Hard clinker is formed by the direct melting of the ash or of some of its constituents. It hardens while in the ash on the grates. If formed through a portion of the ash melt- ing, it will be in the form of a large, hard cake at some point on the grate. If formed through cer- tain constituents of the ash melting, it will be found as a number of small, hard clinkers distributed throughout the ash. Soft clinker remains molten while on the grates, but hardens when its temperature is sufficiently reduced. Once formed, the soft clinker continues to grow in size until practically the entire grate is covered. Soft Clinker. — Soft clinker is a slag formed by the combining of the silica of the ash with the most fusible constituents of the ash. Silica is infusible at ordinary temperatures ; see Table X. Also, the basic oxides of the ash are refractory materials and are quite infusible at furnace temperatures. However, the basic oxides act as fluxes for the silica and pro- mote the fusing of the silica. The silica acts as an acid flux, whereas the oxides act as basic fluxes. When two or three of the basic oxides are brought together in the presence of silica, a given temperature, depending on the proportions of the ingredients and on their melting temperatures, will COAL AND ITS COMBUSTION. 61 cause them to fuse and slag and form a silicate that is called clinker. To bring about this union, suffi- cient heat must be supplied to cause the fusion. A silicate containing one base is usually less fusible than one containing two bases, and much less fusible than one containing three bases, the same proportion of silicate to base being used in the three cases. Silica melts at 3,227° F. ; a silicate formed by the combination of FeO and SiO, fuses at 2,318° F.; if part of the iron of this silica is replaced by 16 per cent. CaO, the resulting iron-lime-silicate will fuse at 2,138° F. TABLE X. Fusing Temperatures of Oxides. Formula Atomic Weights Fusing Temperature Oxide Degrees C Degrees F Silica Si02 ALO, FeO FejOa CaO MkO Na.O K=0 60.30 102.20 71.84 159.68 56.07 60.32 62.00 94.20 1,775 1,880 1,419 1,560 1,900 2,2r)() 700 900 3,227 Alumina 3,416 Ferrous 2,586 Ferric Lime 2,840 3,452 Magnesia Sodium 3,882 1,292 Potash 1,652 Silica -Iron-Lime Slags. — Table XI* feives the formation temperatures of various silicate-iron-lime slags, in which the Hme content is increased from to 52 per cent. The curve, A, Fig. 7, is plotted from this data. From the curve it will be seen that with no lime content, the ferrous silicate forms at 2,318° •Report of Investigations by Prof. H. O. Hofman, Inst, of Tech., Boston, Mass., on the formation temperature at which ferrocalcic silicates are formea, T. A. I. M. E. Vol. 29, Pg. 704. 62 COAL AND ITS COMBUSTION. TABLE XI. Formation Temperature of Sildca-Iron-Lime Slags. Chemical Composition of Slag Equivalent Per Cent, on Si(FeO, CaO) Melting Point SiOj. Per Cent. FeO. Per Cent. CaO. Per Cent. PeO. Per Cent. CaO. Per Cent. Seger Cone. No. Degrees C. 29.20 70.80 100.00 7 1,270 29.75- 66.25 4 92.80 7.20 6 1,250 30.09 61.91 8 85.75 14.25 5% 1,240 30.42 57.58 12 78.87 21.13 4% 1,220 30.76 53.24 16 72.12 27.88 2 1,170 31.07 48.93 20 65.55 34.45 3% 1,205 31.40 44.60 24 59.12 40.88 3 1,190 31.70 40.30 28 52.80 47.20 2 1,170 32.10 35.90 32 46.60 53.40 1 1,150 32.30 31.70 36 40.66 59.34 1 1,130 32.70 27.30 40 34.67 65.33 1 1,150 33.10 22.90 44 28.81 71.19 3 1,190 33.44 18.56 48 23.12 76.88 7 1,270 33.79 14.21 52 17.55 82.45 15 1,430 F. Adding CaO uniformly lowers the formation tem- perature up to 16 per cent, of lime. Increasing the lime from 16 to 20 per cent, raises the temperature of formation to 2,200° F. Increasing the lime above 20 per cent, again causes the formation temperature to be lowered until, with 36 per cent, of CaO, the temperature is only 2,066° F. Further addition of CaO causes the formation temperature to rise rapidly. The curve shows clearly that the formation tem- perature of an ash mixture depends on the relative proportions of the constituents of the ash. Also, it shows (point a on the curve) that with a certain mix- ture the formation temperature may be several hun- dred degrees lower than the fusing temperature of COAL AND ITS COMBUSTION. 63 any of the constituents of the ash. Such a mixture is called an eutectic mixture, by which is meant a compound substance having its components mixed in such proportions that the formation temperature of kyjoo aoo "''°'<^ To to 30 *o Per Cenfatfe of CaO Fig. 7. The Formation of Ferro-Calcic Silicates. the compound is lower than the fusing temperature of any of its components. In the fourth and fifth columns of Table XI, the percentage of equivalents of FeO and CaO is given in order to show the relative fluxing effects produced by the chemical replacement of the FeO by the CaO. ^M COAL AND ITS COMBUSTION. This is calculated as follows : From Table XI, fourth row, SiOa = 30.42; FeO = 57.58; and CaO = 12. The molecular weight of FeO is 71.84; that of CaO, 56.07; therefore, |!|| + ^ = .801 + .214 = 1.015. This number, to be reduced to 100, must be multi- pHed by 98.52, since 1.013 X 98.52 = 100. The FeO, therefore, equals .801 X 98.52 = 78.92 per cent. The CaO = .214 X 98.52 = 21.08 per cent. The Seger cones mentioned in the sixth column of the table will be explained later. Influence of Ash Constituents. — The tendency of an ash to slag depends on both the ratio of silica to basic oxides and the fusibility of the bases. The fluidity of a slag depends on the character of the basic oxides of the ash, and on the amount of super- heating the silicate is subjected to. A slag may be very viscous at the formation temperature, yet it may become quite fluid when superheated. Silica. — Silica, increased from 18 to 30 per cent, does not have much influence on the formation tem- perature of a silica-iron-lime slag, the silicate fusing at 2,174° F. As the silica is increased from 30 to 48 per cent, and the base reduced from 70 to 52 per cent., the formation temperature falls almost uni- formly to 2,057° F. Increasing the silica to 56 per cent, causes another gradual drop of temperature to 2,028° F. Increasing the silica above 60 per cent, causes an abrupt rise of temperature to 2,390° F. Slags with a low percentage of silica have a slightly higher formation temperature than those with higher percentages of silica, but they are very fluid as soon as the formation temperature is COAL AND ITS COMBUSTION. 65 reached. Slags having a high percentage of siUca fuse down very slowly, carry uncombined silica, and are light, but very viscous, or pasty. Alumina. — Alumina replacing silica in an iron- lime silicate has the effect of gradually raising the formation temperature. Also, the slags become less fluid, are opaque, and change from a dark reddish- brown to a dark steel-gray color as the AI2O3 is in- creased. Alumina replacing the iron in the silicate has very little effect on the formation temperature until three-eights of the iron is replaced, when the tem- perature increases suddenly. The slags formed are quite fluid. They are opaque, with a dull luster and a dull, reddish-brown color. Alumina replacing the lime in the silicate pro- duces a slight reduction in the formation tempera- ture until about six-eighths of the lime is replaced, when the temperature gradually increases a small amount. The slags formed are not fluid, but have a tendency toward viscosity, especially with the higher percentages of AI2O3. They are opaque, slightly vit- reous in luster, and grayish-black to black in color. Iron. — ^Iron as a flux for silica alone reduces the fusing temperature of the silica only slightly. Iron in the presence of lime tends to make the slag readily fusible and fluid. U. S. Geological Survey boiler tests show that as the per cent, of iron in the coal increases, there is a decided increase in the per cent. of clinker in the ash. However, as will be seen fur- ther along, iron may be present in a coal in con- siderable quantities and yet not cause clinker. Lime. — Lime replaced with MgO causes a de- 66 COAL AND ITS COMBUSTION. cided rise in the formation temperature, especially when more than half the lime has been replaced. The MgO reduces the fluidity of the slag, which has a vitreous luster and is of a brownish color. Clinker Calculations In a paper delivered before the Coal Mining Institute of America, in 1912, Mr. E. B. Wilson, Editor of Mines and Minerals, presented a paper on "Clinkering of Coal Ashes," in which he advocated the use of Balling's factors in order to calculate whether, from the per cent, of silica and oxides pres- ent in an ash, they were in proper proportions for the coal to clinker in burning. The method consists in calculating the amount of silica necessary to re- duce the basic oxides of the ash to a monosilicate, a monosilicate being a silicate in which the oxygen in the basic oxides is equal to that in the silica. The method of calculation is as follows : Calcium mono- silicate is formed by the combination of lime with silica after the reaction, 2CaO -|- SiOj = 2CaO.Si02. The molecular weights are, 112.14 + 60.03 = 172.17. Dividing the molecular weight of the acid, 60.03, by that of the base, we have, 60.03 ~ 112.14 = .535. This is known as Balling's factor for lime, and it means that .535 part of silica is required to 1 part of lime in order to form 1.535 parts of calcium mono- silicate. The same method is followed in finding the factors for the other bases, and they are as follows : CaO, .535 ; Al.Og, .885 ; FeO, .418 ; and MgO, 747. The following analyses of two coals, with their ash analyses will be used to illustrate the method of slag calculations. COAL AND ITS COMBUSTION. 67 West Virginia Alabama Coal. Coal. Analyses of coal: Moisture 496 1.59 Volatile 19.139 30.15 Fixed Carbon 75.53 50.39 Ash 6.36 15.33 Sulphur 48 2.54 Analyses of ash: SiO, 39.02 29.14 AlA 23.52 15.56 CaO 19.97 20.73 MgO 3.27 11.91 FeO 11.14 13.42 S 24 6.00 Undetermined 2.84 Silica Required to Form Monosilicates West' Virginia Coal. Alabama Coal. Per Silica Re- Per Silica Re- Basic Oxide. Cent. Factor. quired. Cent. Factor quired. A\A 23.52 X .886 = 20.815 15.56 x .885 = 13.776 FeO 10.60 X. 418= 4.443 00.00 x .418 = 00.000 CaO 19.97 X .535 = 10.684 20.73 x .535 = 11.091 MgO 3.27 X .747 = 2.443 1.91 x .757 = 1.446 SiOj required by basic oxides 38.385 26,313 SiOj in coal 39.020 29.140 SiO., in excess 637 2.827 It will be seen that the right proportion of silica is present in each coal to slag all the oxides and form monosilicates. However, this does not signify that both coals will clinker with equal ease when burned in a furnace. The Alabama coal will require a very much higher temperature than the Virginia coal before clinker will form, owing to the fact that there is an absence of available iron in that coal. The slagging temperatures of alumina, lime, and mag- 68 COAL AND ITS COMBUSTION. nesia are so high that, unless sufficient available iron is present, no monosilicate would be formed under ordinary furnace conditions. The Alabama coal may therefore be considered a non-clinkering coal on account of the absence of available iron, the mag- nesium content, and the percentage of lime present. If there is 10 per cent, or more of available iron in the ash of a coal in which there are proportions of other bases and silica present to form monosili- cates, as in the case of the Virginia coal, a fluid slag will form and at a comparatively low temperature. The Virginia coal, therefore, will cause troublesome clinker, on account of the percentage of available iron and of lime it contains, both tending to reduce its fusing temperature. With the increase of avail- able iron in the ash above 10 per cent., the slagging temperature decreases considerably. With 5 per cent, or less available iron in the ash, the percentage, as compared with the more refractory bases, is so small that only a little slag would form, and this at very high temperatures; hence, little trouble would be experienced at ordinary furnace temperature from such an ash. Available Iron. — Iron to be available for slag- ging must be in the form of iron oxide, either as FeO or as FcgOg. Silica will not combine with iron when the iron is in the form of ferrous sulphide, FeS. Therefore, if there is sufficient sulphur in the coal to combine with all the iron, no iron will be available for a ferrous monosilicate. The Virginia coal contained .48 per cent, of sul- phur, half of which burned and the other half, .24 per cent., combined with the iron of the coal. There- fore, while the ash contained 11.14 per cent, of FeO, COAL AND ITS COMBUSTION. 69 only 10.6 per cent, was available in forming mono- silicates. In the Alabama coal, no available iron was present in the ash, because there was just sufficient sulphur present in the coal to combine with all the iron, as will be seen from the following calculation : Ferrous oxide contains — ^^ — = 77.7 per cent, of iron. The 13.42 per cent, of ferrous oxide in the Alabama coal ash contained 13.42 X -777 = 10.44 per cent, of iron. The iron necessary to satisfy the 6 per cent, of sulphur in that ash is — ' „„ — = 10.45 per cent., so that no iron was available in the ash. Effect of Sulphur. — Sulphur is not a slag-form- ing material; on the contrary, it often prevents the formation of clinker by reducing the amount of avail- able iron present in the ash. However, under cer- tain conditions, sulphur in the coal may exert con- siderable influence on the tendency of the ash to clinker. It generally occurs either in the form of pyrites or as calcium sulphate, the pyrites occurring in much larger proportions than the sulphate and being more troublesome on account of the tendency of its iron to form clinker. The tendency to produce clinker depends on the percentage of sulphur in the ash, rather than on the percentage of sulphur in the coal. A coal with a high-sulphur content commonly has a high-ash content. The percentage of sulphur in the ash, therefore, is low, and the sulphur may not prove very troublesome, because under such condi- tions, the temperature of the fuel bed is apt to be low. When the percentage of sulphur to ash is high, especially in low-ash coals, a very troublesome clinker usually results. Ferrous sulphide melts at 2,138° F. ; 70 COAL AND ITS COMBUSTION. therefore, if the fuel bed temperature is greater than this, the FeS will melt and run through the surround- ing ash. As the molten FeS cools, it cements a mass of coal and ash together into a hard clinker. The clinker thus formed shuts off the supply of air through the grates underneath it. The clinker and the grate bars underneath it then become over- heated, the grate bars warp, and the clinker melts and runs into the spaces between the grate bars. The sulphur of the clinker then combines with the metal of the grate bars, and a wasting of the grate results. The combined warping and wasting thus produced results in the destruction of the grates in a comparatively short time. Fusing Temperature of Ash. — While it is pos- sible by the methods just explained to determine from a chemical analysis of a coal whether the ash will slag or not, provided the proper temperature is obtained, yet it is not always possible to say whether the coal will clinker under the conditions of a given furnace. The conditions in one furnace may be such that a coal will not clinker badly, whereas, in another furnace, the same coal may give considerable trouble. The surest method of determining whether a coal will clinker is to try it out in the furnace in which it is to be burned. If this is not practicable, the melt- ing temperature of the ash may be determined ex- perimentally by means of seger cones as follows: Moisten the powdered ash with a 10-per-cent. solution of dextrine, work it into a stiff paste, and mold it into pyramids of the standard form and dimensions of a seger cone. Select several seger cones that will give you the desired range of tem- perature, both below and above the probable forma- tion temperature of the ash slag, and slowly heat the COAL AND ITS COMBUSTION. 71 seger cones and the ash cones in a gas muffler or some other heater. Raise the temperature slowly, at a rate of about 2° C. or 3.6° F. per minute, as the rate of rise of the temperature has considerable effect on the melting temperature of the cones. Com- pare the seger cones at the instant when the ash cones melt, or fuse ; the temperature represented by the seger cone that is bent nearest the standard final form should be taken as the formation, or fusing, temperature of the ash. Seger Cones. — Seger cones are valuable as a means of finding the fusing temperature of ashes, because the ash cones and the seger cones are ex- posed to the same temperature. In order to insure success, the cones must be heated at the rate of temperature, 2° C. per minute, and the Seger cones taken as indicating the temperature must be the one bent nearest to the standard final form. The ash cones must be of the same size and form as the seger cones. Seger cones are three-sided pyramids. Nos. 22 to 25 are 3 inches high and have a base % inch wide ; Nos. 26 to 36 are 25/32 inch high and have a base % inch wide; see Table XII. The number of each cone will be found on its side. Several seger cones representing the desired range in temperature are placed in the furnace with the ash cones, and the temperature of the furnace corresponds to that of the seger cone, the top of which has bent over and touched a horizontal line, called the base, as the ash cone fuses. The seger cone with the lowest number always melts down first, the others following in their respective orders, ac- cording to their number. 72 COAL AND ITS COMBUSTION. TABLE XII. Seger Cones. No. of Cone Composition Melting-Point 022 021 020 019 018 017 016 015 014 013 012 Oil 010 09 08 07 06 05 04 03 02 01 Na.O? PbO J Na,Ol PbO f NajO) PbO j Na^O) PbO J Na,0? PbO f Na201 PbO f Na.01 PbO ( Na^Oi PbO ( Na^O PbO Na,0 PbO Na^O PbO Na^O PbO K.0 CaO KjO CaO K=0 CaO K=0 CaO K,0 CaO K.0 CaO K2O CaO K:0 CaO K.0 CaO K.0 CaO 0.10 AUO3 0.20 AI.O3 0.30 ALO3 0.40 ALO, 0.50 AljOj 0.55 ALO3 0.60 AI.O3 0.65 AUO3 0.70 AUO3 0.75 Al^Oj 0.80 AlzOa 0.20 Fe^Oa 0.30 AI2O3 0.20 FejO, 0:30 AljOs 0.20 FeiOs 0.30 AUO3 0.20 Fe^O, 0.30 AlaO, 0.20 PeiO, 0.30 AhOj 0.20 Fe^Os 0.30 AI2O3 0.20 Fe=03 ALO, Fe^O, ALO3 Fe=03 AI3O, Fe=03 ALO3 0.30 0.20 0.30 0.20 0.30 0.20 0.30 SiOJ B303f SiOJ B=03( Si04 B.03f SiOji BjOsf SiO^l B^O.f Si04 B=Osf SiO^I B2O3I Si04 B.03f SiO=? B^Cf SiO^) B.Onf P. ,094 ,148 ,202 ,256 ,310 ,364 ,418 ,472 ,526 ,580 ,634 ,688 ,742 ,778 ,814 ,850 ,886 ,922 ,958 ,994 2,030 2,066 »C. 590 620 650 680 710 740 770 800 830 860 890 920 950 970 990 1,010 1,030 1,050 1,070 1,090 1,110 1,130 COAL AND ITS COMBUSTION. 73 TABLE XII — Continued. No. of Cone Composition Melting-Polnt 1 0.3 K,0 ) 0.7 CaO 0.20 0.30 FcjO, AUO3 4 Si03 2,102 1,150 2 0.3 K2O 0.7 CaO 0.10 0.40 Fe^Oa ALO, 4 SiO. 2,138 1,170 3 0.3 KjO 0.7 CaO 0.05 Fe^Oa 0.45 AUO. 4 SiO: 2,174 1,190 4 0.3 K:0 0.7 CaO 0.5 AUO3 4 SiO= 2,210 1,210 5 0.3 K,0 0.7 CaO 0.5 AW, 5 SiO, 2,246 1,230 6 0.3 KjO 1 0.7 CaO 0.6 AW, 6 Si03 2,282 1,250 7 0.3 K.0 0.7 CaO 0.7 ALOo 7 SiO= 2,318 1,270 8 0.3 K,0 ) 70.7 CaO 0.8 AUO. 8 Si03 2,354 1,290 9 fO.3 K,0 0.7 CaO 0.9 AW, 9 SiO, 2,390 1,310 10 0.3 K,0 0.7 CaO . 1.0 AUO, 10 Si03 2,426 1,330 11 0.3 K=0 0.7 CaO 1.2 A1,0, 12 Si03 2,462 1,350 12 0.3 K,0 I0.7 CaO 1.4 ALOa 14 SiO, 2,498 1,370 13 (0.3 K,0 )0.7 CaO 1.6 ALO, 16 Si03 2,534 1,390 14 (0.3 K:0 ' (0.7 CaO 1.8 AW, 18 Si03 2,570 1,410 15 (0.3 K,0 ' )0.7 CaO 2.1 AW, 21 SiO. 2,606 1,430 16 (0.3 K.0 |0.7 CaO 2.4 AW, 24 SiO. 2,642 1,450 17 (0.3 K.0 I0.7 CaO • 2.7 AW, 27 SiO, 2,678 1,470 18 (0.3 K,0 I0.7 CaO 3.1 AW, 31 Si03 2,714 1,490 19 (0.3 K»0 70.7 CaO 3.5 AW, 35 SiO, 2,750 1,510 20 (0.3 K,0 70.7 CaO 3.9 AUO3 39 SiO. 2,786 1,530 21 (0.3 K,0 70.7 CaO 4.4 AUO, 44 SiOa 2,822 1,550 22 (0.3 K2O (0.7 CaO 4.9 AUO3 49 SiO= 2,858 1,570 74 COAL AND ITS COMBUSTION. TABLE XII — Continued. No. of Con© Composition Melting-Point °F. "C. 23 (0.3 K2O X 10.7 CaO J 5.4 A1.0, 54 SiO: 2,894 1,590 24 fO.3 K2O ? (0.7 CaO 1 6.0 AhOa 60 Si02 2,930 1,610 25 10.3 K2O \ 10.7 CaO j 6.6 AhOa 66 SiO. 2,966 1,630 26 fO.3 K=0 / 10.7 CaO ( 7.2 AhO, 72 SiO. 3,002 1,650 27 (0.3 K.0 \ 10.7 CaO j 20 AW, 200 SiOj 3,038 1,670 28 AUO3 10 SiO. 3,074 1,690 29 AUO, AUO3 AUO3 AhO, 8 6 5 4 SiOz SiO: SiO= SiO. 3,110 3,146 3,182 3,218 1,710 30 1,730 31 1,750 32 1,770 33 AW, 3 SiO^ 3,254 1,790 34 AW, AW, 2.5 2 SiO= SiO= 3,290 3,326 1,810 35 1,830 36 AW, 1.5 SiO. 3,362 1,850 NOTE.— Table by Prof. H. O. Hofman, T. A. T. M. B., Vol. 29. Hard Clinkers. — Two distinct kinds of clinkers are formed in furnace combustion, one known as soft clinker and the other as hard clinker. Soft clinker is formed by the slagging of the ash. It is not directly chargeable to bad methods of firing, although under some conditions poor firing may be the cause of starting the clinker and may hasten its spread. Soft clinker may have a consist- ency varying from that of a thick paste to that of a COAL AND ITS COMBUSTION. 75 heavy valve oil. The pasty clinker is not so trouble- some as the more fluid clinker, because the more fluid the clinker is the faster will it spread. Also, the very fluid clinker will flow down between the fingers of the grates and into the grate openings and harden, thus blocking the grate bars and shutting off the draft through that portion of the grate. Often it will hang down like icicles from the grate bars and flow into the ashpit. When first formed, a soft clinker is similar in appearance to that of a hard clinker, but it differs from a hard clinker in that it steadily grows in size, until it finally spreads over practically the whole grate area. Inspection shows that the clinker has a crust on the upper surface, underneath which it is fluid. A soft clinker is formed by the silica of the ash combining with the base that has the lowest fusing temperature. Once formed, the silicate dis- solves both the silica and the base and in this way grows in extent. The clinker shuts off the air supply through that part of the grate occupied by it, so that the temperature of the ash at that point is raised to a temperature at which other silicates can form. By the formation of other silicates and by the dissolving of silicates and bases into each other, the fluid slag gradually grows in extent until it eventually covers practically the whole grate surface. Hard clinker is of two kinds, the hard cake- clinker and the small, hard clinker. The hard cake- clinker is usually the direct result of bad firing meth- ods. The temperature of the ash, which is next to the grate, is considerably cooler than that of the burning coal in the firebed, so that an ash that will not fuse when next to the grate will fuse if raised up into the burning coal of the firebed. Once melted, it 76 COAL AND ITS COMBUSTION. runs downward, is cooled, and hardens, cementing pieces of coal and ash together into a hard, cake-like clinker. Also, if the firebed is stirred up so that fresh coal is worked down" onto the grates, the coal in burning will raise the temperature of the ash at that point and very probably will start the formation of soft clinker, provided the ash constituents are in the right proportions, or will fuse some of the ash and produce a hard clinker. Small, hard clinkers are caused by the fusing of certain ingredients of the ash. Usually, such clink- ers do not cause serious trouble. Prevention of Clinker If a coal always clinkers under normal condi- tions and with a proper method of firing, it may safely be charged to the composition of the ash, on account of which the ash fuses or slags at a tem- perature below the regular ash-bed temperature. If the coal clinkers only occasionally, then it may be due to impurities that accidentally became mixed with the coal; to the fact that the slagging or the fusing temperature of the ash is only slightly great- er than that of the working temperature of the ash- bed, and the ash-bed temperature occasionally rises to the fusing temperature of the ash ; or to a wrong method of firing. Use of Limestone. — Since clinker is due to the ash-bed temperature being higher than the slagging or fusing temperature of the ash, the way in which to overcome clinkering is either to lower the ash- bed temperature or to raise the fusing temperature of the ash. Carrying a thin fire and admitting an excess of air through the grates has often been COAL AND ITS COMBUSTION. 77 found effective for reducing the temperature of the ash sufficiently to prevent clinker. The excess air causes a loss in efficiency, but the loss is less than if bad clinker forms. The slagging temperature of the ash may be raised by spreading crushed limestone or broken oyster shells over the thin, clean firebed on starting, the added ingredients making the ash material more refractory. The idea is to add enough lime to the ash to bring its fusing temperature on that part of the curve, Fig. 7, to the right of the point a, so that the ash will have a sufficiently high formation tem- perature to prevent slagging. This method, how- ever, is hardly suitable for every-day use, unless under conditions where a very bad coal must be used. Use of Water Vapor. — ^With high-ash coals that clinker because of the presence of ferrous sulphide, the clinker can often be prevented by keeping the ash-pit doors wide open and this pit clean, so as to reduce the ash-pit temperature, regulating the draft by the uptake damper. Keeping a supply of water in the pit will prove effective also. If the clinker is very fluid and freezes to the grates, the use of steam jets below the grates may not prevent the formation of clinker, but it will prevent the clinker from freez- ing to the grates. The action of water in the ash-pit is the same as the action of the steam jets, only less in amount, since there is less vapor to do the work. Water vapor begins to dissociate when heated to a temperature of about 1,800° F., and is half dissociated at about 4,500° F. On cooling, the mixed gases recombine. In order to decompose water by heat, as much heat must be absorbed by the water as was evolved when the water was formed. From Table XVIII, 1 pound 78 COAL AND ITS COMBUSTION. of hydrogen combining with 8 pounds of oxygen forms 9 pounds of water vapor, and, Table XVII, evolves 62,000 B. T. U. of heat. In forming 1 pound of water about 6,900 B. T. U. are evolved. Each pound of water dissociated, therefore, must absorb 6,900 B. T. U. of heat. The action of water vapor in reducing or pre- venting the formation of clinker, is as follows : The vapor in passing up through the grates and ash absorbs heat and is dissociated. This lowers the temperature of the grates and the ash, and so re- duces, and, in some cases, prevents the slagging of the ash. In bad cases of clinkering with high-ash coals, this treatment may not always prevent clink- ering, but it will prevent the clinker from adhering to the grate bars, thereby making the cleaning of the fire much easier. Care in Use of Rake, Slice Bar, and Shaker. — If pyrite, FeSj, is heated to a low-red heat in an insufficient supply of air, as would be the case of high-ash coal in a firebed so thick as to restrict the air supply, 1 molecule of the sulphur of the pyrite will be driven off, forming SOj gas and reducing the pyrite to ferrous sulphide, FeS. The sulphur in the ferrous sulphide will not combine with oxygen at temperatures as low as that of the ash-bed in a furnace; hence, the iron of the sulphate will not combine with the silica of the ash to form a fusible slag. However, ferrous sulphide often is the cause of very troublesome, hard clinkers. It melts at a temperature of 2,138° F. and attaches itself to sur- rounded coal and ash and forms them into a hard mass or clinker that is very troublesome. The rem- edy for this type of clinker is to carry a thin, clean fire, so as to insure plenty of excess air, and to avoid COAL AND ITS COMBUSTION. 79 mixing the ash with the incandescent coal in the fire- bed. Care in the use of the rake, the slice bar, and the grate shaker will avoid the formation of hard clinkers. Stirring the fire comes next to carrying too thick a fire as the most frequent cause of trouble- some clinker, especially if the fire is broken by means of the slice bar. Running the slice bar under the fuel bed and then prying it up to break a clinker or a coke crust, is a sure method of causing hard clinkers to form. Also, lifting ash up into the hot zone of the fire by the improper use of the rake is a frequent cause of hard clinker. Shaking the grate hard enough to work coal down on the grate will surely cause clinkers. Mixing two coals will sometimes cause clinkers, even though neither of the coals clinker when burned separately. Summary. — Briefly, then, to prevent clinker : Carry a thin, level fire. Use care in shaking the grates. Avoid the use of the slice bar and the rake. Fire in small quantities on the thin spots of the fire. Avoid the formation of banks. Take especial care in firing slack coal to fire small quantities at a time, so as to avoid coking a thick crust. Keep the ash-pit doors wide open and the ash pit clean. If necessary, keep water in the pit, or use steam jets to prevent clinker from sticking to the grates. Avoid shaking coal that will bum into the ash pit. In handling coal, avoid all chance of mixing for- eign impurities with it. 80 COAL AND ITS COMBUSTION. Removing Clinkers. — ^The only way in which to remove soft clinker is to clean the entire furnace and build a new fire. Once a soft clinker starts to form, it generally is only a question of time when it will result in an engine failure or a shut-down. In the case of a hard, cake clinker, it can some- times be broken up by shaking the grates with short, quick jerks. Generally, however, the fire must be cleaned and the clinker broken up and dropped through the door. In some cases, it may be possible to turn the clinker up on edge or to pull it out on top of the firebed and allow the fire to disentegrate it, but this method is very apt to start the formation of new clinkers. Disadvantages of Cljinkers. — ^In bad cases of clinkering, the clinker decreases both the furnace efficiency and the furnace capacity. It increases both the labor and the cost of firing, shortens the life of the grates and the firebrick lining of the furnace, and, in extreme cases, may cause the power plant to be shut down because of the grates becoming clogged. CHAPTER VII Geological History of Coal lENERAL PRINCIPLES. — In order to have a thorough working knowledge of American coals, one must be familiar not only with the nature and the prop- erties of the diiferent classes of coals, but also with the geology of coal, and with the loca- tion and the characteristics of the several coal fields of America. The study of the nature and properties of coal has just been completed; the geology, loca- tion, and characteristics of the coal fields will now be treated briefly. The word geology is from two Greek words sig- nifying "the story of the earth." Geology is the science that treats of the past conditions of the earth and of its inhabitants. It is concerned chiefly about the evolution of the earth's features from former conditions, and about the previous forms and the distribution of animals and plants. The science of geology is based on the fact that nature has writ- ten its own history in the rock formations that have gradually accumulated throughout the past ages. The crust of the earth is estimated to be about 30 miles thick, and the lower strata of rocks form the first pages in the history of time. In writing this history, nature has made use of the rock formations of the different ages for the pages of her book, and has used the fossils of the faunas and floras of each age as the type wherewith to print the history. The rocks of the bygone ages were formed in water by the settling of sediment, so 81 82 COAL AND ITS COMBUSTION. that where no great disturbance has taken place the relative positions of the rock strata indicate the relative ages of the strata, the uppermost, of course, being the youngest. However, all the strata are not represented in any one place, and, usually, only a few are represented, so that the age of the rocks cannot always be determined from the order of their superposition. Hence, the age to which the rock formations belong must be determined by a careful comparison of the character of the rock and the character of the fossils in different localities with one another. To be of the same age, both the rock and the fossils of different localities must be gen- erally similar. In the early ages, the first forms of life of which there is any record were very low. These were fol- lowed by others of higher form of life, and these by others of still higher form, and so on through age after age until the appearance of man. Each change in the form of life to a higher form invariably was preceded by changes in the physical conditions of the earth and in the atmosphere, that made living pos- sible to the higher form of organism. Each of these great changes in the physical conditions, therefore, marks an era in the history of the earth. Each era is distinguished from the others by the fossils of the particular forms of life that were dominant during that era. The plants and animals that lived left relics in the form of leaves, shells, bones, teeth, corals, etc. in the mud, sand, and other deposits as a record of their existence ; consequently, wherever a rock formation is found, the fossils that it contains proclaim the era to which it belongs. Geologists have divided and subdivided the lim- its of the divisions of the rocks, and the correspond- COAL AND ITS COMBUSTION. 8S ing divisions of time, into eras, ages, periods and epochs, as determined by great changes in physical geography, climate, and forms of organisms. These divisions of time are recorded in separate systems, rock series, and rock formations, according to their importance. The eras, ages, periods, etc. usually graduate into each other ; yet there are times of rev- olution in which the steps of change are far more rapid than ordinarily. Thus, geological history, like human history, consists of periods of comparative quiet and prosperity and of periods of revolution. Just as in human history, which marks the sev- eral ages of man in accordance with some dominant characteristic, social force, or principle, as the stone age, the age of chivalry, the age of reason, etc., so, also, in geological history, what is designated as an age is marked by the dominance of some particular class of animals or plants. Thus, there is an age of mollusks, the age of fishes, the age of reptiles, etc., in which each class is successively the dominant type for its age. Each dominant type culminates and then declines and becomes subordinate to the next incoming and higher order of life. Thus, the organic kingdom steadily becomes of higher and higher form of life, and of more complex structure as a whole, as shown in the accompanying schedule of the divi- sions of the rocks and the corresponding divisions of time, Table XIII. Divisions of Geological History. — From the schedule of the division of the history of the earth and the rocks, it will be seen that there are five primary divisions called eras, each embodied in a corresponding system of rocks. The time covered by the five eras is subdivided into seven divisions, called ages, each Age being characterized by a dominant 84 COAL AND ITS COMBUSTION. ■a a m X u o P4 o H g •3 o ^ o ■§ s X V o H Q in Hi pq ^ a o s ■M M 1 "i Qi fi IQ OS «> '2 _ i^ S 3 ^ S IS H O O I1h S (DCS O iX) 0) ■ o C5 ^ CQ ^ o o o O O U 01 Co o C o K si w Hi 2 m =3 « 5 ^1 3 ^1 t< o OS ■a 0) o << j3 c3 O e o o H il> . CS in « Ph M .a ►J O C O ■ «) «H o h-1 O 1) 4) Tt S Pi p. COAL AND ITS COMBUSTION. 85 >-< ,s a) - „ 0) o ft-- o 3 3 o S .2 S O (V n « 3 > < Cretaceous Carboniferous Carboniferous in 12,429 12,382 12,186 u 0 • a> ■M . -fj tn . a C4 . ^ X A m m . Cu •V CQ 4- as *» . ^ a V CQ a tf 0) " M 1 > c *. -^ *■ s « t? c CJ E- ■4- V C «• s •s m 1- c bo c ■> c c st to fir moving Total CO m .3 c c 0) O (U fe IL t IJ tf E O 05 — — — ^ -'— - ^ "— ^ ^ at U m _s 4 -^ 1 '3 K CQ 1 S < 1 Ph <» ash is 11/2 cents. The total cost, therefore, 2 -|- 2 + 11/2 = 51/2 cents for each per cent, of sul- phur in the coal. For cost of a greater per cent, of 116 COAL AND ITS COMBUSTION. sulphur, or for higher-priced coal, proceed as in the case of moisture. The cost of ash is calculated as follows: 1 per cent, of ash displaces 1 per cent, of coal and costs 1 cent. Cost of firing the 1 per cent, of coal, 1 cent; cost of removing the 1 per cent, of ash, 1 cent. The total cost, therefore, is 3 cents. Table XV gives the cost of impurities for coals of different prices. Equating Coals of Different Impurities. — As a general rule, coal purchased under contract is speci- fied according to a certain proximate analysis. As- sume that the contract calls for a coal having 2 per cent, of moisture, 1.0 per cent, of sulphur, and 6 per cent, of ash, with a guaranteed heat value of 14,000 B. T. U., the price per ton, delivered, to be $3.50 net. Assume, also, that the coal delivered analyzes 4 per cent, of moisture, 1.5 per cent, of sulphur, and 8 per cent, of ash, and has a heat value of only 13,500 B. T. U. What should be the equated price of the coal, as furnished? According to the price quoted in the contract, the impurities in the coal contracted for would cost: Cents Moisture, 2 per cent., 2 X 5.68 11.26 Sulphur, 1 per cent., 1 X 10.50 10.50 Ash, 6 per cent., 6 X 5.50 33.00 Total 54.76 The equated price of the coal contracted for, therefore, would be $3.50 plus 54.76, or $4.05 per ton. The total heat value for a ton would be 2,000 X COAL AND ITS COMBUSTION. 117 14,000 = 28,000,000 B. T. U., and the cost per million 4 01=1 B. T. U. would be ^ = 14.46 cents. The cost of the impurities in the coal delivered would be as follows: Cents Moisture, 4 per cent., 4 X 5.63 22.52 Sulphur, 1.5 per cent., 1.5 X 10.5 15.75 Ash, 8 per cent., 8 X 5.50 44.00 Total 82.27 The equated price for the coal delivered, there- fore, would be 3.50 plus 82.27, or 4.32 cents per ton. The total heat value for a ton would equal 2,000 times 13,500, or 27,000,000, B. T. U., and the cost per 4 32 million B. T. U., would equal -^ = 16 cents. This is, 16 — 14.46 = 1.54 cents per million B. T. U. in excess of the price agreed on in the contract, or 27 X 1-54 = 41.5 cents per ton, so that 41.5 cents is subtracted from the contract price of the coal, mak- ing the coal cost 3.50 — .415 = $3,085 per ton, in- stead of $3.50. If the coal delivered is better than the contract calls for, the problem would be worked out in a similar manner, but the difference in the price per ton would have to be added to the original contract price. CHAPTER XI THEORY OF COMBUSTION General Definitions fOMPOSITION of Matter.— Every body or mass of matter is an elementary substance, a compound substance, or a mechanical mixture. An elementary substance is composed of only one ele- ment; therefore, is not formed through chemical combination. Silver and gold and the gases known as oxygen, hydrogen, and nitrogen are some of the elementary substances. A compound substance is formed by the chemical combination of two or more elements. The compound, water, is formed by the chemical combination of hydrogen and oxygen. Since a compound substance is the result of a chem- ical combination, it can be decomposed into its ele- ments. By passing a current of electricity through water it will decompose the water into its elements, hydrogen and oxygen. Any substance, therefore, that can be decomposed into other substances must be a compound. Examples of compounds are coal, fuel and light gas, and water. An elementary substance is composed of only one element ; consequently, it is impossible to decom- pose an element. Its form can be changed only by combining it chemically with one or more other ele- ments. The elements that are of direct interest in the study of the combustion of coal are the gaseous elements oxygen, hydrogen, and nitrogen, and the solid elements carbon, sulphur, and iron. 118 COAL AND ITS COMBUSTION. 119 A mechanical mixture may be composed of two or more elements, of two or more compounds, or of elements and compounds mechanically mixed, but not chemically combined. The air of the atmos- phere is a mechanical mixture composed principally of the elements oxygen and nitrogen. Atoms and Molecules. — All matter, be it an ele- ment, a compound, or a mixture, is made up of a comparatively small number of elementary sub- stances, only about seventy-two elements being known up to the present time. As a matter of convenience, the elements are designated by symbols, which are usually the first letter or letters of their names. Thus, H stands for hydrogen; O, for oxygen; N, for nitrogen; C, for carbon; S, for sulphur; and Fe (from the latin ferrum), for iron. A compound is designated by combining the symbols of its elements. Thus, water is expressed by the symbol HjO, the suffix 2 indicat- ing that 2 atoms of hydrogen have combined with 1 atom of oxygen. The smallest quanity of an element or a com- pound that is capable of separate existence is taken as a physical unit of matter, and is called a molecule. Molecules are composed of atoms of elements. An atom is the smallest part of an element that can enter into a compound or be expelled from it. Atoms never exist singly, but always combine with one or more other atoms to form a molecule. The mole- cules of most elementary gases, like oxygen, hydrogen, and nitrogen, are supposed to consist of 2 atoms. Also, equal volumes of these gases, under the same conditions of temperature and pressure, are supposed to contain the same number of mole- 120 COAL AND ITS COMBUSTION. cules ; hence, the atoms of the gases are supposed to be of equal size. Chemical Combination.— When two or more ele- ments combine, they form a compound unlike any of the elements. The gas hydrogen combines with the gas oxygen and forms the liquid water, the proper- ties of which are entirely different from those of either hydrogen or oxygen. The solid carbon com- bines with the gas oxygen and forms the gas carbon dioxide, COj, the properties of which are opposite to those of oxygen. Oxygen supports both animal life and combustion, whereas carbondioxide extinguishes both. The gas nitrogen combines with the gas hy- drogen and forms the liquid ammonia. When elements combine chemically to form a compound, a definite amount of heat is always pro- duced. If the compound is decomposed into its ele- ments, it will absorb exactly as much heat as was produced when the elements combined. Thus, if 1 pound of carbon combines chemically with oxygen it will produce 14,600 B. T. U. ; to separate the car- bon dioxide into its elements carbon and oxygen, 14,600 B. T. U. will have to be supplied to the com- pound. Again, burning 1 pound of hydrogen will form water vapor and produce 62,000 B. T. U. ; to dissociate this vapor, or break it up into its elements, H and 0, the vapor will have to absorb 62,000 B. T. U. Elements always combine in definite, invariable proportions. For example, 2 volumes of hydrogen always combine with 1 volume of oxygen and forms water. If 2 volumes of hydrogen are mixed with V^ volume of oxygen under favorable conditions, 1 vol- ume of hydrogen will combine with the oxygen in the usual proportions, Hfi, and the remaining 1 volume COAL AND ITS COMBUSTION. 121 of hydrogen will be unassociated. If 1 volume of H is mixed with 1 volume of 0, one-half of the oxygen will remain unassociated. Oxygen, unfortunately for efficiency of combustion, combines with carbon in either of two proportions: as carbon monoxide, C O, or as carbon dioxide, CO^. As C O, the carbon is only partly burned and is capable of combining with another atom of oxygen to form COj. If, as assumed, the atoms of hydrogen, oxygen, nitrogen, and carbon are of equal size, then the rela- tive weights of equal volume of these substances under the same pressure and temperature will be the same as the relative weights of their molecules and, therefore, as their atomic weights. As hydrogen is the lightest substance known, its weight is taken as unity in the table of atomic weights, Table XVI. TABLE XVI. Atomic Weights of Elementary Substances Concerned in Combustion. Symbol. Atomli' Weights. Density, Air = l. Weight, Pounds I'lr Kleiiient. Approxi- mate. Accurate Cubic Foot, at 32» F. Under 1 At- mosphere. Hydrogen H 1 1.008 .0692 .00559 Carbon . . C 12 12.000 Nitrogen . N 14 14.010 .9701 .07831 Oxygen . . 16 16.000 1.10521 .08884 Sulphur . . s 32 32.070 By the aid of Table XVI, the weight of any com- pound substance formed during combustion can be obtained from the chemical formula of the substance. Thus, in water, H^O, the 2 atoms of H weigh 2 and the 1 atom of weighs 16 ; therefore, the molecular 122 COAL AND ITS COMBUSTION. weight of water is 16 + 2 = 18. Water is thus com- posed, by weight, of 2 parts of H and 16 parts of 0, and the ratio of H to 0, by weight, is 1 to 8. By volume, water is composed of 2 volumes of H and 1 volume of O. These 3 volumes unite and form only 2 volumes of water in its gaseous state, the 2 volumes representing the space of the original 2 volumes of H. The relative weights of HjO and H, therefore, are as 18 is to 2 or as 9 is'to 1 ; that is, under the same temperature and pressure, water vapor weighs 9 times as much as the same volume of hydrogen. Elements of Combustion Hydrogen. — Hydrogen is a colorless, tasteless, inodorous gas. It was discovered in 1766 by Caven- dish, who called it inflammable air. Its weight or density, compared with that of air, is as .0692 is to 1. It is very widely distributed, forming 11 per cent, of water, about 5.25 per cent, of wood, and from 3.5 to 6 per cent, of coal. Hydrogen does not unite readily with oxygen at ordinary temperatures, but when heated to its igniting temperature it burns readily with a colorless or slightly blue flame, forming water vapor. When mixed with oxygen, it is explosive. Its density is .0692 (air=l), and its weight at 32° F. under atmospheric pressure is .00559 pound per cubic foot. Carbon. — Carbon uncombined is a solid. It is very widely distributed, being the central element in all organic matter, whether vegetable or animal. It occurs principally in combination with various ele- ments, but is found uncombined as coke, charcoal, lampblack, graphite, diamond, and, in an impure state, as coal. At high temperatures, carbon has a very strong affinity for oxygen with which it com- bines readily. The atomic weight of carbon is 12. COAL AND ITS COMBUSTION. 123 Nitrogen. — The element nitrogen is a gas that has no color, taste, or odor. It will not combine with oxygen ; consequently, it will not bum. However, it combines readily with other elements, forming salt- peter, sodium salt, ammonia, etc. It forms four- fifths of the atmosphere, where it acts as a diluent and renders burning less active that it would be in oxygen alone. Nitrogen plays no part in the com- bustion of a fuel, and it passes through the furnace without change. It dilutes the oxygen and renders the action of the burning less active than it would be if the oxygen were pure ; also, in passing through the furnace it absorbs heat, which is carried with it through the stack and lost. Furthermore, it de- creases the temperature of the products of combus- tion by increasing the volume of gases that must be heated by the combustion of the coal. The density of nitrogen, where air is equal to 1, is .9701; its weight per cubic foot at 32° F. and under atmos- pheric pressure is .07831 pound; its atomic weight is 14. Oxygen. — At ordinary temperatures, oxygen is tasteless, odorless, inodorous gas. It is the most abundant of all the elements, being found in a free state in the air, where it forms one-fifth the volume of the atmosphere. It is combined in water and is found in most substances that form the crust of the earth. It is the only element that will support com- bustion and respiration, and is absolutely necessary in animal and vegetable life. Sulphur. — As has been seen, sulphur may be present in coal in either a free state or in a combined form. In the form of sulphates, it has no heating value. Sulphur is objectionable because the gases formed by its combustion attack the metal of the 124 COAL AND ITS COMBUSTION. boiler, particularly in the presence of moisture, caus- ing rapid corrosion of the metal. The atomic weight of sulphur is 32. Cakbon and Hydrogen Oxygen combines with hydrogen in one propor- tion only, since the combination invariably produces water, according to the reaction 2H + = H„0. Oxygen combines with carbon in two propor- tions. If carbon at a sufficiently high temperature is supplied with sufficient oxygen, each atom of car- bon will unite with 2 atoms of oxygen, according to the reaction C + 20 = COj. The CO2 is a colorless gas that is slightly acid to taste and smell and is called carbon dioxide, or carbonic acid. It is about one and a half times as heavy as air, is incombus- tible, and will support neither life nor combustion. It is not poisonous, but since it is much heavier than the air, weighing 1.529 times as much, it will exclude the oxygen and thus produce death through suffo- cation. The usual amount of oxygen in the air is about 20 per cent. If sufficient CO2 is present to reduce the to 17 per cent., the flame of a lamp will be extinguished. An atmosphere with sufficient CO^ to reduce the oxygen below 10 per cent, is dangerous to life. Since 2 atoms of oxygen are the most that 1 atom of carbon can combine with, the combustion is said to be complete when the carbon is burned to CO2. Since 1 atom of carbon weighs 12 and 2 atoms of oxygen weigh 2 X 16 = 32, the molecular weight of CO, is 12 + 32 = 44; that is, it consists of 12 parts, by weight, of carbon and 32 parts of oxygen. In an insufficient supply of oxygen, carbon unites with oxygen according to the reaction C -f O = CO. Also, under these conditions, if CO, comes COAL AND ITS COMBUSTION. 125 into contact with the incandescent carbon, the fol- lowing reaction will take place : CO^ + C = 2C0. The CO is a colorless, practically inodorous, poison- ous gas, called carbonic oxide or carbonmonoxide, that is destructive to animal life. The presence of but a small volume in the air quickly produces insensibil- ity and death. It combines with the red corpuscles of the blood more readily than oxygen does, and the blood becomes saturated with CO and cannot take up oxygen and distribute it throughout the system. In combining with the red corpuscles, it forms a bright-red compound, called carboxyhemoglobins. Air containing 1.5 per cent, of CO will overpower a man almost in an instant. Haldane states that an atmosphere containing over .2 per cent, of CO would be very dangerous to man, and .02 per cent, might cause headache and disablement; .2 per cent, would probably cause a man at rest to collapse in 1 hour. CO will not support combustion, but it will burn according to the reaction CO + = CO™. An explo- sive mixture is made with 15.5 per cent, of CO in the air. CO is slightly lighter than air, having a spe- cific gravity of .967, where air is equal to 1. The atomic weights of the elements being 12 and 16, the molecular weight is 12 + 16 = 28. Hydkocarbons Carbon and hydrogen are found in the combined state in liquid, solid, and gaseous forms, as the bitu- men of bituminous coal. Bitumen is a natural mix- ture of hydrocarbons; that is, it is a compound formed by the chemical combination of hydrogen with carbon. The hydrocarbons are distilled from coal in the form of gases, oils, and tars. The gases 126 COAL AND ITS COMBUSTION. are distinguished for purposes of combustion as light hydrocarbons and as heavy hydrocarbons. Methane. — Methane, CH^, is commonly known under the name of marsh gas. It derives the name marsh gas from the fact that it escapes as bubbles from decaying vegetation below the surface of water in marshes, etc., and may be collected and burned. Also, it is known as the light hydrocarbon gas of coal, because its molecular weight is only 16, while the molecular weight of the heavier hydrocarbon gas ethylene, C^H^ (olefiant gas), is 26, and benzole, CeHg, or benzine, as it is better known, is 78, Table xvn. Methane is a colorless, tasteless, odorless gas. It is not poisonous, but if present in sufficient quan- tities it will cause death by suffocation. Methane is a very valuable part of the fuel, as it forms the bulk of the hydrocarbon gases and burns at a temperature of 1,202° F. As it consists of 4 parts of H to 1 part of C, it furnishes a good supply of readily available heat with but little tendency to smoke. It possesses practically no illuminating properties on account of its low carbon content; consequently, it burns with a flame that is not very luminous. It forms explosive mixtures between the limits of 5.5 and 13 per cent, of methane in air. The explosion is not violent at the lower limit, and the spread of the fiame can readily be followed with the eye. As the mixture is increased up to about 9.5 per cent., the explosion increases in violence, after which it decreases in violence until the upper limit is reached. Above 13 per cent, and below 5.5 per cent., burning occurs under proper conditions, according to the reaction: CH, + 40 = CO, + 2H,0. Acetylene. — Acetylene, C.H^, is a colorless. COAL AND ITS COMBUSTION. 127 o I s I t a o o Ik > n tasteless, gas of peculiar odor. It burns in air with a brilliant, but smoky flame. It ignites at 900° F., which is lower than the igniting temperature o f any other coal gas or any natural gas. The glowing end of a cigar will ignite acetylene. It is slightly pois- onous, and its ex- plosive limits are between 3 and 65 percent. It burns according to the reaction CoH, + 50 = 2C0o" -f H2„0. 5 (M ■a CO U5 (M 1^ 05 .H t- o ■* C4 r-l rH N i-l WpLi H °7. o ^ ■<>l Ui m CO o i; 2E t' n (N o ■* o N o o 35? d O m o iH Tf CO eg tr us ox. o tH r-t iH T-^ r-t .^^ ■«ii o> OS to in (N a ° ■^ ■« ■o< to r- to Oh M CO r-T to_ ■^s, 13 o o in O o O Tf m 3 tH to 1— CO 00 •<»l 1-t lO ■01 00 eg rt o ■* CM CO iH rH eg 00 Ph to (N (N (N ca th punoj jad SBO JO }99a[ oiqno t3 o XOqiuXg li20fiuaiio mSiSAV JBin09IOI\[ 6 t- O M 05 O -"Jl t-; OJ ■* l> 00 0> eg t> eg CO ei iH tH t- eg tH rH rH to to 00 O 00 th eg eg CO t> o r-i ■* eg -^ to to 00 eg to to 00 o i-H eg eg CO O u) w w w w w u o o o o o 00 »-l to to 00 O 00 eg .-I eg eg CO t- Ethylene and Ethane. — Ethy- lene, C2H1, often called defiant gas, and ethane, CaHe, and benzole, or benzene, CgHj, are the heavy hy- drocarbon gases of the coal. They are very rich in carbon; conse- quently they burn in air with a very luminous but smoky flame. Unless the air conditions and the temperature are just right, it is difficult "2 'S o a o B c M B S g i Ol N oK S Ih eo iC M fO d a « ^" 1 &" o" 0> ^ 0> CO iH — , rH • ^ "N o eo o ^ N -• ^ •* O -^ M cq ^ N CO ej eg ci C3 M ITS CD CO 00 eg CO iH CO eg >« t- 'tj* lA eq oo CM tH eg CO co eo in oo lO ■^ 1— ■* rH CO tH rH r4 W T-l CO c^ a> 00 Ui CS 0i 00 ■* oo U3 eq CO T-l eo tH eg cg«>cgrHt-ioiftegmir- loc-comcgost-fHt-m th -^ eg »h th eg ih r-iiACg-^c^'^eo^eO'^ T-l CO iH r-l iH " rH t-cot-oocot-egt-o CDCOlOOO-^Ot-OO Wr-iooo"0 I^OT ii X a ta ■A Sea CO CO •an' iU3|0B 10 00 -jnsui o} anci t- CJ •diuaj, ui sso'i N 03 CO CO jl 'Saa 'qiuoo s Oi eo >> JO -duiax m rH CO *& ■* oq m •n -J, -a ig IM 10 Tf •}B9H IB^OX OJ"'"* ^ ■o s o .|J •s P,^ 1 So on "m of ■«" a ^P 10 (N o eo 4^ ffi n rH « o OSc 0,0 o^- in is oii n oS^ m spunod eo U5 10 t- ;0 t> 00 10 'jtlddng Jiv »-I »H 156 COAL AND ITS COMBUSTION. Cooling Effect of the Air Supply. — ^It has been shown that the temperature developed in completely burning fuel depends on the number of heat units per pound of fuel and on the amount and the nature of the products of combustion. It will also be shown that the amount of air supply during the burning of a fuel greatly affects the temperature developed. Air in excess of the theoretical amount must be sup- plied for the reason that, otherwise, the coal would not burn completely and generate its full heat value. Some of the air passes through the fire and out the stack without having an opportunity to part with its oxygen. If, therefore, only the theoretical amount of air were admitted to the furnace, it would not supply sufficient oxygen to burn the coal com- pletely. Tests have demonstrated that when the air is properly admitted to the furnace, from 50 to 100 per cent, of excess air must be supplied, de- pending on the furnace and on the nature of the coal, in order to secure complete combustion. This excess air increases the amount of the gases of com- TABLE XXVI. Cooling Effect of the Air Supply. Weight of Stack, Gases, Pounds. Total Heat Generated by 1 Pound of Coal. B. T. XT. o sis OS E-ioD O B . fL,3P3 fe|.tJ o oS Loss in Tempera- ture Due to Ex- cess Air. Deg-. P. CO a Prod- ucts of Com- bustion Excess Air Total. 11.53 17.30 23.06 34.69 12.53 12.53 12.53 12.53 5.77 11.53 23.06 12.53 18.30 24.06 35.59 14,650 14,650 14,650 14,650 4,952 3,124 2,282 1,483 5,409 7,900 9,083 1,828 2,670 3,469 COAL AND ITS COMBUSTION. 157 bustion that must be heated by the coal; conse- quently, it reduces the temperature developed by the combustion, as shown in Table XXVI. Table XXVI not only shows the loss in tem- peratures due to the air that passes through the fur- nace, but also shows, seventh column, the actual loss in B. T. U. due to the excess in air. Heat Absorbed by Vapor in the Air. — Besides the direct loss due to the heat absorbed by the ex- cess air during combustion, there is another loss due to heating the moisture that is contained in the atmosphere. It is to be remembered that the mois- ture in the atmosphere is mixed with the air and is not absorbed by the air. The statement is some- times erroneously made that the air has a certain capacity for moisture, and the expression, saturated air is often seen. The presence of aqueous vapor, or moisture, in the atmosphere is entirely indepen- dent of the presence or the absence of air in the same space, except that the air retards the diffusion of the moisture particles. It is the space that con- tains moisture or is saturated with moisture, and not the air. Table XXVII gives the weight of vapor that is mixed with each pound of air for different temperatures. It will be seen that the capacity of space for moisture increases with the temperature, and doubles with each increase of about 20° F. The values given in the table are for 100-per-cent. sat- urations. For a saturation of less per cent., multi- ply the weight at 100-per-cent. saturation by the per cent, of saturation desired. The moisture vapor in the atmosphere has to be heated from atmospheric temperature to 212° F., and superheated above that to the temperature of the 158 COAL AND ITS COMBUSTION. chimney gases, all this heat being carried out of the stack and lost. Example. — How much heat is lost on account of mois- ture in the atmosphere in burning 1,000 pounds of coal hav- ing a heat value of 12,500 B. T. U. and using 20 pounds of air at 102° F., the humidity being 80 per cent, and the gases of combustion escaping to the chimney at 550° F.? Solution. — At 102° F., 1 pound of air at saturation has .04547 pound of moisture mixed with it, Table XXVII, so that 1,000 X 20 = 20,000 pounds of air must be mixed with 909.4 TABLE XXVII. Weight of Vapor in Atmosphere. Weight, in Pounds, of a Cubic Foot of Weight of Vapor i n 1 Pound of Air Pounds Degress F. Dry Air Vapor Air and Vapor 12 22 32 42 52 62 72 ■ 82 92 102 112 122 132 .0863 .0840 .0821 .0802 .0784 .0766 .0747 .0727 .0706 .0684 .0659 .0631 .0599 .0564 .000079 000130 .000202 .000304 .000440 .000627 .000881 .001221 .001667 .002250 .002997 .003946 .005142 .006639 .086379 .084130 .082302 .080504 .078840 .077227 .075581 .073921 .072267 .070717 .068897 .067046 .065042 .068039 .00092 .00155 .00245 .00379 .00561 .00819 .01179 .01680 .02361 .03289 .04547 .06253 .08584 .11771 pounds of moisture. At 80-per-cent. saturation, the moisture contained in the atmosphere will be .80 X 909.4 = 727.5 pounds. Raising 1 pound of moisture from 102° to 212° F. will absorb 212 — 102 X 1 (the specific heat of water) = 110 B. T. U. ; superheating 1 pound of moisture from 212° to 550° F. will absorb (550 — 212) X -48 = 162.24 B. T. U. COAL AND ITS COMBUSTION. 159 Therefore, heating 727.5 pounds of moisture from 102° to 550° P. will absorb 727.5 X (110 + 162.24) =198,040 B. T. U. This represents the heat value of 198,040 -^ 12,500 = 16 , , 198,040 X 100 pounds of coal, which is j^o 500 — y ■< nnn = 1.6 per cent, of the heat value of the coal. From Table XXVII, it will be seen that the amount of heat wasted through atmospheric mois- ture decreases with the temperature and with a de- crease in the degree of saturation. Also, it depends on the temperature at which the products of com- bustion escape to the stack. In the above example, with 100-per-cent. saturation, the heat loss would be 19.8 B. T. U., or 1.98 per cent, of the heat value; whereas, with 60-per-cent. saturation, the loss would be only 9.9 B. T. U., or only .99 per cent, of the heat value. Heat Loss Due to Moisture in CoaL — The loss due to moisture in coal is represented by the loss of coal displacement, by the loss of vaporization, and by the loss of superheating the steam to the chim- ney temperature. A coal contains 2,000 X .01 = 20 pounds of moisture per ton for each per cent, of moisture; hence, the loss through the water dis- placing coal amounts to 20 pounds of coal per ton for each per cent, of moisture. To raise 1 pound of water from 60° F. and vaporize it at 212° F. will require (212 - 60) + 9,668 = 1,118 B. T. U. There- fore, 20 pounds will require 20 + 1,118 = 22,360 22,360 B. T. U. This would represent ^2500 ~ "'^"'^^ pounds of coal for a coal having a heat value of 12,500 B. T. U. per pound. If the chimney temperature were 550° F., the vapor would be superheated 550 — 212 = 338° ; hence, the superheating would absorb 160 COAL AND ITS COMBUSTION. 20 X .48 X 338 = 3,245 B. T. U., which equals 3,245 ..n --,-- = .26 pounds of coal. The total loss for each 12,500 per cent, of moisture in the coal, therefore, under the above conditions, would be 20 + 1.19 + .26 = 22 pounds coal. If the coal contained 5 per cent, of mois- ture, the loss would equal 5 X 22 = 110 pounds of coal per ton of 2,000 pounds. This equals .55 per cent. Loss of Temperature Through Decomposition. — When oxygen unites with a combustible in burning, heat is generated. To decompose the products of combustion after they have formed, the same quan- tity of heat must be absorbed by the compound as was generated by the union of the elements. P'or example. Table XVII, 1 pound of CO burning to COa generates 4,400 B. T. U., and in decomposing this CO2 into CO, and 0, 4,400 B. T. U. will be absorbed. The air enters the bed of fire from below, so that the oxygen forms CO2 with the carbon of the lower layers of coal. The CO2 in passing through the upper layers of the fire is reduced to CO by taking up another part of the carbon, according to the reaction CO. + C = 2C0. If the CO meets more oxygen, it will burn to CO2 again; otherwise, it will escape as CO. In combining to form CO2, 14,650 heat units are generated. In the reduction of CO2 to CO, 10,250 heat units are absorbed, leaving only 14,650 - 10,250 = 4,400 B. T. U. as a final result of the combination. In burning 1 pound of hydrogen, 9 pounds of water vapor is formed by the chemical combination of oxygen with the hydrogen, Table XVIII. This generates 62,100 B. T. U. If 9 pounds of moisture in COAL AND ITS COMBUSTION. 161 the coal were decomposed into hydrogen and oxygen, it would absorb 62,100 B. T, U. from the fire, thus reducing the heat value of the coal that amount. Every 9 pounds of moisture in the coal that is de- composed by the heat of the furnace, absorbs as much heat as 1 pound of the available hydrogen of the coal can develop. CHAPTER XIV Determining the Heat Value op Coal ULONG'S Formula.— The heating value of a coal is usually determined directly by burning a sample of the coal in a calorimeter. It may, however, be cal- culated from the ultimate analysis of the coal by means of Dulong's formula, which is : B. T. U. = 14,600C + 62,000 (H - §) + 4,000S, o in which the carbon, C, hydrogen, H, oxygen, 0, and sulphur, S, are expressed in per cent. By dividing the quantities on the right of the equation by 100, the formula becomes : B. T. U. = 146C + 620 (H -§) + 40S, o in which C, H, 0, and S are the percentages of the quantities in the coal. Example. — What is the heat value, per pound, of a coal containing 4.45 per cent, of S, 4.97 per cent, of H, 70.45 per cent, of C, 5.5 per cent, of O, and 13.64 per cent, of ash? Solution. — Substituting in the formula, B. T. U. = 146 X 70.45 + 620 X (4.97 — ^) + 40 X 4.45 = 13,117 B. T. U. Unit Coal. — The difficulty of comparing coals for commercial purposes of Dulong's formula lies in the fact that an ultimate analysis of the coal is necessary in order to determine the per cent, of car- bon and hydrogen in the coal. The hydrogen is a variable, and its exact amount is difficult to deter- mine. Also, the formula does not differentiate be- tween the combustible organic matter of the coal 162 COAL AND ITS COMBUSTION. 163 and the inert or non-combustible mineral constitu- ents. In the comparison of coals, it is very import- ant that the formula used take these into account, so that the coals may be compared as free from extraneous matter, such as moisture, ash, and sul- phur. Through the investigations of Prof. S. W. Parr of the University of Illinois, and his first assistant, Mr. W. F. Wheeler, it was found that the ordinary methods of analysis do not take proper account of the water of hydration of the shaly or clayey por- tions of the ash, or of the carbon-dioxide content of the earthy carbonates. These non-coal constituents are driven off as a volatile at red heat and are therefore included as part of the volatile combust- ible of the coal instead of as part of the ash. For example, suppose the shaly or clayey content of the ash contains 8 per cent, of combined water. The ordinary method of analysis will drive off this water of hydration and will include it with the volatile combustible instead of with the ash ; hence, the cor- rect fuel value of the coal is not obtained. Gypsum would produce a like inaccuracy on account of its water of crystallization being included with the vola- tile combustible matter. Also, calcium carbonate would loose carbon dioxide in the process of analysis that would induce an inaccuracy similar to the above. Before making the proximate analysis, the coal should be tested with acid so as to liberate the CO., which should be measured by weight or by volume. If the CO, is more than 3 per cent, or the CO, + CI is 5 per cent, or more, the ash determination of the analysis should be made by blasting in a platinum crucible to a constant weight; to the weight of the ash must then be added the weight of CO, found. 164 COAL AND ITS COMBUSTION. Also, since the heat will drive off any chlorine, CI, that may be present, the amount of CI should be determined and also added to the weight of the ash. To account for the moisture, M, sulphur, S, and ash, and to correct for the water of hydration and for similar impurities in the ash. Parr and Wheeler propose the following formula for comparing the heat values of coals and for classifying them accord- ing to their per cent, of combustible or coal content, and non-coal or mineral content. By the use of this formula, the coal is reduced to actual, or unit, coal, the term unit coal meaning coal free from ash, moisture, pyrites, and volatile organic matter. For coals that are dry and free from carbonates and chlorides, use the formula : _ indicated B. T. U. for dry coal — 5,000S, ^" '^" ^" ~ 1.00 — (1.08 ash + 22/40S) The formula for calculating the heat value for coal based on wet coal values is : indicated B. T. U. for wet coal — 5,000S ^' ~ 1.00 — (M + 1.08 ash + 22/40S) By indicated B. T, U. is meant the heat value of the coal that is obtained from a proximate analysis. Table XXVIII gives a comparison of results obtained from analyses made in the ordinary manner and from calculations by means of Parr and Wheel- er's formula. The values per pound of combustible obtained by the former method are lower and vary more than the values obtained for unit coal. The B. T. U. per pound of combustible is found as follows : From the first volumes in Table XXVIII, the non-combustible is equal to 12.92 + 16.58 -f- 3.82 = 33.32 per cent. ; therefore, the 9,992 B. T, U. rep- resent only 1 — .3322 = .6678 per cent, of combust- ible. The total inorganic matter of the coal is rep- COAL AND ITS COMBUSTION. 165 TABLE XXVin. Heat Values of Unit Coal. Analyses of Samples Received B. T. U. Per Moisture Ash Sulphur B.T.U.Per Pound of Coal B.T.U.Per Pound of Com- bustible Pound of Unit Coal, Calculated 12.92 16.58 3.82 9,992 13,311 14,613 14.22 18.16 4.51 9,540 13,059 14,624 12.45 17.22 4.14 9,950 13,314 14,608 23.00 -19.48 4.31 9,501 12,996 14,601 12.08 17.13 3.67 10,160 13,500 14,801 12.67 16.90 4.26 10,062 13,466 14,757 12.71 16.79 4.22 10,071 13,467 14,752 12.36 18.80 5.17 9,801 13,362 14,794 12.36 16.53 5.07 10,170 13,624 14,800 12.70 15.20 3.89 10,269 13,534 14,655 resented in the formula by M + 1.08 A + 22/40 S, M representing the moisture and 1.08 A the ash and the volatile inorganic constituent, the 8 per cent, being an arbitrary factor representing the latter ; the ash as weighed is corrected for the iron pyrites, FeSj, burned to Fe^Oa by substracting from the ash the factor 22/40 S, which is 22/40 of the weight of the sulphur, as determined. Hence, if .6678 pound of combustible = 9,992 B. T. U., 1 pound will equal 1.3322 X 9,992 = 13,311 B. T. U. The B. T. U. for unit coal is calculated as fol- lows: 9,992 - 5,000 X .0382 B. T. U. 1 - (.1292 + 1.08 X .1658 + 9,992 - 191 22 40 X .0382 1- (.1292 + .1791 + 9,801 _ 9,801 .0210 1 - .3293 .6707 = 14,613 B. T. U. 166 COAL AND ITS COMBUSTION. It will be noted that the values of M, S, and ash in these formulas are expressed in per cent. To avoid this, the formulas have been reduced to the following forms: 100 X indicated B. T. U. - 5000S B. T. U. 100 - (1.08A + ^) „ rr TT 100 X indicated B. T. U. — 5000S o. 1. U. = g-^ 100 - (M + 1.08A + ^) Calculating the B. T. U. for unit coal for the above case with this formula, 100 X 9,992 - 5,000 X 3.82 B.T.U.= 22 100 - (12.93 + 1.08 X 16.58 +|J X 3.82) 999,200 — 19,100 980,100 = = 14,613 B. T. U. 100 - 32.93 67.07 CHAPTER XV Burning Bituminous Coal URNACE Conditions. — In burning coal, two factors must be considered — ^the burning of the volatile ingredients and the burning of the fixed carbon. When fresh coal is thrown on a fire, it begins at once to absorb heat. This heat performs two functions: It does internal work in volatilizing and driving out the gaseous content of the coal, and it raises the temperature of both the fixed carbon and the gases. This absorption of heat cools the temperature of the furnace. When the temperature of the fuel is raised to between 700° and 900° F., the pitch, tar, naphtha, etc. of the coal begins to be driven off, and they continue to be produced until the fuel is at a temperature of about 1,800° F., when practically all are driven off. These constituents of the coal will not bum as tar, etc., but must be heated until they pass into the gaseous state and are broken up into their elements. They constitute a rich, smoky volatile that is produced at moderate temperatures, and, in burning, they will make much dense, black smoke unless conditions are favorable for their smokeless combustion. The hydrogen, Fig. 4, does not volatilize freely below a temperature of about 1,300° F., but above that temperature it is driven off rapidly and uni- formly until the temperature of the coal reaches about 1,800° F., when it is practically all distilled. The fixed carbon of bituminous coal begins to 167 168 COAL AND ITS COMBUSTION. burn at a red heat, about 800° F., Table XX; where- as, the gases under furnace conditions do not begin to burn until their temperature exceeds 1,400° F. Thus, both the fixed carbon and the gases absorb heat from the fire in the beginning, and this reduces the furnace temperature and is one reason why the steam pressure drops when a heavy charge of coal is fired at one time. Also, it may reduce the furnace temperature to a point where the tars and vapors which are first to be liberated and at the lowest tem- peratures, will produce much smoke. A sufficiently high furnace temperature is absolutely necessary to promote the vaporization of the tar and vapors, and the ignition and complete combustion of the gases of the coal. Where the temperature is below their igniting points, the gases will escape unburned, and the burning of the fixed carbon alone will be all that produces heat in the furnace. Thus, a large percen- tage of the heat value of the coal will be wasted. If, when first liberated, the gases are mixed with a sufficient quantity of air at the proper tem- perature, they will be completely burned in the form of a flame. The length of the flame will depend on the furnace temperature, the quantity of the combustible volatile matter to be burned, and on the amount and the distribution of the air in the fur- nace. Coals, like anthracite, with but little volatile gases, burn with a short, transparent, blue flame. Bituminous coals with sufficient air burn with a longer, yellow, smoky flame. When the supply of air above the fire is restricted, the flame becomes longer and more smoky than it would be with sufficient air. If a large volume of cold air passes through the furnace in a solid stream, as when the firedoor is opened wide, the gases surrounding the stream of COAL AND ITS COMBUSTION. 169 cold air are liable to be cooled below their igniting temperature and pass off unbumed. When the gases are heated to the igniting tem- perature in a restricted supply of air, carbon is lib- erated, or disengaged, in the form of a very fine powder, called soot. This soot, or carbon, floats in the gases at a white heat and thus gives luminosity to the flame. As soon as this carbon comes in con- tact with oxygen from the air, it unites and burns. Should it become cooled below its igniting tempera- ture before it comes in contact with a supply of oxy- gen, it will pass off as free carbon, or soot, thus col- oring the gases of combustion and forming smoke. These particles of incandescent free carbon are what give the color and most of the luminosity to the flame of illuminating gas. Regulation of Air Supply. — To bum coal prop- erly in a furnace, the furnace temperature must be high enough to volatilize the oils and tars quickly and to ignite the gases ; the air supply must be just suflJicient to furnish enough oxygen to burn the fuel constituents of the coal completely, it must be intro- duced into the firebox in small streams, so that it will heat quickly to the required temperature, and it must be intimately mixed with the volatile gases, so that its oxygen can come in actual contact with the combustible to the fuel and burn the combustible before it comes in contact with the boiler tubes. If all these conditions are not fulfilled, it will result in incomplete combustion, in loss of part of the gases, and probably in the production of smoke. Tables XVIII and XX show that there will be a loss of furnace temperature and of fuel if the air supply is either too little or too much for the coal used. The calculations tabulated in Table XXI show 170 COAL AND ITS COMBUSTION. that the air required per pound of coal depends on the composition of the coal, on the amount of air that must be supplied in excess of the theoretical amount, on the condition and the thickness of the fire, and on the strength of the draft. The amount of air used should be just sufficient to develop the full heating power of the coal. Admission of Air Supply. — The best method of admitting air to the furnace depends on the kind of coal that is being burned. In burning coal that is very low in volatile, like anthracite or semianthra- cite, the air for combustion can be admitted through the grates. For coals high in volatile, the air must be admitted so as to burn both the coke or fixed car- bon on the grates and the volatile gases. Most of the air for burning the coke can be admitted through the grates, but the air for burning the gases and the upper layers of coal must be supplied above the fire. Carbon dioxide, COj, is indecomposable by heat alone, but it may be decomposed by contact with bodies avid of oxygen. Carbon at red heat will decompose COj, reducing it to CO. This reaction always takes place in a furnace. The air in passing the grates gives up its oxygen to form CO2 with the carbon of the lower layers of coal, generating the full heat value of this union. The CO., which is at a very high tempera- ture, moves upwards and comes in contact with the red-hot coke and unites with another atom of car- bon in passing through the upper layers of the fire, being decomposed to CO and absorbing heat thereby. The CO passes up through the bed of the fire until it comes in contact with oxygen and burns, and if there is not a sufficient supply of oxygen to unite with it and burn it to CO., the CO will pass out of the stack unburned. To prevent this loss, and to insure suffi- COAL AND ITS COMBUSTION. 171 cient oxygen to burn the hydrocarbon gases as they are liberated from the coal, air must be suplied above the fire at such times as the gases are liberated in large volumes. Also, some provision should be made to control this air supply, so that, after a fire has been put in, the air can be diminished as the volume of gases liberated is diminished. If this provision is not made, an excess of air will be admitted after all the gases have been volatilized. The coke remains on the grates until burned, but the gases are in the furnace only a fraction of a second; so, to prevent their loss, conditions for burning them must be most favorable. Air for the combustion of the gases should be admitted above the fire in fine streams, and provi- sion should be made to insure a thorough mixing of the air and the gases while they are in the combus- tion chamber. Large currents of cold air cool the furnace temperature and allow the gases to escape unbumed. This cooling eifect of large streams of air is often taken advantage of by firemen when they open the firedoor to prevent the boiler safety valve from popping. The air admitted through the firedoor does not mix with the gases, but forms through the furnace a distinct current of cold air that chills the surrounding gases below their ignit- ing temperature and they pass off unbumed. CHAPTER XVI Smoke and Its Prevention ORMATION of Smoke. — Smoke consists of water vapor and the gaseous prod- ucts of combustion, colored with fine particles of carbon or soot and with unburned vapors of the tarry constitu- ents of the fuel. Therefore, if the soot and the unburned tarry vapors can be prevented from escap- ing to the stack, the products of combustion will be colorless, and there will be no smoke. Smoke From Soot, — ^The soot of the smoke is not derived from the fixed carbon of the coal, which burns smokelessly, but from the tars and the volatile matter, the illuminants, and the heavier hydrocar- bons, such as ethylene, CaH^, acetylene, CjHj, and benzole, CJtlg. Coals rich in these constituents, espe- cially when the gases distil rapidly at low and med- ium temperatures, will smoke badly, unless burned under conditions very favorable to smokeless com- bustion. On the other hand, coals low in illuminants and higher hydrocarbons will give no trouble from smoke under ordinary conditions of operation. If, when fresh coal is thrown on the fire, the gases as they are driven off are intimately mixed with the proper amount of air at a sufficiently high tem- perature, they will be completely burned and no smoke will be formed, provided the furnace is suited to the kind of coal that is being burned. If it is a high-volatile coal and sufficient air is not present and intimately mixed with the gases to bum all the large 172 COAL AND ITS COMBUSTION. 173 volume given off, the hydrogen will combine with its portion of oxygen before the carbon will combine. For example, in insufficient oxygen, ethylene, C2H4, burns according to the equation CaH^ -(- 20 = 2H2O + 2C. The hydrogen takes its full portion of the oxy- gen first, and the carbon combines with any that may be left. If none remains, all the carbon escapes as free carbon, or soot. If, while on its way to the tubes, the free car- bon comes in contact with oxygen and it is at its igniting temperature, the carbon and oxygen will unite and burn ; otherwise, the carbon will be cooled, and when it strikes the tubes it will pass out of the stack as soot. The greater the deficiency in the air supply, or the less intimately the air is mixed with the gases, the more soot will escape and the blacker will be the smoke from this source. Therefore, to avoid the formation of smoke from soot, the volatile gases as they are liberated must be intimately mixed with a sufficient supply of air while at a temperature high enough to insure combustion, and the gases be completely burned before they enter the tubes. If the air supply is insufficient, if the air and gases are not intimately mixed, if the temperature is not high enough, or if there is not sufficient time in which to burn, smoke will result. Flame. — The flame seen in the furnace is pro- duced by the burning of "the volatile gases of the fuel. Where a fuel, like coke, has no combustible volatile content, it will bum without flame unless furnace conditions are such that CO is formed, when a short, non-luminous flame will be produced. An- thracite coal burns with a very short, bluish flame, due to low volatile content; whereas, the flame from bituminous coals varies in length from a couple oi" 174 COAL AND ITS COMBUSTION. feet to 20 feet, depending on the nature and the amount of the volatile content and on the air supply. The length of the flame, therefore, indicates in a measure the liability of a coal to produce smoke. The color and luminosity of a flame, whether a gas- light flame or the flame in a furnace, is chiefly due to free particles of carbon at a white heat that are floating in the body of the gas. Where the carbon of the gases unites with oxygen at the instant that the carbon is liberated from the hydrocarbons, as in a Bunsen burner, there is no incandescent free car- bon suspended in the gas. The flame, therefore, looses its light-giving properties and produces simply a very feeble, bluish light, due to the luminosity of the gas produced by its temperature. As the flame of anthracite is short and has but little color, it indi- cates a low-volatile content, and that a sufficient supply of air is mixed with the gas to burn the car- bon as it is liberated from the hydrocarbons, which, in anthracite, consists chiefly of methane, CH^. The flame from bituminous coal varies, accord- ing to furnace conditions, from an intense, dazzling white to a dark, smoky, yellow. The intense, white- colored flame is comparatively short and indicates a high furnace temperature and good air supply, since the maximum flame temperature is obtejined by burning a maximum quantity of gas in a minimum volume of flame. A dark, smoky flame is a long flame; it indicates very rich hydrocarbons, a re- stricted air supply, or a poor mixture of air and gases, and a comparatively low furnace temperature, a condition favorable to the production of large volumes of dense, black smoke. Thus, both , the length and the color of the flame are an indication of the completeness of combustion of the gases. COAL AND ITS COMBUSTION. 175 Experiments in Smoke Production. — A few simple experiments will illustrate clearly the condi- tions that lead to the production of smoke from soot. The laws of combustion are the same whether applied to a furnace, a lamp, a candle, a gas jet, or a gas stove flame ; hence, laws that apply to any one of these, apply to all. Pour kerosene oil into a plate and set fire to it ; dense, black clouds of smoke will rise, due to lack of sufficient air properly mixed with the gases to burn the oil completely over the whole surface. A candle having a small wick produces a clear, bright light without smoke. A candle having a large wick has a dark, yellow-colored flame that has a tendency to smoke and does not give as bright a light as the candle with the small wick. The big wick tends to supply more oil than the conditions of the air supply warrant. A torch has a still larger wick, since it is in- tended to burn a larger supply of oil. It smokes badly because the wick supplies more oil than can be burned smokelessly under the conditions of air supply. These examples show that there is a limit to the quality of oil that can be burned smokelessly as a naked light. Consequently, to obtain more liyht than the candle would give, the kerosene lamp was in- vented. One reason for the torch smoking is that the wick is so thick that the air supply cannot inti- mately mix with the gas from the oil brought up through the center of the wick. To obviate this in the lamp, a wide, flat wick is used. Also, a chimney is employed to increase the air supply and to direct a current of air upwards and against the flame, thus insuring a sufficient air supply to burn the increased 176 COAL AND ITS COMBUSTION. amount of oil and give a clear, white light. If the chimney is removed, the flame will smoke, since there is nothing to create a current of air and direct it against the flame; hence, the air supply is deficient. The student's lamp with its circular burner permits the largest size of wick to be used, and since the air through the center of the tube is heated before com- ing into contact with the gases, the burner is well suited to give perfect combustion where a large amount of oil is being burned. This discussion shows that, in order to have smokeless combustion, the air supply must be suffi- cient, and must be intimately mixed with the gases of the fuel while at the proper temperature; also, that the furnace must be suitably constructed to burn the required supply of fuel. A candle will give perfect satisfaction for the consumption of a small amount of oil, but an Argand burner is necessary to burn a large supply of oil satisfactorily. Every lamp has a range through which it will burn smokelessly, but, without exception, if the range be exceeded, and the wick turned up so far as to supply more oil than can be burned perfectly, the lamp will smoke. This shows that if an attempt is made to bum more fuel in a furnace than the furnace is designed to burn, smoke will result. Turn up the flame of a lamp until it produces a clear, bright light, indicating perfect combustion. Gradually close the draft openings at the base of the burner, and watch the flame. As the air supply is diminished, the flame gradually lengthens and be- comes darker and darker, until, flnally, it begins to smoke ; then, if the air is still further restricted, the smoke increases, and when the flame extends above the chimney a stream of dense, black smoke arises COAL AND ITS COMBUSTION. 177 from the flame. The effect vdll be the same whether the air supply is restricted at the burner or at the top of the chimney, the amount of smoke produced being in proportion to the restriction of the air supply. This experiment shows the effect of a restricted air supply on the flame and on the smoke produced. The effect will be the same whether the air supply is cut down below the requirements of the fuel, or the fuel supply is increased above the capacity of the air supply. The flame of a gas stove when properly ad- justed is short and produces a feeble, bluish light, similar to that of a Bunsen burner. Gradually re- strict the air supply, and the flame will gradually lengthen and give off less and less heat; when the air supply is restricted too far, the flame will assume a dark-yellow color and will smoke, owing to the par- ticles of free carbon that the restricted air supply allows to escape unburned. Note the time necessary to boil a quart of water from the same temperature, first, when the flame of the gas stove is short, due to a proper air supply, and second, when the flame is long and yellow, due to a restricted air supply; the short flame will be found to give a great deal more heat than the long flame, since it utilizes all the heat of the gases. Turn the wick of a lamp up until the flame burns brightest, and remove the chimney. The flame will smoke badly. The oil from the wick is converted into a gas by the heat of the flame and if the gas were mixed with air in the proper proportions, a very hot, non-luminous flame would result, similar to that of a Bunsen burner. The luminosity of the lamp flame is due to the fact that the air does not penetrate 178 COAL AND ITS COMBUSTION. within, and mix with, the gas supply. The air simply envelops the flame so that all the combustion is on the surface of the gas supply. As the oil is vaporized, it becomes heated and the hydrocarbons are dissociated. The free carbon floating in the gas supply is then heated to a white heat and travels to the surface of the gas, where it combines with oxy- gen and burns smokelessly. The chimney produces a current of air and deflects it against the flame, thus intimately mixing the air and the gas at the source of the flame. When the chimney is removed, the means of producing sufficient air for the gas and of intimately mixing the air and the gas is absent; hence, a smoky flame results. A gas-light burner tip is designed so to spread the flame as to give complete combustion with full luminosity. Remove the tip so that the gas issues from a round orifice, and a long, very smoky flame will result, because the air is not intimately mixed with the gas, and more time and space are needed for the burning of the gas. These examples indicate the importance of an intimate mixture of sufficient air with the gaseous content of coal, in order to obtain complete combus- tion and to generate the maximum quantity of heat from the gas without smoke. Lower a pan of cold water into the flame of a candle that is burning brightly without smoking, and the flame will smoke badly, owing to particles of free carbon in the flame coming in contact with the cold metal and being chilled before they can burn. This illustrates why a furnace smokes badly when the heating surface is arranged so that the flames can come in contact with it. A pan of cold water placed on a gas-stove flame COAL AND ITS COMBUSTION. 179 does not cause smoke, because the burner mixes the air and the gas before they reach the flame ; hence, the carbon of the gas is completely burned as it is dissociated and there are no free particles of carbon in the gas to produce smoke when the pan cools the flame. Once a flame starts to bum, the heat produced by the combustion of the gas is suflicient to maintain the phenomenon of burning. If the flame is sud- denly cooled at any point, the combustion beyond that point is at once arrested. A fine wire gauze held midway in a gas flame will cool the flame, since the incandescent gas cannot pass through the meshes of the gauze without being cooled below the igniting temperature by contact with the metal, which is a good conductor of heat. Hence, no combustion takes place above the gauze, although smoke is produced and the unburned gas passes through freely. If the gas above the gauze is ignited, it will bum. Also, if the gauze is held in a jet of gas that is escaping unlighted, the gas above the gauze may be burned without the gas below the gauze igniting. These experiments show that if the combustion chamber of a furnace is not of sufficient capacity to \ prevent the flame from coming in contract with the cool surfaces of the boiler, dense, black smoke is sure to result. Prevention of Soot. — From what has been said it will be seen that in order to prevent smoke from being formed from soot, and the following rules must be observed: ' 1. Sufficient air must be supplied to bum all the gases of the fuel completely. 2. The air must be intimately mixed with the 180 COAL AND ITS COMBUSTION. gases, so that each particle of gas is surrounded with air. 3. The temperature of the air and the gases when they mix must be at or above the igniting tem- perature of the free carbon; otherwise, the carbon will escape as soot. 4. If the carbon is cooled below its igniting temperature before coming in contact with a suffi- cient supply of oxygen, it will not burn and will escape as soot. Therefore, the combustion chamber must be of sufficient volume for all the gas to burn before it reaches the tubes. This is indicated by the flames not reaching the tubes. Volatile Matter and Smoke. — The volatile mat- ter of coals consists of light hydrocarbons, as methane; of tarry vapors, illuminants, and other heavy hydrocarbons, as ethylene, ethane, benzole, etc.; and of inert, non-combustible material, as car- bon dioxide, and water vapor. All coals do not have the same per cent, of these constituents, and the behavior of a coal in burning depends on both the character and the quantity of the volatile matter evolved in its heating. The older bituminous coals of the Appalachian region give oif an abundance of volatile rich in tarry vapors and in hydrocarbons that are difficult to burn smokelessly without proper combustion space and without special attention being given to the firing, the air supply, and the furnace temperature. The younger subbituminous and lignite Western coals, while high in volatile, include a large portion of COj and water vapor; hence, they do not tend to cause excessive smoke unless burned at high rates of combustion. The bituminous coals of Indiana and Illinois are inter- COAL AND ITS COMBUSTION. 181 mediate types that, with care, can be burned without objectionable smoke within the capacity of the fur- nace. Thus, the smoke-producing tendency of coals does not depend so much on the relative total quan- tity of volatile matter of the coals as on the com- parative richness of their volatile in hydrocarbons, and on the relative ease with which the volatile is set free at moderate temperatures. The heavy hydro- carbons in the tar and in such gases as ethylene, CoH^, acetylene, C^Hj, benzole, CgHg, and others are the hardest to burn smokelessly, as they are slow- burning and require a large air supply intimately mixed with the gas. TABLE XXIX. Air Bequlred by Carbon and by Hydrocarbons. Combustible h 1. £ u < •a < Weight In 1 pound of Com- bustible, lbs. H c C to CO C to CO CO to CO..... Hydrogen Methane Ethylene Acetylene .... Benzole 152 76 32 454 227 195 175 175 76 126 302 75 43 23 23 454 113 65 35 35 152 76 32 114 130 140 140 1 1/4 1/7 1/13 1/13 1 1 3/7 3/4 6/7 12/13 12/13 Table XXIX gives the total air, in cubic feet, required theoretically to burn 1 pound of the com- bustibles shown, as well as the proportions required by the hydrogen and the carbon in each case. The hydrogen always burns first and takes its air from the total air supply, leaving a greatly reduced 182 COAL AND ITS COMBUSTION. amount for the carbon, which bums last. As will be seen, 1 pound of methane consists of lA pound of H and % pound of C; it requires a total of 227 cubic feet of air, of which the hydrogen takes half, leaving only 114 cubic feet for the % pound of carbon. If only 152 cubic feet of air were supplied per pound of methane, only 38 cubic feet would be left to burn the % pound of carbon. The hydrocarbons require so much more air than carbon or carbon monoxide that it is easily seen how a restricted air supply will liberate large quantities of carbon in the form of soot, and form smoke. Smoke from Tarry Vapors. — In the manufac- ture of coal gas for illuminating purposes, the coal is placed in a retort from which the air is excluded and is gradually heated until all the volatile content is driven off. Besides the gas and the coke that is obtained from this process, a tar or black pitch is distilled as a liquid vapor and condensed into the solid form known as coal tar. When a coal rich in tarry content is thrown onto a fire, the tar is distilled off in the form of a dark-colored liquid vapor, just as it is during dis- tillation for illuminating gas. The process of dis- tillation of the tar vapor is much the same as the distillation of water vapor that issues from the spout of a boiling kettle. If these tarry vapors escape unburned, they color the products of combustion and in this way form smoke. If a piece of cold iron is thrust into the stream of volatile gases from a coal rich in heavy hydrocar- bons and withdrawn before the iron becomes heated, some of the globules of tarry vapor will have con- densed on the iron and will be seen to be a thick, COAL AND ITS COMBUSTION. 183 black liquid having a strong odor of coal tar. Every fuel gives off more or less tarry vapors, but the tar vapor from each fuel has a distinctive odor. It is owing to this fact that different kinds of wood in burning can be distinguished by their odor. A coal rich in tarry vapors is a persistent smoke maker, owing to the difficulty with which the vapor is gasified and burned. The vapor is a liquid in the form of mist of minute tar globules, and these globules must first be converted into gas and then dissociated before they combine with the oxygen and burn. As each globule must be furnished with suffi- cient heat for gasification and for dissociation, a.= well as for raising the temperature of the gas to its igniting temperature, the process of burning may require more time than is afforded the vapor in passing from the fire to the tubes, in which event, the vapor will pass off as smoke. To burn tarry vapors successfully, a large combustion chamber and a sufficiently high furnace temperature, together with an adequate supply of air intimately mixed with the vapor, are imperative, because the vapor is com- paratively slow-burning and requires a large supply of air. Rate of Distillation of Volatile, and Smoke. — Laboratory experiments by Porter and Ovitz show that the quantity and the quality of volatile dis- tilled from a coal depends largely on the rate at which the coal is heated. With a slow rate of heat- ing, the volatile driven off is of gaseous composition, comparatively small in quantity, and contains only a small amount of tarry vapors. With a very rapid rate of heating, the volatile is high in quantity and contains a large amount of tarry vapors. When the hydrogen is distilled slowly from the coal, it takes 184 COAL AND ITS COMBUSTION. only a small quantity of carbon with it in the form of light hydrocarbons or easily burning gases, most of the carbon being burned on the grate as fixed carbon. When distilled off rapidly, the hydrogen takes a large amount of carbon with it in the form of heavy hydrocarbons, such as ethylene, ethane, benzole, etc., and of tarry vapors, leaving a smaller quantity of fixed carbon on the grate. The fixed carbon is easily burned, because it re- mains on the grates until completely consumed. The hydrogen and the light hydrocarbons are easily burned, because they are quick-burning gases that have ample time to burn while in the combustion chamber of the furnace. The tarry vapors and the higher hydrocarbons are hard to burn, because they are slow-burning, and unless special provision is made for burning them, they usually pass out of the furnace before they have time to bum. It is very possible that the combustion of hydrogen and carbon monoxide consists of but a single reaction, whereas the combustion of the heavy hydrocarbons may con- sist of a series of reactions, thus lengthening some- what the time required for their complete combus- tion. The tarry vapors are very dark and make a dense, black smoke. Throw a small piece of coal tar on the fire and note the quantity and the color of the tarry vapor that arises from it; in this way the power of the tarry vapors to color the smoke will be readily understood. Thus may be seen the reason why a coal that gives off clouds of dense, black smoke when hand fired in an ordinary furnace bums smoke- lessly under the coking system of hand firing, or, when a proper mechanical stoker is used. In hand firing, the coal is thrown directly onto the fire and is COAL AND ITS COMBUSTION. 185 heated through a range of about 2,000° F. in from 2 to 3 minutes; whereas, in the coking method of hand firing, or when a well-operated chain-grate stoker is used, it may take from 15 to 20 minutes for the coal to heat through the same temperature range of 2,000° F. Mechanical stokers are designed to feed the coal into the furnace gradually; conse- quently, the rate of heating the coal is slow and conducive to smokeless combustion. It has been pointed out that the tendency of eoo 11/2 1292 MF2 Temfiefattire of Furnace, Decrees rahrenheit Fig. 8. Proportion of Smoke-Producing Compounds of Coals. a coal to produce smoke depends on both the relative total quantity of the volatile matter and on the rela- tive ease with which the smoke-producing volatile matter is given off. Coals differ considerably in the latter respect, as is shown in the diagram, Fig. 8. The curves are plotted from data of a test conducted by the Bureau of Mines in heating 10 grams of air- 186 COAL AND ITS COMBUSTION. dried coal 10 minutes ; the data being taken for the temperatures given. The curves show the total smoke- producing products, consisting of tarry matter and heavy hydrocarbons in the form of CaHg, CjH^, CgHg, etc. The distillation of smoke-producing products from the Connellsville coal begins at about 900° F., and progresses at practically an even rate up to about 1,300° F., when practically all the heavy hydrocar- bons are driven off. The Illinois coal gives off prac- tically two-thirds of its smoke-producing matter be- tween 900° and 1,100° F., the smoke-producing mat- ter distilling quite gradually before 1,100° F. The rapid production of large volumes of smoke-pro- ducing volatile at low temperatures makes both of these coals difficult to burn without objectionable smoke unless special provisions for the prevention of smoke are made. However, the smaller total volume of heavy hydrocarbons produced by the Illinois coal makes that the easier coal of the two to burn smoke- lessly. The Wyoming coal is the next best smoke pro- ducer, as it gives off practically all its heavy hydro- carbons between 1,100° and 1,300° F. The Poca- hontas coal contains about the same amount of smoke-producing matter as the Wyoming coal, but it distils its volatile more gradually and at a higher temperature, distilling between 1,100° and 1,500° F. The maximum quantity of heavy hydrocarbons is about the same for the Wyoming and the West Virginia coals. However, the time required for their distillation varies considerably. The Wyoming coal distils its gas in two-thirds the time required by the Pocohontas, while an equal volume of gas from the Connellsville coal is distilled in one-half the time. The difference in the time element of distillation in COAL AND ITS COMBUSTION. 187 different coals is quite a factor in the production of smoke, the shorter the time element, the more diffi- cult it is to prevent smoke. Prevention of Smoke from Tarry Vapors. — From the foregoing discussion it will be seen that to burn smokelessly coals that are rich in heavy hydrocarbon gases and in tarry vapors; the coal must be heated slowly, so as to reduce to a minimum the amount of tarry vapors and higher hydrocarbons that are driven off ; the temperature of the combustion space must be high enough to furnish sufficient heat quickly to gasify the vapors promptly as they are produced; an adequate supply of air to bum com- pletely the gas thus produced must be admitted into the combustion chamber; the air supply must be intimately mixed with the gases; and the time of flight of the volatile to the tubes must be sufficient, so that the volatile will be completely burned before coming in contact with the cold surfaces of the boiler. Honeycomb. — In locomotive service, coal rich in tarry vapors frequently has to be burned in fireboxes that are not properly designed to burn that type of coal. The result is that clouds of dense, black smoke are formed by the tarry vapors, and honeycomb, or flue sheet clinker, sometimes forms on the tube sheet, covering the ends of the tubes and stopping the flow of hot gases through such tubes. The honeycomb will continue to grow and spread, and eventually it will cover the tube sheet, if they are not knocked off periodically by means of a long iron rod introduced through the firedoor. The honeycomb in this case is formed by the tarry matter that strikes against, and is condensed on, the tube sheet. The tar is "coked" on the sheet by the heat of the firebox, and collects 188 COAL AND ITS COMBUSTION. particles of ash and fine coal that are carried bodily through the furnace by the gases of combustion. This results in the formation of a hard substance that grows or spreads over the face of the tube sheets in a comparatively short time. The formation of honey- comb is aggravated by flue leakage as the leakage tends to reduce the firebox temperature, which in turn retards the vaporization of the tarry globules. Fine particles of a caking coal may cause honeycomb to form also, owing to the particles striking the tube sheet while in a pasty condition and adhering and caking on the sheet. Heat Losses Due to Smoke. — The production of smoke is objectionable both from the standpoint of the public and of the power-plant owner. The pubHc is interested because of the heavy, yearly financial loss through the deterioration of property, etc. caused by soot from smoking chimneys ; also, because of the detrimental effect on the health of a com- munity and on the vegetation in the vicinity of smoky stacks, due to the soot and to harmful, but in- visible, waste gases that escape from the smoke. These waste gases consist of the poisonous carbon monoxide, of unaltered hydrocarbons and tarry vapors, and often of sulphur vapors. The plant owner is directly interested in smoke abatement be- cause of the financial loss sustained through the waste of the fuel gases that escape unburned with the smoke. Black smoke is a sure indication that, for some reason, the combustion is incomplete, consequently, that a direct fuel loss is occurring, and the blacker the smoke, the greater is the fuel loss through the escape of unburned gases. On the other hand, the absence of smoke does not always mean complete COAL AND ITS COMBUSTION. 189 combustion or the elimination of waste of unburned gases, as the stack may be cleared up through ex- cessive air dilution. This method of smoke suppres- sion is very wasteful, since, at times, it produces a loss of furnace temperature, Table XXVI, that causes a great waste of heat through gases that escape unburned. The best economy will be obtained with the air supply cut down until the stack gives off a light smoke the color of gray mist, as this insures against excessive air dilution. Smoke may indicate a loss of heat through un- burned carbon as soot, through unburned gases that escape as carbon monoxide and as unaltered hydro- carbons, and through tarry vapors. The loss through the soot in smoke is very small, seldom exceeding 1 per cent, of the fuel burned. Soot is so light that it requires but a small amount or weight to give the smoke a dense, black color. If, therefore, the soot were the only waste that occurred through smoking, the saving through soot prevention would not war- rant much expense to effect it. However, soot is a danger signal that signifies incomplete combustion, the losses through which may be many times the loss due to the soot. For each pound of carbon monoxide that escapes in the smoke, 10,250 B. T. U. are lost, and this loss, in some cases, may amount to .5 of 1 per cent, of the total heat of the coal. While the amount of CO loss increases usually with the density of the smoke, yet, the density may not indicate the proportion of loss due to CO. With a perfectly clean chimney, the CO loss is very small, not exceeding .05 of 1 per cent, of the total heat of the coal. In the the greater number of instances where chimneys smoke badly and the coal is rich in heavy 190 COAL AND ITS COMBUSTION. hydrocarbons and in tarry vapors, the loss through unburned volatile combustible gases and tarry vapors may amount to 3 to 10 per cent, of the total heat value of the fuel. The number of heat units lost per pound of the different hydrocarbons can be seen from Table XVII. For coals rich in tarry vapors, the vapor loss proba- bly forms the greater part of the heat loss due to incomplete combustion. CHAPTER XVII Burning Coal Smokelessly N the discussion on the smokeless com- bustion of fuel, it was seen that four factors enter into smokeless combus- tion; namely, the air supply, the inti- mate mixture of the volatile matter and the air, the temperature in the combustion chamber of the furnace, and the interval of time allowed the volatile matter in which to burn while in the combustion space. Fixed Carbon. — In burning, carbon is found in three forms that are of interest; namely, as fixed carbon, as gaseous or free carbon, and as soot. The fixed carbon is that part of the coal, called coke, that remains after the gases of the coal have been driven off. Fixed carbon combines with oxygen and burns when at a red heat, and it remains incandescent as long as combustion goes on, the heat produced in burning being sufficient to maintain incandescence. It burns without flame, the coke merely glowing. Coke cannot produce smoke in burning, because its carbon cannot be liberated as free carbon to form soot. It can exist as carbon only in the coke. In burning, it forms invisible gas, CO.. Under certain conditions in a restricted supply of air, it may pass off with only 1 atom of oxygen, as CO, but that gas is invisible also. The problem of smokeless combustion, there- fore, consists in burning the free carbon of the vola- tile matter of the coal. The gases given off by coal 191 192 COAL AND ITS COMBUSTION. can, be burned smokelessly, just as illuminating gas is, if conditions for properly burning them are favor- able. On the other hand, anything that tends to affect the conditions for smokeless combustion un- favorably will tend to cause smoke. Air Supply. — The proper supply of air to the fire is one of the really important matters connected with economical firing. Approximately 250 cubic feet of air is needed to furnish oxygen for the complete burning of 1 pound of bituminous coal. For each scoop of 15 pounds, it will require 15 X 250 = 3,750 cubic feet of air, and, if five scoops are fired at a time 5 X 15 X 250 = 18,750 cubic feet of air must be supplied for each fire put in. With a hand-fired furnace having a grate area of 67 square feet, and burning 20 pounds of coal per square foot of grate surface per hour, 67 X 20 X 250 = 335,000 cubic feet of air per hour, or 5,584 cubic feet per minute must be supplied. This requires a good draft, a good, clean fire, and an ample ashpit opening through which the air can enter the furnace freely. Further- more, provision must be made for a free admission of air into the furnace room. Distillation of Gases. — If the gases were dis- tilled from the coal at a uniform rate, their burning would be very much simphfied, because the air sup- ply could then be accurately regulated to give the proper mixture of air and gas for complete combus- tion. Unfortunately, in hand-fired furnaces, the dis- tillation of the volatile is very irregular. The firing is done at more or less irregular intervals, and after each fire is put in a large volume of gas is distilled within a space of a few minutes while the coal is being heated to the furnace temperature. To burn COAL AND ITS COMBUSTION. 193 completely, the gases require a larger supply of air than should be supplied to the fixed carbon after all the gases have been distilled. If, therefore, the air supply is adjusted to take care of the gases, then it will be too great for the fixed carbon after the gases are distilled, and will cause a loss of heat through excess air, Table XXVI. If the supply is adjusted for the fixed carbon, then it will be insufficient to burn all the gases, so that a loss through unburned gases will result. It is evident, therefore, that to obtain the best results either the coal must be fired at a uniform rate, so that the gases will be distilled uni- formly and continuously, or the air supply must be adjusted to the proper amount for the fixed carbon and their be increased sufficiently to take care of the gases during the time the gases are being distilled. The method of uniformly distilling the gases is made use of in the mechanical stoker, and, approximately, in hand-firing when the coking method of firing is employed. The method of adjusting the air supply to the condition of combustion is used in hand-firing when either automatic or non-automatic air admis- sion above the fire is made use of. Admission of Air. — For furnaces equipped for hand-firing in which the distillation of the gases is not uniform, the air required for firing the fixed car- bon of the coal can be supplied through the grates, but the air for burning the distilled gases and for assisting in the combustion of the upper layers of coal when the fire is very thick must be supplied from above the fire. The air supplied above the fire should be ad- mitted in small streams, so that the air will be heated as quickly as possible and will be more thoroughly mixed with the gases. The greatest volume of air 194 COAL AND ITS COMBUSTION. for the gases should be supplied when the coal is first fired, and the supply should be diminished as the quantity of gases distilled diminishes. Results of tests show conclusively that the weight of the air used to burn 1 pound of combustible decreases as the rate of combustion increases, and this indicates that the rate of combustion more than keeps up with the velocity of the current of air through the fuel bed. In other words, the higher the velocity of the air through the burning fuel, the higher will be the rate of combustion. As an ex- ample, during a test a certain plant using forced draft required 22.5 pounds of air per pound of com- bustible when burning 20 pounds of coal per square foot of grate surface, and only 20 pounds of air when burning 70 pounds of coal. The air supply above the fire should be regu- lated to suit the combustion of different kinds of coal, and it should be supplied automatically, so as to overcome the personal element that enters into hand regulation. When no special means for air admission above the fire are provided, conditions may be helped somewhat by cracking the furnace door for a couple of minutes after each fire and then clos- ing it when the gases are nearly all distilled. The firedoor should not be opened wide for the admission of air, because the large volume of cool air thus allowed to pass through the furnace in a solid stream would not mix with the gases, but would absorb and carry away so much heat that the loss through excess air would far exceed any possible gain through the admission of the air. It is com- mon, but poor, practice with some firemen to open the firedoor when there is a liability of the safety valve opening, so as to cool the furnace and prevent COAL AND ITS COMBUSTION. 195 the safety valve from popping. The same detrimental effect is noticed if holes are allowed to form in the fire. Effect of Clinker Holes and Thick Spots.— Clink- ers, large lumps of coal, and thick spots and thin spots in the fire, all tend to disarrange the proper admission of air through the grates. The draft draws the most air through the spots offering the least resistance — the thin spots — and this tends to burn a hole quickly in the fire at such points. The thick spots, on account of their greater resistance, have less air passing through them, so that the com- bustion is very slow and thus the tendency is for the spots to become thicker and thicker and, with poor coal, to form a clinker. A clinker acts as a "dead plate," because no air can pass through it. Its tend- ency is to form a dead spot in the fire. Large lumps of coal fired unbroken with the fine coal of run-of- mine coal cut down the active grate area to the extent of the area of the lump. Also, the fine coal burns much faster around the edges of the lump, thus tend- ing to burn a hole through the fire around the lump. The effect of dead spots and of light spots is to make the admission of air uneven throughout the surface of the fire, thus causing different rates of combus- tion at different parts of the fire and resulting in the production of smoke and waste of unburned gases. Draft. — It is impossible to burn bituminous coal smokelessly unless there is an ample draft capacity available. Poor draft is a most aggravating source of trouble and loss. Because a chimney is high it does not follow that the chimney will produce suffi- cient draft under all conditions. The cross-sectional area may be too small, thereby causing too great a drop of pressure in overcoming the resistance of the 196 COAL AND ITS COMBUSTION. stack; thus there will not be sufficient draft for the proper acceleration of the gases. The chimney may be high enough to produce the draft and of large enough area, yet the draft may be used up in over- coming the resistance of a number of elbows in the smoke flues leading from the boiler to the stack, or there may be sufficient leakage in the boiler setting, smoke flues, and breeching to use up a good portion of the draft. Also, weather changes have consider- able effect on the draft produced by a chimney. This is very noticeable where all the available draft is required to carry the load of the plant. To obtain the best service, a chimney should be so proportioned as to have draft in reserve above that required for the full load of the plant, the draft being regulated by means of the draft control ar- rangement in the breeching. This is a better method of regulating the draft than by means of the ash- pit doors, since the latter method favors the escape of the volatile gases unburned through the direct action of the draft. Where two or more furnaces are connected to the same chimney, the draft of each furnace should be regulated separately. If this is not done, the fur- nace nearest the chimney will be working above its rating and thus may smoke badly, whereas the furnace furthest away may be working at or below its rating and without smoke. This will be indicated by smoke appearing at the stack, whereas, by equal- izing the rates of combustion in the two furnaces, the smoke may be prevented. Mechanical or artificial draft does not burn coal any more efficiently than natural draft, but it can supply ample air for high rates of combustion or for the burning of inferior grades of coal, and it is inde- COAL AND ITS COMBUSTION. 197 pendent of weather conditions. Also, it places the engineer in absolute control of the draft, so that he can quickly and accurately adjust the draft to sud- den changes of load. Natural draft is practically constant, and its control rests principally on the operation of the dampers, which restrict the flow of air, but do not affect the intensity of the draft pro- duced by the chimney. With mechanical draft, the dampers are usually left wide open and the intensity of the draft is regulated by changing the speed of the fan. For variable conditions of service, the throttle of the fan is operated by an automatic draft regulator so constructed that the throttle is opened wider and the fan speeded up when the steam pres- sure falls, and vice versa, thus obtaining close regu- lation of the steam pressure. Draft has two functions to perform. It must overcome the resistance of the grates, fire, combus- tion chamber, tubes, breeching, uptake, etc., and must be sufficient to impart the necessary velocity to the requisite amount of air for complete combustion at maximum rates of steam production. Under average conditions, about 75 per cent, of the total draft is expended in overcoming the resist- ance of the grates, about 19 per cent, in overcoming the frictional resistance of the flues and chimneys, and only about 6 per cent, in accelerating the gases. Since the rate of combustion in the furnace and the rate of absorption of heat by the boiler are directly proportional, respectively, to the velocity of the air through the fire and to the velocity of the gases of combustion through the tubes, it is very important that the chimney have sufficient height to provide ample draft for the acceleration of the gases under all conditions of operation. Table XXX gives the 198 COAL AND ITS COMBUSTION. draft, in inches of water, produced by chimneys of different heights at sea level. These values must be corrected for elevations above sea level. The height is the distance that the stack extends above the grates. TABLE XXX. Relation of Height of Stack to Draft. Height, Feet Total Draft, Inches of Water Height, Feet Total Draft, Inches of Water 50 .364 130 .948 60 .437 140 1.029 70 .512 150 1.095 80 .583 180 1.313 90 .675 200 1.459 100 .729 225 1.641 110 .802 250 1.825 120 .875 300 2.189 The area of the chimney must be such that the average velocity of the gases in the chimney, in feet per second, multiplied by the area, in square feet, will be slightly greater than the volume of air neces- sary for combustion at the maximum rate at which the coal is to be burned. Steam Jets for Mixing the Air and Gases. — In burning high-volatile, smoky coals, an intimate mix- ture of the air supply above the fire and the volatile matter, while in the combustion chamber and at the proper temperature, is absolutely essential, in order to avoid the production of smoke and the waste of heat through unburned gases. With hand-fired fur- naces, especially, the combustion space, to be most efficient, must have some means of mixing the air and the gases. COAL AND ITS COMBUSTION. 199 When coal of moderate smoking qualities is used, mechanical draft has sufficient power to furnish an adequate supply of air through the grates and fire for complete combustion. Thus admitted, the air is broken up into numerous fine streams that mix thor- oughly with the gases as they are distilled. For rich, smoky, volatile coals, mechanical draft can furnish a portion of the air above the fire (preheated if neces- sary) in the form of jets so directed as to mix inti- mately with the gases as they rise from the bed of the fire. With natural draft, a series of steam jets operated on the principle of the ejector have been employed to induce a flow of air into the furnace above the fire. The jets of steam and air are hand controlled and are directed downwards, so as to pro- duce a thorough mixing of the air and the gases. The second method consists of automatic steam- and-air admission devices that are thrown into opera- tion on opening the firedoors and remain in operation after the doors are closed for an interval depending on the adjustment of a dashpot that regulates the length of time that the steam jets are in operation. The air above the fire is admitted through an air- admission door in the firedoors. The steam jet is directly above the center of the firedoor and is di- rected downwards, so as to intermingle the incoming air and the gases arising from the burning coal thor- oughly. While these methods are quite successful in pre- venting smoke, yet they are objectionable on account of the noise they make while operating, as well as the high cost of operation, due to the large steam consumption. The steam jets, by introducing steam and air 200 COAL AND ITS COMBUSTION. above the fire, cut down the amount of air that passes through the grates and the bed of fire while the jets are in operation. The steam itself is objec- tionable, because it will not burn, it excludes its own volume of air, and it is superheated and carries the heat out of the stack and thus wastes this heat. On the other hand, the mixing action of the jets brings the air that is introduced above the fire into more intimate contact with the gases, thereby insuring better combustion and air economy and less smoke. This, in a measure, oifsets the direct loss due to the use of the steam. The results of using steam jets, therefore, are a quicker and better combustion of the gases, and a slower combustion of the fixed carbon during the time that the steam jets are in operation. In the endeavor to avoid the losses resulting from the use of steam jets, different arrangements of firebrick arches and piers have been employed to mix the air and the gases. However, the difficulty has been to build arches and piers that will with- stand the intense heat emanating from the combus- tion of the intimately mixed gases. Also, the piers and arches increase the resistance to the flow of gases to the stack and thus reduce the available draft, be- sides reducing the capacity of the combustion space. If these factors are not reckoned with in the design of a plant, a reduction in the capacity of the furnace to burn coal will result. Automatic Air- Admission and Steam-Jet Mixing Devices. — The object of the automatic air-admission device is to make the admission of air above the fire, after fuel has been added, independent of the fire- man. Fig. 9 illustrates one of these devices applied to a furnace under a water-tube boiler. 1 is the dash- pot closed after the firedoor has been closed ; 2 is the COAL AND ITS COMBUSTION. 201 Fig. 9. AutomaHc Air Admission Device. air admission through the furnace door 3, the air being split up into fine streams by the perforated plate 9 ; 4 is a cock that controls the supply of steam to the steam jets. The handle 5 of the cock is con- nected both to the spindle of the dashpot 1 and to the link 6, which is connected to, and operated by, the shaft 7. The shaft is operated by the arm 8, which is connected to the furnace door 3. Opening the door 3 turns the shaft 7, which operates the link 6 and raises the handle 5 of the cock .4 to "open" position, indicated by the dotted lines. This opens the cock i. and turns on the steam ; also, it raises the dashpot plunger. After the firedoor has been closed, the steam jets continue to operate for a short inter- val, depending on the adjustment of the dashpot 1, after which they are automatically shut off. In this arrangement, the jet of steam is employed solely to mix the air and the gases. Fig. 10 shows the piping arrangement for dis- 202 COAL AND ITS COMBUSTION. tributing steam to the jets. The piping is located within the furnace walls, in order to protect it from the direct heat of the fire. Fig. 11 shows a vertical section through a re- Flg. 10. Arrangement of Steam Jets. turn-tubular boiler with a similar automatic steam- and-air admission device. With this arrangement, the air for above the fire is admitted to the furnace through the ashpit air admission 2, which is opened by the firedoor and is regulated by the dashpot. in Fig. 11. Automatic Steam and Air Admission Device. Non-Automatic Air Admission. — A method of air admission for use with tubular boilers, which was experimented with by Messrs. Flagg, Cook, and Woodman, of the Bureau of Mines, Technical Paper 34, is shown in Fig. 12. In these tests, two methods of supplementary air supply were tried out. One, COAL AND ITS COMBUSTION. 203 admitted the air at the front end of the furnace ; the other admitted it through the rear face of the bridge wall, as shown. For the front-end air admission were used, eight rectangular openings having a total area of 115 square inches, or about 5 square inches per square foot of grate area. The air openings were equally spaced across the front wall of the furnace, and opened into an air passage about 8 inches by 10 inches. The passage was divided in the middle, so as to separate the air admission openings into two separately controlled groups, one for each half of the furnace. Each of the air passages was provided with a sliding door in the boiler front, for control of the admission of the air to the passage. Fig. 12. Cioss Section of Purr.nce Sliowlng Air Duets. Non-Automatle Air Admission. The bridge-wall arrangement consisted of an air-passage about 8 inches by 10 inches, controlled by means of a sliding door similar to that used for the front-end passage. There were eighteen air openings into the combustion chamber, with an area of 67 square inches, or about 3 square inches per square foot of grate area. The sliding doors per- mitted the fireman to graduate the air admission 204 COAL AND ITS COMBUSTION. from no air, with the doors closed, to full air admis- sion. The front-end admission gave best results dur- ing the tests, due to its admitting air in front of the fire, and, therefore, to the better chance of the air being thoroughly mixed with the gases while in the combustion chamber. Under most conditions, there- fore, front-end admission alone would be sufficient. However, with a very smoky coal, auxiliary air ad- mission at the bridge, with suitable mixing facilities, would very probably burn smokelessly coal that could not be so burned with the front-end admission alone. Capacity of Combustion Chamber. — A furnace well designed for smokeless combustion and properly operated will burn many kinds of coal smokelessly up to a certain number of pounds of coal per square foot of grate area per hour. The maximum rate for the different coals will vary considerably, depending on the percentage and the richness of the volatile mat- ter of the coals, on the draft, and on the manner in which the firing is performed. If the maximum rate for any coal is exceeded, smoke will result, owing to the lack of capacity of the combustion chamber to supply sufficient air and properly mix it with the gases before they reach the tubes. This may be stated in another way, as follows: The combustion chamber of a furnace is smokeless for any given coal up to a given rate of combustion ; this rate is differ- ent for different coals, but should an attempt be made to burn a coal faster than at its limiting rate smoke will result. Therefore, in burning coals in which the per cent, of volatile gas and tarry vapors is high, the size of the combustion chamber of the furnace is very important, both from the standpoint of efficiency and from that of smokeless combustion. COAL AND ITS COMBUSTION. 205 The size of this chamber depends on the maximum volume of volatile combustible to be burned per sec- ond and on the richness of the volatile in heavy hydrocarbons and in tarry vapors. The higher the percentage of volatile combustible, the larger the combustion space must be in order to provide suffi- cient space for the air for combustion, for proper intermingling of the air and gases, and for time in which the gases can completely burn before coming in contact with the cold surface of the boiler. The gases are in the combustion space for only a fraction of a second. Record of tests of marine, locomotive, and stationary boilers show that for the boilers under test, the time, in seconds, that a cubic foot of gas was in the combustion space varied from .07 to .08 second for marine, from .16 to .19 second for loco- motive, and from .45 to .65 second for natural-draft stationary practice, the time interval depending on the construction of the furnace in each case. For equal volumes of volatile to be burned, a slow-burning volatile rich in heavy hydrocarbons and in tarry matter will require much more com- bustion space than will a quick-burning volatile of lighter hydrocarbons. Increasing the size of the combustion chamber by increasing either its length or its area lengthens the time that the volatile is in the chamber. Lengthening the chamber lengthens the path of the gas, while keeping the length con- stant and increasing the area decreases the velocity of the gas through the chamber. Provision for the thorough intermingling of the air and the gases per- mits of a smaller combustion chamber than other- wise ; hence, a combustion chamber in a furnace that is too small may often be assisted by the use of some system for intimately mixing the air and the gases. 206 COAL AND ITS COMBUSTION. Since the size of the combustion chamber de- pends on the maximum rate of burning the gases, anything that will increase that rate will require an increase in the size of the combustion chamber or, with a combustion chamber of given size, will decrease the rate of combustion at which the fur- nace will smoke. The rate of distillation of gases is proportional to the rate of the rise of tempera- ture of the coal. Therefore, since fine pieces of coal will heat more rapidly than large pieces, it follows that to burn fine coal smokelessly in a hand-fired furnace will require a larger combustion space than to burn large coal smokelessly at the same rate of combustion. On the other hand, with mechanical stokers, small sizes of coal can be burned with less smoke than large sizes, but, they will develop lower boiler capacity. If a coal is fired in a continuous stream at a uniform rate, as when mechanical stokers are used, it will make the rate of distillation of the volatile matter uniform and will greatly reduce the maxi- mum rate of distillation. In hand-firing, if large quantities of coal are thrown on the fire at long intervals, the maximum rate of gas distillation will be greatly increased, whereas, if small amounts of coal are fired at fre- quent intervals, the maximum rate will be reduced considerably. It will thus be seen that the method of firing has much influence over the limits of smoke- lessness of a furnace. A certain furnace, hand-fired, was smokeless up to a rate of combustion of 24 pounds of coal per square foot of grate surface per hour ; the same plant fitted with a chain-grate stoker increased the smokeless capacity of the furnace to 42 pounds per square foot of grate surface per hour. COAL AND ITS COMBUSTION. 207 When a fire is burning brightly and smokelessly, gradually close the dampers so as to cut down the draft, and a point will be reached, depending on the rate of combustion, where smoke will be produced. Open the dampers a little so as to increase the draft and thus increase the rate of burning coal, and a second point will be reached where smoke will be produced. Again open the damper a little so as to increase the draft still more and the smoke will again clear up. Increase the rate of burning and smoke will again appear, but it will be cleared up on open- ing the damper farther and increasing the draft. These experiments show that a furnace has a defi- nite smokeless capacity for a definite value of the draft, and that increasing or decreasing the draft increases or decreases the smokeless capacity of the combustion chaniber. Increasing the thickness of a fire reduces its smokeless capacity in two ways — ^by decreasing the effective draft and by decreasing the volume of the combustion space. Increasing the thickness from 8 to 14 inches on a 48-square-foot grate would reduce the volume of the combustion chamber 48 X tt, = 24 cubic feet. If the volume of the combustion cham- ber with an 8-inch fire were 200 cubic feet, increas- ing the thickness of the fire to 14 inches would reduce the volume of the combustion chamber 12 per cent. The range of smokelessness would be af- fected by this reduction and by the decrease in the draft due to the increased thickness of the fire. Also, the thicker fire would produce greater quanti- ties of CO, thus increasing the volume of combus- tion space required. From the foregoing discussion it will be seen 208 COAL AND ITS COMBUSTION. that if a furnace smoke& habitually, the capacity of the combustion chamber has been exceeded for the conditions of the draft, for the kind and size of coal, the method of mixing the air and the gases, or the method, of firing the coal. If the limit of the draft is exceeded, the rate of combustion will have to be cut down or the draft will have to be increased, by mechanical means or otherwise, until the smoking ceases. Adjusting the air admission above the fire and properly mixing the air and the gases may clear up the trouble. If these methods are impracticable, a change in the grade or in the size of the coal used may answer. Carrying a lighter fire and firing in small amounts will frequently assist very materially in reducing the smoke, unless, of course, the fire car- ried is already too thin. If a plant has been operating smokelessly and then begins to smoke habitually, it is possible that some of the baffles in the boiler have been burned out, so that the gases and the flame take a short-cut that allows the flame to strike the tubes or cool boiler sheets and thus cause the smoke. Furnace Temperature, and Power Developed. — The temperatures in the furnace should at all times be uniform and high enough to volatilize the tars and dissociate the gases and to ignite the gases as they are distilled from the fuels. On the other hand, extremely high temperatures should be avoided, be- cause they are due to an air supply that approaches the theoretical amount too closely, thereby resulting in smoke and in loss of heat through unbumed gases, due to restricted air supply. In order to insure a more uniform temperature in a furnace, the combustion chamber is made of fire- brick and of suflScient size to mix the air and the COAL AND ITS COMBUSTION. 209 gases thoroughly and insure their complete combus- tion. The temperature of the furnace rises with the rate of combustion, that is, with each increase in the power that is being developed by the boiler. With natural draft, hand-fired furnaces burning up to 25 pounds of coal per square foot of grate sur- face per hour, the temperature may vary from 1,600° F. under adverse conditions at low boiler capacity to 2,200° F. at or above full boiler capacity. With mechanical stokers, the temperature may vary from 1,800 to 2,600° F. With forced draft and me- chanical stokers burning up to 80 pounds of coal per square foot of grate surface per hour, the tempera- ture may vary from 1,800° to 3,100° F. The furnace temperature for a given rate of combustion is higher and much steadier when a mechanical stoker is used than when the furnace is hand-fired. Temperature and Thickness of Fire. — In order to maintain a uniform temperature in a furnace, the fuel on the grates must be of the proper thickness, loose and penetrable, and without holes or very thin spots. The proper thickness depends on the draft, the kind of coal, and the rate of operation of the boiler. If the fire is too thin, it will admit too much air, which will cool the furnace temperature greatly and will carry away considerable heat, which is a direct loss. Also, the cooling effect of the coal fired is greater with a thin fire than with a thicker fire; therefore, the fluctuations in furnace temperature will be greater. If the fire is too thick, or dirty, it causes trouble- some clinkers and the heavier draft required in- creases air leakage through the boiler settings, thereby lowering the smokeless range, the efficiency, and the capacity of the furnace. 210 COAL AND ITS COMBUSTION. A lighter fire will have to be carried with a poor draft than with a good draft. On the other hand, the stronger the draft, the thicker the fire must be for best economy. A much thicker fire must be car- ried with forced draft than with natural draft. Where a 7-inch or 8-inch fire would be carried with natural draft and allowed to burn down to 3 inches, a 10-inch fire would be carried with forced draft, and it would not be allowed to burn down below 7 inches. Also, for each load carried by the boiler there will be a definite thickness of fire that will give the best efficiency, the thickness of the fire being greatest for full load and decreasing with each decrease in the load. As an example, during a boiler test with a certain boiler plant and grade of coal, the maximum efficiency for ll^ load occurred with an 8-inch fire; for full load, with a 7-inch fire; for % load, with a 6-inch fire; and for V^ load, with about a 5-inch fire, 5 inches being the least depth of fire that could be carried efficiently with the coal burned. Weathered coal requires more draft and a thin- ner fire than fresh coal. Sized coals and coals that lie loosely on the greate may be carried thicker than coals that, by reason of their size and shape, pack closely. The smaller the coal, the thinner the fire may be, but it should not be so thin that the draft will raise the pieces and allow the air to break through. Buckwheat coal may be carried from 2 inches to 5 inches, depending on the draft. Data of sixty-four Government efficiency tests with natural draft and with the same plant burning slack, run-of- mine, pea, nut, and lump coal from sixteen states show the best thickness of fire carried for the dif- ferent tests to vary from 4 inches to 14 inches, with an average of 8.4 inches, as in Table XXXI. COAL AND ITS COMBUSTION. 211 TABLE XXXI. Thickness of Fire Carried in Sixty-four Tests. Kind of Coal No. of Tests Thickness of Fire, Inches 4 5 6 7 ' 9 10 11 lii 14 Slack 1 , , . . 1 Run-of-mine . 13 , , , , 2 5 1 4 1 Pea 1 , , . , , . 1 Nut 45 1 1 3 9 14 4 4 3 5 1 Lump 4 1 1 1 1 •• •• ■• Total 64 1 2 6 9 21 6 9 3 6 1 The amount of slack in the coal varied consid- erably. The pea coal was 50 per cent, of fine coal and 50 per cent, of slack. The nut varied from 20 per cent, of nut and 80 per cent, of slack to 80 per cent, of fine and 20 per cent, of slack. The run-of- mine varied from 10 per cent, of lump, 45 per cent, of fine, and 45 per cent, of slack to 80 per cent, of lump, 10 per cent, of fine, and 10 per cent, of slack. For a given thickness of fire, the furnace tem- perature will vary, depending on the quantity of coal fired at a charge. Both the coal fired and the stream of cold air admitted through the furnace door ab- sorb heat and reduce the furnace temperature ; there- fore, the least variations will occur when the coal is fired in small amounts and frequently, the furnace door being swung shut after every scoopful or else being held open a small amount for a short interval after each fire. Time Factor in Furnace Combustion. — Time has a very important influence on the smokeless and efficient combustion of the gases of a coal, because the gases begin their flight from the combustion chamber the moment they are distilled. They have but a fraction of a second in which to mix intimately 212 COAL AND ITS COMBUSTION. with the air and burn while in the combustion cham- ber and before they come in contact with the tubes and cold parts of the boiler. If they do not have sufficient time in which to burn, they pass off uncon- sumed, because they are cooled below their igniting temperature. Significance of Length, Color and Motion of Flame. — Where provision is made for observation of the appearance of the flame, a knowledge of the length and the color of the flame will assist very materially in the prevention of smoke. The end of the flame indicates the point where the combustion of the gases ends, as it is the burning gases that produce the flame. If the flame is white and quite short and waves violently, like a flag in the wind, and the stack does not smoke, the indications are that the fire is too thin and allows too much air to pass through it. With proper admission of air, the flame will be bright yellow or reddish, and will roll and wave, and, at full capacity, will fill the entire combustion chamber, and the chimney will omit a light-gray smoke. If the flame is long, dark, and smoky looking, and the stack smokes badly, it indicates a restricted supply of air, a poor mixing of air and gases, or a low furnace temperature. Where the flame is dark-yellowish or reddish, indicating a fairly good air supply, but is so long that it reaches the tubes and cool surfaces of the boiler, and the chimney smokes badly, it indi- cates that the capacity of the combustion chamber has been exceeded. The smokeless capacity of the furnace is just reached when the length of the flame is such as to be just short of reaching the tubes and cool surfaces of the boiler. With a proper air sup- ply, the length of the flame is proportional to the COAL AND ITS COMBUSTION. 213 quantity of gases to be burned and to the proportion of hydrocarbons and tarry vapors. The length and the color of the flame for any coal, therefore, indi- cate when the smokeless capacity of the furnace has been reached for that coal. Smokeless Capacity of Furnace. — Every type of furnace has a maximum rate of combustion for a given kind of coal, which, if exceeded, will result in the production of smoke. This rate is dependent on the type of the furnace, the capacity of the combus- tion chamber, the method of baffling the boiler, and the methods used for mingling the air and the gases. Furnaces built with the idea of smoke prevention usually are designed so that, with hand-firing and the proper coal, with average care in firing, and with- out using all the available draft, the maximum smokeless capacity will be attained at from 80 to 100 per cent, of the rated capacity of the boiler. Under like conditions, except with natural draft and with mechanical stokers, the smokeless capacity will be attained at from 100 to 140 per cent, of the rated capacity of the boiler. Usually, a furnace that will give smokeless com- bustion at or above full boiler capacity will not give smokeless combustion much below 50 per cent, of the boiler capacity, as the furnace will be too large for light loads. Also, a furnace that will give smoke- less combustion for light loads will smoke at or near full loads. Therefore, the size of the furnace must be chosen with a view of the range of smokelessness desired. The smokeless capacity of a furnace for a given coal can be increased by lengthening the time inter- val of the gases in passing through the combustion space. This may be accomplished by keeping the 214 COAL AND ITS COMBUSTION. area constant and lengthening the combustion cham- ber; by lengthening the path of the gases through the use of baffles or arches; by decreasing the ve- locity of the gases through the combustion chamber through increasing the volume of the chamber with- out increasing the length ; or, by increasing both the length and the volume of the combustion chamber. If a plant is burning a rich, tarry coal and smokes badly, the smoke can often be reduced to an unobjectionable amount by using a coal low in tarry matter, by using a sized coal, or by changing the size of the coal and the method of firing. When a coal is rich in tars and heavy hydrocarbons, heating the coal slowly during the distillation period will tend to avoid the distillation of the heavy hydrocar- bons and thus reduce the amount of smoke formed. Coals that smoke badly give from 3 to 5 per cent, less efficiency than coals that smoke but little. Influence of Size of Coal. — Data from numerous tests show that small sizes of coal burn with less smoke than large sizes, but that the larger coals burn more readily and produce higher boiler ca- pacities. Also, the large coals use less air per pound of combustible, but they cause considerable black smoke at the higher capacities. To develop high boiler capacities, the coal burned should be sized, with the slack and the dust removed. Coals of different sizes containing slack and dust have a tendency to pack on the grate, owing to the way in which the pieces arrange themselves. Also, such coals contain a higher percentage of ash. This results in less air being forced through the fire for a given draft value, hence in a lower combustion rate and in reduced boiler capacity. Results of tests made on twenty-six different COAL AND ITS COMBUSTION. 215 coals from eleven states and on the same coals washed indicated that most of the washed coals burn freely (non-coking) and seem to burn more rapidly than the unwashed coals ; also, they develop a greater percentage of the rated boiler capacity. The washed coals burn with lower efficiency and make more smoke than the unwashed coals, the lower efficiency being due to burning the coal wet. The average per cent, of moisture for washed coal was about .58 per cent., although in some instances, washed coal con- tained as high as 5.5 per cent, more moisture than unwashed coal. The high water content of washed coal is offset somewhat by a lower ash-and-sulphur content. The ash in the dry coal varied from 5.39 to 23.16 per cent., and the sulphur from .58 to 4.78 per cent. The percentage of difference in the ash in the coals before and after washing varied from 1.23 to 10.07, with an average of 4.64 per cent, in favor of the washed coal; the sulphur difference varied from .02 to 3.64, with an average of .75 per cent, in favor of the washed coal. Lowering the sulphur content, lowers the tendency to clinker, so that washed coal produces a smaller percentage of clinker than unwashed coal. The water taken up by the coal in washing has to be evaporated in the furnace, and the heat thus absorbed and carried away reduces the temperature of the furnace and the capacity of the boiler. Average results of twenty-six compartive tests show an increased ca- pacity for washed coals of about 6.5 per cent., with a decrease in efficiency of about 2.13 per cent. Rocking vs. Flat Grates. — Results from twelve comparative tests of the same coals burned in the same furnace on rocking grates and on flat grates .show an average of 2 per cent, greater efficiency with 216 COAL AND ITS COMBUSTION. the rocking grates than with the flat grates. In five of the tests, the rocking grates show an increased capacity over the flat grates; whereas, in the other seven tests, the flat grates show increased capacity. For the twelve tests, the flat grates show an in- creased capacity of 2.3 per cent, over the rocking grates. More coal is lost through the rocking grate than through the flat grate, and this reduces the efficiency of the rocking grate about 1.5 per cent. The rocking grates gave better results in eleven out of the twelve tests, the one exception being a test of coal having 4.5 per cent, of sulphur, which fused with the ash and made bad clinkers. The clinker fused to the grate bars and rendered the rocking grate inoperative. In burning coals that are high in sulphur and that clinker, a flat grate will be more satisfactory than a rocking grate. The smoke generated was slightly less with the rocking grate, as that grate afforded a better means of keeping the fire clean. In general, most coals that do not clinker badly can be burned on a rocking grate with from 1 to 5 per cent, greater efficiency and with a smaller percentage of black smoke than on a flat grate. Conditions Unfavorable for Smokeless Combus- tion. — Any well-designed and properly proportioned furnace, provided it is fired intelligently with suit- able coal of the right size and at the rates within the capacity of the furnace, may be expected to give smokeless combustion when the proper amount of air is supplied and intimately mixed with gases in the furnace. However, there are conditions of operation so unfavorable to smokeless combustion that even the best furnace will smoke. In building a fire, the furnace and boiler are so COAL AND ITS COMBUSTION. 217 cold that the free carbon and the gases are cooled below their igniting temperatures and escape un- bumed, producing smoke. Also, with natural draft, the draft is so low when the fire is first started that the air supply is greatly restricted, and this further increases the tendency to smoke. Banked fires are difficult to maintain and they waste the gases of the coal on account of the very restricted air supply through the fire and the very low furnace temperature. For similar reasons, in starting up a fire that has been banked, it will smoke badly. If, where the load is variable, a large part of the power falls off quickly, the dampers and often the doors of the ash-pit are closed to check the draft and prevent a quick rise in the steam pressure. The amount of coal that was burning on the grate at the higher power is too large for the lower power being developed, so that the closed dampers restrict the air supply greatly and cause dense, black smoke. With high-volatile coals, where the furnace is forced above its capacity, the volume of gas dis- tilled is such that the length of the flame is longer than the combustion chamber and reaches the cool surfaces of the boiler, thus producing dense, black smoke. Where the coal clinkers badly and the clinker adheres to the grate bars and closes the air spaces of the grates, the supply of air will become so re- stricted that dense, black smoke will result. Gen- erally, coals that clinker the most, smoke the most. If the baffling or the arch in the boiler is broken so as to allow the flame to take a short cut and thus strike the cold surfaces of the boiler, dense, black smoke will result. CHAPTER XVIII Draft Regulation ATE of Combustion, and Weight of Air Supplied. — It is well known that in- creasing the "draft" increases the rate of combustion. It is not so well known, however, that the increase in the rate of combustion is directly proportional to the velocity of the air through the burning fuel ; that is, that there is a straight-line relation between the rate of combustion and the weight of air supplied through the fire per unit of time. Therefore, for best boiler efficiency and boiler economy, it is im- portant that proper provision be made for the regu- lation of the draft. Leaky Boiler Settings. — In a correctly designed power plant, the stack is so constructed as to give a draft in excess of that required for full-load fur- nace capacity, in order to insure sufficient coal-burn- ing capacity under all conditions of operation. Where this draft is properly utilized, the full-load capacity of the boiler will be obtained. On the other hand, leakage through the boiler settings, etc. has an effect similar to a like reduction in stack-draft capacity on the full-load boiler capacity. The leak- age not only increases the volume of stack gases to be handled, but also decreases the temperature of the gases in the stack, thereby reducing the draft. It is very important, therefore, that the brickwork, all doors, etc. be air tight, so that no air can enter the boiler or the furnace except through the grates or other places provided for that purpose. 218 COAL AND ITS COMBUSTION. 219 Tests for leakage can be made by means of a torch, leakage being indicated by the flame being drawn in at the point of leakage. Tests for leaks should be made of all cracks, the plates about the clean-out doors and blow-off pipes, around the arch over the combustion chamber at the rear, around the breeching, etc. Damper Control. — Both the grates and the draft of a well-proportioned boiler plant are designed to burn the maximum amount of fuel per unit of time under conditions of maximum load. If the draft were allowed to operate free and unobstructed all the time, it would be impossible to vary the load from the maximum load. For this reason, means must be provided to vary the draft as necessary. A suitable damper should be placed in the uptake or in the breeching leading from each boiler, and it should be arranged so that it can be operated by means of a system of levers from a convenient point near the furnace door. These dampers should be arranged so that they cannot be closed fully or closed sufficiently to cause the furnace to smoke. The smoking point can be determined by gradually closing the damper and watching the stack for smoke. If several boilers are connected to the same stack, the dampers should be set so that each boiler will carry its proper share of the load. If this is not done, the boiler nearest the stack will operate at or above its greatest capac- ity, while the boilers farther away will operate at reduced capacities, depending on their distance from the stack. The duty of the damper is to check the rate of combustion to suit the varying conditions of the load. Much fuel can be saved by a proper manipu- lation of the dampers, and as much intelligent care 220 COAL AND ITS COMBUSTION. should be exercised in their operation as is taken in firing the coal. The ash-pit door should be kept wide open, and the draft should not be regulated by closing the door unless the damper in its closed posi- tion does not sufficiently retard the draft. Closing the ash-pit door shuts off' the supply of air through the firebed and increases the tendency for leakage of air into the breeching, etc. through cracks and other defects. This results in smoke, in almost a complete loss of the gases of the coal as they are roasted out, and in a further loss through heat absorption by the air that leaks in. Regulating the draft by means of the damper decreases the tendency for air leakage and gives free access for the air through the fire. If the ash-pit door is entirely closed, it so shuts off the air supply through the fuel bed that the grate and the ash becomes overheated. This eventu- ally results in warped grates. Also, the increased temperature tends to fuse the ash and to cause the formation of clinker. Draft Gauges. — Each boiler of a power plant should be fitted with draft gauges conveniently placed for easy reading by the fireman. One, should indicate the draft in the furnace over the fire, and another the draft in the breeching or the chimney. The first will thus indicate the "drop" of draft through the fire, while the second will indicate the "drop" through the tubes, etc. When the fireman is familiar with the amount of draft required with a clean fire and clean tubes, he can readily note any change in the fire or tube conditions by means of the draft readings. An increase in the drop of draft through the fire indicates a fire that is becoming either dirty, coked or too thick; a decrease In the drop indicates a fire too thin or one that has holes COAL AND ITS COMBUSTION. 221 or cracks in it. Increased drop between the furnace and the uptake indicates increased friction, due prob- ably to deposits of soot, ash, etc. upon the tubes and the baffles. Decreased drop indicates reduced fric- tion J possibly the baffling has burned out or broken down, thus allowing the gases to short-circuit. When several boilers are in a battery, their dampers should be adjusted until the draft gauges indicate equalized drafts, so that each boiler will carry its share of the load. A simple form of U-tube draft gauge is shown in Fig. 13. The arm a has attached to it a flexible rubber tube that leads to the point at which the draft is to be measured. The arm 6 is open to the atmosphere. The tube is filled with water to the zero read- ing on the scale when both the arms a and h are open to the at- mosphere. When the arm a is connected up for draft readings, the pressure in that arm is less than atmospheric pressure, owing to the draft ; therefore, the water is raised on that side and lowered in the arm h until a balance is reached. The difference in the heights of the two columns repre- sents the amount of pressure that the atmospheric pressure exceeds the pressure at the point at which the draft is being measured. Each inch difference in height is equivalent to a pressure of .578 ou^ce per square inch. The gauge in Fig. 13 indicates 1.125 inches below the zero mark on the arm h and 1.125 -1- -O^.K l-J-is -2-^1 Fig. 13. Water Draft Gauge. 222 COAL AND ITS COMBUSTION. inches above zero on the arm a, or a total of 2.25 inches. This represents a pressure of 2.25 X -578 = 1.3 ounces per square inch. The readings above and below the zero mark are added for the total, w^hether they are equal or unequal. Table XXXII gives pres- sures corresponding to various differences in the heights of the two columns of water. TABLE XXXII. Draft-Gauge Pressures Corresponding to Various Heads of Water. Head, Inches Head, in Parts of an Inch .0 .1 ■2 3 .4 .5 .6 .7 .8 .9 .06 .12 .17 .23 .29 .35 .40 .46 .52 1 .58 .63 .69 .75 .81 .87 .93 .98 1.04 1.09 2 1.16 1.21 1.27 1.33 1.39 1.44 1.50 1.56 1.62 1.67 3 1.73 1.79 1.85 1.91 1.96 2.02 2.08 2.14 2.19 2.25 4 2.31 2.37 2.42 2.48 2.54 2.60 2.66 2.72 2.77 2.83 5 2.89 2.94 3.00 3.06 3.12 3.18 3.24 3.29 3.35 3.41 A mechanical draft recorder for making per- manent, continuous records of all changes in draft is shown in Fig. 14, and a draft-pressure record is shown on the chart. This gauge is a product of the Crosby Steam Gauge Company. By its use, con- tinuous records of all changes in draft that occur during a run may be obtained and filed away for future reference. The record gives a valuable check on the way in which the fire under a boiler is manipu- lated. Observation and Estimation of Smoke The plan most generally adopted for estimating the relative blackness of smoke and for recording the length of time during which smoke of varying degree of blackness is emitted from chimneys is that devised by Professor Ringelmann, of Paris, and re- COAL AND ITS COMBUSTION. 223 Fig. 14. Hocordlng Draft Gauge. ported in the Transactions of the American Society of Mechanical Engineers, Vol. XXI, Dec. 1899. The plan requires six cards similar to those shown in Fig. 15, the cards in the illustration being very much 4 5 Fiff. 15. Scale for Gradiug Smoke Density. reduced in size. The cards are white with black lines, and are placed in a horizontal row, as shown. They are numbered from to 5. Card is all white. Card 1 has hnes 1 mm. (millimeter) thick and 10 mm. apart, leaving spaces 9 mm. square. Card 2 224 COAL AND ITS COMBUSTION. has lines 2.3 mm. thick, 10 mm. apart, and spaces 7.7 mm. square. Card 3 has lines 3.7 mm. thick, 10 mm. apart, and spaces 6.3 mm. square. Card 4 has lines 5.5 mm. thick, 10 mm. apart, and squares 4.5 mm. square. Card 5 is all black. [] inaii "^flU. 3ZZ33ZBZ2 322 3 4 4 444 3ZSZZS Time. Fig. 16. Result of Tests Plotted for Density of Smoke. The rows of cards are hung in line with the chimney under observation at a point abount 50 feet distant from the observer, at which distance the lines of the cards become invisible and the cards appear to be of different shades of gray, ranging from very light gray to almost black. The observer glances alternately at the smoke and at the cards, makes observations continuously for 1 minute, and decides which card most nearly corresponds with the color of the smoke. The record is then made accord- ingly, noting the time. The color recorded in the estimated average density of the smoke during the entire minute, and records are made for each con- secutive minute during the test. The average of all the records made during the boiler test is taken as the average figure for the smoke density during the test, and the whole of the record is plotted on cross- section paper. Fig. 16, to show the variations in the density of the smoke from time to time. The num- bers at the left represent the scale of the smoke density, while the time scale is laid off on the hori- zontal. CHAPTER XIX BOILER PLANTS for SMOKELESS COMBUSTION Hand-Fired Furnaces Y far the greater number of steam plants throughout the country are fired by hand. As a general rule, however, they are of comparatively small total horse- power, ranging from 50 to 500 horse- power. In some instances they total 1,000 horse- power, but usually mechanical stokers are used in the larger power plants. A large majority of hand- fired plants are persistent smoke producers, due principally to improper furnace construction for the coal burned and to lack of proper mixing devices for mixing the air and the gases. In such plants, the best that can be done is to use a low-volatile or smokeless coal if practicable, to fire carefully and intelligently, to keep a clean fire, and to crack the firedoor for a short interval after each firing. Nu- merous devices have been patented for the preven- tion of smoke in hand-fired furnaces, but most of them have proved to be dismal failures on account of their violating the principles of combustion. Firebrick mixing piers and arches have been tried, but they have not been used extensively, owing to the difficulty of procuring materials that will withstand the intense heat to which they are sub- jected. Also, the piers and arches diminish the combustion space, which, generally, is none too large, and they increase the resistance to the flow of gases, thereby reducing the available draft and the capac- 225 226 COAL AND ITS COMBUSTION. ity of the furnace. However, there are a number of very good hand-fired furnaces that give excellent service with very little smoke when properly oper- ated with suitable coal. Among them are the Haw- Fig. 17. Plain Furnace, Babcock & Wilcox Boiler. ley down-draft, the Dorrance, the Wooley, the Burke,, the Twin-arch, the Dutch Oven, the Puddington, and others. Plain Furnace. — A plain furnace under a Bab- cock & Wilcox boiler is shown in Fig. 17. The fur- nace is situated within the walls of the boiler. Since no provision for smokeless combustion is made in this furnace, it is adapted only to anthracite, semi- anthracite, or short-flame semibituminous coals. It is very efficient for such coals, on account of using the direct radiant heat of the fire. If an attempt were made to bum bituminous or subbituminous coals in this furnace, dense, black smoke would re- sult, as indicated in Fig. 18. The flame is extin- guished when it strikes the tubes, allowing the car- COAL AND ITS COMBUSTION. 227 bon that has been liberated as soot to pass off in a dense, black cloud. This not only wastes the fuel value of a large percentage of the gases of the coal, which pass off unbumed, but also waste the heat Fig. 18. Furuace Unsuitable for Bituminous Coal. absorbed by the gases, owing to the non-conducting properties of the soot that is deposited in the tubes and thus reduce the absorption of the heat. The furnace arrangement shown in Fig. 12 is a good one for burning high-volatile coals smokelessly under return-tubular boilers. The furnace arch does not extend forwards over the grate, so that the boiler receives heat by direct radiation from the fire, thereby increasing the efficiency of the boiler. Also, this cools the furnace temperature somewhat and so reduces the tendency for the ash to clinker because of too high furnace temperature. Dorrance Furnace. — The Dorrance furnace un- der a Babcock & Wilcox boiler is shown in Fig. 19. The furnace extends in front of the boiler and is 228 COAL AND ITS COMBUSTION. virtually a Dutch oven with a long arch sloping toward the rear of the furnace. The arch covers the entire grate and extends back into the combus- tion space ; hence, there is no direct radiation of the heat of the fire to the heating surface of the boiler. Fig. 19. Hand-Fired Dorrance Furnace, Babcock & Wilcox Boiler. The grate also slopes toward the rear of the firebox. The arch in this construction maintains a high, even temperature, while the constriction at the bridge wall and the lower end of the arch tends to mix the air and the gases of combustion, thereby shortening the length of the flame and promoting smokeless combustion. The minimum distance from the grate to the tubes is sufficient for the flame from most coals. Wooley Furnace. — The Wooley furnace, Fig. 20, also extends in front of the boiler. A sectional view of the furnace, Fig. 21, shows the form of the mix- ing wall and the two openings through it, a portion being broken away to show the openings. This is a firebrick wall with a projecting angle for splitting COAL AND ITS COMBUSTION. 229 the gases so as to facilitate their movement through the two openings at the face of the wall. The con- striction at the bridge, the splitting of the gases, their passage through the two openings and their Fig. 20. Hand-Ii'Ired VVooley Furnace and Babcock & Wilsoz Boiler. coming together again, all tend to assist the mixing process. The minimum path for the gases from the grate to the tubes is such as to provide sufficient Fig. 21. Wooley Furnace Plan. space for burning the gases of most coals smoke- lessly. Hawley Down-Draft Furnace. — The Hawley 230 COAL AND ITS COMBUSTION. down-draft furnace, Fig. 22, has two separate grates, as shown. On account of the high temperature to which the upper grate is subjected, it is in the form of a water grate. The lower grate is of common gratebars. The coal is fired on the upper grate only, and the air enters through the upper firedoors and passes downwards through the fire to the space between the two grates. The lower grate is fed from partly consumed fuel falling from the upper grate. Fig. 22. Hawlpy Down-Draft Furnace, Heine Boiler. Air for burning this fuel and for burning the gases from the upper fire bed enters from below the lower grates. The air and gases from the fresh coal are heated in passing through the fuel bed, and are inti- mately mixed and burned in the combustion space, as indicated. The horizontal baffle, extending over the grate and back into the combustion space along the lower row of tubes, lengthens the minimum path of the flame to the tubes the proper amount for smokeless combustion. COAL AND ITS COMBUSTION. 231 The furnace in the illustration is shown built within the boiler setting. In many cases, however, it extends in front of the boiler. Fig. 23. HaiKl-I'Mrcd TwluAioh Fiirnaci' and Return Tubular Boiler. Twin-Arch Furnace. — The twin-arch furnace, shown under a return-tubular boiler in Figs. 22 and 24, promotes smokeless combustion through the use of special arches and mixing piers. It consists of rig. 24. Hnnd-Flred Twin-Arch Furnace Plan. two furnaces, each with its own arch, so that they virtually form two Dutch ovens. Back of this there is a single cone-shaped arch, with air-admission 232 COAL AND ITS COMBUSTION. openings. Another arch is built back of the cone- shaped arch, and a V-shaped mixing pier is built farther back in the combustion space. The gases from the two furnaces mingle in the cone-shaped arch and are mixed with fresh air that enters through the air-admission openings. The rear arch acts as a mixing chamber. After the gases are mixed they expand and are split into two streams by the pier, *hus insuring the gases being properly mixed and burned before the flame reaches the tubes. Methods of Hand Firing Four methods of hand-firing are in more or less general use. They are known as the coking method, the ribbon method, the spreading method, and the alternating method. Coking Method. — The coking method of firing is best adapted for coking coals and for coals rich in higher hydrocarbons and tarry vapors and where the demand for steam is fairly regular. It is not a very flexible method ; therefore, it is not suitable for conditions under which the load varies quickly and calls for a quick, heavy demand for steam. For the reasons mentioned it is not so widely used in prac- tice as the 5ther methods. In the coking method, the coal is first piled on the dead-plate near the firedoor, where it is heated slowly. This gives a slow, uniform evolution of the gases. The furnace door should be perforated with a number of air-holes, and should have a means of regulating the air supply through the door. As the gases are roasted out of the coal, the air, which enters in small streams through the firedoor, mixes with the gases, and the gases are completely burned while passing over the glowing coke on the grates. COAL AND ITS COMBUSTION. 233 When the coal has been thoroughly coked, it is pushed back onto the grates and spread evenly over the surface, care being taken to fill any thin spots or holes in the fire. A new charge is then put on the dead-plate. Since large lumps coke slowly, they should be broken up before being placed on the dead- plate; also, as the coal cokes and forms a crust, the crust should be broken up as frequently as is neces- sary. Ribbon Method. — In the ribbon method of firingy the coal is fired alternately in narrow strips across the entire length of the grate. The coal should be fired frequently and in small amounts, cracking the fire door for a short interval after each fire if auto- matic air admission is not used. This method gives a very high efficiency and practically no smoke. It is well adapted for burning high-volatile coals. Spreading Method. — ^The spreading method of firing is probably the most commonly used system of any. However, with smoky coals, it is the least effi- cient method, and it produces the most smoke. It is best adapted for the larger sizes of anthracite, semi- anthracite, or high-grade bituminous coals, but re- quires very careful firing for good results, even with such coals. The method consists in spreading the fresh coal evenly over the whole grate in a thin layer. The fresh coal lowers the temperature of the furnace, and if the layer is too thick it may lower the tem- perature so much that a large part of the gases will pass off unburned, resulting in a large heat loss and in the production of much smoke. Alternate Method. — The alternate method of fir- ing is the second only to the spreading method of 234 COAL AND ITS COMBUSTION. firing. It is best adapted for non-coking coals, and when properly used it will give excellent satisfac- tion, even with coals rich in volatile matter. For small furnaces, the coal is fired lengthwise on the grate, spreading the coal alternately on each half of the grate. When the grate area is large, it is divided into four or six equal parts, depending on the size of the grate. The fresh coal is fired alter- nately on one-half of these areas, the time interval of firing varying to suit the demand for steam. This method always leaves half of the fire bright, to fur- nish the heat required to burn the gases. Also, the air enters through the bright half of the fire more freely than it does through the thicker half, thereby furnishing the air needed for the consumption of the gases. Burning Slack. — Slack coal is coal that will pass through a 4-mesh-per-square-inch screen. The evap- orative value of a coal decreases with the percentage of slack it contains. A coal that with 10 per cent, of slack will evaporate 8 pounds of water, with 30 per cent, slack will evaporate only Qy^ pounds, and with 70 per cent, will evaporate only about 5% pounds. To burn properly a coal that contains much slack requires skill on the part of the fireman and much hard work. Slack has a strong tendency to fuse and cake into a hard crust, which prevents the passage of air through the fire, except where the crust cracks. The effect of this is to reduce the capacity of the boiler greatly, unless the crust is broken up to let the air through. The more coal fired at a time, the thicker will be the crust that forms; hence, slack should be fired in small amounts and frequently. When so fired, there will form only a light crust that will burn through in a very short time. If necessary. COAL AND ITS COMBUSTION. 235 this crust can be readily broken through with the careful use of the rake without having to resort to the slice bar, the use of which is apt to cause clinker by raising some of the ash up into the hot zone of the fire. In using the rake, it should rest on the firedoor frame; also, the prongs of the rake should be care- fully inserted only through the crust, so as not to disturb the ash and cause clinker. Precautions in Firing. — Keep the fire level and as thin as the character of the coal and the strength of the draft will permit. Keep the fire level by spreading the fresh coal, as it is fired, over the thin spots. Filling up hollows by firing a heap into the thin spot may cause clinker. It is quite sure to result in a high spot. Fire the coal in small quantities and at short intervals. If fires are too far apart, thin spots and holes in the fire may result. Avoid disturbing the fire; it is unnecessary work and may cause clinker. Also, the excess air through the open furnace door reduces furnace temperature, causing a loss of heat. If the rake must be used to level the fire, use it carefully, so as to avoid lifting ash up into the hot zone of the fire, as it will form clinker. Avoid the use of the slice bar. Keep ash-pit doors open and avoid accumula- tions of refuse in the ash-pit. This will result in better furnace economy, will help prevent the grates from warping, and will tend to avoid clinker. At the first signs of clinker formation, keep water in the ash-pit or use ash-pit steam jets, if provided. In firing green coal on holes in the fire, select coal large enough; fine coal will drop through the 236 COAL AND ITS COMBUSTION. grate and burn in the ash-pit. Burning coal in the ash-pit warps the grates, and causes clinker. If neither automatic nor non-automatic air regulation is provided, crack the firedoor for a short time after each fire. The tendency for a coal to coke, or fuse, and thus form a crust is greatly reduced by firing small amounts frequently and spreading the coal in a thin sheet over the fire. Regulate the draft by using the damper in the uptake or breeching, and not by closing the ash-pit doors. Close the damper gradually — just a sufficient amount to get the effect desired. Avoid closing it suddenly the full amount, as this will produce dense, black smoke. Cleaning the Fire. — Cleaning the fire consists in thoroughly removing all clinker and refuse from the grates, and it must be done in such a way as to waste as little combustible as possible. Cleaning is best accomplished by first separating the good coal from the refuse that is below the good coal and next to the grates. The condition of the fire at cleaning should be such that there will be sufficient fire in the furnace to start a good, hot fire as soon as the cleaning is completed. If there is not sufficient fire for this purpose, the fire should be built up to the proper amount before the cleaning is begun. If the fire is too thick, the work will be much more difficult; therefore, such a fire should be allowed to burn down to the proper amount before starting to clean it. During the cleaning, the damper should be partly closed to avoid the rush of too much cold air through the furnace and tubes. COAL AND ITS COMBUSTION. 237 The hoe and the slice bar should be used to move the burning coal from the left half to the right half of the grate, or vice versa, and the left half should then be thoroughly cleaned of all ash and clinker. If any clinker sticks to the grate or side walls, it can be loosened or broken by means of the slice bar so that it may be removed with a hoe. The clinker is removed through the firedoor and dumped into a barrow or some other conveyance. When the left side is cleaned, all the burning coal should be moved to that side and spread evenly over the clean part of the grate, and sufficient fresh coal added to the fire to insure enough burning coal to cover the entire grate after the right side is cleaned. The right side should next be cleaned, after which the fire should be spread over the whole grate and build up as desired by the addition of fresh coal. If the fire must be cleaned quickly during the time of heavy load, the fire should be pushed back and piled up against the bridge wall and the entire grate, except that portion on which the coal is piled, cleaned at the same time. The coal should then be pulled forwards onto the clean grate and fresh coal added as required. This method should be used only as an emergency method, and the fire should be prop- erly cleaned when the load on the boiler will pel-mit. Banking the Fire. — ^Where a fire is to be banked overnight, the burning coal should be banked on the front part of the grate in either corner, and the damper should be almost closed. Banking the fire in the front instead of at the bridge wall, allows the clinker near the bridge wall to cool off overnight. The clinker and refuse should be allowed to remain on the grate until the following morning, as it helps maintain the furnace temperature. Also, it will be 238 COAL AND ITS COMBUSTION. cool by the morning and can then be more readily removed. After the grate is cleaned, the fire should be spread over the clean part, and the refuse that was under the bank should be removed. The fire should then be spread over that part of the grate, and the fire built up as required. Stoker Furnaces Mechanical stokers operate automatically, but this does not mean that they will take care of them- selves under all conditions and will not require any attention. For successful operation, a stoker re- quires the attention of one expert in the operation of the type of stoker used. There are two objects in the use of the mechanical stoker. One, is to reduce labor in the boiler room; the other, and chief object, is so to regulate the supply of coal and air to the fire that the coal will be burned with maximum economy and will produce a maximum boiler capacity at a maximum efficiency and with the least smoke. Stok- ers under ordinary operating conditions will operate with less smoke than hand-fired furnaces, provided they are supplied with the proper class of coal. A stoker will not handle all classes of coal equally well ; therefore, care should be exercised to select the proper stoker for the coal to be used, or vice versa. Stokers are of three types — the traveling grate, the overfeed, and the underfeed. The overfeed type is subdivided into front-feed and side-feed stokers. The traveling-grate type is commonly known as the chain-grate stoker. Traveling Grate Stokers Chain-Grate Stokers. — The chain-grate stoker is illustrated diagrammatically in Fig. 25, in connec- tion with a Babcock & Wilcox boiler. The coal is COAL AND ITS COMBUSTION. 239 fired into a hopper that extends the entire width of the grate and feeds the coal onto the grate. The regulating plate 2 also extends the width of the grate, and its duty is to regulate the thickness of fire carried on the grates. The grates are endless and Fig. 25. Cliain Grate Stoker, Babcock & Wilcox Bolier. revolve continuously from the front toward the rear of the furnace, the speed being regulated as desired. The grate is horizontal, except in special cases, when it is inclined slightly toward the rear, as with low- set tubular or water-tube boilers, where it is inclined in order to get the necessary head room at the rear of the firebrick ignition arch. The ignition arch extends backwards and upwards from the hopper, the length varying somewhat with the different makes of chain grates. Its height above the grate at the hopper end varies from about 11 to 13 inches, while the height of the other end varies from about 15.5 to 26.5 inches. The slope of the arch depends somewhat on the strength of the draft; the stronger 240 COAL AND ITS COMBUSTION. the draft, the less the slope. Too great a slope for the draft of the stack will cause the furnace to smoke. The length and slope of the arch are gen- erally proportional to the draft and to the kind of coal that is to be burned. The stoker operates continuously, feeding the coal into the furnace, igniting and coking it, con- suming all the combustible matter, discharging the refuse into the ash-pit, and automatically keeping the air spaces in the grate clear of clinker. This obviates the necessity of opening the firedoor, be it for firing, for clearing the fire, or for removing refuse. The minimum length of the flame before it strikes the lower tubes is regulated by the length of the bottom baffle, as shown. This type of stoker is best adapted to burning non-coking coals, and will give good satisfaction even with the poorest grades of high-ash coal. The size of coal generally used is slack, screenings up to 2-inch, pea and slack, and nut and slack. The depth of fire carried varies from 4 inches to 7 inches, and averages about 4.5 inches. This type of stoker is used most extensively with water-tube and plain boilers, and frequently with return-tubular boilers. It gives best service with plants that maintain fairly uniform loads, and with proper management it will operate under variable loads with but little smoke. If improperly operated under varying loads, it will produce dense, black smoke. The cost of upkeep of a chain-grate stoker prop- erly operated is low in comparison to the cost of the upkeep of other types of stokers. Also, it has an- other decided advantage in that it can be withdrawn from the furnace for inspection or repairs without in any way interfering with the boiler setting. COAL AND ITS COMBUSTION. 241 Operation of Chain-Grate Stoker. — Coal burned in a stoker is consumed under conditions similar to those which obtain in the coking method of hand- firing. Green coal enters the furnace from the hop- per; for a distance back on the grate, the coal, is in varying stages of distillation ; back of this there is a solid bed of burning coke of varying depth, that in the front being fresh coke. The thickness of the fire progressively decreases from the front backwards, due to the varying length of time that the coke has been burning, until at the end of the grate nothing but refuse remains. Air for the combustion of the gas enters through the thin fire in the rear of the grate. The speed of the grate should be such as will maintain the condition of the fire over the grate con- stant for that rate of combustion. If the speed is too fast for the thickness of the fire carried, the coke will not be completely burned by the time it is dumped into the ash-pit. This will result in a loss from incomplete combustion of the gases and from carbon in the ash, and in damage to the grates through warping and burning. The grate should never be run so fast that it will be hot when reenter- ing the furnace. Carrying a heavier fire at a slower speed will give the same steam capacity with cool grates. If the speed of the grate is too slow for the thickness of the fire, the fire will be entirely burned out long before it reaches the end of the grate. This will cause a considerable drop in the eflSciency of the furnace, due to excess air through the ash. Variations in the load should be taken care of by changing the thickness of the fire, the speed of the grate, and the position of the damper. Attempts to regulate by means of the damper alone will cause 242 COAL AND ITS COMBUSTION. dense, black smoke, owing to the too limited air supply for the rate of combustion. Overfeed Stokers Front-Feed Stoker. — A Roney type of front-feed stoker under a Heine boiler is shown in Fig. 26. In this type of stoker the coal is fed into a hopper at the front end of the furnace, which device delivers it onto the dead- plate and to the grates. The grates Fig. 26. Roney Front-Feed Stoker, Heine Boiler. are inclined downwards toward the rear at an angle of about 45 degrees and are mechanically operated, the grate bars being made to take alternately level and inclined positions at speeds varied to suit condi- tions. This movement of the grate bars causes the fuel as it burns to move downwards toward the bot- tom of the grate, where a flat dumping grate is sup- plied for the purpose of dumping and cleaning the COAL AND ITS COMBUSTION. 243 fire. The coal is coked on the dead plate and the top part of the grate, and the coke is progressively burned, because it is moved down the grate at such a rate that it is completely burned by the time it reaches the bottom, or dumping, grate. Smokeless operation with this type of stoker requires careful operation. Also, to aid in smoke prevention, steam jets are provided in the air pas- sage in the coking arch, as shown in Fig. 26, and an ample air supply is provided. The steam jets, when used, are in continuous operation. The stoker is well adapted to forcing a fire quickly ; hence, it provides a flexible fire for variable loads. It bums various sizes of coal, as screenings, slack, run-of-mine, pea, nut-and-slack, etc. The depth of fire carried usually varies from 3.5 to 7 inches, and averages about 4.5 inches. The fre- quency with which the fires must be cleaned varies from once every 2 hours to once every 14 hours, depending on the kind of coal and on the tendency of the ash to clinker. Fig. 27 shows how Stoll and Finlay, Jr., of the Interborough Rapid Transit Co., of New York City, made use of a second Roney front-feed stoker in the rear of several Babcock & Wilcox boilers with a view of increasing the output of the plant, which was already installed. The front stoker had a grate area of 100 square feet, while the rear stoker had 80 square feet. The addition of the rear stoker almost doubled the amount of coal burned and the boiler absorbed nearly twice as much heat as with the single stoker. Side-Feed Stokers. — Two makes of side-feed stokers in most general use are shown in Figs. 28 to 31, inclusive. Fig. 28 shows a cross-sectional 244 COAL AND ITS COMBUSTION. view of a Murphy stoker under a return tubular boiler; Fig. 29, a Murphy stoker in a Dutch oven and a Babcock & Wilcox boiler; Fig. 30, a Murphy stoker and a Heine boiler; and Fig. 31, a Detroit stoker and a Stirling boiler. Fig. 27. Eoney Double-Stoker Plant. The side-feed stoker differs from the front-feed stoker in that there are two sets of grates sloping downwards from the sides of the boiler, each side being fed by its own magazine 1 . At the bottom of the magazine there is a steel coking plate 2, in which the coal-feeding mechanism 8 rests. Below this plate is the air duct J^. The arch plate 3 supports the fire- COAL AND ITS COMBUSTION. 245 brick arch, which extends over the whole grate area. Above this arch there is a hot-air duct 5, with open- ings 6 into the combustion space. These openings admit hot air at a point just above the coking coal, so that the air and the gases mix intimately as the gases are given off. The stoker boxes S are operated by shafts rotating through a small arc. The shafts move the boxes for- wards, so as to push the coal that is in the front of them onto the grates for coking. A hollow iron bar 9, with projections on its sur- face and supported by a shaft, forms the clinker-breaking de- vice. This device and the movable grates are operated by a small engine that is part of the equipment. When the bar is rotated it grinds up the clinker. The Detroit stoker. Fig. 31, feeds the coal by means of a screw feed 1. The clinker-breaking de- vice consists of heavy iron disks 2 operated by means of reciprocating bars 3. The large combustion space in the furnace be- tween the grates, assists very materially in obtain- ing complete combustion without smoke. Also, the Fig 28. Muruliy Side-Feed Stoker, ReCurn Tubular Boiler. 246 COAL AND ITS COMBUSTION. large coking-plate area allows a boiler to be started up from a banked fire and thrown into service with- out much smoke. Fig. 29. Murphy Side-Feed Stoker, Dutch Oven. N^ Fig. 30. Murphy Side-Feed Stoker, Heine Boiler. This type of stoker is used very extensively under return-tubular boilers and under water-tube boilers. It successfully burns slack, nut-and-slack, COAL AND ITS COMBUSTION. 247 nut, and run-of-mine coal. The depth of fire carried under water-tube boilers varies from 4 to 7 inches, with an average of about 5.5 inches. In return tubular boilers, the depth varies from 5 to 11 inches, with an average of about 6 inches. The stoker gives good satisfaction in both small and large plants, and under both uniform and variable loads. Fig 31. Detroit Side-Feed Stoker, Sterling Boiler. Underfeed Stokers Two makes of underfeed stokers, the Jones type and the American type are in use under power plants. They differ chiefly in the feeding mechanism and in the device for handling the burning coal after it leaves the retort. In the Jones stoker, the coal is 248 COAL AND ITS COMBUSTION. intermittently pushed beneath the burning coal in the retort by means of a ram actuated by a cylinder. In the American stoker, the coal is forced continu- ously into the retort by means of a cone-shaped screw. The Jones stoker and a Heine, boiler are shown in Fig. 32, and in Fig. 33 is shown a cross-section of this same stoker in connection with a return-tubular boiler. It consists of a steam cylinder, or ram, 1, a hopper 2 for holding the coal, and a retort 3 inside the furnace, into which the coal is forced by a ram and above which it is coked. Tuyere blocks ^ ranged around the sides and ends of the retort, having open- ings a through which air for the combustion of the coal is forced. At the bottom of the retort, covered by green coal, a ram or pusher 6, Fig. 33 operates, and it is by means of this that an even distribution of the coal is made in the retort. The ram forces the green coal underneath the coal that is already coking in the retort, each charge raising the preced- ing charge upwards until, finally, it reaches the fire after being thoroughly coked. The coked coal rolls down the sides of the heap and falls on the dead plates 7, where combustion is completed, the air being supplied through the tuyere openings. Air at a low pressure (from 1/2 to 1 ounce) is supplied to the closed air chamber 8 by means of an independent air blower, and it passes into the tuyere blocks through the opening in the bottom of the blocks. The green coal in the retort is so compact that the air takes the path of least resistance and passes upwards; consequently, combustion takes place only above the air slots, and the retort is not subjected to the action of the fire. The gases are liberated slowly under the burning coal, and, in passing COAL AND ITS COMBUSTION. 249 upwards, they are intimately mixed with the air from the tuyere openings and so highly heated that their combustion is completed within a short dis- tance from the top of the burning coal. This results in a bright fire, free from smoke. For the reason stated, less combustion space is required with this type of stoker than with any other. The stoker, as can be seen, is very compact and requires but a very small space above the grate. Fig. 32. Jones Stoker and Heine Boiler. On account of using a blower, the air regula- tion can be anything desired, so that a much smaller stack will be satisfactory with an under-feed stoker than with the other types using natural draft. Also, where the stack capacity of a plant has been reached, the capacity of the boiler plant can be increased by the use of underfeed stokers without any stack changes. The ram is operated by means of the lever 8, 250 COAL AND ITS COMBUSTION. Fig. 32. By shifting the lever, the coal in front of the plunger is forced into the retort. When the plunger is returned to its original position, more coal falls in front of it for the next charge. The charges are fired as frequently as required. This type of stoker is used under both return- tubular and water-tube boilers, the newer installa- tions being fitted with automatic control for both the coal and the air. This stoker uses the same sizes of coal as the other stokers, but will give best service with low-ash coals. With return-tubular boilers, the depth of fire varies from about 12 to 18 inches ; with water-tube boilers, it varies from about 8 to 18 inches. The stoker works successfully under both uniform and variable loads. Fig. 33. Jones Uurler-Fecd Stoker, Cross-Section. It is necessary to clean the fire in some cases very frequently, depending on the quality and the quantity of the ash in the coal. In water-tube boil- ers, cleanings range from once every 3 hours to once COAL AND ITS COMBUSTION. 251 every 9 hours; in return-tubular boilers, they vary from once every 2 hours to once every 14 hours. In this type of stoker, the ash accumulates on the dead plates, where it is subjected to the high tempera- ture of the fire; consequently, a great deal of the ash fuses and forms large clinkers that must be pulled out of the furnace by hand. Cleaning of the fires, therefore, generally results in considerable smoke. APPENDIX Analysis of 319 American Coals. 254 COAL AND ITS COMBUSTION. TABLE A Analyses of 319 American Coals, "Air-Dried" Basis, "With Calorific Value and C: (0+ash) Ratio of Each Coal. Ultimate Analysis 1 2 3 4 5 6 7 8 9 10 No. Designation of Coal Locality- s N. S. H. C. o. < 1 Mass. 1 Halifax p. 1.40 0.58 5.55 40.78 30.95 20.74 2 N. Dak. IB Lehigh L. 0.55 3.95 5.57 44.11 33.07 12.75 2a Mont. 3701 Nr. Miles S. .65 .66 4.51 48.01 28.17 18.00 2b Wyo. 3694 Labarge Range s. .85 .61 4.45 48.65 38.57 6.87 3 N. Dak. 3 Wilton L. 1.39 1.32 5.88 47.45 35.08 8.88 4 Ark. 10 Lester L. .91 .65 5.60 48.51 31.36 12.96 4a Mont. 3816 Nr. Glendive L. .65 1.55 5.63 48.55 34.21 9.41 5 N. D^k. 2B Williston L. .88 .71 5.66 50.79 35.86 6.10 6 Fla. 1 Orlando P. 2.56 .49 6.06 51.18 34.03 5.68 7 Tex. 1 Crockett L. .95 1.04 5.57 52.06 25.53 14.85 8 N. Dak. 1 Lehigh L. .71 2.02 5.22 52.66 27.15 12.24 9 Wyo. 3 Aladdin B. .72 6.86 5.03 49.59 20.60 17.20 9a Wyo. 3892 Fall River S. 1.40 2.85 4.70 52.58 23.72 14.75 10 Ind. T. 5 Lehigh B. 1.22 4.06 4.18 52.39 12.40 25.75 11 Cal. 1 Telsa S. .73 3.40 5.32 52.83 20.41 17.29 12 Mo. 7C Noringer B. .98 3.47 3.95 53.55 10.48 27.57 12a Wyo. 2326 Unita Co. S. .88 4.78 4.86 52.53 19.60 17.35 13 N. Dak. 2 Williston L. .91 .63 5.61 65.16 30.98 6.71 14 111.2 O'Fallon B. .78 4.30 4.57 54.06 12.13 24.10 15 Mo.7A Noringer B. 1.01 3.46 4.65 54.30 14.23 22.35 16 Mo. 3 Mendota B. .92 4.13 4.52 54.79 12.34 23.30 17 N. Mex. 2 Gallup S. .98 1.30 5.05 56.71 16.74 19.22 18 Wyo. 2 Cambria B. .80 4.17 4.54 55.29 12.94 22.26 19 Tex. 2 Hoyt L. 1.06 .71 5.28 57.31 25.83 9.81 20 Wyo. 2B Cambria B. .85 4.22 4.59 65.84 12.72 21.77 21 Mexico B. 1.02 .96 3.97 58.97 58.83 6.36 24,48 29.33 9.96 22 Tex. 4 Hoyt L. .97 .70 5.06 23 Mo. 10 Bevier B. .97 4.28 4.05 57.25 9.69 23.76 24 Tex. 3 Olsen L. 1.18 1.30 5.13 58.43 23.66 10.30 25 Wyo. 1 Monarch S. 1.09 .63 6.09 58.41 28.99 4.79 25a| Mont. 3512 Belt Dis. B. 0.65 1 1.71 4.17 59.65 15.19 18.63 COAL AND ITS COMBUSTION. 255 TABLE A— Continued Analyses of 319 American Coals, "Air-Dried" Basis, With Calorific Value and C: (0+ash) Ratio of Each Coal. Proximate Analysis U 12 13 14 15 16 17 18 19 H s| C Q Age ForiTintion Remarks |s sa 0+ash o n 13.60 18.72 46.94 0.79 4055 7299 Recent 24.82 29.85 32.58 0.96 4321 7778 Tertiary | Fort Union Car sample 15.12 36.54 30.34 1.04 a4432 7969 Tertiary Fort Union Countryb'k 10.88 40.15 39.15 1.07 b4468 8042 Cretaceous Montana Prospect 26.64 27.92 36.56 1.08 4498 8096 Tertiary Fort Union Mine; c. s. 19.13 32.54 35.36 1.09 4714 8485 Eocene Oil rock 24.11 15.80 50.68 1.11 a4522 8140 Tertiary Fort Union Countryb'k 22.77 35.72 34.41 1.21 4922 8860 Tertiary Fort Union Car sample 13.19 24.30 56.83 1.28 4961 8930 Recent Briquetted 13.40 29.00 42.75 1.29 5199 9368 Eocene * * * Mine; c. s. 16.42 33.51 38.73 1.31 5034 9061 Tertiary Fort Union Mine; c. s. 12.58 34.82 35.39 1.31 5108 9194 Cretaceous Montana Mine; c. s. 10.32 30.48 43.46 1.36 b5106 9191 Tert-Cret? Evanston Sur.sample 5.74 37.05 31.46 1.37 5201 9362 Carbonif. Coal Meas. Slack 9.05 34.23 39.43 1.41 5275 9495 Tertiary * * * Mine; c. s. 2.48 38.78 31.17 1.41 5399 9718 Carbonif. Coal Meas. Slack 7.21 36.95 37.96 1.42 5261 9470 Tert-Cret.? Evanston Mine 16.73 39.49 37.10 1.46 5273 9491 Tertiary Fort Union Mine; c. s. 5.31 36.24 34.29 1.48 5471 9848 Carbonif. Coal Meas. Slack 7.41 38.12 32.12 1.48 5503 9905 Carbonif. Coal Meas. Nut coal 5.51 39.11 32.08 1.56 5506 9911 Carbonif. Coal Meas. Slack 8.13 37.83 34.82 1.57 5667 10202 Cretaceous Mesaverde Mine;c. s. 2.73 37.40 37.61 1.57 5758 10364 Cretaceous Montana Mine 10.66 40.11 39.42 1.60 5502 9904 Eocene * * * Mine; c. s. 4.64 35.35 38.24 1.62 5815 10467 Cretaceous Montana Mine 0.91 47.69 22.07 1.63 5920 10656 Unknown * * * 9.76 42.77 37.51 1.71 5682 10228 Eocene * * * Mine; c. s. 1.77 43.97 30.50 1.71 5857 10543 Carbonif. Coal Meas. Screening 9.88 43.65 36.17 1.72 i 5715 10287 * * * * * * Mine; c. s. 17.09 39.56 37.96 1.73 1 5753 10355 Tertiary Fort Union 1 Mine; c. s. 4.57 50.65 26.15 1.76 1 5824 10483 Cretaceous Kootenai 1 Mine sam. 256 COAL AND ITS COMBUSTION. TABLE A— Continued Ultimate Analysis 1 2 3 4 5 6 7 8 9 10 No. Designation Locality ■a s N. S. H. C. O. .s 2 of Coal U ■< 26 111. 7A Collinsvllle B. 0.99 4.63 4.73 57.43 14.00 18.22 27 Tenn. 11 Ozone B. 1.13 .92 3.96 60.56 4.90 28.53 28 Mo. 7B Noringer B. 1.02 4.13 4.23 57.82 8.98 22.82 28a Colo. 3856 Nr. Thompson's B. 1.35 .60 4.86 60.49 13.23 19.47 29 Mont. 2 Fromburg S. 1.14 .62 4.75 60.97 16.60 15.92 30 W. Va. 24 Gary Sb. .66 .55 3.33 62.36 3.97 28.77 31 Mont. 1 Red Lodge s. 1.36 .76 5.25 60.41 20.00 11.22 31a Colo. 3729 Carbon era B. 1.30 .50 5.37 61.17 16.58 15.08 32 Colo. 1 Lafayette S. 1.22 .58 5.75 61.13 24.95 6.32 33 111. 24A Livingston B. .97 4.56 4.71 59.37 12.88 17.51 33a N. Mex. 3811 W. of Putnam S. 1.51 1.92 5.50 60.32 20.61 10.14 34 Ind. 20 Brazil B. 1.16 2.17 4.63 60.96 11.09 19.09 35 Ark. 9 Bonanza Sb. 1.28 1.04 3.59 62.49 5.70 25.90 36 Iowa 5 Charlton B. 1.22 3.42 5.35 59.89 16.57 13.55 37 Mont. 3 Bridger S. 1.09 .56 4.87 62.32 17.34 13.82 38 111. 27 Auburn B. 1.01 4.50 4.93 59.88 14.38 15.30 39 111.4 Troy B. 1.17 1.34 5.33 61.79 18.32 11.85 39a Wyo. 3699 Labarge Range S. 1.09 1.14 5.39 62.05 24.56 5.77 39b Wyo. 3780 N. E. of Hanna S. 1.73 2.41 5.73 60.53 23.55 6.05 40 Ind. 3 Boonville B. 1.18 5.24 4.83 59.58 12.09 17.08 41 Wyo. 4 Hanna S. .90 .29 5.42 62.68 23.23 7.48 42 111.8 Paisley B. 1.08 4.68 5.25 59.88 16.01 13.10 43 Mo. 1 Sprague B. .99 5.53 4.64 60.00 8.46 20.38 44 111.6 Coflfeen B. 1.23 4.45 4.88 60.51 14.20 14.73 44a Wyo. 3693 Labarge Range S. 1.03 2.10 5.74 61.76 25.96 3.41 44b Mont. 3515 Belt Dis. B. .69 3.80 4.02 62.51 9.16 19.82 45 111. 23A Donkville B. 1.04 4.58 4.55 60.93 10.94 17.96 46 Wash. 1 Renton S. 1.30 .68 4.91 63.28 16.92 12.91 46a Colo. 4050 Nr.Glenw'd Sp's B. 1.58 .98 6.04 62.74 19.71 9.95. 47 111. 21B Troy B. 1.24 1.17 5.14 62.84 17.26 12.35 48 Iowa 2 Hamilton B. 1.46 5.20 4.84 60.36 11.15 16.99 49 111. 7B Collinsville B. 1.03 4.69 5.14 60.71 14.77 13.66 50 Wash. IB Renton S. 1.29 .80 5.16 63.35 16.82 12.58 51 Ind. 1 Mildred B. 1.22 2.58 5.20 62.20 14.99 13.81 COAL AND ITS COMBUSTION. 25*; TABLE A— Continued Proximate Analysis U 12 13 14 15 16 17 18 19 Is II c CO Age Ti^r»T*ma tion Remarks o a 2 h u O+ash f4 A/ V» lllCVwI\.FIi 6.80 38.16 36.82 1.78 5863 10663 Carbonif. Coal Meas. Slack 1.26 48.97 21.24 1.81 5836 10505 Carbonif. Pottsville Slack 2.17 40.95 34.06 1.81 6853 10635 Carbonif. Coal Meas. Nut coal 4.14 43.75 32.64 1.85 6029 10862 Cretaceous Mesaverde Small mine 5.39 46.03 32.66 1.87 6020 10836 Cretaceous Eagle Mine; c. s. 0.52 58.60 12.11 1.90 6002 10804 Carbonif. Pottsville Bony layer 9.05 43.03 36.70 1.93 5989 10780 Tertiary Fort Union Mine; c. s. 6.76 44.45 33.71 1.93 6089 10960 Cretaceous Mesaverde Mine sam. 13.49 43.03 37.11 1.95 5995 10791 Cretaceous Laramie Mine; c. s. 4.92 43.89 33.68 1.95 6068 10922 Carbonif. Coal Meas. Screening 8.86 43.13 37.87 1.96 6994 10789 Cretaceous Mesaverde Little depth 4.38 44.73 30.90 1.96 6089 10960 Carbonif. Coal Meas. Screening 1.11 57.64 15.35 1.97 6967 10921 Carbonif. Coal Meas. Slack 9.22 44.62 32.71 1.98 6106 10989 Carbonif. Coal Meas. R. of M. 5.63 47.15 33.40 2.00 6126 11027 Cretaceous Eagle Mine ; c. s. 6.67 42.02 36.01 2.01 6132 11043 Carbonif. Coal Meas. R. of M. 11.40 44.30 32.46 2.03 6106 10991 Carbonif. Coal Meas. Lump 9.02 47.55 36.59 2.04 a6039 10870 Cretaceous Montana Coal drift 10.12 48.13 36.70 2.04 b6040 10872 (?) Up.Laramie Exposed 5.12 42.92 34.88 2.04 6090 10962 Carbonif. Coal Meas. Small size 9.21 42.04 46.27 2.04 6116 11009 Tertiary Fort Union Mine; c. s 9.21 41.78 35.31 2.06 6110 10998 Carbonif. Coal Meas. 3.50 40.77 36.36 2.08 6191 11145 Carbonif. Coal Meas. 15.13 47.46 32.68 2.09 6199 11168 Carbonif. Coal Meas. R.of M. 10.78 i 43.94 40.46 2.10 a6067 10901 Cretaceous Montana Prospect 1.93 ! 51.44 26.81 2.11 6094 10969 Cretaceous Kootenai Countryb'k 2.86 43.14 36.04 2.11 6180 11124 Carbonif. Coal Meas. Lump 5.98 45.96 35.16 2.12 6182 11128 Eocene Pea coal c.s. 7.05 47.60 36.40 2.12 6226 11207 Cretaceous Mesaverde Mine sam. 8.52 46.96 32.18 2.12 6278 11300 Carbonif. Coal Meas. 4.25 41.76 37.02 2.14 6212 11182 Carbonif. Coal Meas. R. of M. 7.60 41.19 37.65 2.14 6229 11212 Carbonif. Coal Meas. 5.20 4.S.68 .^6.64 2.15 6273 11291 Eocene Mine; c. .s 8.66 1 42.67 39.86 2.16 6336 11405 Carbonif. Coal Meas. ' -*4 58 COAL AND ITS COMBUSTION. TABLE A — Continued Ultimate Analysis 1 2 3 i 6 6 7 8 9 10 •a s No. Designation of Coal Locality N. S. H. C. O. < 51a Philip Batan Island S. 1.33 1.36 5.55 62.91 23.39 5.56 52 Iowa 4 Centerville B. .94 4.46 5.31 61.25 16.56 11.48 52a N. Mex. 3952 Nr. Blackrock B. 1.03 1.54 5.45 63.00 12.36 16.62 52b Wyo. 2325 Almy S. 1.23 .22 4.97 64.28 21.56 7.73 52c Colo. 3463 Lay B. 1.16 1.05 5.50 63.43 22.37 6.49 53 111. 25B Germantown B. 1.12 5.06 5.05 60.96 13.57 14.24 53a Wyo. 3917 Nr. Ft. Steele S. 1.56 .85 5.16 63.57 25.05 3.80 54 111. 9C Staunton B. .95 4.39 4.31 62.23 10.41 17.71 55 111. 22A Maryville B. 1.06 5.68 4.83 60.94 13.66 13.83 55a Wyo. 3698 Labarge Range S. 1.08 .84 5.68 63.81 25.75 2.84 56 Wyo. 4B Hanna S. .88 .27 6.18 64.01 21.62 7.04 57 111. 29B Livingston B. .85 4.68 5.11 61.69 14.62 13.05 57a Wyo. 3605 Hanna S. 1.29 .50 5.41 64.07 21.58 7.14 58 111. 6B Coffeen B. 1.10 4.67 4.69 61.96 12.15 15.43 59 111. 29 Livingston B. 1.08 4.71 4.92 61.67 14.07 13.55 60 Iowa 1 Laddsdale B. .97 5.20 4.61 61.80 10.90 16.52 61 Ill.l O'Fallon B. 1.07 4.25 5.09 62.01 13.86 13.72 62 111. 15 Centralia B. 1.09 4.04 4.99 62.25 13.82 13.81 62a Utah 4013 Nr. Sunnyside B. 1.30 .47 4.71 64.88 20.11 8.53 63 Iowa 3 Altoona B. .93 6.83 4.93 60.62 11.16 15.53 64 N. Mex. 1 Gallup S. 1.05 .64 5.73 64.34 21.14 7.10 65 Kans. 2B Yale B. 1.11 5.03 4.26 62.65 5.13 21.82 66 Ind. 14 Seelyville B. .97 5.34 4.99 62.05 11.90 14.75 66a Colo. 3498 Meeker B. 1.26 .76 5.20 64.95 20.41 7.42 67 Ind. 13 Terre Haute B. .87 3.37 5.25 68.39 14.31 12.81 68 Ind. 4 Star City B. 1.24 2.59 4.66 64.10 11.36 16.05 69 111. 30 Shiloh Station B. 1.03 4.80 4.92 62.60 12.20 14.45 70 111. 21 Troy B. 1.22 1.55 4.94 64.76 15.34 12.20 71 111. 22B Maryville B. 1.00 4.90 4.52 62.99 10.23 16.36 72 Ind. T. 4 Lehigh B. 1.38 4.02 4.84 63.21 13.15 13.40 72a Colo. 3545 Book Cliffs Dis. B. 1.47 0.66 5.58 65.05 20.96 6.28 73 111. 31 Worden B. 1.14 4.05 4.83 63.47 11.84 14.67 73a Colo. 3490 Book Cliffs field B. 1.13 .89 5.13 65.51 16.92 10.42 73b Mont. 4115 Stockett Dis. B. .92 2.43 4.33 65.17 12.66 14.49 COAL AND ITS COMBUSTION. 25J TABLE A — Continued Proximate Analysis 11 12 13 14 15 16 17 18 19 m 2 ■Si s« c GQ P OS u*° ed-^ fa Age Formation Remarks E5 II O+ash O "3 7.06 43.44 43.94 2.17 c6101 10982 Miocene? Prob. oxyd. 10.03 41.22 37.27 2.18 6237 11227 Carbonif. Coal Meas. Lump 4.01 40.22 39.12 2.18 6500 11700 Cretaceous Mancos Mine sam. 7.73 44.52 39.45 2.19 6220 11196 Tert-Cret? Evanston Mine 9.87 46.97 36.67 2.19 6198 11156 Cretaceous Mesaverde Prospect 5.79 43.18 37.79 2.19 6337 11407 Carbonif. Coal Meas. Lump 8.70 48.44 39.05 2.20 6310 11358 Cretaceous Lewis Shaft 2.25 47.09 32.95 2.21 6273 11291 Carbonif. Coal Meas. 6.39 41.89 37.89 2.21 6267 11281 Carbonif. Coal Meas. Lump 10.22 45.98 39.47 2.23 a6258 11264 Cretaceous Montana Drift 8.94 42.70 41.32 2.23 6183 11129 Tertiary Fort Union Mine; c. s 7.14 44.09 35.72 2.23 6302 11344 Carbonif. Coal Meas. R. of M. 8.07 42.85 41.93 2.23 6420 11556 Tertiary Fort Union T.b.#lm.s. 4.17 47.77 32.63 2.24 6229 11212 Carbonif. Coal Meas. R. of M. 5.58 45.14 35.73 2.24 6393 11507 Carbonif. Coal Meas. 5.21 46.51 31.76 2.25 6329 11392 Carbonif. Coal Meas. Lump 6.28 41.08 38.92 2.25 6360 11448 Carbonif. Coal Meas. Screened 6.00 43.91 36.28 2.25 6356 11441 Carbonif. Coal Meas. Coarse coal 5.12 53.21 33.14 2.26 6293 11327 Cretaceous Mesaverde From Pros. 4.52 38.99 40.96 2.27 6309 11356 Carbonif. Coal Meas. Lump 10.86 46.90 35.14 2.28 6353 11435 Cretaceous Mesaverde Mine; c. s 1.51 48.42 28.25 2.32 6329 11392 Carbonif. Coal Meas. R. of M. 4. .-54 42.64 38.27 2.33 6430 11574 Carbonif. Coal Meas. R. of M. 7.18 46.50 38.90 2.33 6446 11603 Cretaceous Mesaverde Mine sam. 7.62 42.02 37.55 2.34 6414 11546 Carbonif. Coal Meas. R. of M. 3.58 47.41 32.96 2.34 6426 11632 Carbonif. Coal Meas. Sampled 3.27 43.18 39.10 2.35 6510 11718 Carbonif. Coal Meas. Coal # 6 .1.74 47.17 34.89 2.35 6514 11725 Carbonif. Coal Meas. Lump 2.06 44.81 36.77 2.36 6376 1 11477 Carbonif. Coal Meas. Screenings 4.91 43.90 37.79 2.38 6327 1 11389 Carbonif. Coal Meas. Lump 10.00 50.98 32.74 2.38 b6312 1 11362 Cretaceous Mesaverde Prospect 3.77 i 45.94 35.62 2.39 6394 1 11509 1 Carbonif. Coal Meas. Screenings 6.17 1 47.1 n 136.28 2.39 6532 1 11758 Cretaceous Mesaverde Mine sam. 3.70 1 52.68 ! 29.1.'? 2.40 6348 1 11426 Cretaceous Kootenai Mine sam. 260 COAL AND ITS COMBUSTION. TABLE A — Continued Ultimate Analysis 1 2 3 4 5 6 7 8 9 10 No. Desienation of Coal Locality a N. s. H. C. O. < 73c Wyo. 2283 Mammoth Holl s. 1.03 .58 5.24 65.76 23.96 3.43 74 Ind. 2 Boonville B. 1.25 4.60 5.11 62.97 12.56 13.51 75 Ind. 17 Bicknell B. .94 3.85 5.03 63.70 14.87 11.61 75a Colo. 3462 Lay B. 1.22 1.14 5.53 65.33 20.41 6.37 75b Colo. .3704 Axial B. 1.40 .54 5.24 66.12 21.92 4.78 76 111. 14 Springfield B. 1.19 4.52 5.00 63.85 12.64 12.80 77 Ohio 3 Shawnee B. 1.28 1.88 5.05 65.62 14.12 12.05 78 111. 12 Bush B. 1.14 3.61 4.86 64.85 12.11 13.43 79 Kans. 2 Yale B. .94 6.40 4.56 63.14 6.69 18.27 80 Ind. 6 Hymera B. 1.19 4.63 5.15 64.22 11.50 13.31 81 111. 9A Staunton B. 1.04 4.43 5.18 64.49 13.06 11.80 81a Ariz. 4112 Nr. St. Michaels B. 1.28 0.42 5.75 66.81 21.69 4.05 82 111. 26 Lincoln B. 1.21 4.02 4.75 65.02 11.15 13.85 83 Wyo. 6 Kemmerer S. 1.10 0.55 5.81 66.95 22.07 3.52 84 111. 19E Ziegler B. 1.53 0.54 4.54 67.48 14.99 10.92 84a Colo. 3703 Axial B. 1.12 0.60 5.20 67.42 22.64 3.02 85 Ala. 2B Carbon Hill B. 1.52 1.14 4.46 67.35 10.69 14.84 86 N. Mex. 3A Van Houten B. 1.25 0.74 4.83 67.54 8.63 17.01 87 Ind. 16 Linton B. 1.13 4.50 5.02 64.82 12.04 12.49 88 Kans. 6 Jewett B. 1.14 4.00 4.54 65.65 7.75 16.92 89 Tenn. 9B Coalmont B. 1.26 0.78 4.72 67.76 6.01 19.47 90 Mo. 5 Higbee B. 1.02 5.68 4.69 64.52 8.72 14.37 91 Ind. 12 Hartwell B. 1.25 4.13 5.01 65.28 11.88 12.45 92 Ohio 2 Superior B. 1.25 4.17 5.17 65.14 12.51 11.76 93 N. Mex. 3B Van Houten B. 1.22 0.86 4.60 68.00 8.91 16.41 94 111. 23B Donkville B. 1.03 4.98 4.91 65.10 10.95 13.03 95 111. 19C Ziegler B. 1.49 0.54 5.10 67.19 13.53 11.43 96 111. 24A New Baden B. 1.10 5.33 4.94 64.86 12.20 11.57 97 111.3 Marion B. 1.43 1.77 4.92 67.30 12.99 11.59 98 Ind. 5 Hymera B. 1.16 4.60 5.07 65.44 12.01 11.72 99 111. 9B Staunton B. 1.09 4.40 5.14 65.57 12.32 11.48 100 N. Mex. 3C Van Houten B. 1.20 0.65 4.75 68.66 9.00 15.74 101 Ind. 11 1 Dugger B. 1.44 1.47 5.22 67.63 15.76 8.48 101a Colo. 3550 B. Cliffs field B. 1.26 0.63 5.19 68.46 13.25 11.21 COAL AND ITS COMBUSTION. 261 TABLE A— Continued _- Proximate Analysis u 12 13 14 15 16 ! 17 18 19 "Sg P II C <0 Age Formation Rpmarks ^3 0+ash i ^b^mdrA CV«0 *T 47.20 40.49 2.40 6385 11493 Cretaceous Montana Mine; shal. 6.24 42.76 37.49 2.41 6410 11538 Carbonif. Coal Meas. R. of M. 7.36 46.80 34.23 2.41 6446 11603 Carbonif. Coal Meas. R. of M. 8.66] 47.29 37.68 2.44 b6419 11554 Cretaceous Mesaverde Outcrop 8.91 49.22 37.09 2.48 6534 11761 Cretaceous Mesaverde Mine sam. 5.13 44.31 37.70 2.50 6496 11693 Carbonif. Coal Meas. Lump 6.24 46.68 35.03 2.51 6519 11734 Carbonif. Coal Meas. Sample 4.77 48.34 33.46 2.54 6548 12786 Carbonif. Coal Meas. R. of M. 2.23 47.63 31.87 2.54 6600 11880 Carbonif. Coal Meas. R. of M. 5.91 42.71 38.07 2.58 6555 11799 Carbonif. Coal Meas. R. of M. 4.99 43.99 39.22 2.59 6538 11768 Carbonif. Coal Meas. R. of M. 9.89 46.95 39.07 2.59 6723 12101 Cretaceous Mesaverde 3.41 45.62 37.12 2.60 6579 11842 Carbonif. Coal Meas. R. of M. 8.68 46.49 41.31 2.61 d6456 11621 Cretaceous Montana R.ofM.;c.s. 5.27 52.58 31.23 2.61 6625 11925 Carbonif. Coal Meas. Screened 8.67 49.99 38.32 2.62 6654 11977 Cretaceous Mesaverde 0. D. sam. 2.29 51.64 31.23 2.63 6660 11988 Carbonif. Pottsville R. of M. 1.48 48.80 32.71 2.63 6742 12134 Cretaceous Montana Mine 4.68 44.24 38.59 2.64 6623 11921 Carbonif. Coal Meas. R. of M. 2.09 49.03 31.96 2.66 6663 11993 Carbonif. Coal Meas. Lump 1.03 52.89 26.61 2.66 6693 12047 Carbonif. Pottsville Slack 1.71 44.95 37.97 2.67 6614 11905 Carbonif. Coal Meas. R. of M. 4.45 45.68 37.42 2.68 6688 12038 Carbonif. Coal Meas. R. of M. 5.61 45.44 37.19 2.68 6625 11925 Carbonif. Coal Meas. R. of M. 1.40 48.98 33.21 2.68 6823 12281 Cretaceous Montana Mine 2.23 45.93 38.81 2.71 6598 11876 Carbonif. Coal Meas. Slack 6.01 52.23 30.33 2.72 6595 11873 Carbonif. Coal Meas. R. of M. 4.36 47.43 36.64 2.72 6575 11835 Carbonif. Coal Meas. Screenings 5.96 52.16 30.29 2.74 6724 12103 Carbonif. Coal Meas. R. of M.# 6 5.21 44.65 38.42 2.75 6700 12060 Carbonif. Coal Meas. R.ofM. 4.03 44.18 40.31 2.75 6717 12090 Carbonif. Coal Meas. Lump 1.37 49.23 33.66 2.77 6855 12339 Cretaceous Montana Mine 8.49 1 48.16 34.87 2.79 6806 12251 Carbonif. Coal Meas. Lump 4.30 47.53 33.32 2.79 6757 12163 Cretaceous Mesaverde Mine sam. 262 COAL AND ITS COMBUSTION. TABLE A— Continued Ultimate Analysis 1 2 3 4 6 6 7 8 9 10 No. Designation of Coal Locality a 'n.^- s. H. c. O. < 102 Ind.9 Maxville B. 1.12 3.56 5.19 66.48 12.46 11.20 103 Ind. 18B Winston B. 1.18 1.49 5.50 67.95 16.80 7.08 104 111. 34B Harrisburg B. 1.38 2.96 4.69 67.29 10.95 12.73 105 Ohiol Wellston B. 1.17 4.85 5.12 65.70 10.59 12.57 106 111. 19 Ziegler B. 1.48 0.57 4.85 69.05 14.23 9.82 107 Ind. 9B Maxville B. 1.19 3.53 5.14 66.79 11.30 12.05 108 Ky.4 Wheatcroft B. 1.28 4.67 4.53 66.50 8.43 14.59 109 Ohio 9B Clarion B. 1.12 3.55 4.80 67.31 10.58 12.64 110 111. 10 W. Prankford B. 1.46 1.56 4.88 68.56 11.25 12.29 110a Wyo. 3891 McDougals Mt. B. 1.38 0.33 5.31 69.07 18.99 4.92 111 Ky.3 Barnsley B. 1.43 3.60 5.27 66.75 12.66 10.29 112 111. 12B Bush B. 1.02 1 2.60 4.80 68.30 11.74 11.54 112a Wyo. 3509 Ft. Steele B. 1.79 0.88 5.17 68.93 17.24 5.99 113 Mo. 6 Huntsville B. 1.08 6.34 4.74 65.71 8.85 13.28 114 Ala. 2 Carbon Hill B. 1.55 1.02 4.79 69.24 10.87 12.53 115 Ind. T. 8 (?) B. 1.64 1.93 4.67 68.65 8.86 14.25 116 111. 12C Bush B. 1.19 2.65 4.83 68.36 11.02 11.95 117 Ind. 8 Terre Haute B. 1.13 3.90 5.21 67.17 11.47 11.12 118 N. Mex. 4B Brilliant B. 1.53 0.62 4.97 69.48 8.62 14.78 119 111. IIB Carterville B. 1.37 2.62 4.88 68.25 10.50 12.38 120 111. 18 La Salle B. 1.09 4.28 5.37 66.91 12.61 9.74 121 Ala. 5 Lehigh B. 1.33 1.46 4.40 69.64 6.35 16.82 122 111. 13 Benton B. 1.55 1.62 4.90 69.00 11.94 10.99 123 Ark. IB Huntington Sb. 1.46 1.14 3.86 70.25 4.03 19.26 124 111. 28C Herrin B. 1.25 1.36 4.88 69.54 12.68 10.29 125 Ind. T. 2B Hartshorne B. 1.72 1.88 4.51 69.15 7.71 15.03 L26 N. Mex. 4A Brilliant B. 1.53 0.62 5.03 69.86 9.19 13.77 127 111. 12D Bush B. 1.22 2.70 4.75 68.81 11.54 10.98 L28 Wash. 2 Roslyn B. 1.26 .38 5.08 70.26 10.60 12.42 L29 Ky.7 Central City B. 1.32 2.71 5.06 67.80 12.34 9.77 L30 Ky.2 Earlington B. 1.25 3.72 5.33 67.64 12.68 9.38 L31 Ohio 11 Flushing B. 1.19 4.39 4.71 67.72 8.84 13.15 L32 Ind. 18A Winslow B. 1.38 1.69 5.48 69.08 15.17 7.20 L33 Ky.9A McHenery B. 1.24 3.25 5.41 68.01 12.80 9.29 COAL AND ITS COMBUSTION. 26: TABLE A— Continued Proximate Analysis 11 12 13 11 IB 16 17 18 19 p •2 U II c P Age Formation Remarks a- hQ O+ash a m 6.24 45.73 37.83 2.81 6714 12086 Carbonif. Coal Meas. Lump 8.92 48.57 35.43 2.84 6881 12386 Carbonif. Coal Meas. Lump 2.92 51.25 33.10 2.84 6883 12389 Carbonif. Coal Meas. R. of M. 2.96 44.18 40.29 2.84 6727 12109 Carbonif. Coal Meas. R. of M. 6.39 54.46 29.33 2.86 6697 12055 Carbonif. Coal Meas. Sized coal 3.17 45.81 38.97 2.86 6811 12260 Carbonif. Coal Meas. R. of M. 2.54 46.78 36.08 2.88 6830 12294 Carbonif. Coal Meas. R. of M. 2.65 45.65 39.06 2.89 6805 12249 Carbonif. Slack 2.79 50.57 34.35 2.89 6866 12359 Carbonif. Slack 6.50 48.42 39.95 2.89 6879 12382 Cretaceous Benton Pros. ; new 5.85 46.96 36.90 2.92 6829 12292 Carbonif. Coal Meas. R. of M. 3.97 51.43 36.06 2.93 6756 12161 Carbonif. Coal Meas. R. of M. 5.72 49.76 38.53 2.96 6759 12166 Cretaceous Mesaverde Mine 2.49 45.44 38.79 2.96 6785 12213 Carbonif. Coal Meas. Lump 2.58 51.74 33.15 2.96 6916 12449 Carbonif. Potts ville Sized ?.?.fl 50.21 33.25 2.97 6837 12307 Carbonif. Coal Meas. Car sam. 3.32 51.70 33.03 2.97 6862 12352 Carbonif. Coal Meas. R. of M. 5.19 45.76 37.93 2.97 6848 12327 Carbonif. Coal Meas. Lump; d.c 1.40 49.02 34.80 2.97 6927 12469 Cretaceous Montana Screenings 3.25 51.19 33.18 2.99 6901 12422 Carbonif. Coal Meas. Mixed 4.36 45.63 40.27 2.99 6914 12445 Carbonif. Coal Meas. Lump 1.24 55.74 26.20 3.00 6920 12466 Carbonif. Pottsville R. of M. 3.89 51.94 33.18 3.00 6829 12292 Carbonif. Coal Meas. Egg coal .85 63.64 16.25 3.01 6770 12186 Carbonif. Coal Meas. Slack 4.93 54.11 30.77 3.02 6849 12328 Carbonif. Coal Meas. Lump 1.44 49.49 34.04 3.04 6915 12447 Carbonif. Coal Meas. Slack 1.71 49.25 35.23 3.04 7034 12661 Cretaceous Montana Mine 2.97 53.54 32.51 3.06 6910 12438 Carbonif. Coal Meas. 1.88 48.73 36.97 3.05 7084 12715 Eocene 5.64 48.26 36.33 3.06 6863 12353 Carbonif. Coal Meas. Lump 5.36 46.27 38.99 3.06 6966 12539 Carbonif. Coal Meas. Coarse coal 1.87 48.35 36.63 3.08 6937 12487 Carbonif. Coal Meas. Lump 8.29 48.28 36.23 3.08 6898 12416 Carbonif. Coal Meas. Slack 5.39 49.05 36.27 3.08 6953 12615 Carbonif. Coal Meas. Nut 164 COAL AND ITS COMBUSTION. TABLE A — Continued Ultimate Analysis 1 2 3 4 5 6 7 8 9 10 No. Designation of Coal Locality •3 N. S. H. C. O. < 134 Ala. 3 Garnsey B. 1.15 .56 4.47 70.84 8.45 14.53 134a Colo. 3541 Book Cliffs field B. 1.58 .87 5.14 69.83 16.47 6.11 135 Ky.9B McHenery B. 1.39 3.10 5.07 68.35 11.59 10.50 135a 111. 19B Ziegler B. 1.56 .64 4.51 70.55 13.11 9.63 136 Ind. 15 Linton B. 1.56 1.00 5.11 69.89 13.47 8.97 136a Colo. 3640 Book Cliffs field B. 1.20 .49 5.38 70.52 16.87 5.74 137 Ind. T. 3 Edwards B. 1.50 3.67 4.85 68.18 10.52 11.28 138 Kans. 4 Atchison B. 1.07 8.33 5.04 65.02 7.91 12.63 139 111. 16 Herrin B. 1.56 1.19 4.94 70.14 12.17 10.00 140 Va.5A Blacksburg Sa. .69 .66 3.60 72.23 4.02 18.80 141 N. Mex. 5 Blossburg B. 1.19 .70 4.79 70.95 7.59 14.78 142 Ind. 7 Littles B. 1.25 3.88 5.40 67.99 11.93 9.55 143 Kaps. 1 Fleming B. 1.09 4.34 4.91 68.22 8.30 13.14 144 Wyo.5 Rock Springs S. 1.52 .86 5.37 70.30 18.32 3.63 145 111. 11 Carterville B. 1.39 2.07 4.84 69.91 10.64 1L15 146 Ind. T. 1 Henryetta B. 1.29 1.99 5.14 69.85 11.38 10.35 146a Colo. 3946 Rifle Creek B. 1.63 .71 5.32 70.39 16.47 5.48 146b Colo. 3586 Book Cliffs field B. 1.63 1.31 5.33 70.00 15.34 6.39 146c Wyo. 4302 Willow Creek B. 1.55 .64 4.65 71.09 15.74 6.33 147 111. 19B Ziegler B. 1.48 .96 4.96 70.70 11.98 9.92 147a Colo. 3943 Rifle Creek B. 1.60 1.14 5.36 70.20 15.63 6.07 147b Cal. 3773 Stone Canyon B. 1.19 4.26 6.18 67.50 14.50 6.37 148 Ohio? Danford B. 1.23 3.21 5.14 69.19 10.40 10.83 149 Ind. 7B Littles B. 1.24 4.14 5.11 68.94 10.34 10.23 149a Colo. 3546 Book Cliffs field B. 1.60 .74 5.38 71.03 15.16 6.09 150 Tenn. 6 Waldencia B. 1.01 .80 4.66 72.14 6.53 14.86 151 Tenn. 9A Coalmont B. 1.32 .96 4.64 71.84 6.78 14.46 152 R.I.I Providence G. .17 .07 .69 76.63 2.99 19.45 153 Ind. 10 Rosedale B. 1.26 4.17 5.40 69.07 10.77 9.33 154 Ohio 8 Dixie B. 1.35 2.97 5.21 70.18 11.52 8.76 154a Wyo. 3480 Ft. Steele B. 1.79 .95 5.56 71.24 16.73 3.71 155 Tenn. 1 Fork Ridge B. 1.65 1.63 4.96 71.36 8.92 11.49 156 Pa. 13 Creighton B. 1.23 2.19 5.02 71.25 6.96 13.35 157 Tenn. 1 Clifty B. 1.25 4.84 4.55 69.59 5.36 14.41 COAL AND ITS COMBUSTION. 26; TABLE A— Continued Proximate Analysis 11 12 13 14 15 16 17 18 19 k' 3| n: at II C Eh m Age Formation t? A m rVr 13 O+ash j^emarKB 1.54 54.11 29.82 3.08 7007 12623 Carbonif. Pottsville R. of M. 5.63 61.49 36.77 3.09 6978 12470 Cretaceous Mesaverde Mine sam. 3.91 51.49 34.10 3.09 6985 12483 Carbonif. Coal Meas. R. of M. '3.87 55.19 31.31 3.10 6897 12326 Carbonif. Coal Meas. Lump # 6 i4.93 50.82 35.28' 3.11 6979 12467 Carbonif. Coal Meas. R. of M. 5.21 55.69 33.36 3.11 6908 12344 Cretaceous Pocono Shallow; m. '3.45 47.82 37.46 3.12 6927 12379 Carbonif. Montana R. of M. 3.57 46.80 37.00 3.16 6864 12247 Carbonif. Coal Meas. Lump 4.61 54.05 31.35 3.16 6921 12368 Carbonif. Coal Meas. Lump .73 69.92 10.65 3.16 6929 12382 Carbonif. Montana 1.34 61.58 32.30 3.17 7066 12627 Cretaceous Coal Meas. Mine 5.50 44.99 39.96 3.17 6920 12334 Carbonif. Coal Meas. Lump 3.74 60.01 33.11 3.18 6891 12314 Carbonif. Coal Meas. ■6.00 51.68 38.69 3.20 6966 12429 Cretaceous Montana Mine c. s. 3.11 52.71 33.03 3.21 6978 12470 Carbonif. Coal Meas. 3.87 50.05 35.73 3.21 7011 12531 Carbonif. Coal Meas. 4.24 53.04 37.24 3.21 7075 12646 Cretaceous Mesaverde Mine sam. 4.84 50.49 38.28 3.22 7024 12554 Cretaceous Mesaverde Prospect I 4.51 '5.42 4.31 54.86 34.20 3.22 6911 12361 Cretaceous Benton Prospect 63.03 31.63 3.23 6877 12290 Carbonif. Coal Meas. Lump 51.93 37.68 3.23 7072 12641 Cretaceous Mesaverde Mine sam. 4.86 41.03 47.74 3.24 7086 12666 Miocene Mine sam. ■4.I6 50.17 34.84 3.26 6947 12416 Carbonif. Coal Meas. 2.76 46.55 40.46 3.34 7020 12548 Carbonif. Coal Meas. Screenings 5.49 64.10 34.32 3.34 7069 12636 Cretaceous Mesaverde Deep Pros. 1.02 55.69 28.43 3.37 7159 12798 Carbonif. Pottsville R. of M. M.36 56.22 27.96 3.38 7135 12755 Carbonif. Pottsville Lump ^.42 2.85 75.11 5.02 3.41 6229 11212 Carbonif. Coal Meas. Not a fuel 46.07 42.75 3.43 7113 12803 Carbonif. Coal Meas. Lump >3.19 48.26 39.79 3.46 7055 12699 Carbonif. Coal Meas. R. of M. ^5.45 52.89 37.95 3.48 a6951 12612 Cretaceous Mesaverde W. in mine 1.87 52.71 33.93 3.48 7199 12968 Carbonif. Pottsville R. of M. ^1.27 51.89 33.49 3.60 7221 13098 Carbonif. Coal Meas. R. of M. ix.u 60.87 33.68 3.52 7096 12873 Carbonif. Pottsville R. of M. !66 COAL AND ITS COMBUSTION. TABliE A — Continued Ultimate Analysis 1 2 3 4 6 6 7 8 9 10 No. Designation of Coal Locality 1 N. S. H. C. O. < 158 Tenn. 7A Wilder B. 1.29 3.32 4.92 70.46 6.94 13.07 159 Ala.l Horse Creek B. 1.66 .73 4.96 72.16 7.85 12.64 160 Ind. T. 2 Hartshorne B. 1.72 1.56 5.00 71.49 8.91 11.32 160a Colo. 3936 Newcastle B. 1.40 .44 5.07 72.65 13.49 6.95 161 Ga. 1 Menlo sb. 1.13 1.31 4.09 72.92 5.58 14.97 161a Wyo. 4323 Greys B. 1.48 .28 5.14 72.97 18.45 1.68 162 Va.5B Blacksburg Sa. .74 .70 3.85 74.33 2.91 17.47 163 Pa. 3 Scranton A. .80 .77 2.81 75.21 4.08 16.33 164 Tenn. 8A Clifty B. 1.17 4.45 4.97 70.45 5.50 13.64 165 111. 34A Harrisburg B. 1.53 2.51 4.96 71.55 10.55 8.90 166 Ala. 4 Belle Ellen B. 1.25 1.14 4.89 73.09 5.96 13.67 166a Colo. 3587 Book Cliffs field B. 1.65 1.08 5.64 72.46 13.12 6.05 167 Ohio 12B Bellaire B. 1.25 3.70 5.07 71.13 8.75 10.10 168 Ohio 10 Mineral City B. 1.32 3.00 5.55 71.28 11.14 7.71 169 Pa. 6 E. Millsboro B. 1.27 1.88 4.67 72.87 6.43 12.87 170 111. lie Carte rville B. 1.43 1.76 4.99 72.80 10.84 8.18 171 Ohio 9A Clarion B. B. 1.22 3.25 4.67 72.07 10.23 8.56 171a Colo. 3938 Newcastle B. 1.76 .54 5.05 73.45 14.22 4.98 171b Colo. 3585 Book Cliffs field B. 1.63 1.37 5.52 72.62 13.53 5.33 171c Colo. 3932 Newcastle B. 1.45 .42 5.21 73.98 13.53 5.41 172 Ohio 12A Bellaire B. 1.23 4.07 5.03 71.44 8.60 9.63 173 Kans. 5 Westminster B. 1.09 3.86 4.96 71.90 7.40 10.79 173a Wyo. 3570 Oyster Ridge B. 1.18 .48 5.10 74.41 14.36 4.47 173b Colo. 3939 Newcastle B. 1.73 .52 5.17 73.87 13.62 5.09 174 Tenn. 4 Oliver Springs B. 1.63 1.03 5.13 73.62 8.58 10.00 174a Colo. 4036 N. of Sunlight B. 1.78 .53 5.49 73.65 16.61 1.94 175 W. Va. 22B Hernshaw B. 1.18 1.04 5.06 74.16 8.47 10.09 175a Colo. 4225 Nr. Mancos B. 1.50 1.03 5.69 73.73 12.18 5.87 176 Pa. 17 White B. 1.44 1.56 4.83 74.06 5.80 12.31 176a Colo. 7573 Hesperus B. 1.40 .66 5.32 74.41 12.39 5.82 177 W. Va. 25 Spring Hill B. 1.43 .66 5.02 74.61 10.89 7.39 178 Ohio 4 Crow Hollow B. 1.33 3.52 5.06 72.68 8.16 9.25 179 Ark. 8 Spadra Sa. .53 2.14 3.44 75.77 3.47 14.65 179a Colo. 4048 Sunlight B. 1.86 .96 5.36 74.10 14.72 3.00 COAL AND ITS COMBUSTION. TABLE A— Continued Proximate Analysis 11 12 13 14 15 16 17 18 19 Is £1 II G 'u Age Formation Remarks a^ J+ash 3 n 1.36 60.06 35.51 3.62 7122 12921 Carbonif. Pottsville Lump 1.56 53.71 32.10 3.52 7199 13069 Carbonif. Pottsville Sized 1.70 49.79 37.19 3.53 7205 13070 Carbonif. Coal Meas. R. of M. .2.81 53.45 36.99 3.55 7243 13138 Cretaceous Mesaverde Mine sam. f .62 68.01 16.40 3.56 7341 13315 Carbonif. Pottsville Lump .4.20 .45 56.36 37.60 3.62 7358 13345 Cretaceous Benton Prospect 71.00 11.08 3.65 7112 12903 Carbonif. Pocono 2.08 74.82 7.27 3.68 6929 12673 Carbonif. Coal Meas. Waste culm 1.05 51.26 34.05 3.68 7179 13023 Carbonif. Pottsville Lump ,2.13 53.36 35.61 3.68 7324 13284 Carbonif. Coal Meas. Screenings .98 55.13 30.22 3.72 7287 13218 Carbonif. Pottsville R. of M. 4.17 52.20 37.58 3.77 a7207 13074 Cretaceous Mesaverde Countryb'k 1.69 50.10 38.11 3.77 7280 13206 CailDonif. Coal Meas. 2.24 48.65 41.50 3.78 7368 13364 Carbonif. Coal Meas. Lump 1.27 53.52 32.43 3.78 7301 13244 Carbonif. Coal Meas. R. of M. 2.36 54.84 34.62 3.82 7263 13175 Carbonif. Coal Meas. 2.47 50.89 38.08 3.83 7331 13298 Carbonif. Coal Meas. Lump 2.73 63.60 38.67 3.83 7429 13474 Cretaceous Mesaverde Mine sam. 4.78 52.69 39.20 3.86 7182 13030 Cretaceous Mesaverde Mine sam. 3.19 55.49 35.91 3.91 7364 13367 Cretaceous Mine sam. 1.58 48.44 40.35 3.92 7443 13319 Carbonif. Coal Meas. R. of M. 1.84 54.97 32.40 3.96 7333 13201 Carbonif. Coal Meas. Screened 3.84 55.47 36.06 3.95 7336 13297 Cretaceous Benton Prospect 2.90 53.35 38.66 3.95 7441 13486 Cretaceous Mesaverde Mine sam. 1.77 54.32 33.91 3.96 7333 13201 Carbonif. Pottsville R. of M. 4.18 54.63 39.25 3.97 7465 13529 Cretaceous Mesaverde Mine sam. il.74 53.80 34.37 3.99 7344 13311 Carbonif. Pottsville R. of M. 3.51 51.12 39.50 4.08 a7316 13261 Cretaceous Mesaverde Shallow m. 1.09 57.87 28.71 4.08 7448 13498 Carbonif. Coal Meas. R. of M. 3.33 53.77 37.08 4.08 7461 13522 Cretaceous Mesaverde Mine sam. 1.95 54.42 36.24 4.08 7608 13786 Carbonif. Coal Meas. Lump 2.16 50.61 37.98 4.17 7365 13349 Carbonif. Coal Meas. Screened .83 73.55 10.97 4.18 7244 13131 Carbonif. Coal Meas. Stove coal 3.10 55.32 38.58 4.18 7564 13707 Cretaceous Mesaverde "D" bed 268 COAL AND ITS COMBUSTION. TABLE A— Continued Ultimate Analysis 1 2 3 4 5 6 7 8 9 10 No. Deeignation of Coal Locality s 'n.- S. H. C. O. si to <1 180 Ky.8 Sturgis B. t.23 t22 4.87 74.99 9.51 8.18 181 Ark. 12 (?) Sb. 1.38 1.68 3.78 75.49 4.15 13.52 182 Ark.l Huntington Sb. 1.47 1.27 4.00 75.68 4.70 12.88 183 Ohio 5 Rush Run B. 1.45 1.76 5.06 74.44 9.81 7.48 184 Utah 1 Price B. 1.43 .57 5.55 75.18 12.21 5.06 185 Tenn. 5 Petros B. 1.69 3.38 4.97 73.23 6.53 10.20 186 Tenn. 3 Gatliff B. 1.78 1.02 5.31 74.80 9.81 7.28 187 Ohio 6 NeflFs B. 1.17 3.47 5.16 73.58 7.76 8.87 188 Ind. T. 2C Hartshorne B. 1.88 1.25 5.03 74.50 8.87 8.87 189 Pa. 22 Huflf B. 1.58 1.03 4.77 75.69 6.44 10.49 190 Md. 1 Georges Creek Sb. 1.32 1.51 3.88 76.28 3.69 13.32 191 Pa. 12 Acheson B. 1.46 2.21 4.76 74.89 7.36 9.32 192 W. Va. 22A Hernshaw B. 1.22 .85 5.05 76.01 8.89 7.98 193 Pa. 7 Ligonier B. 1.55 2.15 4.51 75.19 3.72 12.88 194 Tenn. 90 Coalmont B. 1.28 .67 4.83 76.37 7.27 9.58 195 Ark. 3 Jenny Lind Sb. 1.55 1.30 4.07 76.37 4.91 11.80 196 Pa. 21 Connelsville B. 1.57 .90 4.63 76.34 7.47 9.09 197 Pa. 4 Greensburg B. 1.46 1.29 4.82 76.00 5.78 10.64 198 W. Va. 3 Richard B. 1.44 1.07 4.91 76.12 6.09 10.37 199 W. Va. 23B Monarch B. 1.19 1.36 5.04 76.02 8.24 8.15 200 W. Va. 5 Coalton B. 1.48 .99 4.78 76.36 6.21 10.18 201 W. Va. 16 Monongah B. 1.53 1.26 4.80 76.09 7.66 8.76 202 Pa. 19 Herminie B. 1.42 1.08 4.92 76.25 7.76 8.57 203 Mo. 4 Bernet B. .75 5.55 5.77 72.45 10.25 5.23 204 Ky. IB Straight Creek B. 1.73 1.66 5.06 75.89 7.62 8.64 205 W. Va. 2 Clarksburg B. 1.37 3.50 5.09 74.44 7.70 7.90 206 Ark. 7A Midland Sb. 1.32 2.12 3.99 76.37 3.91 12.29 207 Tenn. 2 Gatliff B. 1.81 1.01 5.20 75.97 8.98 7.03 208 W. Va. 4B Bretz B. 1.60 1.10 4.52 76.72 5.68 10.38 208a Wyo. 4303 Willow Creek B. 1.31 .94 5.04 76.84 12.64 3.23 208b Colo. 4010 Gulch B. 1.56 .45 5.16 77.05 9.46 6.32 208c Ala. 3499 Lovick B. 1.69 1.10 4.89 76.64 7.20 8.48 209 W. Va. 23A Monarch B. 1.45 1.24 5.13 76.57 7.90 7.71 210 Va. 6 Richlands B. 1.33 1.27 4.44 77.21 5.45 10.30 .- COAL AND ITS COMBUSTION. TABLE A— Continued 2G{ Proximate Analysis 12 IS f-S ii 14 O+ash 57.48 68.B8 68.12 54.13 48.92 53.32 54.79 51.45 53.08 59.57 69.40 58.64 56.40 64.90 59.26 67.65 60.85 57.44 58.38 55.47 69.97 56.96 57.85 44.47 55.14 50.50 70.00 54.05 60.88 57.53 57.30 59.43 55.50 64.77 16 32.01 4.24 16.68 4.27 17.83 4.30 36.40 4.31 43.66 4.35 35.13 4.37 35.68 4.38 38.21 4.42 36.62 4.45 29.03 4.47 16.34 4.48 30.77 4.49 37.17 4.50 21.30 4.52 29.73 4.54 19.75 4.57 29.09 4.61 30.95 4.62 30.25 4.62 34.92 4.64 20.20 4.65 33.06 4.66 32.57 4.67 44.91 4.68 34.75 4.69 40.14 4.70 17.11 4.71 36.97 4.74 37.39 4.77 37.18 4.84 35.17 4.88 30.90 4.88 35.21 4.90 24.28 4.90 16 n 17 7598 7282 7450 7501 7595 7456 7489 7425 7505 7632 7469 7621 7646 7549 7563 7586 7761 7616 7631 7661 7682 7609 7752 7516 7623 7700 7413 7630 7626 7812 7860 7613 7643 7757 13768 13200 13502 13594 13763 13613 13572 13456 13601 13830 13536 13810 13863 13680 13705 13747 14044 13601 13828 13882 13920 13788 14046 13621 13813 13952 13435 13828 13819 14164 14240 13795 13849 14055 Age Carbonif. Carbonif. Carbonif. Carbonif. Cretaceous Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. I Carbonif. I Carbonif. I Carbonif. I Carbonif. I Cretaceous I Cretaceous I Carbonif. I Carbonif. I Carbonif. 18 Formation Coal Meas. Coal Meas. Coal Meas. Coal Meas. Mesaverde Pottsville Pottsville Coal Meas. Coal Meas. Coal Meas. Coal Meas. Coal Meas. Pottsville Coal Meas. Pottsville Coal Meas. Coal Meas. Coal Meas. Coal Meas. Pottsville Coal Meas. I Coal Meas. I Coal Meas. I Coal Meas. I Pottsville I Coal Meas. I Coal Meas. I Pottsville I Coal Meas. I Benton I Mesaverde I Pottsville I Pottsville I Pottsville 19 Remarks R. of M. Slack s Screened R.ofM. R. of M. R. of M. Lump R. of M. R. of M. Screenings R. of M. Slack R. of M. Lump R. of M. Slack Coarse coal Screenings R. of M. R. of M. R. of M. Slack R. of M. I R. of M. Prospect Mine sam. R. of I\I. t R.ofM. 270 COAL AND ITS COMBUSTION. TABLE A — Continued Ultimate Analysis 1 2 3 i 6 6 7 8 9 10 No. Designation of Coal Locality •o a N. S. H. C. O. 1' 210a Ala. 3745 Coalmont B. 1.13 .88 5.01 77.40 8.28 6.30 211 Ark. 5 Coal Hill Sa. 1.39 2.01 3.74 77.29 3.36 12.21 211a Colo. 3552 Nr. Durango B. 1.50 1.38 5.29 76.63 9.89 5.31 212 Pa. 9 Kimmelton Sb. 1.29 2.09 4.00 77.42 3.58 11.63 213 W. Va. 11 Zenith Sb. 1.04 .53 4.03 79.12 3.78 11.50 214 Pa. 11 Charleroi B. 1.45 1.19 5.09 77.32 7.62 7.33 215 W. Va. 15 Clarksburg B. 1.44 2.56 5.03 76.52 5.82 8.63 215a Wyo. 4299 Willow Creek B. .85 .71 5.59 78.19 11.18 3.48 216 W. Va. 14 Bretz B. 1.50 .90 4.85 78.21 6.11 8.43 216a Ala. 3771 Acton Basin B. 1.53 .44 5.15 78.67 8.46 5.75 217 Va.4 Darby B. 1.35 .81 5.13 78.56 9.73 4.42- 218 Va.2B Crab Orchard B. 1.45 .94 5.08 78.51 8.33 5.69 219 W. Va. 1 Kingmont B. 1.55 .90 5.26 78.31 7.61 6.37 220 Pa. 10 Bruce B. 1.59 1.28 5.14 78.16 7.58 6.25^ 221 Va.l Crab Orchard B. 1.27 1.23 5.17 78.47 9.01 4.85' 222 W. Va. 20 Acme B. 1.37 1.41 5.04 78.39 5.59 8.20 223 W. Va. 8 Ansted B. 1.38 .92 5.16 78.75 6.43 7.36 224 Ky.6 Miller Creek Sp. 1.48 .58 5.36 78.94 10.83 2.82 i 225 W. Va. 17 Nr. Bretz B. 1.41 1.49 4.51 78.95 5.31 8.33 226 Pa. 5 Ellsworth B. 1.55 .89 5.20 78.78 7.47 6.11^ 227 Pa. 16 Hastings Sb. 1.33 1.65 4.46 79.00 5.37 8.19^ 227a Ala. 3769 Acton Basin B. 1.25 1.10 5.01 79.16 8.83 4.65 228 Pa. 20 Seward Sb. 1.16 2.96 4.55 78.23 2.17 10.93 ' 229 Ky.l Straight Creek B. 1.85 1.24 5.36 78.31 8.80 4.44 230 Pa. 15B Wehrum Sb. 1.18 4.06 4.29 77.52 2.40 10.55 231 W. Va. 18 Glen Alum B. 1.45 .68 4.91 79.65 7.39 5.92 231a Ala. 3744 Fall Ston Sb. 1.33 .67 5.26 79.50 10.03 3.21. 231b Colo. 4047 Coal Basin B. 1.83 .52 4.65 79.77 4.59 8.64 232 W. Va. 9 Powellton B. 1.63 .80 5.04 79.35 6.39 6.79 233 Ky.5 Big Black Mtn. B. 1.61 .69 4.99 79.67 9.23 3.81. 234 W. Va. 21 Winifreds B.I. 1.52 1.35 5.21 79.15 7.83 4.95 235 Ala. 6 Dolomite B. 1.45 .63 4.84 80.25 5.94 6.88 236 Ark. 2 Bonanza Sb. 1.40 1.90 4.13 80.03 3.20 9.34 237 Pa. 15 Wehrum Sb. 1.17 3.88 4.43 78.61 1.82 10.09 COAL AND ITS COMBUSTION. 271 TABLE A— Continued Proximate Analysis 12 59.11 73.69 54.22 70.12 70.80 57.03 52.60 57.33 61.87 58.75 56.54 57.02 55.36 57.04 57.66 58.17 58.92 56.88 62.68 57.59 68.78 59.87 72.17 57.08 70.49 59.03 60.68 69.07 62.67 58.56 I 56.39 I 65.47 I 73.66 I 71.45 13 ^5 O+ash 32.92 12.82 38.40 17.75 16.90 34.28 37.65 36.79 28.72 33.64 37.64 35.81 36.92 35.38 35.79 32.89 32.12 37.31 27.99 34.83 22.67 33.86 16.48 36.56 18.48 33.77 34.59 21.53 29.53 36.03 37.16 26.80 16.26 18.12 14 4.96 4.96 5.04 5.09 5.17 5.17 6.29 5.33 6.37 6.63 5.55 5.59 6.60 5.64 6.66 5.68 6.71 5.78 5.78 5.80 5.83 5.87 6.90 5.91 5.98 5.98 6.01 6.03 6.03 6.10 6.19 6.26 6.38 6.60 15 5 O 16 17 Age 7764 14067 7443 13489 b7676 13909 7657 13875 7761 14062 7699 13950 7743 14029 7713 13975 7856 14231 7791 14116 7902 14316 7890 14294 7869 14256 7877 14271 7870 14258 7812 14154 7863 14245 7807 14145 7903 14317 7864 14247 7812 14154 7964 14427 7692 13938 7955 14411 7781 14098 7963 14425 8115 14699 7977 14451 7984 14463 7968 14416 7915 14339 8011 14512 7756 14153 7885 14386 Carbonif. Carbonif. Cretaceous Carbonif. Carbonif. Carbonif. Carbonif. Cretaceous Carbonif. Carbonif. Carbonif. Carbonif, Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Cretaceous Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. Carbonif. 18 Formation Pottsville Coal Meas. Mesaverde Coal Meas. Pottsville Coal Meas. Coal Meas. Benton Coal Meas. Pottsville Pottsville Pottsville Coal Meas. Coal Meas. Pottsville Pottsville Pottsville Pottsville Coal Meas. Coal Meas. Coal Meas. Pottsville Coal Meas. Pottsville Coal Meas. Pottsville Pottsville Mesaverde Pottsville Pottsville Pottsville Pottsville Coal Meas. Coal Meas. 19 Remarks Mine sam. Weathered R. of M. R.ofM.Poca. R.of M.Pitts. R.of M.Pitts. Tunnel R. of M. Helena Screened R. of M. R. of M. Nut R. of M. R. of M. R. of M. Splint Prospect Sc'd Pitts. R. of M. Helena coal R. of M. R. of M. R. of M. R. of M. Buck bed R. of M. R. of M. Split; Pros. R.ofM.;W.c. R.of M. P.c. R. of M. R. of M. 72 COAL AND ITS COMBUSTION. TABLE A — Continued Ultimate Analysis 1 2 3 4 5 6 7 8 9 10 No. Designation of Coal Locality •a c s N. S. H. C. o. 5 238 Pa. 18 Lloydell Sb. 1.23 1.55 4.53 80.74 3.02 8.83 239 W. Va. 14 Loup Creek B. 1.56 1.06 5.15 80.73 8.12 2.38 239a Ark. 3174 Paris Sa. 1.49 2.85 3.87 80.48 2.04 9.27 239b Pa. "L" Johnstown Sb. 1.27 2.29 4.04 81.10 2.99 8.31 240 W. Va. 7 Sun. Sb. 1.05 1.20 4.38 82.41 5.87 5.09 241 Md.2 Frostburg Sb. 1.49 .86 4.54 82.39 3.43 7.29 242 Ind. T. 9 Panama Dis. Sa. 1.68 1.24 4.35 82.06 2.26 8.41 242a Ala. 3770 Sydenton B. 1.55 .49 5.34 82.09 6.69 3.84 243 Va.3 Coeburn B. 1.63 .68 5.04 82.16 5.91 4.58 244 Pa. 8 Ehrenfield Sb. 1.29 .97 4.37 83.11 3.43 6.83 245 W. Va. 13 Page B. 1.36 .91 5.15 82.65 5.91 4.01 246 W. Va. 12A Big Sandy Sb. 1.34 .69 4.36 83.63 3.03 6.95 247 W. Va. 12 Big Sandy Sb. 1.33 .85 5.06 83.18 3.36 6.22 248 W. Va. 6 Rush Run Sb. 1.70 .66 4.70 83.62 4.23 5.09 249 W. Va. 19 McDonald Sb. 1.60 .91 4.66 83.56 4.13 5.13 250 W. Va. 10 Mora Sb. 1.07 .57 4.53 85.91 3.24 4.63 COAL AND ITS COMBUSTION. 278 TABLE A— Continued Proximate Analysis u 13 IS 14 IS IS 17 18 19 ii II is C 1 6 C3 Age Formation O+ash .38 74.69 16.10 6.81 7926 14459 Carbonif. Coal Meas. 2.06 64.67 30.00 7.01 8090 14754 Carbonif. Pottsville R. of M. .69 75.12 15.02 7.11 7824 14375 Carbonif. Coal Meas. .64 76.38 14.67 7.18 7934 14573 Carbonif. Coal Meas. L.Kitt'gc. ,* .76 73.61 20.54 7.52 8254 15249 Carbonif. Pottsville R.ofM.S.c. .74 73.83 18.14 7.68 8086 14947 Carbonif. Coal Meas. Pitts, coal .64 76.66 14.29 7.69 7948 14698 Carbonif. Coal Meas. 1.28 60.32 34.56 7.79 8180 15116 Carbonif. Pottsville Wads'h coal .87 62.19 32.36 7.83 8220 16288 Carbonif. Pottsville Screened .63 75.22 17.32 8.10 8170 16198 Carbonif. Coal Meas. R.ofM. 1.17 62.96 31.87 8.32 8234 16313 Carbonif. Pottsville R. of M. .62 74.38 18.05 8.38 8185 16225 Carbonif. Pottsville R. of M. 1.93 8.68 8300 16433 Carbonif. Pottsville Briquettes .64 72.63 21.74 8.97 8301 16436 Carbonif. Pottsville R.ofM. .68 70.91 23.28 9.01 8203 16268 Carbonif. Pottsville R. of M.,S.c. .65 75.92 18.80 10.91 8439 1 16683 | Carbonif. Pottsville Poca. ; Pros. ABBREVIATIONS USED IN THE TABLE c. B. — Car Sample d. c. — ^Deep coal Klt'E.— Klttannlns Nr. — ^Near O. D.— Old Drift Pros. — ^Prospect R. of M. — ^Run of Mine Sam. — Sample S. o. — Seweu Coal So'd — Screened Shal. — Shallow Wads'h — Wadsworth W.— Weathered INDEX Page. A 'Absorbed by Products of Combustion, Heat 148 Acetylene 126 Acetylene, Burning 132 Acetylene, Temperature Pro- duced by 152 Adapting the Coal to the Plant Ill Admission of Air 193 Admission of Air Supply.. 170 Air Actually Required for Combustion 142 Alr-Admlsslon and Steam- Jet Mixing, Automatic. 200 Alr-Admlsslon, Non-Auto- matic 202 Air, Admission of 193 Air and Oases, Steam Jets for Mixing 198 Air, Effect on Temperature of Insufficient 165 Air for Combustion, Excess 143 Air, Heat Absorbed by Va- por in 157 Air Required for Combus- tion 129 Air Required for Combus- tion, Calculation of.... 140 Air Supplied, Weight of and Rate of Combustion... 218 Air Supply 192 Air Supply, Admission of.. 170 Air Supply, Cooling Effect of 156 Air Supply, Regulation of. 160 Air Supply, Effect of Im- proper 146 Alternate Method of Firing. 233 AInmina, Influence of on Slagging 65 AmerlCB. Coal Fields of.... 91 Page. Analysis, Errors of Coal.. 107 Analysis of Coal 102 Analysis of 300 Kinds of Coal 108 Anthracite Coal, Sizes of.. 8 Anthracite Fields, Pennsyl- vania 91 Appalachian Coal Fields... 92 Ash, Cllnkering of Coal... 68 Ash Constituents, Influence of in Slagging 64 Ash, Constituents of Coal and Lignite 59 Ash, Fusing Temperature of 70 Ash in Coal, Determining the 105 Ash in Coal 41 Atlantic Coast Trlasslc Fields 92 Atoms and Molecules 119 Automatic Air-Admission and Steam-Jet Mixing. 200 B Banking the Fire 237 Benzole 128 Benzole, Burning 132 Benzole, Temperature Pro- duced by 153 Biochemical Process of Coal DeTOlatilizatlon 88 Bituminous Coal, Burning. 167 Bituminous Coals 9 Blacksmith Coals 23 Block Coal, Indiana 12 Boiler Plants for Smoke- less Combustion 225 Boiler Settings, Leaky 218 Bone, Rock and Slate In Coal 44 Page. Burning Acetylene 132 Burning Benzole 132 Burning Bituminous Coal.. 167 Burning Carbon Monoxide to Carbon Dioxide 130 Burning Carbon to Carbon Dioxide 129 Burning Carbon to Carbon Monoxide 130 Burning Coal Smokelessly. 191 Burning, Coals for Cement 25 Burning Ethane 132 Burning Ethylene 131 Burning Hydrogen 131 Burning Methane 131 Burn ing Slack 234 Burning Sulphur 133 By-Product Coking, Coals for 23 C Caking and Non-Caking Coals 11 Calculation of Air Required for Combustion 140 Calculations, Clinker 66 Canada, Coal Fields of 99 Cannel Coal 11 Cannel Coal Formation 90 Capacity of Combustion Chamber 204 Capacity of Furnace, Smoke- less 212 Carbon 122 Carbon and Hydrogen 124 Carbon and Hydrogen In Coals 3 Carbon and Oxygen In Fuels 2 Carbon, Fixed 191 Carbon-Hydrogen Ratios of Coals 5 Carbon In Coal, Determin- ing Fixed 105 Carbon In Coal, Fixed 26 Carbon Monoxide to Carbon Dioxide, Burning 130 Carbon, Temperature Pro- duced by 149 Page. Carbon to Carbon Dioxide, Burning 129 Carbon to Carbon Monoxide, Burning 130 Cement Burning, Coals for. 25 Chain-Grate Stoker, Opera- tion of 241 Chain -Grate Stokers 238 Chamber. Capacity of Com- bustion 204 Characteristics of Coal 8 Chemical Combination 120 Classification of Coals 1 Cleaning the Fire 2.S6 Clinker Calculations 06 Clinkor, Disadvantages of. SO Clinker, Formation of .'jS Clinker Holes and Thick Spots, Effect of 195 Clinker, Prevention of 76 Clinker, Removing 80 Clinker, Soft 60 Clinker, Use of Limestone for Preventing 76 Clinker. TTse of Water Vapor for Preventing 77 Clinkers, Hard 74 Clinkering of Coal Ash 58 Coal, Adapting to the Plant 111 Coal and Lignite Ash, Con- stituents of 69 Coal Analysis, Errors of. . . 107 Coal, Analysis of 102 Coal, Analysis of 300 Kinds of 108 Coal Ash, Clinkering of 58 Coal, Ash In 41 Coal, Burning Bituminous. 167 Coal, Burning Smokelessly. 191 Coal, Cannel n Coal, Characteristics of 8 Coal Classed According to Use 16 Coal. Combustion of 137 Coal, Composition of 26 Coal, Determining Fixed Carbon In 105 Coal, Determining Moisture In 103 Page, fdal, Detonnlnlng tlie Ash In 105 Conl. Determining the Heat Value of ]0." (,'(ial. Dcteimlniiig the Heat Value of 1G2 Coal, Determining the Sul- phur In 105 Coal. Determining Volatile Matter In 104 Coal DevolatlUzatlon, Bio- chemical Process of 88 Coal Devolatlllzatlon, Dyna- moechanlcal Process 89 Coal, Derolatlllzation of 87 Coal, Disintegration of 52 Coal, Effect of Size of 49 Coal, Effects of Weathering 50 Coal Fields, Appalachian... !I2 Coal Fields, Eastern Inter- ior 94 Coal Fields, Northern In- terior 93 Coal Fields of America 91 Coal Fields of Canada 99 Coal Fields of Mexico 99 Coal Fields, Pacific Coast. 98 Coal Fields, Rocky Moun- tain 98 Coal Fields, The Gulf 9T Coal Fields, Western In- terior 95 Coal, Fixed Carbon In 20 Coal Formation, Cannel 90 Coal-Forming Periods 80 Coal, Fuel Elements of 137 Coal, Geological History of 81 Coal, Heat Loss Due to Moisture In I 159 Coal, Hydrogen in 2S Coal Impurities, Cost of... 113 Coal, Indiana Block 12 Coal, Influence of Size of on Combustion 214 Coal Measures, The 86 Coal, Moisture In 38 Coal, Nitrogen In 47 Coal, Oxygen In 45 Coal-PUe Fire, Extinguish- ing a 57 Page. dial rile. Temperature of.. 56 C'lal. Prevention of Spon- taneous Combustion of. Ci (,'oal. Purchasing of Ill Coal, Kock, Bone and Slate In 44 Coal, Semlanthraclte 9 Coal, Semlbltumlnous 9 Coal, Sized 14 Coal, Sizes of Anthracite... S Coal, Splint 12 Coal, Spontaneous Ignition of 53 Coal, Subbituminous 12 Coal, Sulphur In 40 Coal, Unit 102 Coal, Volatile Combustible Matter in 30 Coals, Bituminous U Coals, Blacksmith 23 Coals, Caking and Non-Cak- ing 11 Coals, Carbon and Hydro- gen in 3 Coals, Carbon Hydrogen Batios of 5 Coals, Classification of 1 Coals for By-Product Cok- ing 23 Coals for Cement Burning. 25 Coals for Domestic Use 16 Coals for Heating and Pow- er Plants 17 Coals for Illuminating Gas 24 Coals for Locomotive Serv- ice 21 Coals for Metallurgical Pur- poses 24 Coals for Producer Gas 24 Coals for Steamship Service 23 Coals of Dllfferent Impuri- ties, Equating 110 Coals, Kelative Values of Steam 20 Coking, Coals for By-Pro- duct 23 Coking Method of Firing... 232 Color, Length and Motion of Flame 212 Combination, Chemical 120 Page. Combustible Matter In Coal, Volatile 30 Combustibles, Igniting Tem- perature of 139 Combustion, Air Actually Eequlred for 142 Combustion, Air Bequlred for 129 Combustion, Boiler Plants for Smokeless 225 Combustion, Calculation of Air Required for 140 Combustion Chamber, Ca- pacity of 204 Combustion, Conditions Un- favorable for Smokeless 216 Combustion, Elements of. . . 122 Combustion, Excess Air for 143 Combustion, Heat Absorbed by Products of 148 Combustion, Heat of 146 Combustion, Influence of Size of Coal on 214 Combustion of Coal 137 Combustion of Coal, Pre- vention of Spontaneous 55 Combustion, Kate of and Weight of Air Supplied 218 Combustion, Temperature of 148 Combustion, Theoretical Temperature of 148 Combustion, Theory of 118 Combustion, Time Factor in Furnace 211 Composition of Coal 26 Composition of Matter 118 Conditions Unfavorable for Smokeless Combustion. 216 Cones, Soger 71 Constituents of Coal and Lignite Ash 59 Control, Damper 219 Cooling Effect of Air Sup- ply 156 Cost of Coal Impurities 113 Damper Control 219 Decomposition, Loss of Tem- perature Through 160 Page. Density, Weight and Vol- ume of Gases 133 Determining Fixed Carbon in Coal 105 Determining Moisture in Coal 103 Determining the Ash in Coal 105 Determining the Heat Value of Coal 105 Determining the Heat Value of Coal 162 Determining the Sulphur in Coal 105 Determining Volatile Matter in Coal 104 Devolatilizatlon of Coal 87 Devolatllization of Coal, Biochemical Process.... 88 Devolatilizatlon of Coal. Dynamochemlcal Pro- cess 89 Disadvantages of Clinker.. 80 Disintegration of Coal 52 Distillation of Gases 192 Distillation of Volatile and Smoke, Bate of 183 Divisions of Geological His- tory 83 Domestic Use, Coals for.... 16 Dorrance Furnace 227 Down-Draft Furnace, Havp- ley 229 Draft 195 Draft Gauges 220 Draft Begulation 218 Dnlong's Formula 162 Dynamochemlcal Process of Coal Devolatllization... 89 Eastern Interior Coal Fields 84 Effect of Air Supply, Cool- ing 156 Effect of Clinker Holes and Thick Spots 195 Effect of Improper Air Sup- ply 145 Effect of Impurities on Heat Value Ill Effect of Insufficient Air on Temperature 155 Page. Effect of Size of Coal 49 Effect of Sulphur on Slag- ging 69 Kffeets of \\'<'atlierlLg Coal 00 Elements of Coal, Fuel 137 Elements of Combustion... 122 Equating Coals of Different Impurities 116 Errors of Coal Analysis 107 Estimation and Observation of Smoke 222 Etbane and Ethylene 127 Ethane, Burning 132 Ethylene and Ethane 127 Ethylene, Burning 131 Ethylene, Temperature Pro- duced by 152 Experiments In Smoke Pro- duction 175 Extinguishing a Coal-Pile Fire 57 Factor In Furnace Combus- tion, Time 211 Fields, Appalachian Coal.. 92 Fields, Atlantic Coast Trl- asslc 92 Fields, Eastern Interior Coal 04 Excess Air for Combustion 143 Fields, Northern Interior Coal 93 Fields of America, Coal 91 Fields of Canada, Coal 99 Fields of Mexico, Coal 99 Fields, Pacific Coast Coal.. 98 Fields, Pennsylvania An- thracite 91 Fields, Rocky Mountain Coal 98 Fields, The Gulf Coal 97 Fields, Western Interior Coal 95 Fire, Banking the 237 Fire, Cleaning the 236 Fire. Extinguishing a Coal- Pile 67 Page. Fire. Temperature and Thickness of 209 Firing, Alternate Metbod of 233 Firing, Coking Method of.. 232 Firing, Methods of Hand.. :^2 Firing, Precautions In 235 luring, Bibbon method of. 233 Firing, Spreading Method of 233 Fixed Carbon 191 Fixed Carbon In Coal 20 Fixed Carbon in Coal, De- termining 105 Flame 173 Flame, Length, Motion and Color of 212 Flat vs. Becking Grates... 215 Formation, Cannei Coal... 90 Formation of Clinker 08 Formation of Smoke 172 Formula, Dulong's 162 Front-Feed Stoker 242 Fuel Elements of Coal 137 Fuels, Carbon and Oxygen In 2 Furnace Combustion, Time Factor in 211 Furnace Conditions 167 Furnace, Dorrance 227 Furnace, Hawley Down- Draft 229 Furnace, Plain 220 Furnace, Smokeless Capac- ity of 212 Furnace Temperature and Power Developed 208 Furnace, Twin-Arch 231 Furnace, Wooley 228 Furnaces, Hand-Fired 225 Furnaces, Stoker 238 Fusing Temperature of Ash 70 Fusing Temperature of Ox- Ides 61 Gas, Coals for Illuminating 24 Gas, Coals for Producer... 24 Page. Gases and Air, Steam Jets for Mixing 198 Gasps, Density, Weight and Volume o( 133 Gases, Distillation of 192 Gaseous Products at Var- ious Temperatures 32 Gauges, Draft 220 Geological History, Divi- sions of S3 Geological History of Coal. 81 Grates, Rocking vs. Flat... 215 Gulf Coal Fields, The 97 H Hand-Fired Furnaces 225 Hand Firing, Methods of.. 232 Hawley Down-Draft Fur- nace 229 Hard Clinkers 74 Heat Absorbed by Products of Combustion 148 Heat Absorbed by Vapor In Air 157 Heat Losses Due to Smoke. 188 Heat of Combustion 146 Heat Loss Due to Moisture in Coal 159 Heat Value, Effect of Im- purities on Ill Heat Value of Coal, De- termining the 105 Heat Value of Coal, De- termining the 162 Heating and Power Plants, Coals for 17 History, Divisions of Geo- logical 83 History of Coal, Geological 81 Honeycomb 187 Hydrocarbons 125 Hydrocarbons, Volatilizing the 137 Hydrogen 122 Hydrogen and Carbon 124 Hydrogen and Carbon in Coals 3 Page. Hydrogen, Burning 131 Hydrogen in Coal 28 Hydrogen, Temperature Pro. duced by 151 I Illuminating Gas, Coals for 24 Improper Air Supply, Ef- fect of 145 Impurities, Cost of Coal 113 Impurities, Effect of on Heat Value Ill Impurities, Equating Coals of Different 116 Indiana Block Coal 12 Influence of Alumina on Slagging 65 Influence of Ash Constitu- ents in Slagging 64 Influence of Iron on Slag- ging 65 Influence of Lime on Slag- ging 65 Influence of Silica on Slag- ging 64 Influence of Size of Coal on Combustion 214 Ignition of Coal, Spontane- ous 53 Igniting Temperature of ' Combustibles 139 Insufficient Air, Effect of on Temperature 155 Interior Coal Fields, East- ern 94 Interior Coal Fields, North- em 93 Interior Coal Fields, West- ern 95 Iron Available for Slagging 68 Iron. Influence of on Slag- ging 65 I. Leaky Boiler Settings 218 Length, Motion and Color of Flame 212 Lignite and Coal Ash, Con- stituents of 59 Lignites _ _ J3 Page. Lime, Influence of on Slag- ging (K Limestone for Prevouting Clinker, Use of 70 Locomotive Servlci'. Coals for 21 Loss Dae to Moisture In Coal, Heat 159 Loss of Calorific Value from Weathering 50 Loss of Temperature through Decomposition 160 Losses Due to Smoke, Heat ins Page. O Observation and Estimation of Smoke 222 Operation of Chain-(;rate Stoker 241 Oxides, Fusing Tempera- ture of 61 Oxygen 12.". Oxygen and Carbon in Fuels 2 Oxygen in Coal 4') Oxygen Supply, Source of. V^.> Overfeed Stokers 242 M Matter, Composition of 118 Matter in Smoke, Volatile.. 180 Measures, The Coal 80 Metalurglcal Purposes, Coals for 24 Methane 12C Methane, Burning 131 Methane, Temperature Pro- duced by 151 Method of Firing, Alternate 23r{ Method of Firing, Coking. 23:; Method of Firing, Ribbon. 233 Method of Firing, Spread- ing 233 Methods of Hand Firing.. 232 Mexico, Coal Fields of 'M Moisture in Coal 38 Moisture in Coal, Determin- ing 103 Moisture in Coal, Heat Loss Due to 159 Molecules and Atoms 119 Motion, Length and Color of Flame 212 N Nitrogen 123 Nitrogen in Coal 47 Non-automatic Air Admis- sion 202 Non-Caking and Caking Coals 11 Northern Interior Coal Fields 93 P Pacific Coast Coal Fields.. 98 Peat 13 Pennsylvania Anthracite Fields 91 Periods, Coal- Forming SO Pile, Temperature of Coal.. 50 Plain Furnace 220 Plant, Adapting the Coal to the Ill Plants, Coals for Heating and Power 17 Plants for Smokeless Com- bustion, Boiler 225 Power and Heating Plants, Coals for 17 Power Developed and Fur- nace Temperature 20S Precautions In Firing 23.") Preventing Clinker, Use of Limestone for 70 Preventing Clinker, Use of Water Vapor for 77 Prevention of Clinker 70 Prevention of Smoke from Tarry Vapors 1S7 Prevention of Soot ITil Prevention of Spontaneous Combustion of Coal 55 Prevention, Smoke and Its 172 Producer Gas, Coals f or . . . 24 Production, Experiments In Smoke 175 Products of Combustion, Heat Absorbed by 148 Purchasing of Coal Ill Page. B Rake, Slice-Bar and Sbaker, Use of 78 Eate of Combustion and Weight of Air Supplied. 218 Kate of Distillation of Vol- atile and Smoke 183 Batlos of Coals, Carbon- Hydrogen 5 Regulation, Draft 218 Regulation of Air Supply. 169 Relative Values of Steam Coals 20 Removing Clinker 80 Ribbon Method of Firing... 233 Rocking vs. Flat Grates 215 Rock, Slate and Bone In Coal 44 Rocky Mountain Coal Fields 98 S Seger Cones 71 Semlantbraclte Coal 9 Semibltumlnous Coal 9 Settings, Leaky Boiler 218 Service, Coals for Locomo- tive 21 Service, Coals for Steamship 23 Sbaker, Rake and Slice-Bar, Use of 78 Side-Feed Stoker 243 Silica, Influence of on Slag- ging 64 Slllca-Iron-Lime Slags 61 Size of Coal, Effect of 49 Size of Coal, Influence of on Combustion 214 Sized Coal 14 Sizes of Anthracite Coal... 8 Slack, Burning 234 Slags, Silica-Iron-Lime 61 Slice-Bar, Eake and Shaker, Use of 78 Soft Clinker 60 Soot, Smoke from 172 Page. Soot, Prevention of 179 Sources of Oxygen Supply. 129 Slagging, Effect of Sulphur on 69 Slagging, Influence of Alu- mina on 65 Slagging, Influence of Ash Constituents on 64 Slagging, Influence of Iron on 65 Slagging, Influence of Lime on 65 Slagging, Influence of Silica on 64 Slagging, Iron Available for 68 Slate, Rock and Bone in Coal 44 Smoke and Its Prevention. 172 Smoke and Volatile, Rate of Distillation of 183 Smoke, Formation of 172 Smoke from Soot 172 Smoke from Tarry Vapors. 182 Smoke from Tarry Vapors, Prevention of 187 Smoke, Heat Losses Due to 188 Smoke, Observation and Estimation of 222 Smoke Production, Experi- ments in 175 Smoke, Volatile Matter in.. 180 Smokeless Capacity of Fur- nace 212 Smokeless Combustion, Boil- er Plants for 225 Smokeless Combustion, Con- ditions Unfavorable for. 216 Smokelessly, Burning Coal. 191 Splint Coal 12 Spontaneobs Combustion of Coal, Prevention of 55 Spontaneous Ignition of Coal 53 Spreading Method of Firing 233 Steam Coals, Relative Val- ues of 20 Steam-Jet Mixing and Air- Admission, Automatic.. 200 Steam Jets for Mixing Air and Gases 198 Steamship Service, Coals for 23 Stoker, Front-Feed 242 Page, Stoker Furnaces 238 Stoker, Operation of Cbaln- Qrate 241 Stoker, Side- Feed 243 Stokers, Cbaln-Grate 238 Stokers, Overfeed 242 Stokers, Traveling Grate... 238 Supply of Oxygen, Source of 129 Subbltumlnous Coal 12 Sulphur 123 Sulphur, Burning 133 Sulphur, BSect of on Slag- ging 69 Sulphur In Coal 46 Sulphur In Coal, Determin- ing the 105 Sulphur, Temperature Pro- duced by 153 Supply, Air W2 Supply, Effect of Improper Air 145 Tarry Vapors, Smoke from. 182 Tarry Vapors, Prevention of Smoke from 187 Temperature and Thickness of Fire 209 Temperature, Effect of In- sufficient Air on 155 Temperatures, Gaseous Pro- ducts at Various 32 Temperature, Loss of through Decomposition, 160 Temperature of Ash, Fusing 70 Temperature of Coal Pile. . 66 Temperature of Combustion 148 Temperature of Combustion, Theoretical 148 Temperature of Combusti- bles, Igniting 139 Temperature of Furnace and Power Developed . . 208 Temperature of Oxides, Fusing 61 Temperature Produced by Acetylene 162 Page. Temperature Produced by Benzole 153 Temperature Produced by Carbon 149 Temperature Produced by Ethylene 152 Temperature Produced by Hydrogen 151 Temperature Produced by Methane 151 Temperature Produced by Sulphur 153 Theoretical Temperature of Combustion 148 Theory of Combustion 118 Thickness and Temperature of Fire 209 Time Factor in Furnace Combustion 211 Traveling Orate Stokers... 238 Trlasslc Fields, Atlantic Coast 92 Twin- Arch Furnace 231 U Unit Coal 162 Use, Coal Classed Accord- ing to 10 Use, Coals for Domestic... 16 Use of Limestone for Pre- venting Clinker 76 Use of Rake, Slice-Bar and Shaker 78 Use of Water Vapor for Pre- venting Clinker 77 V Values of Steam Coals, Rel- ative 20 Vapor in Air, Heat Ab- sorbed by 157 Vapors, Prevention of Smoke from Tarry 187 Vapors, Smoke from Tarry. 182 Volatile and Smoke, Rate of Distillation of 183 Volatile Combustible Mat- ter in Coal 30 VolaUle Matter In Coal, De- termining 104 Page. Volatile Matter In Smoke.. 180 Volatilizing the Hydrocar- bons 137 Volume, Weight and Dens- ity of Gases 133 W Water Vapor for Preventing Clinker, Use of 77 Page. Weathering Coal, Effects of 50 Weathering, Loss of Calo- rific Value from 50 Weight, Density and Vol- ume of Gases 133 Weight of Air Supplied and Bate of Combustion 218 Western Interior Coal Fields 95 Wooley Furnace 228 0. I i