Furnace Efficiency 
 
 Combustion and Flue Gases 
 
 BY 
 
 JAMES C. PEEBLES, M. M. E. 
 
 CHICAGO 
 
 THE JOSEPH G. BRANCH PUBLISHING CO. 
 1914. 
 
COPYRIGHT, 1014 
 
 by 
 JOSEPH G. BRANCH 
 
PREFACE 
 
 Coal is the great source of energy from which is de- 
 rived by far the greatest part of the mechanical and 
 electrical power now used in the industrial world. From 
 the beginning of civilization man has made use of this 
 great source of energy apparently with the idea that i- 
 is an inexhuastible supply. But unfortunately the coal 
 supply is not unlimited and the time must come when it 
 will be exhausted. What we will do for power when 
 that time arrives is a problem for future generations to 
 solve. 
 
 The problem for the present, generation to consider is 
 the economical use of our available coal supply, so that 
 the time when the coal will be exhausted may be post- 
 poned as long* as possible. There is perhaps no class of 
 men so intimately in touch with the problem of the con- 
 servation of our coal supply as the operators of steam 
 power plants. A vast amount of coal is consumed every 
 year in the power plants of the world and power plant 
 operators should be able to do much towards the solu- 
 tion of this important problem. 
 
 It is the chief engineer, the man in responsible charge 
 of the power plant, to whom we must look for economy 
 in the use of fuel. He should be familiar with the 
 latest and best work that has 'been done on the problem 
 of combustion, and should instruct his firemen and others 
 in his plant how to operate the furnaces at highest 
 economy. 
 
 The purpose of the author in preparing this -book has 
 been to set forth in convenient form and in as non-tech - 
 nical language as possible the efforts that are now being 
 marie to increase the efficiencv of coal combustion in the 
 
 341821 
 
FURNACE EFFICIENCY 
 
 steam boiler furnace. It should be of special interest to 
 all chief engineers of steam power plants, but it is be- 
 lieved that every man having anything to do with the 
 power plant, from manager or superintendent to fireman, 
 will 'find something of interest and value in its pages. 
 
 Competition in all lines O'f business has now become so 
 keen that all waste and inefficiency must be reduced to 
 the absolute minimum. The power plant operator can 
 no longer waste fuel without being called to account, and 
 hence the chief engineer must keep up with the times in 
 matters of combustion or he may find himself displaced 
 by a more up-to-date man. It is believed that this book 
 wijl make clear to the engineer how he can operate his 
 particular plant at maximum efficiency as regards the 
 boiler room. 
 
 The thanks of the author are hereby extended to the 
 various manufacturers of furnace equipment who have 
 very .kindly supplied" many of the illustrations used. He 
 is particularly indebted to tllfc engineers of the Green 
 Engineering Company for many helpful suggestions. 
 Obligation must also be acknowledged to Air. Joseph 
 W. Hays and Mr. Joseph G. Branch, to the writings of 
 the former for certain data and illustrations, and to the 
 latter for many helpful criticisms and suggestions. 
 
 THE AUTHOR. 
 Chicago, May, 1914. 
 
TABLE OF CONTENTS 
 
 CHAPTER I. 
 Chemistry of Combustion 1 
 
 CHAPTER II. 
 Flue-Gas Analysis 10 
 
 CHAPTER III. 
 Reduction of Losses in the Boiler Furnace 21 
 
 CHAPTER IV. 
 Draft Losses in Furnace and Boiler 29 
 
 CHAPTER V. 
 Smoke and Its Prevention -40 
 
 CHAPTER VI. 
 Smokeless Furnaces 51 
 
 CHAPTER VII. 
 Wilsey Fuel Economy Gauge.. 64 
 
 CHAPTER VIII. 
 Blonck Efficiency Meter 75 
 
 CHAPTER IX. 
 The Chain-Grate Stoker 90 
 
 CHAPTER X. 
 The Murphy Furnace 106 
 
 CHAPTER XI. 
 The Jones L T nder-Feed Stoker 119 
 
 CHAPTER XII. 
 Arches, Breeching, and Smoke-Stack 131 
 
 CHAPTER XIII. 
 Breeching and Chimney 140 
 
Furnace Efficiency 
 
 CHAPTER I. 
 
 In practically all steam-power plants the largest 
 single item of operating expense is the coal bill. If 
 we wish to run the plant economically it would seem 
 to be reasonable to try to save money where we spend 
 the most of it. But the history of operating engineer- 
 ing practice in the steam plant shows that this has not 
 been the case, at least not until very recently. The 
 engineer will spend much time and thought on his 
 engine, putting it in the best possible condition for 
 efficient operation; this is perfectly proper and is a 
 mark of the progressive engineer. Too often, how- 
 ever, his efforts at increased efficiency and economy 
 stop with the engine, in spite of the fact that in the 
 average plant dollars can be saved in the furnace room 
 where dimes are saved at the engine. 
 
 It has been said that necessity is the mother of 
 invention, and it is equally true that competition is the 
 mother of economy and efficiency. The operating 
 engineer is just beginning to feel the competition of 
 the big power and light companies, and that competi- 
 tion is going to become keener as time goes on. It is 
 no exaggeration to say that the central-station solici- 
 tor is after the engineer's job, and he will get it if he 
 :an show the boss that the big company will furnish 
 him with power cheaper than he can generate it in 
 his own plant. On the other hand, if the operating 
 engineer is progressive and up to the minute on all 
 
2 FURNACE EFFICIENCY 
 
 points affecting economy and efficiency of operation, 
 in most cases he will be able to show the power-plant 
 owner a set of figures on power cost which the cen- 
 tral-station man is unable to meet. It's all a question 
 of the most power for the least money, and unless the 
 operating engineer in the small plant can generate 
 power for a little less money than the central station 
 will supply it, his plant will be shut down and he will 
 be out of a job. 
 
 It is our purpose here to discuss some of the prob- 
 lems which arise in the furnace room and which are 
 vital to the economical operation of the plant. In the 
 past too little attention has been given to furnace 
 operation, with the result that in the average plant 
 large fuel waste has become the rule rather than the 
 exception. The statement that the majority of steam 
 plants waste 10 per cent of the coal used is probably 
 not far from the truth, while many " terrible exam- 
 ples " exist where as much as 40 per cent of the fuel 
 is wasted. Wouldn't it be worth while to reduce your 
 coal bill 10 per cent or more? It would make you 
 " solid " with the boss, and the central-station solicitor 
 wouldn't call the second time. 
 
 The function of a boiler furnace is to transform the 
 heat energy of the coal into a form available to the 
 boiler, and to deliver it in that form with the least 
 possible loss. The function of the boiler is to use this 
 energy in the generation of steam. Thus the furnace 
 and the boiler have different functions to perform, and 
 in all of our efforts toward economy of operation we 
 must recognize this fact. The efficiency of the furnace 
 is perhaps more influenced by the manner of its han- 
 dling than is the case with the boiler, and for that 
 reason the furnace offers the more fruitful field for 
 effort toward greater efficiency through increased care 
 in operation. We shall therefore devote the greater 
 part of our attention to the furnace. 
 
FURNACE EFFICIENCY 3 
 
 In the first place, if we wish to improve furnace 
 efficiency and so get more steam with less coal, we 
 must have some standard by which to judge the fur- 
 nace. In other words, we must be able to recognize 
 an efficient furnace when we see it. Most engineers 
 would say that an evaporative test is the best guide 
 to furnace efficiency, but this is not the case, because 
 the evaporative test depends upon both boiler and 
 furnace and is the measure of their combined effi- 
 ciency, while for the present, at least, we are inter- 
 ested only in the furnace. A boiler in bad condition, 
 covered with soot and lined on the inside with scale, 
 might give a low evaporation even when furnace effi- 
 ciency was reasonably good. Thus the evaporative 
 test is not the rule by which to measure furnace effi- 
 ciency. 
 
 One prominent engineer has defined an efficient 
 boiler furnace as one which completely consumes the 
 combustible in the fuel with least possible excess of 
 air. This is the proper test to apply to the furnace, 
 and the only one which tells us all we need to know 
 about it. It is not our purpose in this connection to 
 enter into a discussion of the theory of the combus- 
 tion process. A knowledge of the chemistry of com- 
 bustion may be desirable from an academic point of 
 view, but it doesn't require a chemist to operate a 
 boiler furnace efficiently any more than it requires 
 an expert in thermodynamics to run a steam engine. 
 
 The important question is : Are we burning all the 
 combustible in the fuel with just as small an excess 
 of air as possible? To answer this question we must 
 be able to analyze the gases of combustion coming 
 from the furnace. The practical engineer should not 
 become discouraged at the use of the word " analyze." 
 There is nothing about boiler-flue-gas analysis which 
 any engineer can not understand ; in fact, he can even 
 instruct his fireman how to make the analyses. 
 
4 FURNACE EFFICIENCY 
 
 Every engineer knows that the chief combustible 
 part of coal is carbon. The burning of coal in the 
 furnace is practically nothing more than the combin- 
 ing of this carbon with the oxygen of the air. Air is 
 only about 21 per cent oxygen, the remaining 79 per 
 cent being mostly nitrogen, which takes no part in the 
 burning. The function of the nitrogen in the air is 
 merely to dilute the oxygen. When carbon unites 
 with oxygen it forms a gas, called carbon dioxid, rep- 
 resented by the symbol CO 2 , which means one part 
 of carbon and two parts of oxygen. This carbon 
 dioxid will therefore be present in the gases coming 
 from the furnace, and it is the amount of this CO 2 
 in which we are chiefly interested in the flue-gas 
 analysis. 
 
 If all the 21 per cent of oxygen which the air con- 
 tains were to be consumed in the furnace and turned 
 into CO 2 , then the products of combustion coming 
 from the fire would contain just 21 per cent of this gas. 
 That is, if just the proper amount of air were supplied 
 and if all the combustible in the coal were consumed, 
 the flue gases would contain 21 per cent of CO 2 . But 
 in actual practice it is never possible to realize this 
 ideal condition, due chiefly to the fact that the oxygen 
 of the air can not be brought into close enough con- 
 tact with all of the combustible of the fuel to produce 
 complete combustion unless there is some extra air 
 present. The result is that in all boiler-furnace prac- 
 tice an excess of air is always allowed to pass into 
 the furnace, so as to make sure that all of the com- 
 bustible in "the fuel will be burned. An excess of 
 40 per cent to 50 per cent represents good practice, 
 but many times it runs up to 100 per cent, 200 per 
 cent, and even higher. Suppose that 100 per cent 
 excess air is being used ; this means that just twice 
 as much air is passing into the furnace as is needed 
 under ideal conditions to completely burn the fuel. 
 
FURNACE EFFICIENCY 5 
 
 Under these conditions the gases coming from the 
 furnace will contain only half as much CO 2 as before, 
 because one-half of the air is passing through the 
 furnace unchanged. That is, the CO 2 will now be 
 only Wy 2 per cent instead of 21 per cent. Joseph W. 
 Hays, a well-known expert on combustion engineer- 
 ing, illustrates this point as follows : Suppose that a 
 quart of milk contains 21 per cent of cream; now if 
 \ve add one quart of water to the milk we shall have 
 no more cream than before, but we shall have two 
 quarts of " near " milk. Therefore, the cream is now 
 only I0y 2 per cent of the whole, or just one-half of 
 what it was before. 
 
 The point that must be clearly understood here is 
 that the percentage of CO 2 in the flue gases is a direct 
 index of the amount of excess air which is passing 
 through the furnace. Suppose that the flue gas shows 
 7 per cent CO 2 ; the percentage of excess air under 
 these conditions may be calculated as follows: 
 
 21 ~ 7 X 100 == 200 per cent excess. 
 
 Subtract the observed percentage of CO 2 from 21 ; 
 divide this remainder by the percentage of CO 2 ; mul- 
 tiply this result by 100. Thus the flue gas analysis 
 provides a convenient method for measuring the effi- 
 ciency of the furnace, because, as we have seen, the 
 efficient furnace is one which consumes the com- 
 bustible in the fuel with the least possible excess 
 of air. 
 
 Let us examine this definition of an efficient fur- 
 nace and see, if possible, why excess air reduces fur- 
 nace efficiency. A brief study of the chemistry of 
 the combustion process shows that it requires about 
 10>^ pounds of air to burn 1 pound of coal. Of course, 
 this differs somewhat with different coals, but 
 
6 FURNACE EFFICIENCY 
 
 pounds is a fair average figure. If in addition we allow 
 for an excess of, say, 50 per cent, there will be 15^4 
 pounds of air passing through the furnace for every 
 pound of coal thrown onto the grate. This excess air, 
 5^4 pounds per pound of fuel, passes through the fur- 
 nace and up the smokestack unchanged, except in 
 one important particular. Its temperature has been 
 raised. The average yearly temperature of the air 
 entering the furnace is probably not far from 60 F., 
 while the temperature of the flue gases in uptake or 
 breeching is about 500 F. or more. Hence this excess 
 air, which hasn't helped the combustion any, and has 
 done no useful work, has had its temperature raised at 
 least 440 F., and this takes heat. When the air excess 
 is 50 per cent, as assumed above, it takes approxi- 
 mately 13 per cent of the total heat in the fuel to heat 
 up this air, together with the nitrogen contained in 
 the air actually used. The writer has tested boiler 
 furnaces which showed CO 2 as low as 3 per cent ; this 
 means about 600 per cent excess air, with a loss of 
 approximately 75 per cent of all the heat in the fuel. 
 A furnace operated in such a manner has no place 
 in a steam plant; it is really a hot-air heating plant 
 for all outdoors. 
 
 One point to be kept in mind in connection with 
 heat losses through excess air is the fact that as the 
 percentage of CO 2 in the flue gases goes down, the 
 heat loss goes up, but not proportionally. Suppose, 
 for example, that a test shows 12 per cent CO 2 ; this 
 means about 75 per cent excess air, and will cause a 
 loss of about 17^2 per cent of the fuel. Now if the 
 CO 2 be raised to 13 per cent, the air excess becomes 
 about 61.5 per cent and the heat loss 16 per cent. 
 Thus a gain of 1 per cent in CCX causes a saving of 
 \y 2 per cent in the fuel. On the other hand, take 
 the case of 3 per cent CO 2 cited above ; this means 
 600 per cent excess air and a loss of at least 75 per 
 
FURNACE EFFICIENCY 7 
 
 cent of the total heat of the fuel. Now if the CO 2 
 can be increased to 4 per cent, we shall have an air 
 excess of 425 per cent and a heat loss of about 58 per 
 cent. Thus an increase of 1 per cent in CO 2 means a 
 saving in heat of approximately 17 per cent. So the 
 value of 1 per cent of CO 2 depends very largely upon 
 where it is. When it is as low as 3 per cent or 4 per 
 cent, any earnest effort to decrease air excess is almost 
 sure to result in increased economy, while if CO, is 
 in the neighborhood of 12 per cent to 14 per cent, 
 large increase in economy is not possible. 
 
 Volumes of hot air escaping at the top of the 
 smokestack can not be detected by the eye, and for 
 this reason the question of air excess has received 
 much less attention at the hands of the engineer than 
 it deserves. All other furnace losses are practically 
 sure to be small compared with this one, and yet it 
 is the last one to receive attention. If the power-plant 
 owner, or any one else in authority, should happen to 
 discover a large amount of unburned coal in the ashes 
 from the plant, the engineer would be very likely to 
 receive a call from the office and be asked to explain 
 why he is wasting fuel. Now it may be that the engi- 
 neer is a thoroughly competent man and is operating 
 his plant at maximum efficiency, but the boss can 
 see that coal in the ashes, and it looks like poor econ- 
 omy to him. But let us consider a minute and we 
 may see that the man in the plant is a better engineer 
 than the man in the office. One of the most fruitful 
 sources of excess air is holes in the fire; if the fire 
 burns through in spots vast quantities of cold air 
 rush through the holes and furnace efficiency is seri- 
 ously impaired. To prevent holes in the fire it is 
 often necessary to carry a slightly thicker bed of fuel 
 on the grates than would otherwise be necessary. 
 This is particularly true of the chain-grate stoker, 
 which is coming into such general use, The fuel bed 
 
8 FURNACE EFFICIENCY 
 
 must be thick enough to prevent the fire from burning 
 off at the back of the grate. It is good economy to 
 do this even at the expense of running some unburned 
 coal off the end of the grate into the ash pit. As much 
 as 50 per cent combustible in the ash may be more 
 economical and an evidence of better operating engi- 
 neering than an ash pit which shows no combustible 
 at all. 
 
 Questions and Answers. 
 
 Q. What is the function of a boiler furnace? 
 
 A. To transform the heat energy of the coal into 
 a form available to the boiler. 
 
 Q. What is the function of the steam boiler? 
 
 A. To take the heat from the furnace and use it 
 in the generation of steam. 
 
 Q. Is the evaporative test a good one to deter- 
 mine furnace efficiency? 
 
 A. No. 
 
 Q. Why not? 
 
 A. Because evaporation depends upon both fur- 
 nace and boiler, and is a measure of their combined 
 efficiency. 
 
 Q. How may we define an efficient furnace? 
 
 A. An efficient furnace is one which consumes all 
 the combustible in the fuel with the least possible 
 excess of air. 
 
 Q. How can we tell how much excess air a fur- 
 nace is getting? 
 
 A. By an analysis of the gases coming from the 
 fire. 
 
 Q. What is the chief combustible part of coal? 
 
 A. Carbon. 
 
 Q. In the combustion process, what becomes of 
 this carbon? 
 
 A. It unites with the oxygen of the air to form 
 carbon dioxid, CO 2 . 
 
FURNACE EFFICIENCY 9 
 
 Q. What is the maximum amount of CO 2 that it 
 is possible to have in the boiler furnace gases? 
 
 A. 21 per cent. 
 
 Q. Is this ever realized in practice? 
 
 A. No ; excess air is always used, and this reduces 
 the percentage of CO 2 . 
 
 Q. What is the effect of excess air on furnace 
 efficiency? 
 
 A. It reduces the efficiency. 
 
 Q. Why is this? 
 
 A. Because of the large amount of heat required 
 to heat the excess air. 
 
 Q. How can the percentage of excess air be calcu- 
 lated from the CO 2 in the flue gases? 
 
 A. Subtract the percentage of CO 2 from 21 ; 
 divide the remainder by the percentage of CO 2 ; mul- 
 tiply this result by 100. 
 
 Q. What percentage of C(X represents good prac- 
 tice? 
 
 A. From 12 per cent to 14 per cent. 
 
 Q. Why is excess air such a common cause of 
 low furnace efficiency? 
 
 A. Because it can not be seen, and its effect is 
 therefore not readily realized. 
 
 Q. How much heat is lost in this way? 
 
 A. From 12 per cent to 75 per cent of the total 
 heat in the fuel. 
 
 Q. Does unburned coal in the ashes mean as large 
 a loss as excess air? 
 
 A. No; 50 per cent combustible in the ash may 
 be more economical than holes in the fire, which 
 cause large excess of air. 
 
10 FURNACE EFFICIENCY 
 
 CHAPTER II. 
 
 It has been shown that the only reliable index of 
 furnace efficiency, as distinguished from combined 
 furnace and boiler efficiency, is to be found in the flue- 
 gas analysis. The question of how to make this 
 analysis is therefore one of importance, and should be 
 understood by every engineer. 
 
 Perhaps the best known and most widely used 
 equipment on the market for this purpose is the Orsat 
 gas-analysis apparatus, as shown in Fig. 1. As usually 
 made, this apparatus is designed to test for carbon 
 dioxid (CO 2 ), oxygen and carbon monoxid (CO). The 
 essential parts of the apparatus are the three U-shaped 
 bottles, A, B and C; the measuring burette D, and 
 the leveling bottle E. It will be seen from the figure 
 that the bottles A, B and C really consist of two bot- 
 tles each, connected at the bottom with a bent tube of 
 glass. Also it will be noted that the bottle on one 
 side is closed with a rubber stopper, through which a 
 small glass tube passes to act as an air vent, while 
 the other bottle has a long glass stem provided with 
 a plug cock of ground glass. The measuring burette 
 is provided with a scale, reading in cubic centimeters, 
 the capacity of the burette being 100 cu. cms. The 
 zero of the scale is at the bottom, where it will be seen 
 that the burette is made of comparatively small diam- 
 eter, so as to give a more open scale. At its top the 
 burette D is drawn down into a small tube and con- 
 nected with a piece of rubber tubing H to the glass 
 header F, G. This header is a tube of very small bore, 
 so that its capacity is negligible as compared with that 
 of the measuring burette D, 
 
FURNACE EFFICIENCY 
 
 11 
 
 The leveling bottle E is connected with a rubber 
 tube to the bottom of the burette D. This is for the 
 purpose of drawing flue gas into the measuring bu- 
 
 FIG. i. 
 
 rette and expelling it again, which is done by lowering 
 or raising the leveling bottle. Each of the U-shaped 
 treating bottles, A, B and C, is connected to the glass 
 
12 FURNACE EFFICIENCY 
 
 header F, G, so that they may be connected to the 
 source of gas supply at F or to the measuring burette 
 D as may be desired. 
 
 The treating bottle A contains a solution of caustic 
 potash, which removes the CO 2 from the flue gas. 
 Bottle B contains a solution of potassium pyrogallate, 
 which removes the free oxygen from the gas, and bot- 
 tle C contains a saturated solution of cuprous chlorid 
 for removing CO. These chemicals may be obtained 
 at any chemical supply house, and at most drug stores. 
 The solutions may be prepared as follows : 
 
 The caustic potash solution may be prepared by 
 dissolving one pound of commercial caustic potash 
 in 1,000 c. c. of water. Considerable heat is evolved 
 when the potash is dissolved in the water, and for 
 that reason the bottle should be placed where no dam- 
 age will be done if it should break. Care should be 
 taken to keep the potash solution from coming into 
 contact with the hands or the clothing. It is a power- 
 ful alkali, which is extremely unpleasant when it gets 
 on the hands, and will destroy the clothing almost as 
 quickly as an acid. When the solution is cold it should 
 be put into a stock bottle, which can be drawn on from 
 time to time as needed. 
 
 To make the potassium pyrogallate, take 100 c. c. 
 of the potash solution already prepared and add to it 
 five grams of pyrogallic acid. This acid comes in the 
 form of a white powder, which dissolves readily in 
 the potash solution. After a little experience it will 
 not be necessary to weigh the five grams of pyrogallic 
 acid, as the proper amount can be estimated with suffi- 
 cient accuracy by simply pouring it into the palm of 
 the hand. It must be remembered that this " pyro " 
 solution has a strong affinity for oxygen, and hence 
 it must be kept away from the air in a stoppered bottle. 
 
 The cuprous chlorid solution for removing the CO 
 is the most difficult of all the reagents to prepare, and 
 
FURNACE EFFICIENCY 13 
 
 is, perhaps, the most unsatisfactory in its action. First 
 prepare about two liters of dilute hydrochloric acid, 
 specific gravity 1.10, by diluting muriatic acid with an 
 equal volume of water. Then select a large bottle of 
 at least two liters capacity and cover the bottom about 
 */2 inch deep with copper oxid. Then add a number of 
 pieces of copper wire long enough to reach from the 
 bottom to the top of the bottle. These wires should 
 make a bundle about an inch in diameter. Now fill 
 the bottle with the dilute hydrochloric acid and wait 
 for the copper to dissolve in the acid. Shake the bottle 
 occasionally, to keep the contents well mixed. When 
 the solution has become colorless, or nearly so, it 
 should be poured into a smaller stock bottle ready for 
 use. This stock bottle should contain some pieces of 
 copper wire to keep the solution saturated. Many 
 chemical supply houses keep this cuprous chlorid solu- 
 tion in stock, and the average user will probably find 
 it more satisfactory to buy the solution already pre- 
 pared, when possible. It must be protected from both 
 air and sunlight, which cause it to become weak and 
 turn dark. 
 
 All the reagents having been prepared, the appa- 
 ratus can now be made ready for the flue-gas test. 
 Pour the caustic potash into treating bottle A until 
 the solution stands about half way up in both limbs 
 of the bottle. Pour bottles B and C half full with 
 " pyro " and cuprous chlorid respectively. We must 
 now bring the solutions in the front limb of the treat- 
 ing bottles to exactly the same level. The proper 
 level is indicated by a mark on the glass stem at the 
 top of the bottle. The bore of the stem at this point 
 is very small, so that a slight inaccuracy in the level 
 of the solution will not cause any appreciable error. 
 Suppose that we wish to raise the solution in the 
 front limb of bottle A to the mark on the glass stem. 
 Open the valve K in the header F, G and raise the 
 
14 FURNACE EFFICIENCY 
 
 leveling bottle E. This will fill the measuring burette 
 D with water, the air which it contains being forced 
 out at F. Now close the valve K and open the one 
 over bottle A, marked R. Lower the leveling bottle 
 E, causing the water level to fall in burette D. This 
 will reduce the pressure over the solution in the front 
 limb of bottle A and the liquid will rise there, and fall 
 in the rear limb. Continue to lower the leveling bot- 
 tle until the solution reaches the mark on the stem, 
 and then close valve R. In the same way the solu- 
 tions in the other treating bottles should be brought 
 to the proper level. The apparatus is now ready to 
 make the analysis. 
 
 Slip a piece of rubber tubing over the end of the 
 glass tube at F and connect the free end of the tube 
 to the pipe which is to supply the flue gas. A pinch 
 cock on this rubber tube will be of service. The three- 
 way cock K should then be opened, while cocks R, S 
 and T are closed. Raise the leveling bottle E, thus 
 filling the burette D with water and forcing all the 
 air out at W. Raise the leveling bottle until water 
 reaches the point G, but do not force any of it out at 
 W. Now turn the three-way cock K so as to open 
 up to the pipe from the flue connected at F. The out- 
 let at W will then be closed. Lower the bottle E and 
 thus draw in a charge of gas from the flue. Continue 
 to lower the leveling bottle until the water in the 
 measuring burette D falls below the level of the zero 
 on the scale. Now place the pinch cock on the rubber 
 tube connected at F, thus closing the connection to 
 the flue. Open cock K to the atmosphere and slowly 
 raise the leveling bottle E until the water in burette 
 D reaches the zero on the scale. This will force a 
 small amount of gas out at W, and we shall have left 
 just 100 c. c. under atmospheric pressure. Close the 
 three-way cock K. 
 
 Thus far our attention has been confined to getting 
 
FURNACE EFFICIENCY 15 
 
 a sample of gas for analysis. We shall now proceed 
 with the analysis itself. Open the cock R, raise the 
 leveling bottle E, and thus force the gas sample out 
 of the burette D and into the treating bottle A con- 
 taining the caustic potash solution. The potash will 
 be forced almost entirely out of the front limb of the 
 bottle and into the rear one. In most forms of the 
 Orsat apparatus the front limb of the treating bottle 
 is filled with a bundle of small glass tubes. These 
 tubes become wet with the chemical and offer a large 
 surface for absorption of the gas. Allow the gas to 
 remain in treating bottle A for about a half minute, 
 then lower the leveling bottle and draw the gas back 
 into the measuring burette. This will cause the solu- 
 tion to rise again in the front limb of bottle A and 
 wet the small glass tubes on the inside with fresh 
 potash. Then force the gas back again into A and 
 repeat the operation several times. In order to get 
 a complete absorption of CO 2 the gas must be kept 
 well agitated, which can be accomplished by passing 
 the gas frequently between the burette and the treating 
 bottle. 
 
 When it is thought that the CO 2 has been all 
 absorbed, pass the gas back into D, lowering E until 
 the solution in A rises to the mark on the stem where 
 it was before. Close cock R. Now bring the surface 
 of the water in E to the same level as that in D. This 
 can be done by sighting across the surface of the water 
 in E and is for the purpose of insuring normal atmos- 
 pheric pressure on the gas remaining in D. It will 
 be noted that there is less gas than before, the water 
 level now standing above the zero of the scale. If the 
 water level stands at 10 on the scale it means that 
 10 c. c. of CO 2 has been absorbed, which is 10 per 
 cent of the total 100 c. c., with which we started. The 
 gas may now be passed into bottle A again, and if 
 when it is returned to D the water level still stands 
 
16 FURNACE EFFICIENCY 
 
 at 10 on the scale, one may be sure that all the CO 2 is 
 absorbed. 
 
 The remaining gas is next passed into bottle B, 
 where the free oxygen is absorbed. The procedure is 
 exactly the same as for CO 2 . Suppose that after all 
 the oxygen has been absorbed the scale reads 19.5 per 
 cent. This means that CO 2 plus oxygen equals 19.5 
 per cent ; but since the CO 2 has already been shown to 
 be 10 per cent, it leaves 9.5 per cent for oxygen. 
 
 Next pass the gas into bottle C, where the CO is 
 absorbed. This gas is usually present in flue gases, 
 in very small quantities, if at all, and its determination 
 must be made with care to insure accuracy. The 
 method is exactly the same as for the other gases. If 
 the reading on the scale after the CO has been ab- 
 sorbed is 20^4 per cent, the amount of CO is evidently 
 20>4 l9*/2 = 24 per cent, the 19^ per cent being 
 the sum of CO 2 and oxygen already determined. 
 
 The chemical reagents used with the Orsat appa- 
 ratus will wear out after a time and must be replaced. 
 The caustic potash solution will absorb about forty 
 times its volume of CO . If the treating bottle A con- 
 tains 100 c. c. of the po"tash, it will dissolve 40 X 100 
 = 4,000 c. c. of CO 2 . If the average amount of CO 2 
 in the flue gas were 10 per cent, that is, 10 c. c. to every 
 100 c. c. of gas, then the caustic potash would be good 
 for about four hundred tests. 
 
 The capacity of the potassium pyrogallate solution 
 to absorb oxygen is much less, 1 c. c. of the " pyro " 
 being able to absorb only 2 c. c. of oxygen. If we 
 assume again 10 per cent CO 2 and about 10 per cent 
 of oxygen as the average, then the potassium pyro- 
 gallate must be replaced after twenty tests. 
 
 The cuprous chlorid will absorb only its own vol- 
 ume of CO, but since the CO is present in flue gas in 
 such small quantities the solution is good for a large 
 number of tests, provided it is not exposed to air and 
 
FURNACE EFFICIENCY 17 
 
 sunlight. It is well not to work the solutions to the 
 limit, but to replace them when they begin to grow 
 weak. Weakness of the solutions will be indicated 
 by an increasing amount of time required to complete 
 the absorption of the various gases. 
 
 One very important point in flue-gas analysis is 
 the obtaining of a sample for test which shall be a 
 fair average of all the gas in the flue. A number of 
 rather elaborate and costly devices for drawing off 
 the test sample have been devised, none of which the 
 average engineer is likely to use. The writer is of the 
 opinion that a single pipe or tube, open at the end, and 
 perforated throughout a portion of its length, will give 
 a very fair average sample of the gas. This pipe should 
 be placed in the boiler pass, uptake, breeching, or wher- 
 ever the gas sample is to be drawn, with its open end 
 at the point where the gas velocity is greatest. Wher- 
 ever the pipe is inserted care must be taken not to 
 allow a large leakage of air into the boiler setting to 
 dilute the sample. If the pipe is inserted through an 
 inspection or a clean-out door, don't leave the door 
 ajar. Use every possible precaution to keep the air 
 out. If the sampling pipe is inserted through a hole 
 in the breeching, make the hole just large enough for 
 the pipe. 
 
 When drawing a sample in this way for use with 
 the Orsat apparatus, care must be taken to draw all 
 the air from the pipe and its rubber hose connection 
 before beginning to make an analysis. This can best 
 be done by discarding the first four or five samples 
 of gas which are drawn into the apparatus by simply 
 discharging them through the three-way cock K, Fig. 
 1, into the atmosphere. In this way all the air in the 
 sampling pipe and its connection is drawn out and a 
 good sample of gas obtained. 
 
 Fig. 2 shows an extremely compact and handy flue- 
 gas apparatus designed by Mr. Joseph W. Hays. It 
 
18 
 
 FURNACE EFFICIENCY 
 
 FIG. 2. 
 
 consists of measuring burette, reagent bottles for de- 
 termination of CO 2 , oxygen and CO, much the same 
 as the Orsat apparatus. The leveling bottle L is con- 
 nected to the bottom of the measuring burette B and 
 
FURNACE EFFICIENCY 19 
 
 is used in exactly the same way as in the Orsat. One 
 good feature of this apparatus is the rubber tube and 
 bulb A, connected between the top of the measuring 
 burette and the gas-sampling pipe. With the leveling 
 bottle L filled with water, gas may be drawn from the 
 flue through the measuring burette B by simply press- 
 ing bulb A until it bubbles through the water in L. 
 In this way a large amount of gas may be drawn 
 through the apparatus and discharged until a good 
 sample of gas is obtained. This Hays apparatus is 
 smaller and more compact than the Orsat, contains 
 less glass, and is therefore not so easily broken, and 
 is put up in portable form. 
 
 Questions and Answers. 
 
 Q. What is the best known apparatus for boiler- 
 flue-gas apparatus? 
 
 A. The Orsat. 
 
 Q. What gases are usually determined with this 
 apparatus? 
 
 A. CO.,, CO and free oxygen. 
 
 Q. What chemicals are used to dissolve or absorb 
 these gases? 
 
 A. Caustic potash for CO 2 , potassium pyrogallate 
 for oxygen, and cuprous chlorid for CO. 
 
 Q. How large a sample of flue gas is tested in the 
 Orsat apparatus? 
 
 A. 100 c. c. 
 
 Q. How is this gas sample measured? 
 
 A. In a graduated measuring burette. 
 
 Q. What important point must be kept in mind 
 when measuring the gas? 
 
 A. To measure it under atmospheric pressure. 
 
 O. How can this be done? 
 
 A. By having the three-way cock open to the 
 atmosphere when the final leveling is made. 
 
20 FURNACE EFFICIENCY 
 
 O. Before beginning the test where must the 
 chemicals stand in the reagent bottles? 
 
 A. The surface of the chemical must stand at the 
 mark on the neck of the bottle. 
 
 Q. Must the chemicals be brought back to this 
 same point when the test is finished? 
 
 A. Yes. 
 
 Q. How much CO 2 - will caustic potash absorb? 
 
 A. About forty times its volume. 
 
 Q. How much oxygen will potassium pyrogallate 
 absorb? 
 
 A. Twice its volume. 
 
 Q. How much CO will cuprous chlorid absorb? 
 
 A. An amount equal to its volume. 
 
 Q. How should the gas be drawn from the flue? 
 
 A. Through a single pipe, open at the end and 
 perforated for a portion of its length. 
 
 Q. Will the first charge drawn into the Orsat 
 apparatus be a fair sample of the gas? 
 
 A. No ; it will probably contain air drawn from 
 the sampling pipe. 
 
 Q. What should be done with this first sample of 
 gas? 
 
 A. It should be blown out to the atmosphere 
 through the three-way cock. 
 
 Q. How many charges should be wasted in this 
 way? 
 
 A. Probably four or five; at least until the oper- 
 ator is sure that all the air has been drawn from the 
 sampling pipe. 
 
FURNACE EFFICIENCY 21 
 
 CHAPTER III. 
 
 It has been shown that the most efficient boiler 
 furnace is the one that consumes all the combustible 
 in the fuel with the least excess of air. It has also 
 been explained that only by means of the flue-gas 
 analysis can the engineer tell how much excess air 
 is passing through his furnace. We shall assume, 
 then, that these two facts are well understood, and 
 also that the method of making the flue-gas test, as 
 explained in Chapter II, is fully mastered. Let us now 
 consider how an engineer can make a practical appli- 
 cation of these principles to improve the efficiency of 
 his boiler furnace. 
 
 He must first supply himself with a hand flue-gas 
 instrument, of which there are a number of good 
 makes on the market, the average cost of which is 
 probably not far from $30. A good, reliable draft 
 gauge will be found extremely desirable, and will 
 probably cost about $10. A thermometer to give the 
 temperature of the flue gases will be of much assist- 
 ance; instruments specially designed for this pur- 
 pose are on the market, but any reliable thermometer 
 can be used, and will prove less expensive than the 
 special flue-gas instrument. A thermometer suffi- 
 ciently accurate for all practical purposes can prob- 
 ably be bought for about $5. These three items of 
 expense will comprise the whole outlay for apparatus, 
 and if properly used the instruments will pay for 
 themselves many times over in reduced coal bills. 
 
 Begin with the flue-gas apparatus, to determine 
 just what kind of a furnace you have, whether good, 
 
22 FURNACE EFFICIENCY 
 
 bad or indifferent, from a standpoint of efficiency. 
 Make a flue-gas test on the boiler side of the damper ; 
 if the conditions are about as they are in the average 
 plant, about 7 per cent or 8 per cent of CO 2 will be 
 found in the flue gases. Now put the sampling pipe 
 into the first pass of the boiler if it be a water-tube 
 boiler, or at the rear tube sheet if it be a horizontal 
 tubular boiler. This will give a sample of the fur- 
 nace gases just as they leave the combustion space 
 of the furnace and before they come into contact with 
 the heating surfaces of the boiler. It will probably 
 be found that the percentage of CO 2 at this point is 
 somewhat greater than was found just below the 
 damper. The only explanation for this state of affairs 
 is that the furnace gases are being diluted as they pass 
 through the boiler. This dilution of the gases is 
 caused by air leaking into the setting through cracks 
 in the brickwork. It is easy to underestimate the 
 amount of this air leakage, many engineers believing 
 that it has practically no effect upon furnace efficiency. 
 Unless your brickwork is better than the average, you 
 will probably find from 1 per cent to 2 per cent less 
 CO 2 at the damper than at the first pass, and this 
 difference is due entirely to air leakage. 
 
 If this is found to be the case, attention must be 
 given to the brickwork, to make it just as nearly air- 
 tight as possible. When it is remembered that the 
 average air pressure inside the setting is about ^2 
 inch of water below atmosphere, and that all the 
 cracks and holes in the brickwork are trying to sat- 
 isfy that partial vacuum, an idea may be gained of how 
 large an amount of air gets in in this way. 
 
 These leaks must be located and stopped. Take 
 a coal oil torch and go carefully over all the brick- 
 work; whenever a leak is found the flame will be 
 drawn into the crack, showing that air is passing in 
 at that point. Examine particularly around clean-out 
 
FURNACE EFFICIENCY 23 
 
 and inspection doors, along the line where the brick- 
 work closes in around the shell in the case of a tubu- 
 lar boiler, and at all points where for any reason the 
 brickwork may be defective. If there are two or 
 more boilers set in a battery, and the boiler next to 
 the one under examination is " dead," examine the 
 dividing wall with care. Frequently these walls are 
 poorly built and serious leakage may occur through 
 them when one boiler is out of service. 
 
 The moment a leak is discovered, stop it up. A 
 pail of whitewash, into which some glue has been dis- 
 solved, will make a good filler for the cracks. Paint 
 the brickwork over generously with this solution 
 wherever a crack is found, care being taken to work 
 it well into the holes. When dry, test again with 
 the torch to make sure that the leak has been stopped. 
 This will require considerable patience and involve 
 work, but there is no doubt but that in the average 
 boiler plant it will mean a saving in coal large enough 
 to make all the work and trouble decidedly worth 
 while. 
 
 Many engineers are so convinced of the importance 
 of a tight boiler setting that they provide a complete 
 insulating covering for the brickwork. Such a cov- 
 ering may be made as follows : Cover the surface of 
 the setting with a layer of asbestos cement or plaster- 
 from 1 inch to 2 inches thick; cover this plaster with 
 canvas and then apply a generous coat of paint to the 
 canvas. This produces a setting which is as near air- 
 tight as it is possible to make it, and while it is con- 
 siderably more expensive than filling the cracks with 
 whitewash and glue, it makes a much more finished 
 job and will last a considerable length of time. 
 
 When the leaks in the setting have been stopped 
 it will be found that the CCX at the damper is prac- 
 tically the same as at the first pass. But even yet the 
 percentage of CO 2 may be less than it should be and 
 
X 
 
 24 FURNACE EFFICIENCY 
 
 it will be necessary to look further for the causes of 
 excess air. In this connection a careful study of draft 
 conditions will be of great importance, for it will 
 assist in arriving at the most efficient operating con- 
 ditions. 
 
 Draft, as every engineer knows, is caused by the 
 difference in weight between the hot gases inside the 
 smoke stack and a column of air of equal height and 
 diameter outside of the stack. There is, therefore, a 
 difference in pressure between the inside of the fur- 
 nace and the outside, and this difference in pressure 
 forces air through the furnace and boiler and up the 
 chimney. The function of the draft is therefore to 
 supply air to burn the fuel, and in general the greater 
 the draft the more fuel can be burned. If the draft 
 in any particular case is too great, an excessive amount 
 of air will be forced through the fuel bed; portions 
 of the grate will be burned bare of coal, producing 
 holes in the fire, through which large quantities of 
 air will rush, thus further increasing the excess. If 
 the draft is insufficient, the combustion will be incom- 
 plete with the formation of smoke and CO in the flue 
 gases, and it will be impossible to carry the load. 
 
 In order to determine what is the proper draft for 
 a particular boiler operating under given load con- 
 ditions, a series of tests must be made with the flue- 
 gas apparatus and the draft gauge. The tendency in 
 many cases is to use too much draft rather than too 
 little, with the result that too great an excess of air 
 is drawn through the fuel bed. Measure the draft 
 over the fire and at the same time make an analysis 
 of the combustion gases from the first pass of the 
 boiler. Then either increase or decrease the draft 
 very slightly by opening or closing the damper 
 respectively, and again observe draft and CO.,. If the 
 CO., has increased you are moving in the right direc- 
 tion ; if not, move' in the opposite direction. In this 
 
FURNACE EFFICIENCY 25 
 
 way, by making very small changes each time, dis- 
 cover what draft gives the highest possible percentage 
 of CO., consistent with satisfactory operation. You 
 must, of course, carry your load, no matter what hap- 
 pens to the CO 2 , and the draft must not be reduced to 
 the point where the steam gauge begins to fall. Also, 
 when reducing the draft, watch for CO in the flue 
 gases; this indicates incomplete combustion, and 
 marks the point beyond which draft reduction must 
 not be carried. 
 
 By a careful study of flue gas and draft it will thus 
 be discovered what is the proper draft for maximum 
 efficiency with your particular load. Note the posi- 
 tion of the damper and keep it there as long as the load 
 remains the same. When the load changes, a differ- 
 ent draft and a different position of the damper will 
 be necessary. An engineer should know accurately 
 how much draft is required for a light, medium and 
 heavy load, and should siee that the damper is kept in 
 the proper position to give that draft. Of course, it 
 is much easier to operate under all conditions of load 
 with a wide-open damper, but it is wasteful of coal, 
 and coal costs money. 
 
 In changing the draft to meet varying conditions 
 of operation, it is usually better to do it with the 
 damper as suggested above, rather than with the ash- 
 pit doors. If the draft is varied by means of the 
 ash-pit doors while the damper remains wide open all 
 the time, the full draft of the stack is pulling on the 
 furnace continually. If the ash-pit doors are nearly 
 closed, the effect of such an arrangement is to greatly 
 increase the amount of air drawn into the furnace at 
 all other points. The amount of air drawn in over the 
 fire, as well as that getting in at any imperfect places 
 in the setting, will be increased. On the other hand, if 
 the damper be partly closed when less draft is desired, 
 the " pull " of the stack will be reduced, which will 
 
26 FURNACE EFFICIENCY 
 
 cause a proportional drop in the draft at all parts of 
 the setting. Thus the same relative amounts of air 
 will be drawn in over the fire and under it as before, 
 so that combustion conditions will remain about as 
 they were. 
 
 The relation between air admitted through the fire 
 to that admitted over it is one that must be deter- 
 mined by each engineer for his particular conditions. 
 It will vary considerably with the method of firing 
 and the kind of fuel used. A bituminous coal which 
 has a high volatile content and which is fired by hand 
 requires a considerable amount of air over the fire. 
 When a charge of such coal is thrown into the fur- 
 nace a large volume of volatile combustible gas is 
 distilled. Considerable air must be admitted over the 
 fire to consume this gas, otherwise CO and smoke 
 will be produced. When the volatile gas has all been 
 consumed and only fixed carbon remains, the air com- 
 ing through the fire will be 'sufficient for combustion 
 and that coming in over the fire may be shut off. 
 Thus in a hand-fired furnace the amount of air over 
 the fire must be changed from time to time to suit 
 conditions. Here again the flue-gas apparatus will be 
 a reliable indicator of furnace conditions. Too much 
 air over the fire will be just as serious from a stand- 
 point of efficiency as too much through it. Discover 
 by means of the flue-gas test the proper manner of air 
 control for your furnace and then stick to it. 
 
 It has been pointed out that too much draft has a 
 tendency to burn holes in the fire through which a 
 large amount of air passes, diluting the furnace gases 
 and reducing efficiency. The remedy is to reduce the 
 draft and carry a thicker fire. In the case of a boiler 
 under very light load it may happen that if the fire 
 is thickened much the safety valve will blow off, while 
 if the draft is reduced enough to prevent holes in the 
 fire imperfect combustion and smoke will result. 
 
FURNACE EFFICIENCY 27 
 
 This is an extremely difficult condition under which 
 to operate a boiler furnace efficiently, because there 
 is too much grate surface for the work required of 
 the furnace. If the boiler operates habitually under 
 such a light load, steps should be taken to reduce the 
 grate area. If, however, the underload occurs only 
 for a comparatively small portion of the time, all that 
 can be done to improve efficiency is to reduce the draft 
 as much as practicable and then carry as uniform a 
 fire as possible, care being taken to prevent holes. 
 
 A boiler served with a chain-grate stoker and 
 operated under a light load is almost sure to show 
 inefficient combustion. A bare space a foot or more 
 in width will be seen at the back of the grate as well 
 as holes here and there in the fire. Since the grate 
 surface can not be reduced, there is no remedy except 
 to increase the load. In fact, with water-tube boilers 
 and chain-grate stokers it may be put down as a prac- 
 tically invariable rule that it is good economy to oper- 
 ate one unit at 50 per cent or more overload than two 
 units at 75 per cent of rating. 
 
 In all questions about air supply to a boiler fur- 
 nace, rely on the flue-gas apparatus to give the correct 
 answer. 
 
 Questions and Answers. 
 
 Q. Where should a flue-gas sample be taken for 
 analysis to show combustion conditions? 
 
 A. Usually on the boiler side of the damper. 
 
 Q. What would a test at the first boiler pass 
 show ? 
 
 A. The quality of the gas as it comes from the 
 fire. 
 
 Q. Will there be any difference in the gas at these 
 two points? 
 
 A. Yes; the CCX will usually be higher at the 
 first pass than at the damper. 
 
28 FURNACE EFFICIENCY 
 
 Q. What is the reason for this? 
 
 A. Infiltration of air through the setting. 
 
 Q. How may the leaks in the setting be located? 
 
 A. With a flaming torch ; the flame will be drawn 
 into the cracks by the draft. 
 
 Q. How may the leaks be stopped? 
 
 A. By filling them with whitewash in which glue 
 has been dissolved. 
 
 Q. How may a boiler setting be covered to pre- 
 vent all leakage? 
 
 A. With asbestos cement or plaster, covered with 
 canvas and painted. 
 
 Q. What is the function of draft in a boiler fur- 
 nace? 
 
 A. To burn fuel. 
 
 Q. What happens when the draft is too strong? 
 
 A. Holes are burned in the fire, and efficiency 
 goes down. 
 
 Q. What happens when the draft is too weak? 
 
 A. Imperfect combustion results, with the forma- 
 tion of CO and smoke. 
 
 Q. How may the proper draft conditions for a 
 given load be discovered? 
 
 A. By flue-gas analysis at different drafts. 
 
 Q. How should the draft be varied? 
 
 A. By the damper. 
 
 Q. Is it possible to operate a furnace at high effi- 
 ciency under light load? 
 
 A. No. 
 
 Q. Why not? 
 
 A. There is too much grate area for the work 
 required. 
 
 Q. Should a boiler ever be worked at light load 
 if it can be avoided? 
 
 A. No ; it is much better to run fewer boilers at 
 an overload. 
 
FURNACE EFFICIENCY 20 
 
 CHAPTER IV. 
 
 It was shown in a previous chapter that a careful 
 control of draft is absolutely essential to high fur- 
 nace efficiency. When the load on a boiler varies, 
 the amount of fuel charged into the furnace is varied 
 in proportion to the load demands. If good efficiency 
 of combustion is to be maintained, the amount of air 
 admitted to the furnace must be varied in practically 
 the same proportion as the coal, so that combustion 
 conditions may be maintained practically constant. 
 This necessitates a careful supervision over the draft 
 at all times, and under all conditions of load. 
 
 It has been pointed out that the proper draft for 
 a given furnace, using a given quality of coal and 
 operating under a given load, can only be determined 
 by a careful study of the flue gas, together with the 
 draft-gauge readings. It will be of considerable 
 assistance in determining the proper draft to use 
 under any set of conditions, if the engineer is familiar 
 with average draft-pressure losses through a few of 
 the boilers which are used most widely in commercial 
 practice. With such figures at hand it will be easier 
 to reach good conditions in any particular boiler. 
 Also sources of trouble, such as faulty design, defect- 
 ive baffles, or dirty tubes, may be located simply by 
 an analysis of the draft-gauge readings. 
 
 Fig. 3 shows a horizontal return tubular boiler 
 served with a chain-grate stoker. The figures in the 
 small circles show the average value of the draft at 
 that particular point, expressed in inches of water. 
 These figures are the average taken from a large 
 
30 
 
 FURNACE EFFICIENCY 
 
 number of observations, and may be relied upon as 
 fairly representative of average draft conditions in a 
 boiler of this type. It should be observed, however, 
 that the absolute values given are not of so much 
 importance as a guide in arriving at good draft con- 
 ditions as the 'relative values. For example, if the 
 load on the boiler were to decrease considerably, a 
 thinner fuel bed would have to be carried. In order 
 to prevent too great a quantity of air being drawn 
 through the fire the damper must be partially closed. 
 This might reduce the draft at the front tube sheet 
 from 0.52 to, say, 0.40. But if the boiler and setting 
 were properly designed and in good condition there 
 would be a proportional decrease in the draft at all 
 other points. Over the fire it would probably be 
 reduced to about 0.23 instead of 0.30. 
 
 On the other hand, if the dampers were not par- 
 tially closed when the load decreased, wasteful fur- 
 nace conditions would result and the draft readings 
 would show it. The draft at the front tube sheet 
 
FURNACE EFFICIENCY 31 
 
 would still remain at about 0.52 because the position 
 of the damper is unchanged. But since the fuel bed 
 is now much thinner than before, the pressure drop 
 through it would be much less than it was. The read- 
 ing over the fire would be reduced to 0.20 or even less. 
 Since the draft below the damper is unchanged, this 
 would mean a vast excess of air drawn through the 
 thin fire, with a consequent loss in furnace efficiency. 
 It will be evident, therefore, that much may be learned 
 about furnace and boiler conditions by a study of the 
 draft at various points in the setting. If the draft 
 readings bear the same general relation to each other 
 as is shown in Fig. 3^the conditions are about right. 
 Any marked departure from these proportions indi- 
 cates poor practice. 
 
 Suppose, for example, that the draft in the com- 
 bustion chamber back of the bridge wall were found 
 to be 0.40 instead of 0.33. This would mean too great 
 a loss of draft pressure over the bridge wall. The 
 only explanation for such a state of affairs is that 
 the space over the bridge wall is too small, requiring 
 a high gas velocity at this point with a consequent 
 large drop in pressure. The remedy is to provide 
 greater space at this point by lowering the bridge 
 wall. In general, this space should be large enough 
 to allow for a maximum gas velocity not to exceed 
 35 to 40 feet per second. If the maximum rate of 
 combustion for the furnace has been predetermined 
 (by an analysis of the probable load), and the kind 
 of fuel to be used has been decided upon, it is possible 
 to calculate the volume of gases which must pass 
 over the bridge wall, furnace temperature being taken 
 into account. It is then a comparatively simple mat- 
 ter to calculate the area required over the bridge wall. 
 But if the boiler is overloaded more than was orig- 
 inally anticipated, or if a coal is used which has a 
 larger volatile content than was expected, then the 
 
32 FURNACE EFFICIENCY 
 
 calculated area will prove insufficient. The result 
 will be too large a drop in draft pressure over the 
 bridge wall, which can be detected immediately by 
 means of the draft-gauge readings. 
 
 In like manner faulty boiler design can be de- 
 tected by the draft readings. If the tube area is too 
 small the draft loss through the boiler will be exces- 
 sive, while if it is too large the draft loss will be less 
 than that shown in the figure. Tubes clogged with 
 soot and dirt will increase the loss through the boiler, 
 so that it is possible to tell the condition of the tubes, 
 to a certain extent at least, by the draft readings. 
 
 Fig. 4 shows a water-tube boiler of the B. & W. 
 type, served with a chain-grate' stoker, and with the 
 average draft readings at various points given. It 
 will be noted that the draft over the fire in this case 
 is 0.32, just one-half of what it is at the damper. This 
 is the same relation as was shown for the horizontal 
 tubular boiler of Fig. 3. The boiler shown in this 
 figure is vertically baffled, the gases passing three 
 times across the tubes. The pressure drop is fairly 
 uniform from fire to damper, showing no restricted 
 portion in the gas passage, and no short circuit. 
 
 A boiler baffled in this way does not readily form 
 short circuits through which the gases may pass, 
 because there are no points in close proximity to each 
 other which differ widely in draft pressure. Consider, 
 however, what would take place if the front baffle 
 should burn through at the bottom. Instead of pass- 
 ing up across the tubes the gases would pass through 
 the hole in the baffle, thus finding a much shorter path 
 to the stack. The result would be a serious loss in 
 efficiency because the gases are not coming in contact 
 with the tubes as they should, and hence do not give 
 up their heat properly. A fault of this kind will 
 usually be made apparent to one who understands 
 the situation simply from the draft readings. In the 
 
FURNACE EFFICIENCY 
 
 33 
 
34 FURNACE EFFICIENCY 
 
 case of a short circuit as described the pressure drop 
 between the fire and the rear of the bridge wall would 
 be much less than 0.12, as shown in the figure. Such 
 a short circuit can almost always be located by a 
 study of draft-pressure drops from point to point 
 through the setting in the normal path of the gases. 
 
 Restricted passages can be located in the same 
 way, because in this case the normal draft-pressure 
 drop will be increased. 
 
 Fig. 5 shows a Heine boiler, horizontally baffled. 
 This boiler is quite similar to the B. & W. horizon- 
 tally baffled type, so far as draft-pressure losses are 
 concerned. It will be noted in this case that the total 
 pressure drop through this boiler is greater than 
 through the vertically baffled unit. The ratio between 
 draft over the fire and at the damper is almost 1 to 3, 
 while in the previous case it is 1 to 2. In a boiler 
 baffled in this way the gases pass to the near of the 
 combustion chamber before striking the tubes. They 
 then pass once over the tubes in the direction of their 
 length instead of across the tubes as in the previous 
 case. The bottom row of tubes has a covering of fire- 
 brick tile, carried back to within 3 or 4 feet of the rear 
 end. This forms a fire-brick roof for the furnace and 
 greatly assists in the combustion. 
 
 A boiler baffled in this way has a tendency to de- 
 velop short circuits, as will be apparent from a con- 
 sideration of the figure. Over the fire the draft 
 pressure is 0.28, while directly above, on the other 
 side of the tile roof, it is 0.46. The same condition 
 exists on opposite sides of the baffle on the top row 
 of tubes. Below this baffle the pressure is about 0.36, 
 while above it there is a pressure of 0.62. Thus there 
 is a pressure difference on opposite sides of this baffle 
 of 0.26 inches, which tends to produce a short circuit 
 at that point. For this reason both the tile roof and 
 the upper baffle must be watched closely for leaks, 
 
FURNACE EFFICIENCY 
 
 35 
 
36 
 
 FURNACE EFFICIENCY 
 
 which become quite serious on account of the large 
 pressure differences. Here again the draft gauge fur- 
 nishes the information as to conditions inside the 
 setting, if one is able to interpret these readings. 
 
 Fig. 6 shows a Stirling boiler with the draft-pres- 
 sure readings indicated. It will be noted that the total 
 
 FIG. 6. 
 
 draft loss in this boiler is practically the same as in 
 the case of the Heine type, horizontally baffled. The 
 ratio between draft over the fire and at the uptake is 
 practically 1 to 3, the same as for the Heine boiler. 
 An inspection of the figure will show the points at 
 which short circuits through the baffles are most 
 
FURNACE EFFICIENCY 37 
 
 likely to occur. Such a point exists at the lower part 
 of the first baffle just above the bottom drum. The 
 tendency is for the hot gases from the rire to pass 
 back over the bridge wall, through the first bank of 
 tubes, and impinge on the baffle at this point. The 
 tile becomes cracked and burned after a while and 
 a leak is established. Draft readings taken over the 
 fire and in the bottom of the second bank of tubes 
 will furnish reliable information as to the condition 
 of the baffle at this point. A very small pressure 
 drop between these two points indicates a leak. The 
 second baffle may be examined for leaks in the same 
 way. 
 
 In all the figures shown thus far it will be noted 
 that the draft over the fire is from 0.25 to 0.30. As 
 has been already pointed out, this will vary with the 
 thickness of the fuel bed. In general, the amount of 
 coal which can be burned on the grate depends upon 
 the available draft over the fire. Within certain 
 limits, ten pounds of coal can be burned per square 
 foot of grate area per hour for each 0.1 inch of draft 
 available at the fire. This relation holds up to a com- 
 bustion rate of about thirty pounds per square foot 
 per hour, after which a disproportionate increase in 
 draft is required for a given increase in combustion 
 rate. The drafts given in the figures would therefore 
 make possible a combustion rate of from twenty-five 
 to thirty pounds per square foot per hour. When it is 
 remembered that these furnaces are served with chain- 
 grate stokers, which are efficient even at high rates 
 of working, this rate of combustion will not seem 
 excessive. 
 
 The importance of accurate information in regard 
 to normal draft conditions in the different boilers is 
 not easily overestimated. One is then in a position 
 to note any departure from normal conditions, and to 
 assign a reason for it. With the possible exception 
 
38 FURNACE EFFICIENCY 
 
 of the instrument for flue-gas analysis, there is no 
 single device which will give as much information 
 about furnace and boiler conditions as the draft gauge, 
 if intelligently used. 
 
 Questions and Answers. 
 
 Q. Why must the draft be regulated carefully as 
 the load on a boiler changes? 
 
 A. Because the air admitted to the furnace must 
 be properly proportioned to the fuel if good efficiency 
 is to be maintained. 
 
 Q. How may the proper draft for any set of con- 
 ditions be determined? 
 
 A. By means of the flue-gas analysis. 
 
 Q. Of what value is an accurate knowledge of 
 average draft conditions throughout a boiler setting? 
 
 A. It makes it possible to locate furnace and 
 boiler troubles. 
 
 Q. How would tubes or flues clogged with soot 
 and dirt affect the draft readings? 
 
 A. This condition would be indicated by an abnor- 
 mally large draft-pressure loss between the front and 
 rear tube sheets. 
 
 Q. How would too small an area over the bridge 
 wall be indicated in the draft readings? 
 
 A. By too large a drop between front and rear 
 of bridge wall. Such a condition would also probably 
 produce hot side walls and grates, due to the bottling 
 up the hot gases in the furnace. 
 
 Q. How large an area should be provided over 
 the bridge wall? 
 
 A. Large enough so that the maximum velocity 
 of the gases will not exceed 35 to 40 feet per second. 
 
 Q. How would a leaky or broken baffle be indi- 
 cated by the draft readings? 
 
 A. By abnormally low draft-pressure drop be- 
 tween opposite sides of the affected baffle. 
 
FURNACE EFFICIENCY 39 
 
 Q. What is the chief factor determining the 
 amount of coal which can be burned on a furnace 
 grate ? 
 
 A. The amount of draft available over the fire. 
 
 Q. What relation is there between available 
 draft and rate of combustion? 
 
 A. About ten pounds of coal can be burned per 
 square foot of grate area per hour for each 0.1 inch 
 of draft. 
 
 Q. Does this relation hold indefinitely? 
 
 A. Xo ; when the rate of combustion exceeds 
 thirty pounds per square foot per hour the draft must 
 be increased faster than the rate of combustion. To 
 burn forty pounds of coal would require 0.42 inch of 
 draft at least. 
 
40 FURNACE EFFICIENCY 
 
 CHAPTER V. 
 
 It was shown in an earlier chapter that an efficient 
 boiler furnace is one which burns all of the combust- 
 ible of the fuel with the least possible excess of air. 
 It was also pointed out, however, that there is a limit 
 beyond which air reduction can not be carried without 
 a drop in efficiency. This -loss in efficiency is due to 
 incomplete combustion, the most noticeable effect of 
 which is the production of smoke. But smoke is only 
 the visible effect of incomplete combustion, and is 
 usually less serious from the standpoint of efficiency 
 than the invisible effects, of which the smoke is the 
 sign. 
 
 The Formation of Smoke. 
 
 When coal is fed into a boiler furnace, either by 
 hand or mechanically, the first effect of the heat is to 
 drive off the volatile gases which all coal contains in 
 larger or smaller amounts. Anthracite coal may con- 
 tain as low as 3 per cent of these volatile gases, while 
 lignite may contain as much as 50 per cent. They are 
 composed of hydrogen and carbon united in different 
 proportions, and are usually referred to under the 
 comprehensive term, " hydrocarbons." 
 
 The exact chemical action which takes place in the 
 furnace when these hydrocarbons are brought into 
 contact with air is probably not definitely understood. 
 It appears, however, that at the temperature of the 
 furnace some of these gases may be broken up into 
 the elements of which they are composed ; that is, into 
 carbon and hydrogen. The latter element promptly 
 
FURXACE EFFICIENCY 41 
 
 unites with the oxygen of the entering air, forming 
 water vapor. If there is an abundant supply of air 
 present, the free carbon also unites with the oxygen 
 to form CO 2 . But if the air supply is insufficient, part 
 of the carbon will form CO instead of CO,, and part 
 of it may even escape from the furnace in the free state, 
 that is, entirely uncombined with oxygen. This free 
 carbon, deposited from the volatile hydrocarbon in the 
 manner indicated, is what constitutes smoke. 
 
 The amount of free carbon which escapes in this 
 way from the furnace and appears in the chimney gases 
 is probably considerably less than is generally sup- 
 posed, particularly by the public. A comparatively 
 small amount of free carbon issuing from the top of 
 the chimney is sufficient to give the gases a dense 
 black appearance. In fact, it is unlikely if the amount 
 of carbon lost in this way ever greatly exceeds 1 per 
 cent of the total fuel. Thus from the standpoint of 
 efficiency smoke in itself is not such a serious matter 
 as is many times supposed. 
 
 But if the manner in which smoke is formed be 
 kept clearly in mind it will be plain that there are 
 other effects of incomplete combustion besides the 
 visible smoke. These are CO, free hydrogen, and 
 unburned hydrocarbons, all of which are invisible 
 gases, and which may reduce furnace efficiency very 
 seriously. For example, for each pound of carbon 
 burned to CO instead of CO 2 , the loss is about 
 10,000 heat units. Thus, while smoke itself may not 
 be serious from the standpoint of efficiency, it is of 
 value as an index of bad furnace condition and poor 
 efficiency. 
 
 Of course, it can not be denied that smoke is open 
 to serious objection on humanitarian grounds, on 
 account of its evil effect upon public health. For this 
 reason the smoke problem has received a great amount 
 of study, particularly in large cities. But to the power 
 
42 
 
 FURNACE EFFICIENCY 
 
 plant owner smoke is important because it indicates 
 serious conditions in the furnace which need attention 
 if high furnace efficiency is to be maintained. 
 
 The problem for the operator of the boiler furnace 
 is to secure complete combustion at all times with as 
 little excess air as possible. This is by no means an 
 easy task, and one that calls for a thorough under- 
 standing of combustion problems, and constant atten- 
 tion to furnace conditions. With a properly con- 
 structed furnace, a capable attendant and intelligent 
 use of instruments such as draft gauges, CO 2 appa- 
 ratus and thermometer, it is possible to obtain com- 
 plete combustion with a fair grade of soft coal on as 
 low as 30 per cent excess air. The United States Geo- 
 logical Survey gives the following table for an approx- 
 imate heat distribution for Illinois coal. The same 
 figures will hold true for all similar soft coals : 
 
 
 Percentage of Heat. 
 
 1 
 
 2 
 
 3 
 
 1. 
 
 2. 
 3. 
 4. 
 
 5. 
 6. 
 
 Absorbed by boiler 
 Carried away in dry chimney 
 gases 
 
 50.0 
 24.0 
 15.0 
 
 4.0 
 2.0 
 5.0 
 
 65.0 
 16.0 
 12.0 
 
 3.5 
 2.0 
 1.5 
 
 75.0 
 10.0 
 10.0 
 
 3.0 
 1.5 
 0.5 
 
 Radiation and unaccounted for 
 losses 
 
 Moisture formed by burning of 
 hydrogen . . 
 
 Evaporating moisture in coal 
 Incomplete combustion of carbon . 
 
 Total heat . . 
 
 100.0 
 
 100.0 
 
 100.0 
 
 TABLE No. T. 
 
 Column 1 above gives the heat distribution under 
 poor conditions, Column 2 average conditions and Col- 
 umn 3 the best conditions practically attainable. These 
 
FURNACE EFFICIENCY 43 
 
 best conditions are rarely attained in present practice, 
 but they are not impossible, and present a practical 
 ideal toward which to strive. 
 
 The Observation of Smoke. 
 
 The casual observation of a smoking chimney may 
 lead to very erroneous conclusions as to the amount 
 of smoke coming from it. A stack may be practically 
 free from smoke for 90 per. cent of the time, and if 
 smoke observations are made during the remaining 
 10 per cent of the day, a false idea is obtained as to 
 the nature of the combustion in the plant. A stand- 
 ard of smoke densities is required, by means of which 
 various smoking chimneys may be compared. Also 
 careful time observations should be taken to determine 
 the duration of the smoking, and the observations 
 should be made at regular intervals throughout the 
 day. Only by such a method can reliable results be 
 attained. 
 
 The standard of densities which has the widest 
 application in observing smoke is in the Ringelmann 
 chart, devised by Professor Ringelmann, of Paris. 
 This chart is shown in Fig. 7. Card 1 is made with 
 black lines 1 mm. thick, 10 mm. apart, leaving spaces 
 9 mm. square. Card 2 has lines 2.3 mm. thick, with 
 spaces 7.7 mm. square. Card 3 has lines 3.7 mm. thick, 
 with spaces 6.3 mm. square. Card 4 has lines 5.5 mm. 
 thick, with spaces 4.5 mm. square. In addition to the 
 four cards shown in the figure > an all-white one is 
 sometimes used and numbered 0, while an all-black 
 card is numbered 5. 
 
 When making smoke observations, a chart is pre- 
 pared which has the four cards shown in Fig. 7 ar- 
 ranged in a horizontal row. The all-white card and 
 the all-black one may also be used. When this chart 
 is observed at a distance of about 50 feet, the lines on 
 
44 
 
 FURNACE EFFICIENCY 
 
FURNACE EFFICIENCY 
 
 45 
 
 fO 
 
 
46 FURNACE EFFICIENCY 
 
 the cards can no longer be distinguished, the whole 
 surface assuming a gray appearance. The heavier the 
 lines on the card the darker the shade of gray which 
 the surface appears to be. 
 
 In determining the density of the smoke, the 
 observer glances from cards to smokestack and back 
 again until he can pick out the card which most nearly 
 corresponds in color to the smoke. If he should select 
 Card No. 2 as most closely corresponding to the den- 
 sity of the smoke, then the latter is called No. 2 smoke. 
 In the same way, one may speak of No. 1 smoke, No. 
 4, etc. In a boiler test these observations should be 
 made at regular intervals throughout the day and the 
 results platted on a smoke record chart, the smoke 
 number being platted as an ordinate against the time 
 as abscissa. In this way the smoke record for the 
 whole day may be seen at a single glance. 
 
 Fig. 8 shows smoke of densities approximating the 
 five cards of the Ringelmann chart. It will be noted 
 that No. 1 smoke is a very light gray, such as is seen 
 coming from many chimneys practically all the time. 
 Such smoke is usually allowed by most city smoke 
 ordinances. A chimney which never shows anything 
 worse than No. 2 smoke would be considered good, 
 while as dense as No. 3 may be permitted for brief 
 intervals. 
 
 The Prevention of Smoke. 
 
 Smokeless combustion can only be secured by 
 properly designed furnaces and eternal vigilance in 
 operation. The first requirement is suggested by the 
 way in which smoke is produced. Since it is caused 
 by insufficient air supply, the first measure for its 
 prevention is an adequate supply of air to the furnace 
 at all times. The measures for smoke prevention may 
 be enumerated as follows : 
 
 1. An adequate supply of air. 
 
FURNACE EFFICIENCY 47 
 
48 Ft'KXACE EFFICIENCY 
 
 2. A temperature throughout the combustion zone 
 high enough to provide for the complete combustion 
 of the volatile gases or hydrocarbons. 
 
 3. A slow and uniform distillation of the hydro- 
 carbons. 
 
 4. An intimate mixture of gases and air. 
 
 If these four requirements be met satisfactorily, 
 then practically any soft coal can be burned without 
 smoke. 
 
 The first requirement presents no great difficulty, 
 since in the majority of steam plants far too great an 
 excess of air is being used. The second requirement 
 is very largely a matter of design, as it requires a brick 
 or tile enclosed combustion chamber of such size and 
 length that the hydrocarbon gases may be completely 
 burned before reaching the heating surfaces of the 
 boiler. Whenever a boiler is set over a furnace in such 
 a way that the gases can come into contact with either 
 shell or tubes before combustion is complete, smoke 
 and poor economy are almost sure to result. When 
 the flames strike the relatively cold heating surfaces 
 they are chilled below the ignition temperature of the 
 gases, combustion is arrested, and smoke produced. 
 For this reason a tubular boiler set directly over the 
 furnace almost always smokes when the flames 
 come in contact with the shell. A brick or tile roof 
 must be provided for the furnace or an arch must be 
 built over the grates so that the flames can not strike 
 the boiler until combustion is complete. 
 
 The third requirement, a slow and uniform distilla- 
 tion of the gases from the coal, is practically impos- 
 sible when the furnace is fired by hand. In order that 
 the distillation of the gases shall be slow and uniform, 
 the fuel must be fed to the furnace at a uniform rate, 
 and this is exactly what hand-firing does not do. When 
 a charge of coal is thrown into the fire by hand there 
 is a sudden evolution of gas while the coal is coking. 
 
FURNACE EFFICIENCY 49 
 
 The quantity of gas given off at the time will very 
 likely be beyond the capacity of the furnace to con- 
 sume, and imperfect combustion will result. When the 
 charge of coal has been completely coked, very much 
 less air will be required to burn the fixed carbon. 
 Unless the supply of air is reduced somewhat, too 
 great an excess will be present, with a consequent loss 
 in efficiency. Thus, on account of the widely varying 
 demands for air on the part of a hand-fired furnace, it 
 becomes extremely difficult to operate such equipment 
 without smoke. The mechanical stoker which feeds 
 the coal into the furnace uniformly and steadily makes 
 smokeless combustion entirely practicable. 
 
 To promote the mixing of the gases and air, spe- 
 cial features of design have been used, such as baffle 
 piers, wingwalls, etc. In the next chapter these fea- 
 tures will be discussed, as well as the general design of 
 furnaces to promote smokeless combustion. 
 
 Questions and Answers. 
 
 Q. How is smoke formed? 
 
 A. By the incomplete or arrested combustion of 
 the volatile hydrocarbons in the coal. 
 
 Q. Is smoke the only result of such imperfect 
 combustion? 
 
 A. No, there is CO and unconsumed hydrocarbons 
 in the chimney gases when smoke is found. 
 
 Q. How much heat is lost, due to the formation of 
 smoke? 
 
 A. Much less than is generally supposed, probably 
 not much more than 1 per cent of the total heat of the 
 coal. 
 
 Q. Why, then, is smoke objectionable? 
 
 A. On humanitarian grounds, and because it is the 
 visible sign of poor conditions in the furnace. 
 
 Q. How is the density of smoke estimated? 
 
50 FURNACE EFFICIENCY 
 
 A. By comparing it with the cards of the Ring- 
 gelmann chart. 
 
 Q. What is the first requirement for smokeless 
 combustion? 
 
 A. An adequate air supply. 
 
 Q. Name some other requirements. 
 
 A. A high temperature in the combustion zone, a 
 slow and uniform distillation of the gas from the coal, 
 and a proper mixing of gas and air. 
 
FURNACE EFFICIENCY 51 
 
 CHAPTER VI. 
 
 In Chapter V the requirements for smokeless com- 
 bustion were enumerated and discussed somewhat in 
 detail. We shall now consider some of the best types 
 of modern furnaces, designed to burn high volatile 
 soft coal without smoke, and note wherein they meet 
 the conditions of smokeless combustion and wherein 
 they fail to come up to the requirements. 
 
 Fig. 9 shows a Babcock & Wilcox boiler of 220 
 horse-power rated capacity, described by Professor 
 Breckenridge. It is served" with a Roney stoker, and 
 equipped with the usual vertical baffling. Perhaps the 
 chief feature of this furnace is the coking arch, placed 
 over the front end of the stoker, so that the fresh coal 
 is fed in directly under it. 
 
 This arch is of fire brick and is sprung between the 
 side walls, the distance between grate and arch being 
 shown in the figure. This arch is maintained at a 
 high^temperature, its purpose being to assist in the 
 combustion of the volatile gases as they are distilled 
 from the incoming coal. Experience has shown that 
 this arch should be kept well down near the grates, 
 to insure complete combustion of the gases. Profes- 
 sor Breckenridge states that, with careful handling, 
 this furnace could be operated up to capacity without 
 smoke above No. 2 on the Ringelmann chart. At 110 
 per cent of capacity and above it could not be operated 
 without objectionable smoke, except by an expert 
 fireman. The reason why this furnace smoked when 
 operated much above normal boiler capacity is prob- 
 ablv not difficult to see. 
 
FURNACE EFFICIENCY 
 
FURNACE EFFICIENCY 
 
 53 
 
64 FURNACE EFFICIENCY 
 
 It will be noted that the distance between grates 
 and boiler tubes is comparatively short. When the 
 boiler was run at rated capacity the amount of coal 
 burned, and hence the volume of gases to be consumed, 
 was such that complete combustion was secured before 
 the gaseous products of combustion reached the boiler 
 tubes. Hence combustion was comparatively smoke- 
 less. On the other hand, when the boiler was forced 
 beyond its rated capacity the volume of gases dis- 
 tilled from the coal was so great that complete com- 
 bustion was impossible in the short distance from 
 grates to boiler tubes. Hence the gases were chilled 
 below their ignition point on striking the compara- 
 tively cold tubes, combustion was arrested and smoke 
 produced. The chief trouble with this furnace is that 
 it does not have a combustion space of sufficient length 
 to provide for efficient combustion at high rates of 
 working. 
 
 In general, it may be said that the area and length 
 of the combustion space depend upon the rate of com- 
 bustion and the character of the fuel. Or what amounts 
 to the same thing, the combustion space must be de- 
 signed with reference to the volume of gases which 
 must be consumed per second. By combustion space 
 is meant that portion of the furnace which is sur- 
 rounded by fire brick, tile, or other refractory material, 
 which may be maintained at a high temperature. The 
 furnace under consideration has boiler tubes at the 
 top of the furnace, which has the effect of greatly 
 reducing the effective combustion space. 
 
 Fig. 10 shows a setting similar to Fig. 9, except that 
 the boiler is horizontally baffled instead of vertically. 
 A tile roof is provided for the furnace by means of 
 specially designed tube tiles placed on the lower row 
 of tubes. Professor Breckenridge states that this fur 
 nace could be operated at capacities up to 100 per cent 
 of rating without smoke, and at greater capacities 
 
FURNACE EFFICIENCY 55 
 
 without objectionable smoke. In this furnace the path 
 of the gases is along the line ABC, and not until the 
 point C is reached do the products of combustion come 
 in contact with the heating surfaces of the boiler. 
 Except at very high rates of working, the combustion 
 space is sufficiently long to provide for complete com- 
 bustion of the hydrocarbon gases before the point C 
 is reached. Thus a furnace designed in t^iis way is 
 much better from the standpoint of smokeless com- 
 bustion than the one shown in Fig. 9. 
 
 The draft required for this furnace will probably 
 be somewhat greater than for the one with the verti- 
 cal baffles shown in Fig. 9. But if sufficient draft is 
 available there is probably no doubt that this furnace 
 will prove superior to the vertical baffle so far as 
 smokeless operation is concerned, particularly at the 
 higher rates of working. 
 
 Fig. 11 shows a 210 horse-power Heine boiler, 
 equipped with Green chain-grate stoker, and provided 
 with mechanically induced draft. This boiler is in- 
 stalled in the Engineering Experiment Station at the 
 University of Illinois, and has been used by the sta- 
 tion in many practical fuel tests. It will be noted 
 that the furnace is provided with a flat combustion 
 arch over the front end of the grate, and that a roof 
 is supplied by means of tiles on the bottom row of 
 tubes. Experiments on this boiler show that it can 
 be operated without smoke at practically any rate of 
 working and under almost any conditions of oper- 
 ation. Ample draft being available, this boiler can 
 be operated efficiently at very high overloads; in fact, 
 Professor Breckenridge states that it was found to be 
 almost impossible to make it smoke. 
 
 The chief features of design which are respon- 
 sible for the smokeless operation of this furnace are : 
 (1) The chain-grate stoker, which feeds the fuel into 
 the furnace at a uniform rate, thus giving a steady 
 
FURNACE EFFICIENCY 
 
FURNACE EFFICIENCY 
 
 57 
 
 evolution of hydrocarbon gases, an important point 
 in efficient combustion ; (2) the combustion arch over 
 the front of the grate, which ignites the gases as they 
 come from the coal; (3) the tile roof, which prevents 
 the gases from coming into contact with the boiler 
 tubes until combustion is complete. 
 
 Fig. 12 shows a smokeless setting designed by Mr. 
 
 FIG. 12.. 
 
 A. Bement, and described in the " Proceedings of the 
 Western Society of Engineers," October, 1906. This 
 is a Babcock & Wilcox boiler, with chain-grate stoker. 
 A sprung combustion arch is provided over the grate, 
 nnd a tile roof is placed on the bottom row of tubes. 
 Unlike the setting shown in Fig. 10, this boiler has 
 vertical baffles, the path of the gases being shown by 
 
58 FURNACE EFFICIENCY 
 
 the irregular line ABCDEF. On account of such a 
 devious gas path, considerable draft will be required 
 to operate such a furnace satisfactorily, particularly 
 at overloads. Also the area of the gas path through 
 the various passes must be proportional with consid- 
 erable care if good results are to be insured. Such 
 a furnace, however, meets practically all the require- 
 ments for smokeless operation, and may be operated 
 through a wide range of capacities without serious 
 smoke. 
 
 Fig. 13 shows a Stirling boiler served with a chain- 
 grate stoker, with a furnace designed for smokeless 
 combustion. The chief features of this furnace are 
 the flat ignition arch R, over the front of the grate, 
 and the sprung arch P, above and behind the ignition 
 arch. The function of the ignition arch is to assist 
 in igniting and coking the fresh coal as it is fed into 
 the furnace, the volatile gases being distilled grad- 
 ually at this point. The sprung arch assists in the 
 combustion of these gases; it is maintained at a high 
 temperature and the gases roll over the edge of the 
 arch and so are well mixed with air, which is an impor- 
 tant point in smokeless combustion. This furnace, 
 therefore, depends upon these two arches for g-ood 
 combustion, which is effected by the uniform distilling 
 action of the first, and the mixing action of both. 
 
 It might seem at first sight that this furnace might 
 smoke, inasmuch as the first bank of tubes is unpro- 
 tected from the flame and hot gases. But experience 
 has shown that such a furnace gives very good results 
 from the standpoint of smokeless combustion, even at 
 considerable variations in the rate of working. The 
 path of the gases and products of combustion is shown 
 by the irregular line ABCDEF; it will be noted that 
 the gases do not impinge on the bottom of the first 
 bank of tubes, but turn almost directly upward from 
 under the end of the arch. By the time the gases 
 
FURNACE EFFICIENCY 
 
 59 
 
 FIG. 13. 
 
60 FURNACE EFFICIENCY 
 
 strike the tubes combustion is complete, except pos- 
 sibly at very high rates of working. 
 
 If the bottom of the first bank of tubes were cov- 
 ered with fire-clay tile, as in the case of certain other 
 furnaces already described, combustion would hardly 
 be improved to any extent because the gases do not 
 strike the tubes at this point. On the contrary, the 
 efficiency and capacity would probably be somewhat 
 reduced, because the tubes at this point receive a con- 
 siderable amount of heat from the fire in the form of 
 radiant energy. If these tubes were covered with 
 tile much of this radiant energy would be lost. 
 
 All of the smokeless furnaces discussed thus far 
 are in connection with water-tube boilers and mechan- 
 ical stokers. But there are a large number of fire- 
 tube boilers in use in all parts of the country, the great 
 majority of which are fired by hand. Such boilers are 
 usually found in small plants, where hand firing is 
 cheaper than mechanical stokers. The question of 
 smokeless combustion in such a case as this is very 
 difficult of solution and has not yet been satisfactorily 
 solved. 
 
 In the first place, hand firing violates one of the 
 chief requirements for smokeless combustion, namely, 
 a slow and uniform distillation of the volatile gases 
 in the coal. When a charge of coal is thrown into the 
 fire by hand the gases are distilled faster than they 
 can be consumed by the furnace, and smoke results. 
 Hence smokeless combustion in a hand-fired furnace 
 under all conditions of operation is almost impossible. 
 
 In Fig. 14 is shown a perspective view of a setting 
 designed by the Department of Smoke Inspection of 
 the City of Chicago, and recommended by them for 
 use with the hand-fired horizontal tubular boiler. This 
 is what is known as the double-arch bridge-wall fur- 
 nace, and has given very good results when carefully 
 operated. 
 
FURXACE EFFICIENCY 
 
 61 
 
62 FURNACE EFFICIENCY 
 
 It will be noted that the gases coming from the 
 furnace are divided at the bridge wall into two 
 streams by means of a double arch rising from the 
 center of the bridge wall. A bulkhead is built up 
 around the shell to prevent the gases from escaping 
 above the arch and so coming into contact with the 
 boiler shell. Behind this double arch there is a short 
 single arch sprung between the side walls. This is 
 known as the deflection arch, its function being to 
 deflect the gases downward after they leave the dou- 
 ble arch, and so prevent them from impinging on the 
 shell. The object of such a construction is to prevent 
 the hot gases from coming into contact with the shell 
 throughout practically its whole length. 
 
 A furnace of this kind will probably require more 
 draft than the usual setting provided for such a boiler, 
 on account of the devious path of the gases. Given 
 sufficient draft, however, such a furnace greatly re- 
 duces the smoke nuisance when the firing is carefully 
 done. 
 
 Questions and Answers. 
 
 Q. In practically all smokeless furnaces, how is 
 a uniform distillation of the volatile combustible gases 
 effected? 
 
 A. By an ignition or coking arch placed over the 
 front of the grate. 
 
 Q. How is a uniform feed of fuel obtained in such 
 a furnace? 
 
 A. By means of a mechanical stoker, usually some 
 form of movable or traveling grate. 
 
 Q. What is the object in placing fire tiles on the 
 bottom row of tubes in a horizontal water-tube boiler? 
 
 A. To provide a tile roof for the furnace and so 
 prevent the gases from coming into contact with the 
 tubes before combustion is complete. 
 
FURNACE EFFICIENCY 63 
 
 Q. Can a hand-fired tubular boiler furnace be 
 operated without smoke? 
 
 A. Yes, under favorable conditions and with care- 
 ful handling. 
 
 Q. What kind of furnace has proved most satis- 
 factory for such a boiler? 
 
 A. The double-arch bridge-wall furnace. 
 
64 FURNACE EFFICIENCY 
 
 CHAPTER VII. 
 
 It will be evident from a reading of the foregoing 
 chapters that furnace efficiency depends upon a number 
 of conditions, such as character of flue gases, draft, 
 design of furnace and grate, kind and condition of fuel, 
 method of firing, etc. Many of these conditions are 
 subject to considerable change, so that the problem of 
 maintaining high furnace efficiency involves a constant 
 attention to all the details of furnace operation. Fur- 
 thermore, these conditions are such that a change 
 which would adversely affect the efficiency might not 
 be apparent to the fireman or man in charge. For 
 example, it has been shown that in general a relatively 
 high percentage of CO 2 in the flue gases is essential to 
 high furnace efficiency. Also, we have seen that a 
 leaky setting allows infiltration of air, which dilutes 
 the gases, lowers the percentage of CO 2 at the uptake 
 and decreases efficiency. Now, such a state of affairs 
 can only be detected by a flue-gas analysis, as already 
 explained, and this takes some time. The result is that 
 in spite of flue-gas instruments, CO 2 records, draft 
 gauges and thermometers, all of which are extremely 
 valuable in their proper places and not for one moment 
 to be underestimated, the fireman still does not have 
 before him a constant and reliable index of what is 
 taking place inside the furnace walls. 
 
 From a proper use of the instruments mentioned the 
 engineer in charge has learned the best way to operate 
 the furnaces under certain conditions of load. But he 
 can not spend all of his time in the furnace-room 
 watching the fires, so that for a part of the time, at 
 
FURNACE EFFICIENCY 65 
 
 least, the fireman does not know if he is operating his 
 furnace to the best advantage. If some instrument 
 could be devised which might be placed on the boiler 
 front, in plain view of the fireman, which would indi- 
 cate at all times the efficiency of the whole steam- 
 generating process, it would be a most valuable aid in 
 maintaining proper furnace and boiler conditions. 
 
 It should be kept clearly in mind that these condi- 
 tions can be determined with a fair degree of accuracy 
 from the flue-gas analysis, draft and temperature read 
 ings, and the evaporation test. But the difficulty lies 
 in maintaining conditions favorable to high efficiency 
 after they have been determined. In the past it has 
 been done by eternal vigilance, or (more often) not 
 done at all. It will be apparent, therefore, what a vast 
 amount of time and trouble would be saved, and what 
 savings in fuel could be realized if some instrument 
 were available which would give at a glance the effi- 
 ciency of the whole steam-generating unit. 
 
 The Wilsey Fuel Economy Gauge is an instrument 
 designed to meet just these requirements. It indicates 
 to the fireman just what his combined furnace and 
 boiler efficiency is at all times, and is practically as 
 reliable in its action as the steam gauge. A fireman 
 can usually be depended upon to keep the steam pres- 
 sure at the right point, because he has the gauge always 
 before him to guide him in his work. With the fuel 
 economy gauge also before his eye he has a reliable 
 guide to keep him in the path of high efficiency. Chang- 
 ing conditions in the furnace are immediately indicated 
 on the economy gauge, and the fireman can go to work 
 at once to correct them, without waiting for informa- 
 tion from flue-gas apparatus or draft gauge. 
 
 One important distinction is to be made, between 
 the Wilsey Fuel Economy Gauge and all other instru- 
 ments from which a knowledge of furnace conditions 
 is obtained. These latter instruments give information 
 
66 FURNACE EFFICIENCY 
 
 in regard to a single part or phase of the steam-gener- 
 ating process. For example, the CO 2 recorder gives 
 information in regard to the character of the combus- 
 tion, perhaps the most important step in the entire 
 operation of steammaking. But still it is not the whole 
 process, and the over-all efficiency may be relatively 
 low, even with high CO 2 . Tubes lined with scale and 
 covered with soot and dirt may produce just such a 
 result. Similarly, the draft gauge and the pyrometer 
 give information in regard to a single phase, respect- 
 ively, of the steammaking process, not to the whole. 
 
 The Wilsey Fuel Economy Gauge is designed and 
 constructed in such a way that it gives information in 
 regard to the combined furnace and boiler efficiency. 
 That is to say, it is affected not only by the efficiency 
 of heat transfer from furnace gases to boiler heating 
 surfaces, but also by the combustion conditions in the 
 furnace. Thus the instrument is able to approximate 
 very closely the efficiency of the whole process of 
 steammaking, from coal to steam. In fact, if corrected 
 for certain features, the neglect of which would intro- 
 duce error, it will indicate efficiency with as great accu- 
 racy as an evaporative test. 
 
 In considering the principle upon which this instru- 
 ment is based, think for a moment of what takes place 
 in a furnace and boiler. The heat liberated from the 
 fuel on the grate is carried away chiefly in two ways : 
 
 (1) By radiation to the boiler and the furnace walls; 
 
 (2) by heating the furnace gases, from which the heat 
 passes to the boiler-heating surfaces by convection 
 and conduction. By far the larger amount of heat 
 passes to the furnace gases, and only a comparatively 
 small amount is given off by radiation. 
 
 Now, if we neglect for the present the heat given 
 off by radiation and other minor items, the heat liber- 
 ated on the grate depends on the mass of furnace gas, 
 its temperature and its specific heat. This gas passes 
 
FURXACE EFFICIENCY 67 
 
 across the heating surfaces of the boiler and gives up 
 its heat to the water. The heat remaining in the gases 
 after they leave the boiler is lost up the stack. This 
 lost heat depends upon the mass of gas, its specific 
 heat and its temperature at the point where it leaves 
 the boiler. The efficiency of the process is equal to the 
 ratio of the heat used to the total heat liberated. In 
 expressing this ratio it is not necessary to know the 
 total mass of gas generated, because the heat in each 
 individual unit mass is the same, being equal to the 
 product of its absolute temperature and specific heat. 
 Let T = the absolute temperature of the furnace 
 gases in the combustion chamber, just before they 
 strike the boiler surfaces ; let S = the specific heat of 
 these gases. Similarly, let T 1 and S 1 = the absolute 
 temperature and specific heat, respectively, of the gases 
 leaving the boiler. Then the total heat per unit mass 
 of gas coming from the furnace is TS; also the total 
 heat per unit mass of gas leaving the boiler is T 1 S 1 . 
 The heat absorbed is TS T^ 1 , and the efficiency 
 
 r ps T J S : 
 
 of the process is - ~^ . If R = a correction to 
 
 be made for radiation, then the expression for effi- 
 
 XS T 1 S 1 
 
 ciency becomes E = \- R. 
 
 From a study of the formula it would appear to 
 consider only heat absorption, and to disregard com- 
 bustion entirely. But the better the combustion, the 
 higher will be the value of T, and hence the higher 
 will E become, if T 1 remains constant, that is, if the 
 efficiency of heat absorption remains the same. This 
 is an important point and merits some further con- 
 sideration. Suppose, for example, that a boiler and 
 furnace are operating under good conditions. Sup- 
 pose draft and air supply are right, and the gases show 
 14 per cent CO 2 . The combined efficiency under these 
 
68 FURNACE EFFICIENCY 
 
 conditions might be 70 per cent. If now there should 
 be a considerable falling off in the load on the boiler, 
 a much thinner fire will have to be carried on the grate. 
 But if the draft is not promptly reduced so as to cut 
 down the total amount of air passing through the fur- 
 nace in proportion to the reduced rate of combustion, 
 there will be a marked falling off in efficiency. But 
 this, loss in efficiency will be immediately indicated by 
 the economy gauge, because the furnace gases will 
 have their temperature reduced by the large excess of 
 cold air which is being admitted to the furnace. 
 
 On the other hand, if an error in operation be made 
 in the opposite direction and draft and air supply are 
 too greatly reduced, incomplete combustion will result 
 with the formation of CO and smoke. Again there 
 will be a loss in efficiency, but this also will be indi- 
 cated by the economy gauge, because the moment that 
 the furnace gases are bottled up in the furnace and 
 boiler passages, due to insufficient draft, there will be 
 a rise in the temperature of the gases below the 
 damper. Since the indication of the economy gauge 
 depends upon T - - T 1 , a rise in T 1 reduces that differ- 
 ence and the instrument gives a lower reading. 
 
 Fig. 15 shows a diagram of the Wilsey Fuel Econ- 
 omy Gauge attached to a B. & W. water-tube boiler. 
 It will be noted that one platinum loop is placed in 
 the combustion chamber and the other in the uptake, 
 and that these loops are connected to form two arms 
 of a Wheatstone bridge. Two adjustable resistances 
 within the instrument made up the other arms of the 
 bridge. Across the bridge the indicating galvanometer 
 is connected, with a series and a shunt resistance in 
 its circuit. 
 
 A small battery current is passed through the 
 bridge, and as the resistances of the platinum coils in 
 the boiler vary by reason of the changing tempera- 
 tures to which they are subjected, the bridge is thrown 
 
FURNACE EFFICIENCY 
 
70 FURNACE EFFICIENCY 
 
 out of balance in proportion to the changing tempera- 
 ture at the two points. Now, in series with each plati- 
 num cojl is connected an external resistance, the mag- 
 nitude of which is proportional to the specific heat of 
 the gases at the point where its respective platinum 
 coil is located. That is to say, the coil in the combus- 
 tion chamber has in series with it a resistance propor- 
 tional to the specific heat of the gases at that point, 
 and the coil in the uptake has connected to it a resist- 
 ance proportional to the specific heat of the gases 
 there. 
 
 Thus the current flowing in the two platinum coils 
 becomes a function of the total heat of the gases at the 
 points where the coils are respectively located, and the 
 galvanometer will be deflected according to the ratio 
 of the total heats at the two points. The correction 
 for the effect of radiant heat from the fire is made by 
 adjusting the resistance in series and in shunt with 
 the galvanometer circuit. 
 
 It will be evident that an instrument of this kind 
 must be carefully adjusted for each particular installa- 
 tion. To do this the boiler is run under the most effi- 
 cient conditions possible, as shown by a careful test, 
 and then the resistances in the four arms of the bridge 
 are adjusted until the instrument indicates the effi- 
 ciency shown by the test. After being properly ad- 
 justed, the economy gauge will instantly indicate any 
 departure from the efficient conditions under which 
 it was set. Thus the instrument exercises a watch on 
 efficiency, and careful tests have demonstrated that its 
 accuracy is only limited by the accuracy of the data 
 upon which it is adjusted. 
 
 The coils, Wheatstone bridge and galvanometer are 
 placed in a cast-iron box mounted on the boiler front 
 in plain view of the fireman. The needle of the gal- 
 vanometer shows through the glass front of the box, 
 
FURNACE EFFICIENCY 
 
 71 
 
 the general appearance of the instrument being as 
 shown in Fig. 16. 
 
 FIG. 16. 
 
 Table No. 2 gives the results of a number of 
 tests run on a 500 horse-power Babcock & Wilcox 
 boiler, under different conditions of operation. 
 
72 
 
 FURXACE EFFICIENCY 
 
 be noted that the efficiency as shown by the Wilsey 
 Fuel Economy Gauge agrees closely in each case with 
 the results of the evaporative test. 
 
 Efficiency by 
 Evaporation 
 Per Cent. 
 
 Efficiency by 
 W. F. E. G. 
 Per Cent. 
 
 B. T. U. 
 Per 
 Pound. 
 
 Per Cent 
 Ash. 
 
 C0 2 . 
 
 Per Cent 
 Rated 
 Capacity 
 Developed 
 
 68.9 
 
 69.1 
 
 9,580 
 
 17.2 
 
 12.4 
 
 158 
 
 68.7 
 
 69.1 
 
 9,850 
 
 16.7 
 
 12.2 
 
 130 
 
 66.7 
 
 67.4 
 
 10,584 
 
 11.8 
 
 11.8 
 
 141 
 
 66.2 
 
 67.4 
 
 9,505 
 
 19.8 
 
 11.3 
 
 146 
 
 65.9 
 
 66.5 
 
 9,598 
 
 19.5 
 
 11.7 
 
 147 
 
 67.1 
 
 66.8 
 
 9,815 
 
 16.6 
 
 12.2 
 
 153 
 
 65 8 
 
 64.6 
 
 9,440 
 
 19.5 
 
 10 6 
 
 127 
 
 65.8 
 
 64.7 
 
 10,053 
 
 13.8 
 
 12.2 
 
 156 
 
 TABLE No. 2. 
 
 It is a comparatively simple matter to connect a 
 recording galvanometer to the economy gauge and 
 thus get a continuous efficiency record throughout the 
 twenty-four hours of the day. Fig. 17 shows a chart 
 from such a recording instrument, taken on a 350 
 horse-power Stirling boiler. The period from mid- 
 night to about 4 a.m., during which the fire was 
 banked, is clearly shown on the chart. 
 
 The chief value of such an instrument as the one 
 described here is probably to be found not so much in 
 that it shows the efficiency at all times, as that it shows 
 instantly any departure from proper operating condi- 
 tions. The fireman can fire by the economy gauge to 
 keep the efficiency high, just as he fires by the steam 
 gauge to keep the pressure constant, 
 
FURNACE EFFICIENCY 
 
 73 
 
 FIG. 17. 
 
74 FURNACE EFFICIENCY 
 
 Questions and Answers. 
 
 Q. What is the function of the Wilsey Fuel Econ- 
 omy Gauge? 
 
 A. To indicate at all times the efficiency of the 
 steam-generating process. 
 
 Q. Upon what does it depend for its operation? 
 
 A. Upon the difference in temperature of the fur- 
 nace gases in combustion chamber and uptake. 
 
 Q. Does all the heat of the fuel pass to the gases? 
 
 A. No; some passes to boiler and furnace walls 
 by radiation, and the fuel-economy gauge must be cor- 
 rected for this heat. 
 
 Q. How is the Wilsey instrument constructed? 
 
 A. Two platinum coils are placed in the furnace 
 and boiler, one in the combustion chamber and the 
 other in the uptake. These coils form two arms of a 
 Wheatstone bridge, so that any change in temperature 
 of the furnace gases throws the bridge out of balance. 
 
 Q. What degree of accuracy will this instrument 
 show? 
 
 A. Its indications will usually agree with the 
 results of an evaporative test to within 2 per cent. 
 
FURNACE EFFICIENCY 75 
 
 CHAPTER VIII. 
 
 It was shown in a previous chapter that proper 
 draft conditions in furnace and boiler are of great 
 importance in securing high efficiency. It was pointed 
 out that a certain rather definite relation must exist 
 between the draft pressure in the furnace and the 
 different passes of the boiler if satisfactory operating 
 conditions are to be realized. For example: the loss 
 in draft pressure through the fire bears a relation to 
 the loss through the boiler which is very nearly con- 
 stant for any particular installation, even though there 
 may be considerable variation in load. Of course, this 
 relation varies in furnaces and boilers of different 
 design, and must be determined experimentally and by 
 experience for each particular type. But after this rela- 
 tion has been determined it furnishes a guide to effi- 
 cient operating conditions which is of considerable 
 value. 
 
 This -fact has been utilized by Mr. W. A. Blomck 
 to produce a boiler efficiency meter, which gives con- 
 siderable information in regard to furnace conditions. 
 This instrument, as will be seen from Fig. 18, consists 
 of two sensitive draft gauges, mounted in a suitable 
 case, one above the other. They are both differential 
 gauges, the upper one being connected between the 
 furnace and the boiler side of the damper and the 
 lower one between the furnace and the outside atmos- 
 phere. Thus one gauge shows the draft pressure drop 
 through the boiler and the other the drop through the 
 fire. The tube of the upper gauge is filled with blue 
 oil and the lower one with red oil. 
 
76 FURNACE EFFICIENCY 
 
 Fig. 19 shows the complete meter, in shape to be 
 mounted on the boiler front in view of the fireman. 
 It will be noted that each draft gauge is provided with 
 a pointer ; these pointers are movable and are set by 
 experiment on each installation. That is, a 'careful 
 test of the boiler sho-ws where each gauge should 
 stand when conditions are known to be good. Then 
 the movable pointers are set at these two points, and it 
 becomes the duty oi the fireman to keep the oil in the 
 gauges as near them as possible. 
 
 BOIL /P &WG /5-/v c y Ms r> 
 Went Applied for. 
 
 FIG. 18. 
 
 The function of a differential draft gauge is ta 
 indicate the difference in pressure between the two 
 points to which it is connected. The situation is sim- 
 ilar in principle to the manner in which a voltmeter 
 indicates the difference in electrical pressure between 
 two points. Now, as every engineer knows, the dif- 
 ference in pressure between the inside of the boiler 
 and the outside is due to the difference in weight 
 
FURNACE EFFICIENCY 
 
 77 
 
 between the furnace gases and an equal volume of air. 
 This difference in weight causes a pressure which 
 forces air through the furnace and boiler and up the 
 chimney. As the air and gases pass through the 
 setting from ash pit to chimney they encounter a 
 
 FIG. 19. 
 
 certain resistance to their flow. This resistance 
 causes a drop in draft pressure, just as the electrical 
 resistance of a conductor causes a drop in potential. 
 The magnitude of this draft pressure loss depends 
 upon the resistance encountered in the boiler passages 
 and the rate of flow of the gases. That is, if one or 
 both of the above quantities should increase, the pres- 
 sure drop increases, while if one or both decrease, 
 the drop decreases. 
 
 With the causes of draft pressure loss kept clearly 
 in mind, it is possible to gain a fair idea of the prin- 
 ciples underlying the operation of the Blonck effi- 
 ciency meter. Consider first the lower gauge, which 
 is connected between the furnace and the outside at- 
 mosphere. This gauge shows the difference in draft 
 pressures between the two points to which it is con- 
 nected ; that is, it shows the pressure drop through 
 
78 FURNACE EFFICIENCY 
 
 the fire. This drop, as already explained, will depend 
 upon the resistance of the fuel bed and the rate of 
 flow of air through the fuel. If the fuel bed is too 
 thick or the fire is choked with ashes or slag, there 
 will be a high resistance to the flow of air and conse- 
 quently a large pressure drop through the fuel bed. 
 This will be indicated by a high reading on the lower 
 gauge. On the other hand, if the fire is too thin or 
 there are holes in it, the resistance to the flow of air 
 will be reduced to almost zero, and the pressure drop 
 through the fuel bed will be greatly reduced. 
 
 Thus it follows that the reading of the lower gauge 
 gives at all times a fairly accurate measure of the 
 resistance of the fuel bed. This information, used in 
 connection with the draft pressure drop through the 
 boiler passages, is extremely valuable as a guide to 
 correct furnace conditions. 
 
 Consider now the upper gauge of the meter, which 
 is connected between the furnace and the boiler side 
 of the damper. This gauge gives a measure of the 
 draft pressure loss through the boiler, as distinguished 
 from the furnace. Now the resistance to the flow of 
 the furnace gases through the boiler is not subject to 
 wide and sudden fluctuation as it is in the 'Case of the 
 fuel bed. Of course this resistance is subject to some 
 change, such, for example, as might be due to accu- 
 mulations of soot on the tubes or in the flues, defective 
 baffles, etc., and the Blonck meter will give informa- 
 tion in regard to just such conditions. But the point 
 to be kept clearly in mind here is that changes in 
 draft pressure loss in the boiler are chiefly due to 
 changes in the rate of flow of the gases. It must be 
 remembered that draft loss depends upon rate of flow 
 and resistance, and since in normal operation the lat- 
 ter is nearly constant or at most varies but slowly, 
 the draft loss becomes a fairly accurate measure of 
 the rate of flow of the gases. Thus the blue upper 
 
FURNACE EFFICIENCY 79 
 
 gauge gives a reading which is closely proportional 
 to the amount of furnace gases passing through the 
 boiler per unit of time. 
 
 If we wish to revert again to electrical terms, the 
 upper gauge is an ammeter which shows the rate of 
 flow through the boiler. The lower gauge partakes 
 of the nature of a voltmeter, showing the difference in 
 draft pressure tending to force air through the fuel bed. 
 
 When the Blonck efficiency meter is to be applied 
 to a steam generating unit the chief consideration is 
 to get it properly set. This should be done during the 
 longest daily period of average load on the boiler, 
 which will give as nearly average load conditions as it 
 is possible to get. All operating conditions, such as 
 thickness of fire, position of damper, method of firing, 
 frequency of cleaning fires, etc., should be carefully 
 regulated to give the most efficient operating condi- 
 tions obtainable. In determining these conditions the 
 hand- flue gas instrument will be found to give much 
 valuable information. When the desired conditions 
 have been obtained the movable pointers shown in 
 Fig. 19 are set to the points where the oil stands in the 
 two gauges. It is now the duty of the furnace oper- 
 ator to keep the gauges as nearly as possible at these 
 two fixed points. The manner in which the meter is 
 connected to the boiler and the location of the draft 
 tubes is shown in Fig. 20. 
 
 The action of the meter under different conditions 
 of operation is as follows: Suppose that the fire 
 becomes too thin, or holes burn in it, or it burns short 
 at the back. This means that the draft loss through 
 the fire will be small, and the red gauge will give a 
 smaller reading than it should. But the large volume 
 of air passing through the furnace and boiler will 
 cause an increase in draft pressure drop between fur- 
 nace and uptake. This will be indicated by a larger 
 reading on the blue gauge. Such a condition as this is 
 
80 
 
 FURNACE EFFICIENCY 
 
 shown in Fig. 21, Example No. 2 The relative position 
 of the two gauges for normal operation is shown in 
 Example No. 1. 
 
 When the fire is too thick, or choked with ashes 
 and slag, there will be a greater drop than normal 
 through the fire, while on account of the reduced air 
 supply there will be less drop through the boiler. 
 
 Ai FUBNACC? CONNK.TION. 
 D. 
 
 CONNECTIONS OF BOILER EFFICIENCY MFTER TO 
 WATER TUBE BOILER. 
 
 This condition is shown in Example No. 3. It will 
 be noted that in the two 'Cases considered thus far the 
 two gauges moved in opposite directions from their 
 normal points. This w r ill be the case when the load 
 remains practically constant, and the only change is 
 in the condition of the fire. 
 
 In Example No. 4 is shown the indications of the 
 meter when the boiler is running with an overload. 
 
FURNACE EFFICIENCY 
 
 81 
 
 In this case comparatively thick fuel bed must be 
 carried in order to supply the necessary rate of com- 
 bustion. But the damper must now be wide open so 
 as to furnish enough draft to force the required 
 amount of air through the thick fuel bed. The result 
 is an increase in the pressure drop through the fire, 
 
 /, Normal operation of boiter\ 
 
 2, Too much oir,jel bed too thin or holes' 
 
 3, Too little air, fiiel bed hothictfor 
 
 ChofC<sdbystacj\ 
 
 , Boiler running with overload-^ 
 
 5, Boifer running with under food * 
 
 FIB. 21. 
 
 DIAGRAM OF BOILER EFFICIENCY METER AND PRINCIPAL 
 INDICATIONS? OF INSTRUMENT. 
 
 because both resistance and rate of air flow have 
 increased. This gives an increased reading on the red 
 gauge, the oil moving to the right as shown. But 
 since more air is flowing through the fire than before, 
 the pressure drop through the boiler increases. This 
 gives a larger reading on the blue gauge, the oil mov- 
 ing to the right as shown. The conditions indicated 
 by such a reading of the gauge (see No. 4) are satis- 
 factory, because the ratio between furnace drop and 
 boiler drop has not been changed to any extent. 
 
82 
 
 FURNACE EFFICIENCY 
 
 Example No. 5 shows the indication of the meter 
 under light load. In this case the fire is thin and the 
 pressure drop through it is small, which gives a 
 reduced reading on the red gauge. But the stack 
 
 Boit.ee E:F&'ctNc Y M&r&a . 
 
 H&M& Boiler 
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 FIG. 22. 
 TYPICAL, READINGS FOR A WATER TUBE BOIER. 
 
 draft has been reduced by partially closing the dam- 
 per, so that less air is being forced through the fire in 
 proportion to the reduced rate of combustion. This 
 gives less pressure drop through the boiler and a 
 reduced reading on the blue gauge, as shown. Here 
 again the ratio of the two drops remains practically 
 constant? so that conditions are about as they should 
 be for this particular load. 
 
 The manner in which the indications of the meter 
 show the conditions within the furnace and boiler is 
 shown in Fig. 22. The upper curve in the figure shows 
 
FURNACE EFFICIENCY 
 
 83 
 
 the percentage of CO 2 , which runs from a minimum 
 of 6 per cent to a maximum of 11.5 per cent. The 
 dotted curves show the reading of the upper and lower 
 gauges, respectively, in hundredths of an inch. At the 
 beginning of the test the CO 2 was 6 per cent, the 
 upper gauge read 80 and the lower one 22. Now 6 
 per cent CO 2 indicates too much air. The fire was 
 therefore gradually thickened, which increased the 
 
 BOILER EFFICIENCY METER 
 
 MNtt -BOILER 575 M p CAPACITY, GKECN CHAIN &RATC. RUMNINC FULULOAD 
 TEST OCTOBER IO, 1912 
 
 FIG. 23. 
 
 RESULTS OF TEST ON BOILER WITH CHAIN GRATE 
 SHOWING EFFECT OF OPEN ASH DOOR. 
 
 pressure drop through the fire, but decreased the air 
 supply. Therefore the lower gauge read more, the 
 upper one less, and the CO 2 increased. This was 
 continued until 11.5 per cent CO 2 was reached, when 
 the lower gauge read 35 and the upper one 70. A 
 further increase in thickness of fire carried air reduc- 
 tion too far, which resulted in the formation of smoke 
 
84 FURNACE EFFICIENCY 
 
 and CO, with less CO 2 . Therefore the movable 
 pointers on the efficiency meter were set at 70 for the 
 upper gauge and 35 for the lower one. 
 
 Fig. 23 shows the result of a test of a 375 horse- 
 power Stirling boiler, with Green chain grate stoker. 
 The chief point of interest in these curves is the sud- 
 den drop in CO 2 at 11 :05 a.m. It will be noted that 
 the reading of the upper gauge of the meter increased 
 at this time, while the lower one decreased. This 
 expansion of the distance between the two gauges is 
 an indication of inefficient conditions, as we have 
 already seen, and thus agrees with the low CO 2 noted 
 at that time. This condition was caused by the open- 
 ing of an ash clean-out door in the basement, which 
 resulted in excess air being admitted to the furnace. 
 It will be seen from this figure that whenever the 
 readings of the two gauges approach each other the 
 CO 2 is high and combustion conditions are good, and 
 that when the distance between the gauges increases 
 the opposite results are noticed. This is true until 
 the position of normal setting is reached. 
 
 Fig. 24 shows the results of a test on a 375 horse- 
 power Wickes boiler, served with a Murphy stoker. 
 These curves show the behavior of the meter during 
 period's of excess air and lack of air, the shaded por- 
 tions showing the nature of the air supply. The nor- 
 mal setting of the gauges is 77 for the upper one and 
 18 for the lower one. When the difference is greater 
 than this there is excess air and low CO 2 , as at 12 :17 
 p.m., for example. When the difference between the 
 two gauges is less than normal there is fair CO 2 , but 
 reduced steaming capacity, as shown at 11:52 a.m. 
 This shows that CO 2 is not always a safe guide to 
 high efficiency. When the air supply is unduly re- 
 stricted the CO 2 may be fairly high, but there will also 
 be CO, smoke, reduced capacity, and reduced effi- 
 ciency. This condition is plainly shown by the meter, 
 
FURNACE EFFICIENCY 
 
 85 
 
 the difference between the two gauges being less than 
 normal. 
 
 Fig. 25 shows results taken from a test of a B. & 
 W. boiler, with B. & W. chain grate stoker. The 
 effect upon the efficiency meter of length of fire and 
 
 BOILER EFFICIENCY METER 
 
 PMV STOKCIt KUNNIMq FULL LOAD 
 TEST JANUARY 9, 191.3 
 
 FIG. 24. 
 
 TEST SHOWING RELATION BETWEEN AIR STTPPY AND 
 CO, IN FLUE GAS. 
 
 thickness of fuel bed is clearly shown. The test was 
 begun with a 9-inch fire, the upper gauge reading 
 about 80 and the lower one 60. As the test continued 
 the distance between the gauge readings increased, 
 and the CO 2 dropped, indicating excess air and reduced 
 efficiency. 
 
 At about 11:10 a. m. the thickness of the fire was 
 increased to 10J4 inches, but the results did not be- 
 come noticeable until about 11 :35 a.m., because of the 
 
86 
 
 E S 
 
 to 
 
 09 
 H 
 ^ 
 
FURNACE EFFICIENCY 87 
 
 slow travel of the grate. At this point it will be seen 
 that the curves representing gauge readings crossed 
 each other. That is, the draft pressure drop through 
 the fire became greater than that through the boiler. 
 This indicates too thick a fire, insufficient air passing 
 through the boiler, and hence reduced steaming capac- 
 ity, even though the CO 2 is fairly high. 
 
 At 12:05 p.m. the thickness of fire was reduced to 
 8 inches, with the result that the gauge reading curves 
 recrossed each other, indicating that conditions were 
 about correct again. A study of these curves will 
 show that thickness of fire and" length of fire, whether 
 short or long, have an immediate effect upon the effi- 
 ciency meter. 
 
 Fig. 26 shows the results of a test on the same B. & 
 W. boiler, the object being to show the effect upon 
 the efficiency meter of different rates of working, as 
 shown by a General Electric Steam Flow Meter. The 
 upper curve shows the instantaneous flow meter read- 
 ings, while the average is shown by the dotted line. 
 It will be seen that the curve representing average 
 rate of evaporation is practically parallel to the curves 
 showing the readings of the meter gauges. Thus the 
 relative distances of both gauges from their normal 
 points, indicated by the fixed arrows or pointers, are 
 a measure of the lead carried by the boiler. If both 
 gauges go above this normal point, there is an over- 
 load ; if below, there is an underload. (See Fig. 20.) 
 
 It will be evident from the curves that have been 
 presented herewith that the Blonck Efficiency Meter 
 "can be relied upon to give much valuable information 
 in regard to conditions in the furnace. Also, it gives 
 this information almost instantly, so that faulty con- 
 ditions can be corrected before serious loss can occur. 
 If its indications are intelligently made use of, there 
 can be no doubt but that the Blonck meter will 
 greatly assist in maintaining high furnace efficiency. 
 
FURNACE EFFICIENCY 89 
 
 Questions and Aswers. 
 
 Q. What are the essential parts of the Blonck 
 Boiler Efficiency Meter? 
 
 A. It consists of two differential draft gauges. 
 
 Q. How are these gauges connected in the fur- 
 nace and boiler? 
 
 A. One is connected between furnace and outside 
 atmosphere, and the other between furnace and boiler 
 side of damper. 
 
 Q. What do these gauges show? 
 
 A. One shows draft pressure loss through the fire 
 and the other the loss through the boiler. 
 
 Q. How can these readings indicate efficiency? 
 
 A. They show the relation between furnace loss 
 and boiler loss, which have a nearly constant relation 
 when efficient conditions are maintained. 
 
90 FURNACE EFFICIENCY 
 
 CHAFER IX. 
 The Chain Grate Stoker. 
 
 It was shown in a previous chapter that one of the 
 most essential conditions for efficient and smokeless 
 combustion is a slow and uniform distillation of the 
 volatile gases from the coal. This requires a gradual 
 and continuous feeding of the fuel into the furnace, 
 so that the evolution of the gas may be maintained at 
 a uniform rate. 
 
 This principle has been recognized by engineers for 
 some time, and has been kept prominently in mind in 
 the design of most mechanical stoking devices. It is 
 known as the principle of progressive combustion, the 
 fuel being carried gradually forward into the furnace 
 as the combustion progresses. Even before the days 
 of mechanical stokers when all boiler furnaces were 
 fired by hand, this principle was applied to a limited 
 extent. It consisted in charging the green fuel onto a 
 dead plate just inside the furnace door, where the 
 volatile gas was driven off. When the coal had be- 
 come fairly well coked it was then pushed back on the 
 grate where the combustion of the fixed carbon took 
 place. This method of firing is still made use of in 
 many hand-fired furnaces, but it is, of course, open to 
 the serious objection that large quantities of cold air 
 enter the furnace while the fire-door is open, and thus 
 the efficiency is reduced. This same objection applies 
 to a greater or less extent to any method of firing by 
 hand. 
 
 The chain grate stoker is a device which provides 
 for this method of progressive combustion, while at 
 
FURNACE EFFICIENCY 
 
 91 
 
 the same time excluding all unnecessary air from the 
 furnace. The first stoker of this kind was designed in 
 England, but it is now used very largely in this coun- 
 try, American designers and engineers having added 
 many improvements over the original design, by which 
 it is better adapted to American coals. It consists of a 
 moving endless chain mounted on a frame, the fuel 
 being carried forward on the chain. This method of 
 feeding the coal into the furnace is an almost ideal 
 application of the principle of progressive combustion. 
 The volatile gases are first driven off by the heat 
 radiated from the incandescent parts of the furnace. 
 Then the fixed carbon is completely consumed, and 
 when the chain reaches the end of its travel the asnes 
 are dumped and the chain kept clean and free from 
 ash or clinker. 
 
 FIG. 27. 
 CHAIN GRATE STOKER. 
 
 A good idea of the construction and general ap- 
 pearance of the chain grate stoker may be obtained 
 from Fig. 27. It will be noted that the whole device is 
 
92 FURNACE EFFICIENCY 
 
 mounted on rollers running on a track, thus making it 
 comparatively easy to remove the stoker from under 
 the boiler in case extensive repairs are required. Small 
 repairs like the replacing of broken links, can be made 
 without removing the stoker and usually without even 
 stopping it. Fig. 28 shows a front view of the stoker 
 with the chain removed, and Fig. 29 a rear view. 
 
 FIG. 28. 
 FRONT VIEW OF STOKER WITH CHAIN REMOVED. 
 
 In the design of a machine of this kind there are a 
 number of important points to be considered if it is to 
 give satisfaction under severe conditions of operation. 
 In the first place, the frame upon which the chain is 
 mounted must not be exposed too directly to the heat 
 of the furnace, for it would warp and crack and would 
 soon be destroyed. A glance at Fig. 27 will show that 
 in the modern chain-grate stoker the side girders of 
 the frame are removed a considerable distance from 
 the fire, and they are also provided with large air 
 spaces. This keeps the side girders 'Cool and assists 
 in providing a uniform supply of air to the underside 
 of the chain, that is, beneath the fuel bed. 
 
FURNACE EFFICIENCY 93 
 
 When such a stoker is subjected to hard and con- 
 tinuous service it is to be expected that a link will 
 occasionally break or burn out and will have to be 
 replaced by a new one. In the early designs the links 
 were simply strung on a round rod, holes being pro- 
 vided in the links to receive the rod. This made the 
 removal of a wornout link a rather troublesome job, 
 since it could not be taken out without disturbing all 
 the other links between it and the end of the rod. This 
 involved stopping the stoker and possibly a shut-down 
 of the boiler, for a short time at least. Fig. 30 shows 
 the links used on the Green chain-grate stoker, by 
 means of which this trouble is avoided. The links 
 have slotted openings and the connecting bar upon 
 
 FIG. 29. 
 REAR VIEW OF STOKER WITH CHAIN REMOVED. 
 
 which they are mounted is oval in cross section. In a 
 certain position this connecting bar will slip into the 
 slot in a link, but when the bar is turned slightly it 
 is locked in position and can not be removed. The 
 
FURNACE EFFICIENCY 
 
 PIG. 30. 
 LINKS FOR CHAIN. 
 
FURNACE EFFICIENCY 95 
 
 binder links are provided with holes instead of slots, 
 and are placed one at each end of the connecting bars. 
 Cotter pins are then applied to hold the binder links 
 in place ; these cotters and end links are shown clearly 
 in Fig. 27. 
 
 With such an arrangement, when a link is to be 
 removed it is only necessary to remove cotter pins 
 and binder link, turn the connecting bar slightly and 
 lift the link out. . This operation can be done quickly, 
 it being unnecessary in many cases to even stop the 
 stoker, as already mentioned. 
 
 In the Green grate, in sizes exceeding 7 feet 6 inches 
 in width, the chain surface is ''double web." That is, 
 the chain surface consists of two continuous sections, 
 the connecting bars extending only half way across 
 the total width of chain. This requires binder links in 
 the middle of the chain, a special design being used 
 which does not require the removal of the link in 
 order to turn the connecting bar when some inside link 
 is to be removed. 
 
 FIG. 31. 
 TENSION ADJUSTING DEVICE. 
 
 It is also very essential that chain tension be ad- 
 justable without removing the stoker from the furnace 
 space. The method by which this is done may be seen 
 from Fig. 29, and also more in detail from Fig, 31. 
 
96 FURNACE EFFICIENCY 
 
 The adjusting screws are accessible from the rear 
 while the stoker is in place. 
 
 The stoker is driven from an eccentric on a line 
 shaft, placed either overhead or below the floor. The 
 driving mechanism is shown from two different points 
 of view in Figs. 32 and 33. It will be seen to consist 
 
 FIG. 32. 
 DRIVING MECHANISM. 
 
 of a ratchet operated by the rod from the overhead 
 (in this case) eccentric ; cast-steel pawls and cast-steel 
 spur gear train. The whole is carried on an inde- 
 pendent frame, bolted to the stoker frame. A study of 
 Figs. 32 and 33 in connection with Fig. 27 will make 
 plain just how the stoker is driven. 
 
 Fig. 34 shows the design of the sprockets which 
 carry the chain. They are mounted on the front and 
 rear sprocket shafts, Fig. 28 plainly showing the ar- 
 
FURNACE EFFICIENCY 97 
 
 rangement. It will be noted that these sprockets are 
 made scalloped between the teeth, the purpose being 
 to insure the proper seating of the drive links of the 
 chain upon the sprockets. This proper seating might 
 not occur if the chain should reach the front sprockets 
 covered with ashes accumulated during its return 
 travel from rear to front sprocket shaft. 
 
 The thickness of full bed which the stoker receives 
 is controlled by a regulating feed gate. It is supported 
 from a square shaft shown plainly in Fig. 28, and 
 
 FIG. 33. 
 DRIVING MECHANISM. 
 
 moves up and down between vertical guides. The 
 square shaft carries a sector on one end engaging 
 a worm on the opposite side of the frame from the 
 driving mechanism. In this way the gate may be 
 
98 FURNACE EFFICIENCY 
 
 readily raised or lowered to vary the thickness of the 
 fire. A lining of fire brick is used to protect the metal 
 of the gate from the heat of the furnace. A frequient 
 source of trouble with the feed gate has been the ten- 
 dency of the fire to eat back into the coal hopper and 
 
 FIG. 34. 
 SPROCKET. 
 
 thus in time damage and destroy the gate. This 
 trouble is now prevented in the Green stoker by pla- 
 cing removable shields on the gate in such a manner 
 as to maintain a ventilated air space between the 
 shield and the outside of the gate, thus protecting the 
 latter from the heat. The shields extend below the 
 bottom o>f the tile lining to protect it from injury, and 
 thus the shields determine the thickness of the fuel 
 bed. Details of the gate constraction are shown in 
 Fig. 35. 
 
 An important point in connection with the opera- 
 tion of a chain-grate stoker is the proper ignition of 
 the fuel as it enters the furnace. Perhaps the most 
 successful method at the present time is a flat ignition 
 arch placed over the front of the grate. This arch re- 
 
FURXACE EFFICIENCY 
 
 09 
 
 ceives heat from the fire and reflects it down on the 
 incoming coal, thus raising the temperature until the 
 volatile gases are driven off and the coke is ignited. A 
 flat arch of this kind is much easier to build and main- 
 tain than a sprung arch, and being equally distant from 
 the fuel all the way across the furnace it gives a uni- 
 form igniting effect. 
 
 Figs. 36 and 37 show the construction and method 
 of support of a flat ignition arch designed and patented 
 by the Green Engineering Company. Two channels 
 comprise the main supporting frame ; between these 
 channels a number of I-beams are run, the latter sup- 
 porting the special fire tiles as shown in Fig. 36. This 
 
 FIG. 35. 
 DETAILS OF REGULATING FEED GRATE. 
 
 method of construction removes all side thrust upon 
 the side walls cf the boiler setting, which is impossible 
 with any form of sprung arch. 
 
 In connection with the chain-grate stoker the water 
 back is an important feature. Fig. 39 shows a pressure 
 
i( FURNACE EFFICIENCY 
 
 water back in position in the furnace. It will be seen 
 to consist of two lengths of pipe connected together 
 at one end, and at the other connected to the water 
 space of the boiler. Thus the water back becomes a 
 
 FIG. 36 
 METHOD OF SUPPORTING FIRE TILE IN IGNITION ARCH. 
 
 part of the water circulation system of the boiler, 
 water flowing through it at all times. The water back 
 is placed just above the chain at the rear end, and 
 under the overhang of the bridge wall. In this position 
 it protects the bridge wall from the excessive heat of 
 the furnace, and also adds to the heating surface of the 
 boiler. It is not improbable that as much as one 
 boiler horse-power is generated per square foot of 
 water-back surface. 
 
 In order to get high furnace efficiency with a chain- 
 grate stoker it is necessary to prevent the infiltration 
 of excess air at all points, as indeed it is with any form 
 of furnace. Leakage is very likely to occur at the end 
 of the grate between the chain and the overhanging' 
 bridge wall. The water back helps to close up this 
 space, but there must, of course, be enough free space 
 to allow for the discharge of the ashes. In order to 
 
FURNACE EFFICIENCY ; ' 1'H 
 
 make sure that no leakage of air will occur at this 
 point a damper is plaiced below in such a manner as 
 to effectually prevent the entrance of air. This 
 damper is shown in the setting elevation, Fig. 38. 
 
 The chain-grate stoker described thus far is de- 
 signed for use with free-burning, high-volatile coal. 
 When low-volatile coals are to be used a somewhat 
 different design is required. Fig. 40 shows the Green 
 L Type Stoker, designed for this purpose. The chief 
 difference between this stoker and the type already 
 described is the inclined plate at the front, down which 
 the coal is made to slide by a slight agitation of the 
 plate. This serves to break up the coal and deliver it 
 to the chain in a fragmentary condition. The tendency 
 of this ccal is to cake as the volatile is driven off and 
 the agitation of the plate sie'rves to prevent its forming 
 in a more or less solid mass. 
 
 The chain-grate stoker in the forms described here 
 has a wide application in steam boiler pratice. With 
 
 FIG. 37. 
 METHOD OF SUPPORTING IGNITION ARCH. 
 
 a properly constructed furnace it can be operated with- 
 out smoke and with high economy with very low-grade 
 coal. The charges for stoker and furnace maintenance 
 and repair are probably as low as for any other me- 
 
104 
 
 FURNACE EFFICIENCY 
 
 chanical stoker on the market, and lower than many. 
 It adapts itself well to heavy overload conditions, with 
 very little loss in efficiency. The increasing number 
 
 FIG. 40. 
 CHAIN GRATE STOKER FOR CODING COALS. 
 
 of these stokers in use indicates that it meets satis- 
 factorily a wide range of conditions in steam-boiler 
 practice. 
 
 Questions and Answers. 
 
 Q. What is one of the most important require- 
 ments for smokeless combustion? 
 
 A. A uniform distillation of the volatile gases 
 from the coal. 
 
 Q. How is this best effected? 
 
 A. By a uniform rate of feed of the fuel to the 
 furnace. 
 
 Q. Name one device designe.d for this purpose? 
 
 A. The chain-grate stoker. 
 
 Q. What' is the essential part of the stoker? 
 
FURNACE EFFICIENCY 105 
 
 A. A moving endless chain which carries the fuel 
 into the furnace. 
 
 Q. How is this chain moved? 
 
 A. Power is supplied from an eccentric on a line 
 shaft; the rod from the eccentric operates a ratchet 
 and pawl which drive the stoker by means of a train 
 of spur gears. 
 
 Q. Can the rate of travel of the stoker be changed? 
 
 A. Yes, the point where the eccentric rod is fas- 
 tened to the ratchet is adjustable, which varies the 
 travel of the pawl. 
 
 Q. How is the thickness of the fuel bed con- 
 trolled? 
 
 A. By an adjustable gate at the front of the sto- 
 ker. 
 
 Q. What is a water back? 
 
 A. A pipe placed at the back end of the grate in 
 front of the bridge wall, through which water circu- 
 lates. 
 
 Q. What is its purpose? 
 
 A. To protect the bridge wall and assist in sealing 
 the rear of the furnace. 
 
 Q. What is an ignition arch? 
 
 A. A flat arch in the front of the furnace which 
 helps to ignite the incoming coal. 
 
106 FURNACE EFFICIENCY 
 
 CHAPTER X. 
 The Murphy Automatic Furnace. 
 
 The chain-grate stoker discussed in the previous 
 chapter is perhaps the best known example of the front 
 feed principle in automatic stoking devices. Another 
 well-known and widely used method is that of the 
 "side feed/' in which the fuel is fed into the furnace 
 from two magazines, one on either side of the setting. 
 Perhaps the best known example of the side-feed prin- 
 ciple in automatic stokers is the Murphy furnace. 
 
 A good idea of this furnace may be obtained from 
 Fig. 41, which shows a transverse section viewed from 
 the rear end. A similar view is shown in Fig. 42, in 
 which more of the details of construction may be seen. 
 This stoker will be seen to consist essentially of two 
 inclined grates, one on each side of the furnace, the 
 upper end being at the side and the lower end near the 
 center. These grates are made up of two different 
 kinds of bars arranged alternately. In. Fig. 43 is shown 
 the general appearance and design of these grate bars, 
 one of which is stationary and the other movable. The 
 movable bars are pivoted at their upper ends, and are 
 given a rocking motion at their lower ends by means 
 of a rocker bar. This gives them a motion alternately 
 above and below the stationary bars and in this way 
 the fuel bed is kept broken up and the movement of the 
 coal down the incline is facilitated. It will be noted 
 from Fig. 43 that the stationary grate bars are pro- 
 vided with ribs on both sides for the upper half, ap- 
 proximately, of their length. This is for the purpose 
 of preventing the droppage of fine coal through the 
 grate before the coking process is complete, and also 
 
FURNACE EFFICIENCY 
 
 107 
 
 to exclude excess air at this particular point in the 
 combustion process. 
 
 The method of feeding the coal onto these inclined 
 grates is interesting, and may be seen clearly from 
 Fig. 42. On either side of the furnace, and extending 
 its entire length from front to back, is a coal magazine 
 into which coal may be discharged by a down spout 
 
 FIG. 41. 
 
 from an overhead bunker, or shoveled by hand. Just 
 at the bottom cf this magazine is the coking plate (see 
 Fig. 42) upon which the coal is first discharged from 
 the magazine. This plate furnishes the bearing for the 
 
108 
 
 FURNACE EFFICIENCY 
 
 upper end of the grate bars, the movable bars turning 
 on pins as shown in the figure. Below the coking plate 
 is an air duct through which air is drawn from the 
 front of the furnace and discharged at the back into the 
 
 FIG. 42. 
 
 air chamber in the arch. This keeps the coking plate 
 from becoming overheated, thus adding greatly to its 
 length of life. 
 
 The stoker boxes are for the purpose of pushing the 
 coal from the magazine out onto the coking plate. 
 They are shown in Fig. 42 and also more in detail in 
 Fig. 44. These boxes are moved back and forth by 
 means of segment gears and racks, the gears being 
 mounted on the stoker shaft which is driven from an. 
 outside source of power. The reciprocating motion of 
 the stoker boxes produces the feed of the fuel, and can 
 
FURNACE EFFICIENCY 
 
 109 
 
 be regulated to suit the character of the coal and the 
 rate of combustion. 
 
 FIG. 43. 
 
 The lower ends of the grate bars are supported on 
 two heavy plates known as the "grate bearers/' one 
 for each side of the funace. These grate bearers are 
 supported on I-beam cross' girders, as shown plainly in 
 Fig. 41. In addition to carrying the lower ends of the 
 grate bars, they furnish a support for the rotating 
 clinker grinder. The latter may be single as shown in 
 Fig. 45, or double, as shown in Fig. 46. 
 
 This clinker grinder consists of a square steel shaft 
 upon which are placed small toothed cast-iron seg- 
 ments. The latter may be easily and cheaply renewed 
 in case of wear or breakage. As its name implies, the 
 function of the clinker grinder is to break up the large 
 lumps of ash and clinker which might otherwise clog 
 
110 
 
 FURNACE EFFICIENCY 
 
 the furnace, and discharge them into the ash pit below. 
 Just below the clinker grinder is a small perforated 
 pipe connected with the exhaust from the stoker en- 
 
 FIG. 44. 
 
 gine. This pipe is shown plainly in the longitudinal 
 section of the furnace. Fig. 47. The exhaust steam 
 emitted directly beneath the clinker grinder serves to 
 soften the clinker and so assist in the cleaning process. 
 The rate of feed of tne grinder is adjustable, so that it 
 can be varied to suit the aniout of ash in the coal. 
 
 An important feature of this furnace is the double 
 sprung arch, The arch is supported at each side of the 
 furnace on the arch plate shown in detail in Fig. 48. It 
 will be noted that on this arch plate are cast a number 
 of ribs which form a series of air ducts immediately 
 under the arch and over the coking plate. The manner 
 in which the arch is sprung from the arch plate, and 
 also the air ducts just below the arch, are shown plain- 
 ly in Fig. 41. Further details are shown in Fig. 49. 
 
FURNACE EFFICIENCY 
 
 111 
 
 The lower arch is built of special fire brick, varying 
 in thickness from 6 inches to 12 inches according to the 
 size of the furnace. Above this fire-brick arch is an air 
 space from 3^ inches to 5 inches in thickness. It was 
 stated above that air from the duct under the coking 
 
 FIG. 45 
 
 plate is discharged into this space in the arch. Here 
 it is heated by the radiant heat from the furnace, and 
 
 finally discharged through the ribbed arch plate, over 
 the coal on the coking plate. This supply of hot air 
 
il FURNACE EFFICIENCY 
 
 being discharged over the coal during the coking 
 process greatly assists in the 'combustion of the vola- 
 tile gases. It is 'because of this feature that the Mur- 
 phy furnace can be operated practically without smoke. 
 
 FIG. 47. 
 
 The upper arch is really a double arch of common 
 brick, and over this is placed a steel covering, rolled to 
 conform wit'h the curve of the arch. In such a con- 
 struction as this the furnace requires no side walls but 
 is enclosed instead in sheet steel sides which the 
 makers supply with the furnace. 
 
 In the operation of this furnace there are five shafts 
 or bars which must be given an oscillating motion, as 
 
FURKACE EFFICIENCY 
 
 11.1 
 
 follows. Two rocker bars, two stoker shafts, and one 
 clinker grinder. In the case of a double clinker grinder 
 this becomes six instead of five. The power to operate 
 these shafts is supplied by a reciprocating bar across 
 the front of the furnace. This is a heavy forged steel 
 bar to which the operating parts are connected by 
 
 FIG. 48. 
 
 means of links. The construction and arrangement of 
 parts is shown in Fig. 50, which shows the Murphy 
 furnace applied to a horizontal tubular boiler. The 
 operating links can be adjusted- or removed at any 
 time, so that one furnace of a battery may be thrown 
 out of service without interfering with the others. 
 
 The reciprocating bar which operates the furnace 
 may be driven directly from a small stoker engine as 
 shown in Fig. 51, or if convenient an electric motor 
 may be substituted for the engine. 
 
 In the operation of this furnace, as the coal leaves 
 the magazine it is fed alternately and intermittently 
 onto the coking plate by the action of the stoker boxes. 
 
114 FURNACE EFFICIENCY 
 
 It rests for a short time on the coking plate, where the 
 volatile gases are distilled. These gases are then 
 mixed with hot air which is being discharged from 
 the ducts in the arch plate. This forms a readily com- 
 bustible mixture, all the requirements for complete 
 combustion being present. Thus the volatile part of 
 the coal is consumed without the formation of smoke. 
 
 The fuel next passes out onto the inclined grates 
 where it receives the necessary amount of air coming 
 through the grates from below. When the carbon is 
 practically all consumed and the lower end of the grate 
 bars has been reached the motion of the moveable bars 
 tends to prevent the formation of large clinkers. In as 
 much as these bars are pivoted at their upper ends they 
 have their greatest motion at the lower ends, where the 
 motion is needed to assist in the prevention of large 
 clinkers. When the bottom of the grate has been 
 reached the ash and clinker are received by the clinker 
 grinder and reduced to small size, after which they are 
 dropped through to the ash pit below. 
 
 This furnace is usually installed by the makers to 
 give its best efficiency at from 100 to 150 per cent of 
 boiler rating. This, however, by no means represents 
 the limit of capacity of the furnace. As much as 200 
 per cent of boiler rating may be secured with but little 
 loss in efficiency. The question of high efficiency at 
 high rates of working is very largely one of the proper 
 proportioning of furnace and draft. In fact with a 
 good grade of coal and sufficient draft there seems to> 
 be no reason why this furnace can not be operated at a 
 capacity close to the maximum ability of the boiler to 
 absorb heat. 
 
 Questions and Aswers. 
 
 Q. To what class of automatic stokers does the 
 Murphy Furnace belong? 
 A. To the side feed class. 
 
FURNACE EFFICIENCY 
 
 115 
 
 FIG. 49. 
 
116 
 
 FURNACE EFFICIENCY 
 
FURNACE EFFICIENCY 
 
 117 
 
 Q. Of what does the chief part of this furnace con- 
 sist? 
 
 A. It consists of two grate surfaces, inclined from 
 the side and meeting in the middle of the furnace. 
 
 FIG. 51. 
 
 Q. How many kinds of grate bars are used? 
 A. Two kinds, stationary and movable. 
 
118 FURNACE EFFICIENCY 
 
 Q. How are the movable bars placed in the fur- 
 nace? 
 
 A. They are pivoted at their upper ends and given 
 a rocking- motion at their lower ends by means of two 
 rocker bars. 
 
 Q. Where is the coal supply fed to the furnace? 
 
 A. Into two magazines, one. on. each side. 
 
 Q. What is the coking plate? 
 
 A. A flat plate at the bottom of the coal magazine 
 upon which the coal is discharged. 
 
 Q. How is the coal fed to the coking plate? 
 
 A. By means of the stoker boxes, operated by seg- 
 ment gears and racks. 
 
 Q. What is the clinker grinder? 
 
 A. It is a heavy steel shaft on which toothed cast- 
 iron segments are placed, to break up the clinker. 
 
 Q. Where is the clinker grinder placed? 
 
 A. At the bottom of the inclined grates at the cen- 
 ter of the furnace. 
 
 Q. What kind of an arch is used in this furnace? 
 
 A. A double arch, sprung between the sides cf the 
 furnace. 
 
 Q. What is the object of the airspace in the arch? 
 
 A. To heat air to assist in the combustion of the 
 fuel. It also makes a better arch. 
 
 Q. How is the furnace operated? 
 
 A. By a reciprocating bar across the front, driven 
 by a small stoker engine. 
 
FURNACE EFFICIENCY 
 
 119 
 
 CHAPTER XL 
 The Jones Under-feed Stoker. 
 
 In our discussion of mechanical stokers nothing 
 has been said thus far of the under-feed principle. It 
 consists essentially in feeding the coal in at the bot- 
 tom of a retort in which it rises gradually to the com- 
 bustion zone at the top. As the coal rises to the top, 
 of the retort its temperature rises gradually, the vola- 
 
 
 FIG. 52. 
 
 tile gases being distilled in the process. These gases 
 must then rise through the fire at the top when com- 
 plete combustion takes place. Finally the coal itself, 
 which by this time has been reduced to coke, reaches 
 the surface and is burned. 
 
 Perhaps the best known example of this principle 
 is the Jones Under-feed Mechanical Stoker. In Fig. 52 
 
120 
 
 FURNACE EFFICIENCY 
 
 is shown a view of the fuel retort, which is the only 
 part of this stoker which is inside the furnace and 
 therefore in contact with the fire. This retort can be 
 made heavy and durable, and since there are abso- 
 lutely no moving parts to come into contact with the 
 fire, the maintenance charges on a stoker of this kind 
 are extremely small. 
 
 FIG. 53. 
 
 It will be seen from Fig. 52 that there is a small 
 rod in the bottom of the retort, upon which are 
 mounted two rectangular shaped lugs. This rod is 
 known as the auxiliary pusher rod, and is given a re- 
 ciprocating motion from the main ram, which will be 
 described later. This auxiliary pusher is for the pur- 
 pose of securing a more even distribution of the fuel 
 within the furnace, after it has been delivered to the 
 retort by the main ram. 
 
 The Jones Under-feed Stoker is used entirely with 
 forced 'draft, and so in this particular also it differs 
 greatly from any stoker discussed thus far. The air 
 for combustion is supplied through tuyere blocks 
 which are placed at the top of the retort an;l on both 
 
FURNACE EFFICIENCY 
 
 121 
 
 sides. Hence the air passing through these tuyere 
 blocks blows from both sides toward the center of the 
 fire, and can at all times be adjusted exactly as the rate 
 of combustion may require. The manner in which 
 
 FIG. 54. 
 
 these tuyere blocks are attached to the retort is shown 
 clearly in Fig. 53. It will be noted that each tuyere 
 block is provided on its under side with a hook or eye- 
 hole, similar to an eye-bolt. \Yhen "all the blocks are 
 in place a rod is run through all the eye-holes, and the 
 tuyere blocks are thus held- securely in place. Re- 
 placing one of these blocks which may have become 
 worn or broken is a simple operation and fairly inex- 
 pensive. A good view of the tuyere blocks in position 
 in the complete stoker may be seen from Fig. 54. 
 
 That portion of the stoker which is outside of the 
 furnace is shown in Fig. 55. It consists of the cylinder, 
 the ram case, and the coal hopper. The ram case is 
 bolted securely to the retort, the two being joined 
 together at the boiler front. This case contains the 
 main ram, the purpose of which is to take the coal as it 
 flows down from the hopper and push it forward into 
 the retort in the furnace. This ram is driven by a 
 steam piston contained in the cylinder shown at the 
 
122 FURNACE EFFICIENCY 
 
 right-hand side of the illustration in Fig-. 54. This pis- 
 ton is usually about 12 inches in' diameter and has a 
 stroke of approximately 14 inches. It has a recip- 
 
 FIG. 55. 
 
 rocating motion similar to the steam piston of a direct- 
 acting pump, this motion being controlled by specially 
 designed automatic valves. 
 
 Fig. 56 shows a section through the Jones stoker, 
 from which a good idea of its construction may be 
 obtained. The steam piston and main ram are clearly 
 shown, as well as the/ auxiliary pusher rod in the bot- 
 tom' of the retort. 
 
 Fig. 57 shows the Jones stoker applied to a horizon- 
 tal return tubular boiler. The air duct supplying air 
 to the chamber below the fire is shown plainly in this 
 view. Also it will be noted that on either side of the 
 furnace, and extending from the retort to the side wall, 
 there is a dead-plate. The fire spills over from the 
 retort onto these dead-plates, and they also serve to 
 catch and hold the ashes until they are removed. 
 
FURXACE EFFICIENCY 
 
 1-23 
 
 The automatic features of the Jones stoker are par- 
 ticularly interesting, and merit special attention. It 
 was stated in an early chapter that the rate of supply 
 of both fuel and air must be carefully proportioned at 
 all times to the demand for steam, that is, to the raU 
 
 FIG. 56. 
 
 of combustion, if high furnace efficiency is to be main- 
 tained. This is just what the Jones stoker does, and 
 for this reason it is able to show good economy at 
 widely varying rates of working and particularly at 
 light loads, a feature not possessed by any of the 
 stokers discussed thus far. 
 
 The fan which supplies air to the furnace is driven 
 by a special vertical engine which is equipped with a 
 regulating valve. \Yhenever the steam pressure rises 
 above a certain amount the regulating valve throttles 
 the steam supply and thus slows down the 'engine. If 
 the steam pressure falls too low the regulating valve 
 opens up and admits more steam to the engine, thus 
 increasing its speed. In this wav the amount of air 
 supplied to the furnace is proportioned to the demand 
 for steam. 
 
 The rate at which the fuel is fed to the furnace is 
 also made proportional to the demand for steam by the 
 following method. It will be remembered that the ram 
 which forces the coal into the hopper is actuated by a 
 steam-driven piston working in a cylinder similar to 
 
m FURNACE EFFICIENCY 
 
 that of a direct-acting steam pump. Now the admis- 
 sion of steam to this cylinder is controlled by a rotary 
 disc valve, a separate admission valve being required 
 for each stoker cylinder. Fig. 58 shows a bank of four 
 of these disk valves, piped up ready for connection to 
 
 FIG. 57. 
 
 steam and exhaust lines. The frame carrying these 
 valves is placed near the blower which supplies the air 
 to the furnace. The valves are rotated by means of a 
 belt running on a pulley on the blower shaft, the rela- 
 tive sizes of blower pulley and valve pulley being so 
 adjusted as to maintain the proper relation between air 
 
FURXACE EFFICIENCY 125 
 
 supply and fuel supply. The disk valves control the 
 amount of steam admitted to- the stoker cylinder, and 
 thus the rate of motion of the main ram is controlled. 
 If the steam pressure falls, the regulating valve causes 
 the blower engine to speed up. This increases the 
 
 FIG. 58. 
 
 speed of the blower and more air is delivered to the 
 furnace. At the same time the rotary disk valves are 
 driven faster, more steam is admitted to the stoker 
 cylinder, the ram moves faster, and more coal is sup- 
 plied to the furnace. 
 
 When the steam pressure rises above the desired 
 point just the reverse takes place, and the rate of 
 
i>6 FURNACE EFFICIENCY 
 
 bustion is reduced. In this way both fuel supply and 
 air supply are controlled automatically, and thus effi- 
 cient conditions are maintained at all times. 
 
 The stoker cylinder receives steam throughout the 
 whole stroke of the piston, no earlier cut-off being pro- 
 vided for by the rotary valves. A moment's consider- 
 ation will make it evident that it would not be prac- 
 ticable to use the steam expansively in service of this 
 kind. When the ram begins its forward stroke the 
 first few inches of its travel simply serve to pack the 
 coal firmly together in the throat of the ram case. 
 Then as the motion continues the whole charge is 
 pushed forward into the retort, the fuel already there 
 being displaced upward. It follows therefore that the 
 heaviest load on the ram is near the end of the stroke, 
 and hence the piston must receive full steam pressure 
 for the whole stroke, inasmuch as there is no fly-wheel 
 to carry it past this point of greatest load. 
 
 Fig. 59 gives a good view of an installation of 
 Jones stokers, showing boilers, stokers, blower engine, 
 blower, and rotary disk valves. The space in front ot 
 the boilers occupied by the stoker cylinder, ram case, 
 and hopper, is not large, being about 4 feet 8^ inches 
 in length outward from the boiler front, and 17 inches 
 in greatest width. 
 
 The operation of the Jones Under-feed Stoker is 
 extremely simple, and at the same time shows a high 
 degree of efficiency. The coal is fed into the hopper 
 either by hand or from a downspout from an over- 
 head bunker. Any fair grade of coal burns well in 
 this stoker, provided it is small enough not to choke 
 the throat of the ram case, which is about 8 inches in 
 diameter. The ram receives the coal from the hopper 
 and pushes it forward into the retort. The auxiliary 
 pusher rod in the bottom of the retort agitates the 
 fuel therein, and causes it to work upward toward 
 the surface. As the coal nears the surface the volatile 
 
FURNACE EFFICIENCY 12? 
 
 gas is gradually driven oft by the heat of the fire, and 
 burned as it passes through the fire. Finally the coal 
 reaches the surface where combustion is completed. 
 
 In the usual form of Jones stoker, the ashes are 
 allowed to collect on the dead-plates on either side of 
 the retort. They are then removed by hand, being 
 pulled out at two doors in the front of the setting. 
 
FURNACE EFFICIENCY 
 
 Fig. GO shows the appearance of a boiler front equipped 
 with Jones stokers. The two upper doors shown 1.1 
 the figure are for the purpose of removing the ash arr.l 
 clinker. A recent improvement to this stoker provides 
 a mechanical arrangement for agitating and cleanin ? 
 the fires and removing the ashes. In this form th2 
 
 FIG. 60. 
 
 stoker is entirely automatic, the only attention which 
 it requires being directed to the removal of the ashes 
 from the ash-pit. 
 
 In summing up the points of superiority charac- 
 teristic of this stoker, it should be noted first of all 
 that it possesses all the advantages of mechanical 
 forced draft. This consists chiefly in a nice adjust- 
 ment between air supply and rate of combustion. This 
 adjustment is made automatically and practically in- 
 stantaneously, so that no matter what the load fluctua- 
 
FURNACE EFFICIENCY 129 
 
 tions may be, the proper draft is always maintained.' 
 The automatic control of the fuel supply insures eco- 
 nomical adjustment at all times and leaves almost 
 nothing to be desired in the way of automatic furnace 
 control. In this particular the Jones stoker is the 
 equal, if not the superior, of any other furnace which 
 has come to our attention. 
 
 The combustion is such that no fire-brick arches 
 are required to render the furnace practically smoke- 
 less. The coal rises in the retort like a slow-moving 
 fountain, the gases being distilled as the coal reaches 
 the surface. As they pass through the fire, they are 
 thoroughly mixed with the proper amount of air at a 
 high temperature, which as we have seen in an early 
 chapter, is all that is required for smokeless combus- 
 tion. The absence of all arches makes an economical 
 furnace to build and maintain. There is probably 
 little doubt that the Jones stoker in the form described 
 here, will have as low maintenance charges as any 
 mechanical stoker on the market. 
 
 Questions and Answers. 
 
 Q. What principle is used in the Jones stoker? 
 
 A. The under-feed principle. 
 
 Q. What are the chief parts of the Jones stoker? 
 
 A. The retort, ram case, ram and stoker cylinder. 
 
 Q. Which of the above parts are inside the fur- 
 nace? 
 
 A. The retort. 
 
 Q. How is the coal fed into this retort? 
 
 A. By a ram actuated by a steam-driven piston. 
 
 Q. How is the air supply provided for this stoker? 
 
 A. By a blower driven by a special engine. 
 
 Q. How is the speed of this engine controlled? 
 
 A. By a regulating valve, w r hich in turn is con- 
 trolled by the steam pressure. 
 
130 FURNACE EFFICIENCY 
 
 Q. How is the speed of the piston which drives 
 the main ram controlled? 
 
 A. By rotating disk valves driven from a pulley on 
 the blower shaft. 
 
 Q. Are both air supply and coal supply controlled 
 automatically? 
 
 A. Yes. 
 
FURNACE EFFICIENCY 131 
 
 CHAPTER XII. 
 The Ignition Arch. 
 
 In the course of the preceding pages frequent 
 reference has been made to the firebrick arch in a 
 boiler furnace. It has been shown that such an arch 
 assists to a considerable extent in securing smokeless 
 and efficient combustion by providing- a roof of re- 
 fractory material for the furnace, and so preventing 
 the volatile gases from the coal from coming into con- 
 tact with the boiler heating surfaces until combustion 
 has been completed. In the present chapter the fire- 
 brick arch will be considered somewhat more in detail, 
 with a view to making clear the principles underlying 1 
 its action. 
 
 For our present purpose it will be well to divide all 
 boiler furnace arches into two general classes. First, 
 the ignition arch, the chief function of which is to 
 assist in the ignition of the fresh coal as it comes into 
 the furnace. Second, the deflecting arch, the function 
 of which is to deflect the burning gases away from the 
 boiler heating surfaces, and at the same time to assist 
 in the proper mixing of gases and air so as to promote 
 complete combustion. It will be evident that both 
 kinds of arches have an important part to play in the 
 solution of the problem of efficient combustion. 
 
 The ignition arch has undergone quite radical 
 changes in design within the last few years, the 
 changes being prompted by a better understanding 
 of the principles underlying its action. In the early 
 designs the ignition arch was often made as short as 
 two feet; a length of three feet was considered quite 
 
132 
 
 FURNACE EFFICIENCY 
 
 generous, while an ignition arch four feet in length 
 was regarded as extreme. These arches were built flat, 
 with a slight upward pitch toward the rear, and were 
 set quite close to the grate. These early designs lo- 
 cated the arch entirely with reference to its distance 
 from the grate, without regard to the thickness of fuel 
 bed that would have to be carried. The result was 
 
 FIG. 61. 
 
 that those arches were frequently only two or three 
 inches above the fuel when a thick fire was carried. 
 Present practice places an ignition arch with reference 
 to its distance from the surface of the fuel bed, in 
 which case the character of fuel and average thickness 
 of fire must be carefully considered when designing 
 the arch. 
 
 The action of the short flat ignition arch just de- 
 scribed was probably about as .follows : The volatile 
 gases liberated from the coal ignited at the surface of 
 the fuel bed. The heat liberated by this combustion 
 heated the arch immediately above to a state of in- 
 candescence, and the hot arch in turn reflected the heat 
 back again onto the incoming fuel. In this way a 
 prompt ignition of the fresh coal was effected, the arch 
 acting as a mirror to reflect the heat forward to the 
 point where it was most needed. 
 
FURNACE EFFICIENCY 
 
 133 
 
 Experience with ignition arches has taught en- 
 gineers that the greatest intensity of radiation is in a 
 direction perpendicular to the radiating surface, and 
 from its center. Also, the temperature produced at 
 any point in the green fuel bed by the action of the 
 
 FIG. 
 
 radiant energy from the- arch is inversely proportional 
 to the distance from Jthe arch. That is, the farther a 
 
 FIG. 63. 
 
 given point is from the arch the less heat it will re- 
 ceive. 
 
 If a flat arch be placed parallel to the grate it fol- 
 lows from the principles just stated that the maximum 
 radiation and hence the maximum igniting effect will 
 
134 FURNACE EFFICIENCY 
 
 be directly under the center of the arch. Fig. 61 shows 
 the distribution of radiant heat under such an arch, 
 the semicircle showing the character of the distribu- 
 tion, and the shading the intensity of radiation. Fig. 
 62 shows how the point of most intense radiation is 
 thrown forward when the arch is tilted upward 
 toward the rear, and Fig. 63 shows how the radiation 
 is reduced and thrown still farther forward in the fur- 
 nace when the arch is inclined still more. 
 
 An arch of this kind will give an igniting effect 
 across practically the whok of the furnace, and al- 
 though the figures show that this effect is greatest at 
 the center, still the radiation from the side walls assists 
 ignition at the sides, so that a flat arch gives practic- 
 ally uniform ignition across the entire width of the 
 furnace. The figures show further that in order to 
 get the maximum igniting effect near the front of the 
 furnace where it is most needed the arch should be 
 horizontal, or at least should have but a slight upward 
 incline toward the rear. 
 
 When a sprung ignition arch is used the igniting 
 effect is not so satisfactory in general as it is with the 
 flat arch. The center of the arch being farther from 
 the fuel bed than is the case with the sides of the arch, 
 the igniting effect is greater at the sides of the furnace 
 than at the center. The radiation from the side walls 
 also tends to increase this discrepancy, so that even 
 although the curvature of the arch may be slight the 
 igniting effect is not uniform across the furnace. In 
 view of this fact there seems to be no reason why the 
 flat arch should not displace the sprung variety where- 
 ever the conditions make it possible, particularly when 
 the mechanical difficulties in the way of the construc- 
 tion and maintenance of a sprung arch are considered. 
 
 From the foregoing discussion it should be evident 
 that the short ignition arch, whether flat or sprung, 
 merely takes heat from the burning volatiles and de- 
 
FURNACE EFFICIENCY 135 
 
 fleets that heat forward onto the green incoming fuel. 
 In general the flat arch is to be preferred to the curved 
 one because the ignition is more uniform across the 
 furnace with the former. Later experience with the 
 ignition arch has demonstrated the possibility of using 
 the heat from the rear of the fuel bed for purposes of 
 ignition. At this point in the furnace the fixed carbon 
 of the coal is being consumed and it is here that the 
 greatest amount of heat is liberated, and hence the 
 highest temperatures exist. 
 
 In order to utilize this heat from the rear of the 
 furnace a radical change was made in ignition arch 
 design. This change consisted chiefly in making the 
 arch very much longer than before, lengths of six to 
 eight feet being not at all uncommon. The action of 
 such a long arch is almost exactly like that of a mirror, 
 reflecting heat from the rear of the furnace to the front. 
 Keeping in mind the well known law of reflecting sur- 
 faces that the angle of incidence is equal to the angle 
 of reflection, it is possible to calculate the length and 
 position of an arch for any particular furnace, provided 
 the characteristics of the fuel and the load conditions 
 are known accurately. 
 
 FIG. 64. 
 
 Fig. 64 shows how heat coming from a point "a" 
 in the rear of the furnace is reflected by the arch to 
 various points in the front of the furnace. The arch 
 
136 FURNACE EFFICIENCY 
 
 shown is flat and inclined upward toward the rear of 
 the furnace. This pitch is usually not more than three 
 inches to the foot and in many cases it is less. In fact, 
 with certain kinds of coal a horizontal arch six or 
 seven feet long may be used to good advantage. Fig. 
 65 shows how the heat is reflected by a horizontal arch 
 from the rear to the front of the furnace. 
 
 Let us now consider a few features of ignition arch 
 design as affected particularly by the kind of fuel 
 which is to be used. Consider first of all a clean free- 
 burning bituminous coal, fairly low in ash and con- 
 taining thirty per cent of volatiles. Such a coal will 
 ignite with comparative ease, and will burn out free 
 from clinker or other troublesome ash. If such a coal 
 
 W/////W///P///////^^^ 
 
 FIG. 65. 
 
 is to be burned on a chain grate or similar stoker, the 
 arch should be designed as follows: 
 
 Inasmuch as the fuel ignites easily, the igniting 
 action may properly be confined to a comparatively 
 narrow zone at the front of the furnace. If the stoker 
 is approximately ten feet long the arch need not be 
 more than six feet in length. It should be set about 
 fifteen inches above the grate at the front, which will 
 give a space ranging from five to ten inches between 
 fuel and' arch. The arch should have a pitch of about 
 2 T / 2 or 3 inches to the foot, inclining upward toward 
 the rear. The reason for the pitch of the arch is to 
 provide an increasing furnace cross-section from front 
 to rear, so as to handle the increasing volume of fur- 
 nace gases without undue restriction. 
 
FURNACE EFFICIENCY 137 
 
 Consider next a coal containing as high as 20 per 
 cent to 30 per cent of ash, having a high moisture con- 
 tent, and possibly in the neighborhood of 20 per cent 
 of volatiles. Coals similar to this are found in many 
 of the western States and are now being burned suc- 
 cessfully on chain grate stokers. Such a fuel will 
 ignite much less readily than the first one considered, 
 and for this reason the igniting action must be con- 
 tinued over a much wider zone than before. Also, the 
 front of the furnace must be maintained at a-s high a 
 temperature as possible, to assist the ignition. For 
 this reason the hot gases must not pass so rea'dily from 
 the furnace, but must be "bottled up" by restricting 
 their path somewhat. 
 
 Assuming the same size of furnace as before, an 
 arch to burn this fuel successfully should be about 7^4 
 feet long, not more than 11 or 1*2 inches above the 
 grate at the front, and should have only a slight up- 
 ward pitch toward the rear. The action of this long, 
 almost horizontal arch will be to reflect heat from the 
 rear of the furnace over a zone of considerable width 
 in the front. Thus the igniting effect of the arch will 
 be continued for a considerable time after the fuel 
 enters the furnace, a necessary condition for satis- 
 factory burning of such coal, particularly at high rates 
 of combustion and high speed of grate travel. 
 
 The arch being set almost parallel with the grate, 
 the heated gases do not have such a ready escape from 
 the furnace as when the arch has considerable pitch. 
 Being retained for a time in the furnace in this way, 
 these hot gases raise the temperature of the entering 
 coal, and thus assist ignition. 
 
 Consider as a third example, the case of certain coal 
 found in some of the southwestern States, particularly 
 Texas. This coal contains 50 per cent or more of ash- 
 forming materials, and at one time was considered 
 practically useless for steam-making purposes. It is 
 
138 FURNACE EFFICIENCY 
 
 extremely slow and difficult to ignite, and would seem 
 -to be almost "impossible'' when used in connection 
 with a mechanical stoker of the "progressive combus- 
 tion" type. 
 
 To ignite such a coal successfully requires an arch 
 just as long as the size of the furnace will permit. 
 The limit to the length is imposed, of course, by the 
 fact that sufficient space must be left between the end 
 of the arch and the bridge wall for the escape of the 
 furnace gases. The arch should be horizontal and set 
 only about 10 or 11 inches above the grate. Such an 
 arch will give an extremely wide ignition zone in the 
 front of the furnace, and will" bottle up" the hot gases 
 to such an extent as to assist materially in maintaining 
 a high furnace temperature, particularly near the front. 
 To operate a furnace designed in such a manner as this 
 will, of course, require a good draft on account of the 
 restriction at the furnace throat. But it is the only 
 design of furnace which makes it possible to burn fuel 
 of this kind on a mechanical stoker, and it really repre- 
 sents a long step forward in furnace design to meet a 
 particular set of conditions. 
 
 From what has been said it should be apparent that 
 the long ignition arch, set comparatively low, and 
 either horizontal or with a pitch toward the rear not 
 to exceed 3 inches to the foot, is as correct in principle 
 as it has proved successful in operation. 
 
 Questions and Answers. 
 
 Q. Into what two general classes may furnace 
 arches be divided? 
 
 A. Into deflection arches and ignition arches. 
 
 O. What is an ignition arch? 
 
 A. A firebrick arch placed over the front of the 
 furnace to reflect heat on the incoming coal. 
 
 Q. How long should this arch be ? 
 
FURNACE EFFICIENCY 139 
 
 A. Early design made it only 3 or 4 feet long, but 
 it is now made as much as 6 to 8 feet long in a furnace 
 10 feet long. 
 
 Q. How should the arch be placed with respect 
 to the grate? 
 
 A. About 10 to 15 inches above the grate, and 
 either parallel to it or with a slight pitch toward the 
 rear. 
 
 Q. How much should this pitch be? 
 
 A. Probably not to exceed 3 inches to the foot. 
 
140 FURNACE EFFICIENCY 
 
 CHAPTER XIII. . 
 Breeching and Chimney. 
 
 It may sometimes happen that a well designed 
 furnace, properly operated, will fail to give satisfac- 
 tory capacity or efficiency. In such a case it is often 
 necessary to look for the trouble outside of the furnace 
 itself. 
 
 One very important part of a boiler room instal- 
 lation, and one which frequently receives much less 
 attention than it deserves, is the breeching through 
 which the furnace gases pass from the boiler setting 
 to the chimney. Unless this breeching is intelligently 
 designed and carefully constructed it may cut down 
 the capacity and economy of the furnace to a con- 
 siderable extent. 
 
 The cross section of the breeching is perhaps the 
 first point to receive consideration. It should be 
 designed with reference to the total volume of fur- 
 nace gases which it will be required to handle, rather 
 than as a function of the grate area served. An ap- 
 proximate rule for the size of a breeching, and one 
 which has frequently been used as a guide at least, is 
 to make the section of the breeching about 1/6 that 
 of the grate served. But this rule takes no account of 
 the kind of fuel which is to be used, nor the rate of 
 combustion, the latter varying over a wide range in 
 different plants. 
 
 Evidently if the character of the fuel which is to 
 be used is known, and if the maximum load which 
 the boilers will be required to carry, as well as their 
 approximate efficiency is known, the amount of fuel 
 
FURNACE EFFICIENCY 
 
 141 
 
 required per hour, and the amount of air needed per 
 pound of fuel, can be predetermined with a fair de- 
 gree of accuracy. Thus the weight of furnace gases 
 produced per minute or per second, can be estimated, 
 and if the breeching temperature be taken as 400 F. 
 to 500 F. according to conditions, the volume of gases 
 passing through the breeching per second can be cal- 
 culated. 
 
 FIG. 66. 
 
 It is well to make the breeching of such a size 
 that the velocity of gas flow will not exceed 35 feet 
 per second. If the velocity exceeds this amount the 
 friction of the gases against the wall of the breeching 
 causes a drop in draft pressure which for a long run 
 of breeching may become quite serious. 
 
 This matter of draft pressure loss depends not 
 only on the size of the breeching but also upon its 
 shape, length, number and character of bends, ma- 
 terial of construction, etc. Experience has shown 
 that a circular section gives less draft loss than a 
 square or rectangular section, other conditions being 
 the same. This is probably due to the fact that any 
 fluid meets with less frictional resistance when flow- 
 
142 FURNACE EFFICIENCY 
 
 ing through a pipe of circular section than in any 
 other shape. 
 
 The draft loss due to length is practically pro- 
 portional to the length for any shape of section. 
 Hence it follows that not only from considerations 
 of economy in first cost, but also to produce economy 
 of operation, a plant should be laid out with just as 
 short a run of breeching as conditions will permit. 
 In a well designed breeching the draft loss will prob- 
 ably not exceed 0-1 inch of water per 100 feet of 
 straight run. 
 
 The number of bends in a breeching should be 
 kept as few as possible, because at each one there is 
 an appreciable loss in draft pressure. A single right- 
 angle bend will cause a draft loss of about 0.05 inch 
 of water, due to the eddies formed in the gas flow 
 when striking the turn. Figure 66 shows a plan 
 view of a breeching in which there is a right angle 
 bend. The gases flowing from right to left as shown 
 by the arrow strike the bend at the point A with a 
 certain amount of momentum, due to their weight and 
 velocity. The flow of the gases is retarded and a 
 "swirl" or eddy is formed, which causes a loss in 
 draft pressure. The effect of the eddy is similar to a 
 restriction in the breeching, because at the point 
 B there is practically no gas flow. If it be considered 
 in this way it is comparatively easy to see how a loss 
 in draft pressure occurs. This effect can be reduced 
 to a considerable extent by using a long radius bend 
 as shown by the dotted lines. But a bend of this 
 kind requires more space which in many city plants 
 is not to be had. In such a case the draft loss due 
 to a right angle bend must be put up with, and suffi- 
 cient height added to the stack to compensate for the 
 loss. 
 
 Breechings are usually made of steel or brick- 
 work, and sometimes possibly of concrete. From 
 
FURNACE EFFICIENCY 
 
 143 
 
 the point of draft loss an all steel breeching is prob- 
 ably to be preferred, but it should be well lagged or 
 covered with an insulating material to prevent radia- 
 tion and infiltration of air. This is an important 
 consideration, because the chimney draft depends up- 
 on the temperature of the gases therein, and if they 
 are cooled while passing through the breeching the 
 draft will be reduced. 
 
 A 
 
 FIG. 67. 
 
 In the case of a comparatively long run of breech- 
 ing into which the uptakes from two or more boilers 
 discharge, the manner in which the connection be- 
 tween uptake and breeching is made has an important 
 bearing on the draft loss. In figure *67 is shown an 
 elevation of a breeching into which two uptakes dis- 
 charge at right angles. Unless the corners are re- 
 lieved somewhat practically the same action will take 
 place as in a right-angle bend. Figure 66. The gas 
 from uptake A will strike the opposite wall of the 
 breeching at C, and the gas from B will strike at D. 
 The result will be the formation of eddies with com- 
 paratively quiescent portions at E and F. As was 
 described in connection with Figure 66 this restricted 
 portion reduces the effective breeching area and a 
 loss in draft pressure takes place at that point. 
 
144 
 
 FURNACE EFFICIENCY 
 
 The draft loss which takes place at these points 
 can be remedied somewhat by relieving the corner on 
 the side of the uptake towards which the gas is to 
 flow. Thus if the corners be extended as shown in 
 the dotted curves, the gases will be deflected some- 
 what to the left and no quiescent pocket will be 
 formed at E or F. 
 
 Conditions sometimes make it necessary to place 
 the chimney out of the line of the breeching. In 
 
 FIG. 68. 
 
 this case a construction similar to that shown in 
 Figure 68 results. Here the gases from the two 
 halves of the breeching meet in collision at the point 
 A and their flow is thereby seriously restricted. 
 
 * Mr. T. A. Marsh states that a draft pressure loss of 
 as much as 0.25 of an inch of water has befen known to 
 result from this cause. Again in this case consider- 
 able improvement will result if the corners be 
 rounded as shown by the dotted lines in the figure. 
 Marsh states that a curved deflecter D placed in the 
 
 * Design of Breechings and Smoke Flues. T. A. Marsh, Industrial 
 Engineering, Nov. 1912. 
 
FURNACE EFFICIENCY 
 
 145 
 
 breeching may prove beneficial in changing the direc- 
 tion of flow of the gases without excessive draft 
 loss. 
 
 A condition similar to the one just discussed ar- 
 rises when breechings enter a chimney on opposite 
 sides. Here again a collision of the gases takes place 
 and a drop in draft pressure results. Figure 69 shows 
 a construction which is being used with success in 
 such a case as this. AB is a baffle placed across the 
 chimney where the breeching enters which assists in 
 deflecting the .gases in the direction of the draft. 
 Even with this construction there must still be con- 
 siderable draft loss at this point because the gases 
 will strike this baffle almost at right angles and must 
 lose considerable momentum thereby. 
 
 Marsh recommends a curved baffle as shown at 
 CD in Figure G9. The shape and position of this 
 
 FIG 
 
 baffle is such that the gases do not meet it at right 
 angles, but are deflected upward in a spiral path 
 without much loss of velocity, and w r ith only a small 
 draft loss. 
 
 When designing a breeching the main point to 
 be kept in mind is the fact that the furnace gases 
 must flow through it with as little friction as possible. 
 Anything which produces friction must be avoided so 
 far as possible, particularly sharp bends, and places 
 where two streams of furnace gas may meet in direct 
 collision. 
 
146 FURNACE EFFICIENCY 
 
 The one remaining feature of the boiler plant 
 which has an important part to play in the combus- 
 tion problem is the smoke stack or chimney. While 
 the complete discussion of the principles entering- into 
 the design of a smoke stack does not come within the 
 scope of this work, still a very few considerations 
 which .govern the design may be mentioned. 
 
 The sectional area of a chimney should be suf- 
 ficent to carry away the furnace gases at a velocity 
 not to exceed 25 to 30 feet per second. Since the av- 
 erage temperature of the chimney gases is consider- 
 ably less than that of the gas in the breeching the 
 size of the chimney can be somewhat smaller than 
 the breeching. An average figure is to make the 
 chimney 15 to 20% less than the combined area of 
 breeching entering it. This provides for a reduced 
 gas velocity in the chimney and keeps down the draft 
 pressure loss. 
 
 The proper height for the chimney is almost en- 
 tirely a question of the draft require:!. Draft de- 
 pends upon temperature of chimney gases and 0:1 
 elevation above the sea level as well as upon height of 
 chimney, but the height is the chief consideration. 
 
 The following formula may be used to calculate 
 the height of stack required to give a certain draft. 
 (Stirling rule.) 
 
 1 1 
 
 D = 0.52 H X P (- -) 
 T T, 
 in which D = draft produced, in inches of wate 1 *. 
 
 H = height of stack in feet above grate. 
 
 P atmospheric pressure, pounds per square inch. 
 
 T = absolute temperature of atmosphere, degrees 
 F. 
 
 T! = absolute temperature of chimney gases, de- 
 grees F. 
 
FURNACE EFFICIENCY UT 
 
 From this formula the height of stack required 
 to give any desired draft may be calculated. 
 
 Questions and Answers. 
 
 Q. What is the connection between boiler uptake 
 and chimney called? 
 
 A. The breeching. 
 
 Q. How large should this breeching be? 
 
 A. Large enough to carry away the furnace 
 gases with a velocity not to exceed 35 feet per sec- 
 ond. 
 
 Q. Give a "rule of thumb'' for the size of a 
 breeching? 
 
 A. It should be equal to 1/6 of the grate area 
 served. 
 
 Q. What is the best shape for the section of the 
 breeching? 
 
 A. The section should be circular. 
 
 Q. Why? 
 
 A. Because the draft loss i". less in a circular 
 breeching than in one having any other shape of sec- 
 tion. 
 
 Q. How is a draft affected by a right-angle bend 
 in a breeching? 
 
 A. There is a loss of about 0.05 of an inch for each 
 bend. 
 
 Q. Is there any draft loss due to friction? 
 
 A. Yes, about 0.1 of an inch per 100 feet of straight 
 breeching. 
 
 Q. How may the dra-ft loss due to bends be re- 
 duced? 
 
 A. Bv using long radius bends so that the change 
 in direction of gas flo\v is more gradual. 
 
 Q. When two breechings enter a stack at opposite 
 sides, what should be done to reduce the draft loss 
 at that point? 
 
148 FURNACE EFFICIENCY 
 
 A. A curved baffle should be placed in the base 
 of the stack to deflect the gases upward. 
 
 Q. What should be the section of a smoke stack? 
 A. About 20% less than the breeching- section. 
 
FURNIACE EFFICIENCY UD 
 
 Alphabetical Index. 
 
 Absorption of Heat 67 
 
 Action of Blonck Meter 
 
 Actjon of Flat Ignition Arch 98 
 
 Action of Ignition Arch 
 
 Action of Long Ignition Arch 135 
 
 Adjustment of Wilsey Gauge 
 
 Air, Excess of, in Boiler Furnace 
 
 Air Leakage, Amount of 
 
 Air Leakage, Remedy for 22 
 
 Air Leakage Through Boiler Walls 23 
 
 Air Leaks How to Stop 23 
 
 Air Leaks, Location of 22 
 
 Air Over Fire. Necessity for 26 
 
 Air Through Fire and Over Fire 26 
 
 Appearance of Wilsey Gauge 
 
 Application of Progressive Combustion to Hand Firing.. 90 
 
 Area of Gas Path 58 
 
 Asbestos Cement Covering for Boiler Brickwork 23 
 
 Automatic Features of Jones Stoker 123 
 
 B 
 
 Baffle Piers 48 
 
 Bement, A., Smokeless Furnace Design 57 
 
 Binder Links 95 
 
 Bituminous Coal, Air Required for 26 
 
 Boiler Efficiency Gauge 65 
 
 Boiler Under Light Load ; 26 
 
 Blonck Boiler Efficiency Meter 75 
 
 Blonck Meter, Action of 79 
 
 Blonck Meter. Setting of 79 
 
 Blue Gauge in Blonck Meter 75 
 
 Breeching, Curved Deflector in 144 
 
 Breeching Design 140 
 
 Breechi'ngs. Draft Pressure Loss in 141 
 
 Breechings, Material of 142 
 
 Breechings, Velocity of Gas in 141 
 
150 FURNACE EFFICIENCY 
 
 Bulkhead 62 
 
 B. and W. Water Tube Boiler 32 
 
 B. and W. Boiler, Draft Losses Through 32 
 
 C 
 
 Carbon Dioxid, Amount in Flue Gases 4 
 
 Chain-Grate Stoker . 55-90 
 
 Chain-Grate Stoker, Construction 91 
 
 Chain-Grate Stoker, Feed Gate for 97 
 
 Chain-Grate Stoker, First Design 91 
 
 Chain Grate Stoker with Light Load 26 
 
 Chain-Grate Stoker, Design of 92 
 
 Chain-Grate Stokers, Chain Tension in . 95 
 
 Chain-Grate Stokers, Double Web 95 
 
 Chain-Grate Stokers, Method of Driving 96 
 
 Chain-Tension in Chain-Grate Stokers 95 
 
 Chemical Action on Hydrocarbons in Furnace 40 
 
 Chemical Reagents 16 
 
 City of Chicago, Department of Smoke Inspection 60 
 
 Clinker Grinder 109 
 
 Clinker Grinder, Exhaust Steam Under 110 
 
 Coal Magazine for Murphy Furnace 107 
 
 Coal of Low Combustible, Ignition Arch for 137 
 
 CO, Formation of 41 
 
 Coking Arch 51 
 
 Coking Arch, Function of, in Combustion 51 
 
 Coking Arch, Location of 51 
 
 Coking Plate for Murphy Furnace 107 
 
 Combustible in Ash 7, 8 
 
 Cumbustion Arch 55-57 
 
 Combustion Space, Definition of 54 
 
 Combustion Space, Size of 54 
 
 Conditions for Furnace Efficiency 64 
 
 Conditions for Setting Blonck M.eter 79 
 
 Conditions for Smokeless Combustion 46 
 
 Conduction 65 
 
 Connection of Blonck Meter to Boiler 75 
 
 Connection between Uptake and- Breeching 143 
 
 Construction of Blonck Meter 75 
 
 Construction of Chain-Grate Stoker 91 
 
 Construction of Clinker Grinder 109 
 
 Construction of Double Sprung Arch... Ill 
 
 Construction of Wilsey Gauge 68 
 
 Control of Draft, How Best Accomplished 25 
 
 Convection 66 
 
 Covering for Brickwork 23 
 
FURNACE EFFICIENCY 151 
 
 Cuprous Chlorid 16 
 
 Curved Deflector in Breeching 144 
 
 D 
 
 Damper, Effect of Position on Draft 25 
 
 Damper to Prevent Infiltration of Air 101 
 
 Dead Plate in Jones Stoker 122 
 
 Dead Plate, Purpose of 122 
 
 Deflecting Arch 62-131 
 
 Defective Baffles. Effect of, on Draft Losses 32 
 
 Design of Breeching 140 
 
 Design of Chain-Grate Stoker 92 
 
 Design of Furnace for High Temperatures 48 
 
 Design of Ignition Arch 131 
 
 Design of Links for Stoker 93 
 
 Design for Smokeless Combustion 55 
 
 Diagram of Wilsey Gauge 68 
 
 Differential Draft Gauge. Function of 76 
 
 Dilution of Furnace Gases 22 
 
 Dirty Tubes. Effect of. on Draft Losses 32 
 
 Disc Valves for Jones Stoker 124 
 
 Distillation of Gases from Coal 48 
 
 Double-Arch 62 
 
 Double-Arch Bridge-Wall Furnace 60 
 
 Double Sprung Arch, Construction of Ill 
 
 Double Sprung Arch for Murphy Furnace 110 
 
 Double Sprung Arch, Support for 110 
 
 "Double-Web" Chain-Grate Stokers 95 
 
 Draft, Control of. with Light Load 29, 30 
 
 Draft, Determination of Proper 24 
 
 Draft, Effect of Too Much 24 
 
 Draft, Effect of Too Little 24 
 
 Draft for Jones Stoker 120 
 
 Draft. Function of 23 
 
 Draft Gauge, Cost of 21 
 
 Draft, Loss over Bridge Wall, Meaning of 31 
 
 Draft, over Fire 37 
 
 Draft Pressure Losses. Causes of 77 
 
 Draft Pressure Loss in Breechings 141 
 
 Draft, Production of 24 
 
 Draft Required with Horizontal Baffles 55 
 
 E 
 
 Effect of Heat on Coal 40 
 
 Efficiency and Capacity 60 
 
 Efficiency of Heat Transfer 66 
 
 Efficiencv of Heat Transfer, Formula for.... . 67 
 
152 FURNACE EFFICIENCY 
 
 Efficient Furnace, Definition of 3 
 
 Engineering Experiment Station 55 
 
 Essential Condition for Smokeless Combustion 90 
 
 Excess Air, Formula for 5 
 
 Excess Air, Further Causes 24 
 
 F 
 
 Fans for Jones Stoker 123 
 
 Faulty Boiler Design, Effect of, on Draft Losses 32 
 
 Feed Gate for Chain-Grate Stoker 97 
 
 Feeding Coal to Murphy Furnace 106 
 
 Fire-Clay Tile 60 
 
 Fire-Tube Boilers 60 
 
 Flat Arch, Radiation from 133 
 
 Flat Ignition Arch 58-98 
 
 Flue Gas Apparatus, Cost of 21 
 
 Flue Gas, Obtaining Sample of 17 
 
 Flue Gases, Heat Carried Away by 6 
 
 Flue Gases, Temperature of - 6 
 
 Flue Gas Tests to Determine Efficiency 22 
 
 Formula for Height of Smoke Stack 146 
 
 Free-Burning Coal, Ignition Arch for 136 
 
 Free-Carbon in Smoke, Amount of 41 
 
 Fuel Economy Gauge 65 
 
 Fuel Economy Gauge, Design and Construction of 66 
 
 Function of Boiler 2 
 
 Function of Boiler Furnace .- 2 
 
 Function of Clinker Grinder 109 
 
 Function of Deflecting Arch 62-131 
 
 Function of Ignition Arch 58-131 
 
 Function of Sprung Arch 58 
 
 Function of Stoker Boxes 108 
 
 Function of Water-Back 100 
 
 Furnace Gases, Velocity of, over Bridge-Wall 31 
 
 Furnace Gases, Volume of 31 
 
 G 
 
 Galvanometer 68 
 
 Grate Bar, Construction of in Murphy Furnace 106 
 
 Grate Bearers for Murhpy Furnace. 109 
 
 Grate Bearers, Support for 109 
 
 Green Chain-Grate Stoker 55-93 
 
 Green L. Type Stoker 101 
 
 Green Stoker, L. Type 101 
 
 H 
 
 Hand Firing 48 
 
 Hay's Flue Gas Apparatus... 17 
 
FURNACE EFFICIENCY 153 
 
 Heat Distribution for Illinois Coal 42 
 
 Heat in Furnace Gases 66 
 
 Heat Liberated from Furnace 66 
 
 Heat Lost in Smoke Stack 66 
 
 Height of Smoke Stack, Formula for 146 
 
 Heine Boiler 55 
 
 Heine Boiler, Direction of Gas Flow through 34 
 
 Heine Boiler, Draft Losses through 34 
 
 Holes in Fire, Loss Due to 7 
 
 Horizontal and Vertical Baffles as Regards Smoke 55 
 
 Hydrocarbons 40 
 
 I 
 
 Ignition Arch 131 
 
 Ignition Arch, Action of 132 
 
 Ignition Arch, Construction of 99 
 
 Ignition Arch, Design of 131 
 
 Ignition Arch for Coal of Low Combustible 137 
 
 Ignition Arch for Free-Burning Coal 136 
 
 Ignition Arch for Texas Coal 137 
 
 Ignition Arch, Intensity of Radiation from 133 
 
 Ignition Arch, Length of 138 
 
 Ignition of Entering Fuel 98 
 
 Incomplete Combustion, Effects of 41 
 
 Infiltration of Air ICO 
 
 Intensity of Radiation from Ignition Arch 133 
 
 J 
 
 Jones Stoker, Automatic Features of 123 
 
 Jones Stoker, Dead Plate in 122 
 
 Jones Stoker, Disc Valve for 124 
 
 Jones Stoker, Draft for 120 
 
 Jones Stoker. Fan for 123 
 
 Jones Stoker, Operation of 126 
 
 Jones Stoker, Points of Superiority 128 
 
 Jones Stoker, Ram Case for 121 
 
 Jones Stoker, Rate of Fuel Feed to 123 
 
 Jones Stoker, Removal of Ashes from 127 
 
 Jones Stoker, Tuyer Blocks for 121 
 
 Jones Under-Feed Mechanical Stoker 119 
 
 L 
 
 Length of Ignition Arch 138 
 
 Links for Stoker Chain 94 
 
 Links for Stoker, Design of 93 
 
 Location of Water-Back 100 
 
 Location of Wilsey Gauge on Boiler 70 
 
 Long Ignition Arch, Action of 135 
 
154 FURNiACE EFFICIENCY 
 
 Loss of Heat when CO. is Formed 41 
 
 Lo..wer Gauge 78 
 
 L. Type Stoker, Action of.... .. 101 
 
 M 
 
 Maintaining Furnace Conditions 65 
 
 Material of Breechings 142 
 
 Mechanical Stoker 48 
 
 Mechanical Stoking, Under-Feed Principle 119 
 
 Method of Driving Cha : n-Grate Stokers 96 
 
 Motion of Stoker Boxes 108 
 
 Murphy Furnace 106 
 
 Murphy Furnace, Coal Magazine for 107 
 
 Murphy Furnace, Coking Plate for 107 
 
 Murphy Furnace, Construction of , 106 
 
 Murphy Furnace, Double Sprung Arch for 110 
 
 Murphy Furnace, Feeding Coal to 106, 107 
 
 Murphy Furnace, Grate Bearers for 109 
 
 Murphy Furnace, Motion of Bars 106 
 
 Murphy Furnace, Operation of 112,113 
 
 Murphy Furnace, Stoker Boxes for 108 
 
 N 
 Normal Draft Conditions, Importance of 37 
 
 O 
 
 Observation of Smoke 43 
 
 Operation of Jones Stoker 126 
 
 Operation of 'Murphy Furnace 112 
 
 Operation of Wilsey Gauge T 69 
 
 Orsat Apparatus, Operation of 13 
 
 Orsat Apparatus, Reagents for 12 
 
 Orsat Gas-Analysis Apparatus 10 
 
 P 
 
 Path of Furnace Gases 54-58 
 
 Path of Gases 57 
 
 Platinum Coils 68 
 
 Points of Superiority of Jones Stoker .. 128 
 
 Poorly Designed Furnace as Cause of Smoke 48 
 
 Potassium Pyrogallate 16 
 
 Pressure Water-Back 
 
 Prevention of Smoke 46 
 
 Principle of Blonck Meter 
 
 Principle of Fuel Economy Gauge 66 
 
 Principle of Progressive Combustion 90 
 
 Problem of High Efficiency 64 
 
 Progressive Combustion 90 
 
FURNACE EFFICIENCY 155 
 
 Proper Draft, How Determined 25 
 
 Proper Heights of Smoke Stack 146 
 
 Purpose of Ram for Jones Stoker- 
 
 Pyrometer 66 
 
 R 
 
 Radiation 66 
 
 Radiation from Flat Arch 133 
 
 Ram Case for Jones Stoker 
 
 Ram for Jones Stoker, Purpose of 121 
 
 Rate of Combustion as Affected by Furnace Draft 37 
 
 Rate of Fuel Feed to Jones Stoker 123 
 
 Ratio of Furnace Draft to Uptake Draft 36 
 
 Reason for Smoking 51. 54 
 
 Red Gauge in Blonck Meter 75 
 
 Relation of Draft Losses for Good Economy 30 
 
 Removal- of Ashes from Jones Stoker 127 
 
 Removal of Broken Links in Chain-Grate Stoker 93 
 
 Return Tubular Boiler, Draft Losses through 29 
 
 Ringleman Chart 
 
 Ringleman Chart, Construction of 43 
 
 Ringleman, Chart, Use of 43 
 
 S 
 
 Sampling Pipe 17 
 
 Sampling Pipe, Air 
 
 Sectional Area of Smoke Stack 146 
 
 Setting Blonck Meter 75 
 
 Short-Circuits through Baffles 34 
 
 "Side-Feed" Principle in Mechanical Stoking .. 106 
 
 Single Arch 62 
 
 Smoke -'- 40 
 
 Smoke as Index to Furnace Conditions 41 
 
 Smoke Densities, Designation of 46 
 
 Smoke, Formation of 41 
 
 Smokeless Combustion 58 
 
 Smokeless Combustion with Fire-Tube Boilers 60 
 
 Smokeless Furnaces. Design of 51 
 
 Smoke, Objections to 
 
 Smoke Record 46 
 
 Smoke Stack 146 
 
 Smoke Stack, Proper Heights of 146 
 
 Smoke Stack. Sectional Area of 146 
 
 Smoke Stack. Velocity of Gases in 146 
 
 Sprockets for Carrying Chain 96 
 
 Sprung Arch 57 
 
 Sprung Ignition Arch 134 
 
15G FURNACE EFFICIENCY 
 
 Stirling Boiler, Draft Losses through 36 
 
 Stoker Boxes, Function of 108 
 
 Stoker Boxes, Motion of 108 
 
 Stoker Boxes for Murphy Furnace 108 
 
 Support for Double Sprung Arch 110 
 
 Support for Grate-Bearers . .. 109 
 
 T 
 
 Table No. 1 42 
 
 Table No. 2 71 
 
 Texas Coal, Ignition Arch for 137 
 
 Thermometer, Cost of 21 
 
 Thin Fire, Effect of, on Draft Losses 29 
 
 Tile Roof 54,57 
 
 Torch for Locating Air Leaks 22 
 
 Tube Tiles 54 
 
 Tuyer Blocks for Jones Stoker 121 
 
 U 
 
 Under-Feed Principle in Mechanical Stoking- 119 
 
 Upper Gauge 78 
 
 V 
 
 Value of Wilsey Gauge 72 
 
 Velocity of Gases in Smoke Stack 146 
 
 Velocity of Gas in Breedings 141 
 
 Volatile Gases, Composition of 40 
 
 Volatile Gases in Coal 40 
 
 W 
 
 Water-Back 99 
 
 Water-Back, Function of 100 
 
 Water-Back, Location of 100 
 
 Western Society of Engineers 57 
 
 Wheatstone Bridge 68 
 
 Whitewash for Stopping Air Leaks 
 
 Wilsey Fuel Economy Gauge 65 
 
 Wilsey Recording Gauge 72 
 
 Wing Walls 48 
 
One Thousand Questions and 
 
 Answers for Engineers, Applicants 
 for License and Electricians 
 
 By JOSEPH G. BRANCH, former Member of the 
 
 Board of Examining Engineers of the 
 
 City of St. Louis, Editor "Practical 
 
 Electricity and Engineering." 
 
 This book contains questions with answers, 
 asked by Examining Boards for'engineer's license, 
 and for electrician's card, and also questions and 
 answers covering the entire field of steam engin- 
 eering and practical electricity, including wiring 
 diagrams. 
 
 It is a complete library in one volume, and 
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 The book is printed in large type, fully il- 
 lustrated. 180 pages, 5^x7^ inches, and is 
 strictly up to date. 
 
 If you wish immediate delivery you must 
 write today as the first edition is already about 
 Price is *1.50 Postpaid. sold. 
 
 The Electric Motor 
 
 and Its Practical Operation 
 
 By ELMER E. BURXS 
 
 The only book giving a simple, clear and 
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 tion of all kinds of electric motors. 
 
 CONTEXTS 
 
 Chapter 1. How an Electric Current Can 
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 Chapter II. The Beginning and Growth of 
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 Chapter III. Power and Efficiency of a Motor. 
 
 Chapter IV. Counter-electromotive force. 
 
 Chapter V. How Power is Lost in a Motor. 
 
 Chapter VI. Armatures and Cummutators. 
 
 Chapter VII. Types of Direct-current Motors. 
 
 Chapter VIII. Starting Boxes and Their Connections 
 
 Chapter IX. Curve Tracing. 
 
 Chapter X. How to Understand Alternating-current Motors 
 
 Chapter XI. Operation of Alternating Current Motors 
 
 Chapter XII. Speed Control of Motors. 
 
 Chapter XIII. Motor Troubles and How to Cure Them 
 
 Chapter XIV. Selecting and Installing Motors 
 
 Appendix. Horse-power Required to Drive Various Machines. 
 
 Size 5%x7Vfe inches; 200 pages; fully illustrated. 
 
 The Joseph G. Branch Publishing Company 
 
 608 South Dearborn St., CHICAGO, ILL. 
 
 Price, $1.50, Postpaid. 
 
Steam Publications 
 
 STATIONARY ENGINEERING 
 
 By JOSEPH G. BRANCH, B. S., M. E. 
 
 Former Chief of the Department of Inspection Boilers and Eleva- 
 tors. Member of the Board of Examining Engineers for the 
 City of St. Louis. Member of the American Society of Me- 
 chanical Engineers, Etc. 
 
 The entire subject of Stationary Engineering: is fully covered, 
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 The subject is systematically treated. The headings and 
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 One thousand and fifty-seven pages of text, three hundred and 
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 Volume 3. Mechanical Refrigeration, Elevators and Steam 
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 Price of the three volumes, postpaid $10.00 
 
Practical Mathematics 
 
 FOR THE 
 
 Engineer and Electrician 
 
 By ELMER E. BURNS and JOSEPH G. BRANCH. 
 
 This book was writ- 
 ten especially for the 
 operating engineer 
 and electrician by a 
 chief engineer and a 
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 gives only what the 
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 essary. 
 
 CONTENTS 
 
 1. Common fractions. 
 
 2. Decimal fractions. 
 
 3. Use of decimal fractions in finding circumference and 
 area of a circle. 
 
 4. Adding and subtracting common fractions. 
 
 5. Reducing common fractions to decimals and decimals to 
 common fractions. 
 
 6. Finding the horse-power of an engine. 
 
 7. Finding the capacity of tanks and boilers. 
 
 8. Finding the cost of power. 
 
 9. ALGEBRA. The use of letters to represent numbers. 
 
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 simple equations. 
 
 11. TRIGONOMETRY. Measuring angles and triangles. 
 
 12. Power factor and sine curve. 
 
 Handsomely bound in cloth ; in large type, on good paper. 
 
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Practical Kinks, Recipes 
 and Tables 
 
 By JOSEPH G. BRANCH, B. S., M. E. 
 
 This book has been 
 compiled especially for 
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 ready reference book. 
 
 Every kink and recipe 
 is something new, orig- 
 inal and useful. 
 
 It is a practical book 
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 Fully illustrated and 
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 Pressure of Water. 
 Standard Steam, Gas and 
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 of Various Fuels. Met- 
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 Different Kinds of Kiln-dried Woods, and Their Evaporative 
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 of Circles. Wiring Tables for Electric-light Conductors. Com- 
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 ductivity of Conductors. Temperature Coefficients. 
 
 Handsomely bound in cloth ; in large type, on good paper. 
 
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