ee sacs a honk oy. P heeds “A Pith aN ‘ i Ley wef i ads 8 °g bs Aye WL bf : Pieterhations ip Correspondence — ~—ochools SCRANTON, PA. REG. U.6. PAT. OFR / ~—sC INSTRUCTION PAPER with Examination Questions ee . FIRST EDITION Sey E _ Furnace Efficiency and _- Flue-Gas Analysis 1744, BASS i Aes \ : a Ba. WES 5 Nee iad * mo fe SCRANTON, PA. ‘ {INTERNATIONAL TEXTBOOK COMPANY 1921 ADVICE TO THESTUDENT You learn only by thinking. Therefore, read your lesson slowly enough to think about what you read and try not to think of anything else. You cannot learn about a subject while thinking about other things. Think of the meaning of every word and every group of — words. Sometimes you may need to read the text slowly several times in order to understand it and to remember the thought in it.. This is what is meant by study. Begin with the first line on page 1 and study every part of the leds in its regular order. Do not skip anything. 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Remember, too, that you will get more good from your Course if you learn all that you can without © asking for help. fia] ~ INTERNATIONAL CORRESPONDENCE SCHOOLS Copyright, 1916, by INTERNATIONAL TEXTBOOK Company. Copyright in Great Britain. All rights reserved ‘ eat fee f- ee e 6) Bote ees § ei os Bh ee mo ety ean ee ee te ep eR’ we FEO) Sd anh , ft >, “ fee } fa’ ! Ks -* . ow 4 NG LT ) i] / ae 44], A FURNACE. EFFICIENCY AND FLUE-GAS S ANALYSIS _ FURNACE EFFICIENCY OF STEAM BOILERS GENERAL CONSIDERATIONS oe DEFINITIONS edd. The efficiency of a boiler is the ratio of the amount of \ heat that it absorbs and uses in making steam, to the amount ro f heat furnished to it. The heat that is furnished to the grate ‘is all the heat contained in all the coal, as fired. But the heat _ furnished to the furnace and boiler is that in the coal that is . ib urned. If a part of the good coal drops through the grate % the boiler and furnace must not be charged with its heat. Pi, 2. The American Society of Mechanical Engineers’ Com- m ittee on Boiler Tests recommends the consideration of two Ve eff ficiencies, which are stated as follows: | Efficiency of boiler : % Heat absorbed per pound of combustible burned (1) Calorific value of 1 pound of combustible Efficiency of boiler and grate. _ Heat absorbed per pound of coal fired (2) 4 a — Calorific value of 1 pound of coal oe _ These two efficiencies necessitate the grate efficiency being _ found separately ; that is, as ¥ Pie, Ber RIGHTED BY INTERNATIONAL TEXTBOOK COMPANY ALL RIGHTS RESIRVED - $25 2 FURNACE EFFICIENCY ok bo Ot Bi beney operate Pounds of saith burned (3) Pounds of combustible fired Later recommendations give the following efficiencies: Efficiency of boiler, furnace, and grate _ Heat absorbed per pound of coal fired Calorific value of 1 pound of coal _ Heat absorbed per pound of combustible fired 4 Calorific value of 1 pound of combustible 4) Efficiency of boiler and furnace _ Heat absorbed per pound of combustible burned (B) Calorific value of 1 pound of combustible 3. It is difficult to determine the actual efficiency of a boiler alone, as distinguished from the combined efficiency of boiler, grate, and furnace. ‘This is owing to the fact that the losses due to excess air cannot be charged to either the boiler or the furnace, but only to the apparatus asa whole. Attempts have been made to divide the losses proportionately between the boiler and the furnace, but without success. General practice, however, has established the use of the efficiency based on combustible as representing the efficiency of the boiler alone. When that efficiency 1 is used, its exact meaning should be understood. 4. To illustrate the application of the statements made, consider the following data obtained during a boiler trial: Steam pressure, gauge, in pounds per square INCH yi toga ak Ae se ee ee 180 Feedwater temperature...................5 170° F. Total weight of coal fired, in pounds........ 17,300 Percent) moisturein coals. e. ve ce eee Se Total ash and refuse, in pounds............ 2,300 Total water evaporated, in pounds........ _.. 152,000 Per cent. moisture in steam.. —s 6 Heat value per pound of dry en in fae T. U 13,500 Heat value per pound of combustible, in ~ >. e 80406 [2] § 25 AND FLUE-GAS ANALYSIS 3 The actual evaporation corrected for moisture in the steam is 152,000 — (152,000 x .006) = 151,088 pounds. Equivalent evaporation from and at 212° F. is 151,088 x 1.096 = 165,592+ pounds. Total dry fuel is 17,800 (1—.03)=16,781 pounds. Evaporation per pound of dry fuel from and at 212° F. is 165,592+ 16,781=9.87 pounds, closely. Heat absorbed per pound of dry fuel will be 9.87 X966.1=9,535+ B. T. U. Therefore the efficiency of boiler, furnace, and grate, by for- mula 4, Art. 2, is 9,535+13,500=.706+, or 70.6 per cent.; the total combustible burned is 16,781 —2,300 = 14,481 pounds; and the evaporation from and at 212° F. per pound of com- bustible is 165,592 + 14,481 =11.44 pounds, closely. There- fore the efficiency of boiler and furnace, based on combustible burned, by formula 5, Art. 2, is (11.44966.1) + 15,350 =.7199-+ =71.99 per cent. 5. Boiler efficiencies will vary over a wide range, depending on a variety of factors and surrounding conditions. With coal as the fuel, an efficiency of 82 per cent. has been obtained and it has been known to go below 50 percent. The difference between the efficiency obtained in any case and perfect efficiency (100 per cent.) includes the losses that occur, some of which are unavoidable. HEAT LOSSES 6. The various heat losses that occur may be stated as follows: Loss from fuel dropping through the grate. Loss due to unburned fuel carried away in small particles up the stack by the intensity of the draft. Loss due in heating the moisture in the fuel from atmospheric temperature to the boiling point, which at sea level is 212° F., to evaporate it at that temperature and to superheat the steam - so formed to’the temperature of the flue gases. This steam is just heated to the temperature of the furnace, but as it gives up a portion of this heat in passing through the furnace, the superheating to the temperature of gases entering the chimney is the loss to be considered. 4 FURNACE EFFICIENCY ‘98-25 Loss due to the forming of water through the burning of the hydrogen in the fuel, which water must be evaporated and superheated, the same as the moisture content of the fuel. Loss due to superheating the moisture in the air supplied, from the atmospheric temperature to the temperature of the flue gases. Loss due to heating the dry products of combustion to the temperature of the flue gases. Loss due to incomplete combustion, when the carbon burns to carbon monoxide, CO, instead of to carbon dioxide, COs. 7. Elaborate tests would have to be made if all the items just enumerated were to be determined accurately. In practice it is customary to compute the loss due to heating the moisture in the fuel from the atmospheric temperature to the boiling point, which at sea level is 212° F., evaporating it at that tem- perature, and superheating it to the temperature of the flue gases, by the following formula: A=W[(11—-)+L+.48(T — T;)] in which W=moisture in coal, in per cent., expressed decimally; t=temperature of air in boiler room; T =temperature of flue gases; T,=temperature of boiling point of water, tefl taken as 212° F. unless otherwise stated or required; L=B. T. U. necessary to evaporate 1 pound of water at boiling point to steam at atmospheric pressure; 48 = specific heat of superheated steam at atmospheric pressure and at temperature of flue gases; A=heat loss, in B. T. U., per pound of coal. EXAMPLE.—A quantity of coal contains 2 per cent. of moisture. The temperature of the air in the boiler room is 80° F., the temperature of boil- ing water at the pressure of the atmosphere at sea level is 212° F., the latent heat of steam at atmospheric pressure is 966.1 B.*T. U., and the temperature of the flue gases at the last pass in the furnace setting is 500° F. What is the loss, in B. T. U., per pound of coal? SOLUTION.—Applying the formula, A= 02 X[(212—80) + 966. 1+.48 X (500 —212)] = 24.73 B. T. U. per Ib., closely. Ans. s § 25 AND FLUE-GAS ANALYSIS 5 8. The heat loss due to the heat taken away in the steam by the burning of the eee uk in the fuel is expressed by the following formula: A=9H[(T:—-1)+L+.48(T— 7] in which H=percentage, by weight, of hydrogen, expressed decimally, and the other letters have the meaning givenin Art. 7. Where an ultimate analysis of the fuel is not given, this item is generally considered as part of the unaccounted for loss. EXAMPLE.—A certain coal contains 5 per cent. of hydrogen, the temper- ature of the air in the boiler room is 80° F., the temperature of boiling water at the pressure of the atmosphere at sea level is 212° F., the latent heat of steam at atmospheric pressure is 966.1 B. T. U., and the temperature of the flue gases at the last pass in the furnace setting is 500° F. What is the loss, in B. T. U., per pound of coal? SoLuTION.—Applying the formula, A=9xX.05 X [(212—80) +966.1-+.48 x (500 —212)] =556.35+ B. T. U. per lb. Ans. 9. The heat loss due to the heat taken away by the dry chimney gases depends on the weight of gas per pound of fuel, which weight may be determined by this formula: _11C0,+80+7(CO+N) 1) 3(CO;+C0) in which W=weight of flue gases per pound of carbon; CO.=percentage of carbon dioxide, as found from a flue-gas analysis; O=percentage of oxygen, as found from an analysis; CO=percentage of carbon monoxide, as found from an analysis; N= percentage of nitrogen, as found from an analysis; C=percentage of carbon, by weight, in dry fuel, as found from an ultimate analysis. All percentages are to be expressed decimally in this formula. ExamPte.—A flue-gas analysis gave the following values: Carbon dioxide, CO2z, 14 per cent.; oxygen, O, 4 per cent.; carbon monoxide, CO, .2 per cent.; and nitrogen, N, 81.8 per cent. The percentage of carbon, by weight, in the coal used was 78. What was the weight of gas per pound of coal? I ‘ong SPD OnI4 Ul 2709 JO “yUusD 4dq N pup 0‘209 Ajuo buiuipjuoD saspy anj4 Auq ul 4Ss0]7 4DaH Jo sbp,UDD4Nq A 4JuD|SUOD JO SNIVA Huipuly s0j JapyD X jo SOn|DA § 25 AND FLUE-GAS ANALYSIS 7 _ SoLutTion.—Applying the formula, _11X.144+8X.04+7 x (.002+.818) iy 3X (.14+.002) WwW X.78=13.92— lb. Ans. The heat loss per pound of dry coal is given by the formula A= .24W,(T —t?) (2) in which .24=specific heat of chimney gases; W,=weight of dry chimney gas per pound of dry coal; T =temperature of flue gases; t=temperature of air in boiler room; A=heat loss per pound of dry coal, in B. T. U. EXAMPLE.—In a given case, the weight of chimney gas per pound of dry coal is 13 pounds, the temperature of the flue gases at the last pass is 500° F., and the temperature of the air in the boiler room is 80° F. What is the heat loss per pound of dry coal? SOLUTION.—Applying the formula, A =.24X13 X (500—80) =1,310.4 B. T. U. per lb. Ans. 10. beeeacs no 2.00 Dry;coal pounds per hotur.. tite vip ee . tle wel. ne 5,586 Ashes, pounds per DOUBs 3 gan. wap cis pusigatcs storu tas fee ae 550 Ash-per cent."OF Ury COdie:. ge... ty oe a oe 9.84 Actual evaporation, pounds per hour....................6- 57,000 Carbon in the coal, per cent. 78.52 Hydrogen in the coal, per cent. 5.46 Oxygen in the coal, per cent. Ultimate analysis of dry 7.00 Nitrogen in the coal, per cent. COAL. oc. ® cole se ile 1.21 Ash in the coal, per cent. 6.5) Sulphur in the coal, per cent. 1.30 Heat value of dry coal, British thermal units, per pound, as determined. by..a.calorimeter is... cre oak - « ae ae 14,230 Heat value of combustible, British thermal units, per pound, as determined by calculation, involving items 9 and 17... 15,783 Combustible, per cent., in the ash, by analysis............. 18.00 CO per Centon VION. I, TEE Lk 14.35 CO percent IT fPtse-s analysis "9 JV. OT) CO be Liban aolageuo de re: Saal ane eee 81.03 COMPUTATIONS PERTAINING TO HEAT BALANCE 53. One pound of carbon completely burned to carbon dioxide, COs, gives out by its combustion 14,600 B. T. U., approximately. One pound of hydrogen when burned to form water gives out 62,000 B. T. U., approximately. From this data the following formula has been derived: A = 14,600 C+62,000(# 5) in which A=heat of combustion, in B. T. U.; C=percentage of carbon in fuel; H =percentage of hydrogen in fuel; O=percentage of oxygen in fuel. The small amount of sulphur that may be in coal is neglected in the calculations for heat value. It will be noticed that one- § 25 AND FLUE-GAS ANALYSIS 37 eighth of the percentage of oxygen is subtracted from the per- centage of hydrogen before multiplying by the heat value of the hydrogen. This is done because the oxygen in the fuel combines with one-eighth of its weight of hydrogen and so renders this amount of the hydrogen unavailable for combus- tion, so that only the remainder may be considered, or H -< By the use of the formula, the heating value of a coal may be determined sufficiently accurate for all practical purposes, and serve as a guide as to what may be expected of a given coal when fed to the furnace of a steam boiler. EXAMPLE.—A bituminous coal has the following composition: Carbon, 76 per cent.; hydrogen, 6 per cent.; oxygen, 12 per cent.; nitrogen, 1 per cent.; sulphur and ash, 5 per cent. Find the heat of combustion. SOLUTION.—Applying the formula, 12 A = 14,600 X .76+-62,000 x (.00-%) =13,886 B. T. U. Ans. 54. When finding the heating value of a coal there will be a slight difference in the final result according to whether an’ ultimate or a proximate analysis of the fuel has been made. The difference is rather slight, however. The formula just given is that used in an ultimate analysis, and if this formula is applied to the data given on the heat-balance data sheet, already shown, it will be found that a heat value of 14,306+ B. T. U: is obtained, instead of the value of 14,230 B. T. U. given, which is the result of a proximate analysis. The differ- ence is so slight as to be of no practical account; consequently, in practice the heating value obtained by whatever analysis is most convenient will be used in heat-balance calculations. 55. The factor of evaporation is found from the following formula: _H-h+32 966.1 in which f=factor of evaporation; H=total heat of steam at observed pressure; h=temperature of feedwater entering boiler. I 38 FURNACE EFFICIENCY § 25 The actual evaporation multiplied by the factor of evapora- tion gives the equivalent evay oration from and at 212° F. EXAMPLE.—From the data recorded on the heat-balance data sheet in Art. 52, determine the equivalent evaporation per pound of coal, the B. T. U. of heat utilized, and the efficiency of the boiler, furnace, and grate, SOLUTION.—From the Steam Tables, the total heat of steam at 190 lb. gauge pressure is 1,198.93 B. T. U. Applying the formula, _ 1,198.93 —200+32 ue 966.1 | Then, equivalent evaporation is 57,000 X 1.067 =60,819 lb., and equiva- lent evaporation per pound of dry coal fired is 60,819+5,586=10.89 Ib., nearly. Ans. The heat utilized by the boiler is 10.89 966.1 =10,520.8 B. T. U. per Ib. of dry coal. Ans. The efficiency of the boiler, furnace, and grate, by Art. 2, is 10,520.8 + 14,230 =.739 =73.9+ per cent. Ans. = 1.067+ 96. The formula by which the loss due to moisture in the coal is computed was given in Art. 7. An application of the formula to the balance sheet under consideration is given in the following example. EXAMPLE.—From the data given on the heat-balance data sheet, deter- mine the heat loss per pound of coal due to moisture in the coal, and also the heat loss in per cent. SOLUTION.—Applying the formula given in Art. 7, A =.02X[(212—80) +966.1-+-.48 x (478 — 212)] = 24.52 B. T. U. Percentage of heat loss is 24.52+14,230=.0017 =.17, say .2, per cent. Ans. 57. The formula for calculating the heat loss due to burn- ing of the hydrogen was given in Art. 8. The application to the balance sheet under consideration is given in the following example. EXAMPLE.—From the data given on the heat-balance data sheet, deter- mine the heat loss per pound of coal due to the burning of the hydrogen in the fuel, and also the heat loss in per cent. SOLUTION.—Applying the formula in Art. 8, A=9X.0546 X [(212 —80) +966.1+.48 x (478 —212)] = 602.35 B. T. U. per lb. The heat loss is 602.35 + 14,230 = .0423+ =4.23+ per cent. Ans. § 25 AND FLUE-GAS ANALYSIS 39 58. To compute the loss in the heat taken away by the dry chimney gases per pound of coal, the weight of such gases must first be found by formula 1, Art. 9, and then the heat loss is calculated by formula 2. EXxAmMPLE.—From the data given on the heat-balance data sheet in Art. 52, determine the percentage of loss of heat by the escaping chimney gases, per pound of dry coal, and also in per cent. SOLUTION,—Applying formula 1, Art. 9, and remembering that the quotient is to be multiplied by the percentage of carbon in the coal, w= 11X.14385+8 X .045+7 X (.0012+-.8103) 3X (.1485+.0012) =13.78+ Ib. per lb. of dry coal Applying formula 2, A =.24X13.78 X (478—80) =1,316 B. T. U. per Ib. of dry coal Hence, heat loss in per cent. =1,316+14,230=.093=9.3 per cent., closely. Ans. X .7852 59. The heat loss due to incomplete. combustion is ccm- puted from the percentage of carbon monoxide shown by a flue-gas analysis, using the formula presented in Art. 11. EXAMPLE.—From the data given on the heat-balance data sheet pre- sented in Art. 52, find the heat loss, in per cent., by incomplete com- bustion of the coal. F SOLUTION.—Applying the formula in Art. 11, 10,150 X .0012 A =.7852X ——_———— = 66.09+ B. T. U. lb. of d ] "1435 -+.0012 vs Bia lis OB adh st Percentage of heat loss is 66.09+ 14,230 = .0046 =.46, say .5, per cent. Ans. 60. The manner in which the heat loss due to unconsumed carbon in the ash is found has been explained in Art. 12. EXAMPLE.—From the data given on the heat-balance data sheet in Art. 52, determine the percentage of heat loss due to unconsumed carbon in the ash. SOLUTION.—By Art. 12, the heat loss per pound of dry coal is .0984 X<.18 x 14,600 = 258.6 B. T. U. and the percentage of loss is 258.6 + 14,230 =.0181=1.81 per cent. Ans. 61. The manner in which the unaccounted for losses are found was stated in Art. 17. Applying this article to the data 4() FURNACE EFFICIENCY § 25 of the heat-balance data sheet, the heat loss unaccounted for is found in B. T. U. and in per cent. as follows: By the method in Art. 4, the heat absorbed per pound of dry fuel is 10,520.8 B. T. U., or 73.9 per cent. By Arts. 7 to 12, the accounted for heat losses per pound of dry coal are 24.52, 602.35, 1,316, 66.09, and 258.4 B. T. U., or .15, 4.23, 9.3, .46, and 1.81 per cent. Hence, the unaccounted for heat loss per pound of dry coal is 14,230 — (10,520.8-++24.52+ 602.35 +1,316+ 66.09+258.4) = 1,441.84 B. T. U., and in per cent. 100—(73.9+.15+4.23 +9.3+.46-+1.81) = 10.15, say 10.1, per cent. 62. Afterall the various items of the heat balance have been calculated from the data obtained during a boiler test, they may conveniently be arranged in tabular form as here shown. HEAT-BALANCE TABLE B. avs | Per Cent. Values Values Items ee a 1. Heat absorbed by the boilers, per pound dry COCLDRITL I Erneta 3). a's ow ss vbteee eee enol 10,520.80 73.9 2. Loss due to evaporation of moisture in coal. . 24.52 2 3. Loss due to moisture by burning of hydrogen. . 602.35 4.2 4. Loss due to heat taken away in the dry chim- | TIGY SASESF ecca as « x’ sigiegh a's p coer kee Ghee eee 1,316.00 9.3 5. Loss due to incomplete combustion.......... 66.09 5 6. Loss due to combustible in the ash........... 258.40 1.8 7. Loss due to radiation and unaccounted losses..| 1,441.84 10.1 Totals (B. T. U. per pound of dry coal, 14,230) | 14,230.00 100.00 A heat-balance scheme may be made more elaborate than here explained, but for practical power-plant purposes that which is given fulfils all reasonable requirements including that of simplicity. , APPLICATION OF HEAT BALANCE 63. oh de] ee et ea al Strid SABRE SHAG, BRS REEL IBESaSS . ER EeSSRE SELES [| SVG G88 AR > Bi pe | at foo fal ee batt | tek | Laid ops & Ler er ee ee re ae ee WN i) ito) - Ww ite) Oo or as pe Pe ADIDM jo saudu] Ul ‘yjoug Fic 10 draft. The horizontal row of figures at the base represent The vertical row of figures at the left-hand side of the diagram represent the draft in inches of water, as measured by a draft gauge. ounces per square inch draft pressure. Knowing the draft in inches of water, in any given case, the corresponding pressure per square inch is found by locating the § 25 AND+FLUE-GAS ANALYSIS 45 point on the diagram from the indication of the draft gauge, and then running horizontally to the right to the intersection of the diagonal line, and down to the base where the corre- sponding pressure is found. EXAMPLE 1.—The draft, as measured by a water gauge, is linch. What is the corresponding pressure? SOLUTION.—Following the horizontal line representing the 1-inch draft to its intersection with the diagonal line and then following the nearest vertical line to the scale on the bottom shows that the corresponding pres- sure is .58 oz. per sq. in. Ans. EXAMPLE 2.—If the draft pressure is .9 ounce, what is the corresponding height of water in inches? SOLUTION.—Following the vertical line representing the pressure of .9 ounce to its intersection with the diagonal line and then following the nearest horizontal line to the scale on the left, it is found that the height of the water column is 1.5 in. Ans. NATURAL DRAFT 70. The difference between the weight of a column of hot gases in a chimney and the weight of an equal column of cool air outside results in an upward motion of the hot gases in the chimney, which motion is termed natural draft. Any gas is lighter when heated than when it is cool, considering a given volume. ‘The force acting upwards is greater than that acting downwards, hence the phenomenon that is called draft. In any chimney, the higher the temperature, the greater the difference in pressure and velocity of flow of the gases; but, as the density of the gases decreases with the increase of temper- ature, there is a point where as much is lost in weight of gas passed, by the lightness of the gas, as is gained by the increased velocity. G1. The temperature of the gases in a chimney may vary, but under usual conditions of operation they will be from 400° F. to 500° F. while the air outside the chimney may have a temperature of from 40° F. to 90°F. Asa result, the pressure in the chimney is less than the pressure of the air outside, so ILT 168—45 ; 46 FURNACE EFFICIENCY § 25 that air will flow through the furnace and up the chimney. As an example, assume that the temperature of the gases in a chimney 150 feet high and having a cross-section of 1 square foot is 500° F. As such a gas column weighs approximately 4 pounds while at 60° F. the column weighs approximately 114 pounds, the difference in pressure at the foot of the chimney of the gases inside and the air outside the chimney is 113 —63 =5 pounds. This difference in pressure of the air inside and outside the chimney is known as the draft pressure. 72. Since natural draft is dependent on the difference in weight between the hot gas in the chimney and the outside air, the hotter, and therefore the lighter, the gas, the stronger is the draft. A high chimney will cause a stronger draft than a short one; with chimneys of moderate height a strong natural draft requires a high temperature of escaping gases, with a consequent loss of heat and economy. With natural draft, the tate of combustion will range from 12-to 20 pounds of coal per square foot of grate surface per hour, depending on the quality of the coal and surrounding conditions. 73. The capacity of a chimney varies as the square of the diameter and as the square root of the height. The velocity of flow of the gases, which is also a measure of volume, increases as the square root of the pressure, and the pressure varies directly as the height. By doubling the height of a chimney, the intensity, or, in other words, the pressure of draft, will also be doubled; but the velocity of flow of the gases will increase only as the square root of the pressure, which is the same as saying as the square root of the height. Ina chimney 200 feet high, the theoretical velocity of flow of gases will be twice that of a chimney 50 feet high, for the square root of 200 is 14.1421 and of 50 is 7.0711; therefore, twice as much gas will be discharged in a given time. In the foregoing, frictional resistances have not been con- sidered, but in practice these may be taken into account. The extent to which these resistances will affect the results, though, cannot be determined by any general law, for they will be greatly affected by the conditions of each case. § 25 AND FLUE-GAS ANALYSIS 47 74. The capacity of a chimney is not measured by the ' intensity of draft. The capacity, for the same temperature, varies as the square root of the intensity, where the greater intensity is gained by an increase in chimney height. But if the temperature also is raised so as to double the volume of gas discharged, the intensity of the draft is doubled, and the velocity increased 1.414 times, but the velocity must be increased two times to pass twice the volume of gas in-the same period of time. ° 75. Changes in draft should be made by manipulating the chimney damper and not the ash-pit doors. If the draft is varied by means of the ash-pit doors, while the regular damper remains wide open, the full draft of the chimney is exerted on the furnace all-the time. If the ash-pit doors are nearly closed the effect is to increase greatly 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 through cracks in the setting will be increased. On the other hand, if the damper is partly closed, with the ash-pit doors open, when less draft is required, there will be a drop in the draft at all parts of the setting, and, relatively, the amount of air drawn in both under and over the fire will be the same as before. 76. Differences in pressure in boiler furnaces and chimneys are measured by draft gauges. They will not directly measure the flow and velocity of the gas, but the indications of the gauge will give an idea of the variation of velocity. When fires are clean and of uniform thickness, with the furnace doors closed and the ash-pit doors open, the greater the intensity of draft, the greater will be the velocity of flow of gases. If the ash-pit doors are closed, the draft, as indicated by the gauge, will be increased but the movement of the gases will be decreased, since the supply of air is shut off. If now the furnace doors are opened, air will rush into the furnace with considerable velocity but the gauge will show that there is less: draft; that is, less difference in pressure than before the furnace doors were opened. 48 FURNACE EFFICIENCY § 25 MECHANICAL DRAFT 77. Mechanical, or artificial, draft is produced by means of steam jets or fan blowers. The object is to increase the differ- ence of pressure between the ash-pit and the chimney beyond that obtained with a chimney producing only natural draft, and at the same time to provide for a full supply of air to the grates as required by the rate of combustion desired. ; BALANCED DRAFT 78. The term balanced draft is applied to a system of oper- ating boiler furnaces by which the supply of air and the rate of flow of waste gases from the chimney are so controlled that an approximately uniform atmospheric pressure is- maintained above the fire in the furnace for varying rates of combustion. By the use of this system, the air supplied to the fuel can be limited to the required amount for any desired rate of com- bustion. With it there will be neither an excess of pressure nor a partial vacuum in the furnace, thus differing from the natural and mechanical draft systems as usually applied. 79. The draft is balanced by throttling the gases escaping to the chimney by varying the opening of the damper to suit the speed of the fan blower that supplies air to the asb-pits. The speed of the blower is governed by variations in steam pressure in the boiler. The position of the damper changes with change of speed of the blower, which in turn may be con- trolled by the steam pressure running the blower engine. The blower is so designed that it will deliver, approximately, a constant volume of air of variable pressure for any given speed. The volume varies with the speed, and the pressure varies with the resistance. The pressure in the ash-pit varies with the thickness of the fuel bed, and the volume of air varies with the demands for steam made on the boiler, with the result that only the least amount of air required for the necessary rate of combustion is furnished. 80. The object of moving the damper in relation to the speed of the blower is to maintain atmospheric pressure in the § 25 AND FLUE-GAS ANALYSIS 49 furnace. The damper regulator is so adjusted that the damper is open just enough to accommodate the gases escaping from the furnace without creating a pressure therein, and without Opening so wide as to allow the chimney draft to produce a partial vacuum in the furnace. The chimney simply removes the gases from the furnace. The draft created by the chimney is throttled by the partly closed damper until the suction is sufficient to overcome the friction of the gases against the surfaces with which they come in contact. 81. With balanced draft, the amount of hot gases is reduced to a minimum, and therefore they can take a longer time to pass through the furnace on the way to the chimney, and thus will give up a greater percentage of heat than would otherwise be the case. Although the furnace is kept at atmospheric pressure, the pressure falls slightly at the point where the gases leave the boiler, so that a partial vacuum exists in the passages leading to the chimney. This reduction of pressure is sufficient to overcome the frictional resistances of the passage of the gases, resulting in the gases being brought in contact with all the heating surfaces. When balanced draft is employed, leak- age of air through openings and cracks into the furnace will not so readily occur. 82. The causes of low carbon-dioxide percentages are excess air, insufficient air, and improper mixture of air with the gases from the fuel. The causes of excess air are too strong a draft, too thin a fire-bed, holes in the fire, leaks in various parts of the boiler setting, doors, and chimney connections. The causes of insufficient air are insufficient draft, too thick a fire-bed, ashes on the grate, and too heavy a charge of fresh fuel. 83. The remedies for these troubles are as follows: If the draft is too strong, it should be reduced or the thickness of the fire-bed increased. If the fires are too thin, the draft should be reduced or the thickness of the fire-bed increased. For insufficient draft, the thickness of the fire-bed should be decreased and the air spaces in the grates kept free and clear of slag. 50 FURNACE EFFICIENCY § 25 Leaks in the setting should be located by asing a lighted candle, as shown in Fig. 11. The leaks should then be plugged | with waste and asbestos Glebe mceelt mixed with a thin solution of fireclay and water. Air should not enter the fur- nace except through the means provided for that purpose and where it can be controlled. The tubes and flues should be cleaned rt ‘i M(t of soot and ashes, and holes Alas Z [| “Wy pieeneen ease. and the bed leveled, but they should not be filled with fresh fuel. If the covering of fresh fuel is too thick, a lighter cover should be given at next firing, and meanwhile air should be admitted above the fire-bed through the openings in the furnace doors. The combustion of the gases driven off the surface of the fire- bed will thus be assisted. DIRECT-READING DRAFT GAUGES 84. The simplest form of draft gauge is that known as a direct-reading draft gauge, and is shown in Fig. 12. It consists of a bent U tube partly filled with water, and a scale located be- tween the inverted legs of the gauge. The ends are open at the top, and when the gauge is in use the ends are connected by tubing to the two places between which the difference of pressure is desired, as, for example, the ash-pit and the fur- nace above the fire; or, between the external air and the base of the chimney. With equal pres- sure in both places, the water will stand at the same height in both legs. With a difference of pressure, the water will rise in one leg and fall in the other, the movement of the water being toward the place of lesser pressure. Pigsae in the fire should be covered | § 25 AND FLUE-GAS ANALYSIS 51 The difference in pressure is then measured by tlie weight of a column of water equal to the difference in height between the two columns. In Fig. 12 the difference in the two water levels h and 2, represents the intensity of the draft and measures 2 inches of water. 85. With ordinary chimney draft, the pressure is usually from % to 2 inch; with light forced draft, it is from 4 to 1 inch; and with heavier forced draft, it is from 1 to 3 inches; in torpedo boats, the draft pressure may rise to a height of 6, or even 7, inches. DIFFERENTIAL DRAFT GAUGES 86. é y re Te “— Ths, . ; ne 3 "eh . . : Bae ly? t Fe ae i : 4’ } 1d fdd ae a . Bud: aera f ‘en : : ( 47 th: LPC ORC MET WTR T 2 Se Be a, | f bay ta By t4a4 py ge t tt Pape Ke | iy j | oe Mee ge A ge ; Me PE DO Ke: ‘ “oe. ‘ « ’ ’ t 4 , in ¢ Z 4 », Ls al Fay Dh) Die iy fal? bn A ; Pi \ ‘ e qs Lae ‘ 7 >. hae ta oat j ad Ne 3 } Rowe o 7 ‘ ae ae In order to do good work, it is very necessary for our students to secure the best val ‘4 . > © _ / materials, instruments, etc. used in their Courses. We have often found that inexperi- Vet” fi enced students have paid exorbitant prices for inferior supplies, and their progress has ‘\ —s been greatly retarded thereby. To insure our students against such error, arrangements 4 _ have been made with the Technical Supply Company, of Scranton, Pa., to furnish such as : _ desire them with all the supplies necessary in the different Courses. Prati (Wa, SEE PRICES ON SEPARATE LIST LIGHT-WEIGHT PRINTED ANSWER PAPER bes _ 8%"x14". This papes is very tough, durable, and has a fine writing surface. It will last > A for years, and the student is thus enabled to keep a permanent record of the work sent to the Schools. © aati ; I.C.S. COLD-PRESSED DRAWING PAPER Size 15”x 20”. Buff color—easy on the eyes. It is unusually strong and tough; takes 1 x a clean, clear line; is not brittle; is not easily soiled. Best for both ink and pencil. 9 oe | “TESCO” TRACING CLOTH : 3 Used extensively by_draftsmen, architects, engineers, and contractors—a_ high recom: “ mendation of quality. It is transparent, strong, free from knots and other imperfections and contains no air bubbles. IC.S. instructors assure their students it is thoroughly dependable. Furnished in sheets. 15” x 20”. PORTFOLIOS Cae For keeping your Examination Papers and drawing plates neat and clean and in order. yee Don’t roli them up and then forget where they are, or leave them where they will become _ . goiled or damaged. Some of these days an employer may ask to see them. “TESCO” LIQUID DRAWING INK “Tesco” Ink flows smoothly and evenly from the pen and leaves a clear, sharp line of aniform intensity, free from cracks and bubbles. eos : : - FOUNTAIN PENS / c -.. As answers to Examination Questions must be written in ink, you can, with a fountain y " -pen, answer your papers any time—anywhere—whether it is in the office, shop, factory, | “-<0r home. ¢ DICTIONARIES ___ No matter which Course you are studying, no matter what kind of work you do, a dictionary is valuable. Keep it near you when you read and when you study. Don’t skip the words you don’t understand; look them up, for that is the best way to acquire a . yocabulary.- ' . att Se)" RUBBER HAND STAMPS Stamp your name, address, and class letters and number on every lesson and drawing wou send to the Schools. Useful for marking envelopes, books, papers, etc. ‘eae DRAWING OUTFITS The I.C.S. Outfits are not simply “gotten up” to provide something for the student to use during his Course. These Outfits will last long after he has gotten into actual work. They are practical Outfits—made up from specifications furnished by I.C.S. Instructors. Naturally, then, such Outfits must be right. All instruments must be of a_high quality to give long and efficient service. All material must be honest, sincere, dependable, anfe The busy man cannot be annoyed. with poor material, and the student must not be retarded ~ by the use of it. ss COMBINATION DRAWING AND STUDY TABLE, ee The table is made of oak, and can be folded and placed out of the way; and, althougn it weighs but 19%4 pounds, it will-support a direct weight of 200 pounds. The braces are _of nickeled rolled steel. : chee an - CATALOGS : __ Any of the following catalogs will be mailed free on application to the Technical Supply Co.:; Building Trades, Practical Books Relating to Electricity, Practical Books Relating to Mechanical and Civil Engineering, Practical Books Relating te Mining, Metallurgy, and _ Chemistry. Send orders to TECHNICAL SUPPLY COMPANY, Scranton, Pa, me: ee « SEE PRICES ON SEPARATE LIST ‘ j PPLIES FOR STUDENTS With printed headings especially adapted for use of, students of the I.C.S. Size “Drawing Instruments and Materials, Practical Books Relating to Architecture and. = awe INTERNATIONAL CORRESPONDENCE SCHOOLS INSTRUCTION BY MAIL