tfr 133 STATE OF ILLINOIS D WIGHT H. GREEN, Governor DEPARTMENT OF REGISTRATION AND EDUCATION FRANK G. THOMPSON, Director DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief URBANA REPORT OF INVESTIGATIONS— NO. 133 CORRELATION OF DOMESTIC STOKER COMBUSTION WITH LABORATORY TESTS AND TYPES OF FUELS III. EFFECT OF COAL SIZE UPON COMBUSTION CHARACTERISTICS &s Roy J. Helfinstinf. PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1948 ORGANIZATION STATE OF ILLINOIS HON. DWIGHT H. GREEN, Governor DEPARTMENT OF REGISTRATION AND EDUCATION HON. FRANK G. THOMPSON, Director BOARD OF NATURAL RESOURCES AND CONSERVATION. HON. FRANK G. THOMPSON, Chairman W. H. NEWHOUSE, PhD., Geology ROGER ADAMS, PhD., D.Sc, Chemistry LOUIS R. HOWSON, C.E., Engineering A. E. EMERSON, Ph.D., Biology LEWIS H. TIFFANY, Ph.D., Forestry GEORGE D. STODDARD, Ph.D., Litt.D., LL.D., L.H.D. President of the University of Illinois GEOLOGICAL SURVEY DIVISION M. M. LEIGHTON, Ph.D., Chief . © x: rH ,£ w S3 -P © O o « • £ M o rH •»; tn vH O/— sTJ o x M -P O •- © rH > Ctf to v^ O £ HH o to -P J- Q 3 T* r-4 • © 3 00 rO o >h W • o •» rH X £ O £3 S# r-I to TJ 121 DO 0j X © n c rH O B 05 to (S5 - O co CO £ 8 o to O to o © -P f-H c5 XJ ^ © Ht ^ 05 en feO 4> CQ N e -P Jh o •H •H M o -P w -P tn * CQ to CO h4 W Jh rH £ o G3 o C o rH <£> £ P^i M • • t^ No. 1 is the ve rating varying from (unsuitable) to 5 (ideal). he l 1 ^ inch by coal; No. 3 is the % inch by coal; No. S has equal parts of No. 1 and No. 3 coals. J4 DOMESTIC STOKER COMBUSTION inch by 0. The two exceptions to this trend were, coals, from Vermilion and Madison counties (20 and. 70 series, respectively). The maximum improvement was 280 B.t.u. per pound. Briefly stated, the effect of size of the Illinois coals tested upon heat obtained was of no practical importance. However, a slight improvement with the smaller coals was detectable in the laboratory. It should be emphasized that the coals were well mixed before shoveling into the hopper. Thus the results of these tests will not show the effect of feeding a coal of varying size to the hopper with a fixed air setting, such as would be the case if segregation of coal sizes occurred in a bin before feeding to the stoker. A previous report 5 showed that a close relationship existed between the heat ob- tained per pound and the heating value of the coal when size was constant. Theoreti- cally,, the heating value of each series of three coals should be the same on a moisture-free basis. However, some differences in re- ported values would be expected because of imperfect mixing, sampling, and analysis. Incidental variations in moisture would cause additional differences on the as-fired basis. The maximum variation reported (table 3) was a loss of 193 B.t.u. per pound with a coal from LaSalle County. This appreciable reduction in heating value with the LaSalle County coal was probably the result of slight heating in the storage bins prior to crushing and sampling. The average differences in reported heat- ing value on the as-fired basis for the three size ranges tested were 6, 24, and 30 B.t.u. per pound. It is therefore apparent that each series of coals may be considered iden- tical in respect to heating value on the as- fired basis. 5 Helfinstine and Boley, op. cit. 2. EFFECT UPON ATTENTION REQUIRED The coals used for the size study were from the same original sample, hence the differences in percentage of ash reported would be caused by imperfect sampling, analysis, mixing, and moisture control. Table 4 lists these differences on the as- fired basis. Obviously the differences shown would not affect the attention required. The size of the coal burned had little apparent effect upon the rating given to the clinker at the time of removal (table 5). Only the clinkers from the coals prepared from Franklin County nut and Madison County screenings received different ratings. No significance should be attached to these differences. Although no measurements were made to indicate the relative amount of dust caused by handling the three size ranges tested, the finer sizes undoubtedly made the most dust, and would be less desirable from this standpoint. 3. EFFECT UPON ABILITY TO MAINTAIN DESIRED HEAT OUTPUT a. Uniformity of heat release. — Some im- provement in uniformity of heat release was caused by crushing to a Ya inch top size for every coal tested (table 6 and fig. 5). The coals from Madison County (60 and 70 series) showed the greatest improvement. The 1|4 inch by coal prepared from nut coal (No. 71) had an average variation of 20.1 percent, which is very poor in this re- spect. However, the same coal crushed to 14 inch top size (No. 73) burned fairly uniformly (7.5 percent variation). The Madison County coal prepared from screen- ings exhibited the same tendency, but to a lesser degree. The average improvement in uniformity with the J4 inch over the 1|4 inch coals for all the coals tested was 3.6 percentage figures, which is more than 30 percent. RESULTS 15 Table 6. — Effect of Coal Size upon Uniformity of Heat Release (Data are given in percent variation from average rate of heat release.) Size code a Improvement Coal Series 1 3 5 3 over 1 5 over 1 3 over 5 20 5.9 5.2 4.4 0.7 1.5 -0.8 30 6.4 5.4 5.2 1.0 1.2 -0.2 40 10.4 9.5 8.8 0.9 1.6 -0.7 50 11.6 8.2 11.5 3.4 0.1 3.3 60 12.6 6.5 7.8 6.1 4.8 1.3 70 20.1 7.5 9.3 12.6 10.8 1.8 80 6.0 5.1 4.6 0.9 1.4 -0.5 90 7.4 4.3 4.1 3.1 3.3 -0.2 Average 10.1 6.5 7.0 3.6 3.1 0.5 No. 1 is 1 % inch by coal; No. 3 is the % inch by coal; No. 5 has equal parts of No. 1 and No. 3 coals. 10 H 20 30 40 50 60 70 80 90 Coal series Fig. 5. — Effect of crushing on uniformity. (1\4 inch coal crushed to J4 inc ^ t0 P size.) 12 r 3 an «H 10 _ 0) em f M- 2 u 1 1 £ 20 30 40 50 60 Coal series Fig. K 70 80 6. — Effect of "loading" with fines on uni- formity. The I14 inch by coals which were loaded with fines (coals with size code 5) also burned more uniformly than the regu- lar I14 inch by coals (table 6 and fig. 6). The greatest improvement was with the Madison County coals. The average im- provement for the eight coals tested was 3.1 percentage figures. Although the average I/4 inch by coal burned more uniformly than the I14 mc ^ by coal which was loaded with fines by 0.5 percentage figures (table 6), this dif- ference does not seem to be significant. G b. Responsiveness. — Another indicator of the ability of a coal to maintain the desired heat output was the responsiveness of the fire to a demand for heat after a pro- longed hold-fire period (see p. 8). The size of the coal had no significant effect upon the responsiveness ratio 7 obtained with most of the coals tested (table 7 and figs. "The minimum variation considered significant depended upon the coal, with a range from one percentage figure with the more uniformly burning coal to five percentage figures for the coals with extreme variability. 7 The ratio of the rate of heat release during the first 30 minutes of stoker operation, following the hold-fire period, to the average rate with continuous stoker operation. 16 DOMESTIC STOKER COMBUSTION Table 7. — Effect of Coal Size upon Responst Ratio* Coal Series Size code b Improvement 1 3 5 3 over 1 5 over 1 3 over 5 20 0.33 0.34 0.31 0.01 -0.02 0.03 30 0.33 0.21 0.30 -0.12 -0.03 -0.09 40 0.16 0.16 0.18 0.00 0.02 -0.02 50 0.22 0.17 0.21 -0.05 -0.01 -0.04 60 0.22 0.24 0.23 0.02 0.01 0.01 70 0.20 0.19 0.24 -0.01 0.04 -0.05 80 0.18 0.23 0.33 0.05 0.15 -0.10 90 0.21 0.25 0.24 0.04 0.03 0.01 Average 0.23 0.22 0.25 -0.01 0.02 -0.03 n Ratio of rate of heat release during the first 30-minutes of stoker operation following the hold-fire period, to the average rate during the test with continuous stoker operation. h No. 1 is the 1% inch by coal; No. 3 is the % inch by coal; No. S has equal parts of No. 1 and No. 3 coals. Fig, ■0.10 20 30 40 50 60 Coal series 7. — Effect of crushing on responsiveness ratio. (114 inch coal crushed to 14 inch top size.) .S 0.15 "5 c 0.10 0.05 £ -0.05 average A, 20 30 40 50 60 70 80 Coal series Fig. 8. — Effect of "loading" with fines on responsiveness ratio. 90 7 and 8). As these data were obtained from only one test with each coal, the variation shown, with the possible exceptions of the 30 and 80 series, does not exceed the varia- tion which might be expected from duplicate tests of the same coal. c. Pickup. — The pickup ratio 8 was lower with the |4 inch by coal than with the 1]4 inch by coal in five out of eight com- parative tests (table 8 and fig. 9). The reduction is considered significant with the coals prepared from Franklin County screenings and Madison County nut (40 and 70 series, respectively). The reduction in average ratio of 0.01 for the 8 compara- tive tests is not considered significant. The only significant change in pickup ratio caused by "loading" the \]/\ inch by coal with fines was an increase in ratio of 0.05 with the stoker coal prepared from s The ratio of the average rate of heat release during the first five minutes of stoker operation, following the 45- minute "off" periods, to the average rate with continu- ous stoker operation. LaSalle County nut (table 8 and fig. 10). There was no change in average ratio. d. Overrun. — The overrun ratio 9 with the 1 14 inch by coals was superior to that obtained with the ]4 inch by coals with six out of eight comparative tests (table 9 and fig. 11). The maximum superiority was 0.05 (which was obtained with both Franklin county coals) and the average was 0.02. "Loading" the \\/\ inch by coals with fines did not have a consistent influence on the overrun ratio (table 9 and fig. 12). The maximum spread with comparative tests was the 0.09 greater ratio with the "loaded" 1|4 inch by coal prepared from LaSalle County nut (90 series). The aver- age overrun ratio for the eight comparative tests was 0.01 greater with the 1]4 inch by coals that were loaded with fines. The ratio of the average rate of heat release during the first five minutes after stoker shut off, following the 15-minute "on" periods, to the average rate with con- tinuous stoker operation. RESULTS 17 Ta Effect of Coal Size upon Pickup Ratio 0, Coal Series Size code b Improvement 1 3 5 3 over 1 5 over 1 3 over 5 20 0.25 0.25 0.25 0.00 0.00 0.00 30 0.23 0.21 0.23 -0.02 0.00 -0.02 40 0.26 0.22 0.24 -0.04 -0.02 -0.02 50 0.24 0.23 0.24 -0.01 0.00 -0.01 60 0.25 0.23 0.25 -0.02 0.00 -0.02 70 0.26 0.21 0.23 -0.05 -0.03 -0.02 80 0.24 0.25 0.25 0.01 0.01 0.00 90 0.22 0.24 0.27 0.02 0.05 -0.03 Average 0.24 0.23 0.24 -0.01 0.00 -0.01 il Ratio of rate of heat release during first five minutes of stoker operation following a 45-minute "off" period, to the average rate during test with continuous stoker operation. b No. 1 is the 1% inch by coal; No. 3 is the % inch by coal; No. 5 has equal parts of No. 1 and No. 3 coals. 20 30 40 50 60 70 80 90 ►h Coal series Fig. 9. — Effect of crushing on pickup ratio. (1J4 0.05 • 0.05 average 20 30 40 50 60 70 80 90 Coal series Fig. 10. — Effect of "loading" with fines on pick- up ratio. inch coal crushed to 14 inch top size.) Table 9. — Effect of Coal Size upon Overrun Ratio Coal Series Size code b Improvement 1 3 5 3 over 1 5 over 1 3 over 5 20 0.51 0.48 0.49 0.03 0.02 0.01 30 0.46 0.44 0.46 0.02 0.00 0.02 40 0.42 0.47 0.41 -0.05 0.01 -0.06 50 0.42 0.47 0.41 -0.05 0.01 -0.06 60 0.44 0.48 0.48 -O.Oi -0.04 0.00 70 0.43 0.47 0.43 -0.01 0.00 -0.04 80 0.46 0.49 0.49 -0.03 -0.03 0.00 90 0.44 0.48 0.53 -0.04 -0.09 0.05 Average 0.45 0.47 0.46 -0.02 -0.01 -0.01 a Ratio of rate of heat release during the first five minutes after stoker shut off, following the 15-minute "on" period, to the average rate with continuous stoker operation. b No. 1 is the 1^4 inch by coal; No. 3 is the *4 inch by coal; No. 5 has equal parts of No. 1 and No. 3 coals. 0.05 -0.05 40 50 60 Coal series Fig. 11. — Effect of crushing on overrun ratio. (1|4 inch coal crushed to V4 i^b t0 P size.) 53 0.05 « -0.05 o I •°- 10 20 1 80 90 Fig. 12— Effect of 40 50 60 70 Coal series "loading" with fines on over- run ratio. 18 DOMESTIC STOKER COMBUSTION Table 10. — Effect of Coal Size upon (In pounds per hour) Fei Raj Coal Series Size code a Change 1 3 . 5 3 minus 1 5 minus 1 3 minus 5 20 24.1 25.9 26.1 1.8 2.0 -0.2 30 23.1 25.0 24.4 1.9 1.3 0.6 40 26.3 26.6 26.0 0.3 -0.3 0.6 50 25.0 26.1 25.7 1.1 0.7 0.4 60 25.0 26.6 26.7 1.6 1.7 -0.1 70 23.5 26.2 25.1 2.7 1.6 1.1 80 24.3 25.9 25.6 1.6 1.3 0.3 90 23.1 24.2 24.3 1.1 1.2 -0.1 Average 24.3 25.8 25.5 1.5 1.2 0.3 a No. 1 is the \y± inch by coal; No. 3 is the % inch by coal; No. 5 has equal parts of No. 1 and No. 3 coals. Table 11. -Effect of Coal Size upon Ratio of Minimum and Average Rates of Heat Release with Continuous Stoker Operation Coal Series Size code a Improvement 1 3 5 3 over 1 5 over 1 3 over 5 20 0.92 0.83 0.88 -0.09 -0.04 -0.05 30 0.78 0.92 0.89 0.14 0.11 0.03 40 0.77 0.80 0.71 0.03 -0.06 0.09 50 0.73 0.82 0.84 0.09 0.11 -0.02 60 0.29 0.85 0.71 0.56 0.42 0.14 70 0.39 0.85 0.75 0.46 0.36 0.10 80 0.80 0.88 0.90 0.08 0.10 -0.02 90 0.61 0.91 0.90 0.30 . 0.29 0.01 Average 0.66 0.86 0.82 0.20 0.16 0.04 a No. 1 is the Hi inch by coal; No. 3 is the % inch by coal; No. 5 has equal parts of No. 1 and No. 3 coals. Table 12. — Effect of Coal Size upon Pressure in Stoker Air Duct (In inches of water, static pressure) Size range and cod( Coal 1M inch X 1M inch X 10 mesh M inch X l A inch X 10 mesh \ l /i inch X a Series (1) (2) (3) (4) (5) Aver- Maxi- Aver- Maxi- Aver- Maxi- Aver- Maxi- Aver- Maxi- age mum age mum age mum age mum age mum 20 0.85 1.60 0.85 1.22 1.12 1.62 0.72 1.20 1.09 1.55 30 0.81 1.56 0.68 1.20 1.00 1.55 0.82 1.60 1.00 1.59 40 1.26 1.61 1.05 1.50 1.31 1.62 0.92 1.57 1.25 1.61 50 1.20 1.55 0.96 1.66 1.31 1.59 1.01 1.59 1.40 1.68 60 1.00 1.59 0.80 1.37 1.27 1.58 0.39 1.46 1.19 1.58 70 0.76 1.47 0.66 1.48 1.32 1.67 0.39 1.57 1.23 1.59 80 0.90 1.48 0.76 1.12 1.29 1.50 0.87 1.18 1.15 1.67 90 0.96 1.66 0.78 1.22 • 1.18 1.51 0.83 1.31 1.12 1.52 Average 0.97 1.57 0.82 1.35 1.23 1.58 0.87 1.44 1.18 1.60 Equal parts of original 1% inch by and % inch by coals. RESULTS 19 e. Heat output factor. — The heat out- put is largely dependent upon the coal feed- ing rate, which will vary with the size of the coal fed, even though the speed of the feed worm remains constant. Table 10 shows the effect of size upon the feeding rate. The average increase in rate with the |4 inch by coal over the I14 inch by was 1.5 pounds per hour, or 6.2 percent. The 1J4 inch by which was loaded with fines fed nearly 5 percent faster than the regular 1|4 inch by 0. However, the capacity of a heating plant is not entirely dependent upon feeding rate. One factor of importance is the relation- ship between the rate of heat release during a period of poor fire with continuous stoker operation and the average rate. The tests showed that crushing the I14 inch by coal to 14 inch by resulted in an average improvement in ratio of 0.20, which is ap- proximately 30 percent (table 11). The maximum improvement in ratio was 0.56, or 193 percent, with the coal prepared from trie Madison County screenings (60 series). The coal prepared from Madison County nut (70 series) was also markedly improved in this respect by crushing. The *4 inch by coal prepared from Vermilion County screenings (20 series) was the only excep- tion to the general tendency for improve- ment over the lj4 inch by coal in respect to the minimum divided by the average rate of heat release. The lj4 inch by coals, which were "loaded" with fines, were usually superior to the regular lj4 inch by in respect to the ratio of the minimum divided by the average. There were two minor exceptions. The average increase in ratio was 0.16 or 24 percent. 4. EFFECT UPON SMOKE, APPEARANCE OF FIRE, AND "HOLD-FIRE" ABILITY No significant difference in the amount of smoke or appearance of the fire was at- tributed to size. All the coals tested main- tained a responsive fire with stoker opera- tion of 3 minutes out of each 1^4 hours, hence they were considered excellent in this respect. 5. EFFECT UPON STATIC PRESSURE IN STOKER AIR DUCT The air regulator on the stoker used for the tests maintains a substantially constant rate of air delivery with a fixed setting, irrespective of the resistance of the fuel bed, up to the maximum capacity of the fan. Since the coals which include the finer sizes feed at a faster rate than the coarser coals, the air adjustment was set for a higher rate of delivery when burning the finer coals. In addition, the resistance to air passage with the finer coal may be greater than with the coarser coal. These two factors re- sulted in the maintenance of higher static pressures when burning the fine coal. There is a definite possibility that under certain conditions some stokers can not sup- ply sufficient air to burn coal as fine as that tested at the maximum rate of coal feed. Although a study of this mechanical char- acteristic of stokers is not considered to be within the scope of the present investigation, the average and maximum static pressures in the air duct leading from the stoker fan to the retort are given to aid those who desire to study this condition (table 12). It should be emphasized that the static pres- sures with the fine coal would have been less if the rate of coal feed had been the same as with the larger coal. In fact, it is the author's opinion that much of the in- crease in static pressure was required be- cause of the increased feeding rate, since the coal did not exist as discrete particles in the fuel bed for any appreciable time. Instead, these particles combined into masses of coke in very much the same manner as with the larger coal. Little or no difference in resist- ance to air flow was indicated by the appear- ance of the fuel bed. This opinion was strengthened further by the observation of the random shifting of the zone of most active combustion over the entire hearth. If the resistance of the fuel bed were materially less with coarse coal, the section of the hearth nearest to the stoker hopper would be the most active zone of combustion, since the largest portion of coarse coal is fed to this section. 20 DOMESTIC STOKER COMBUSTION Table 13. — Effect of Coal Size upon Quantity of Fly Ash (In percentage of coal burned) Size range and code Coal 1M inch X \ l A inch X 10 mesh M inch X M inch X 10 mesh \\i inch X a Series (1) (2) (3) (4) (5) Collec- Calcu- Collec- Calcu- Collec- Calcu- Collec- Calcu- Collec- Calcu- ted lated ted lated ted lated ted lated ted lated 20 0.16 0.41 0.12 -0.01 0.22 0.54 0.14 0.19 0.18 0.24 30 0.17 0.75 0.13 0.50 0.21 0.65 0.17 0.78 0.20 0.40 40 0.17 0.35 0.16 0.41 0.22 0.25 0.12 0.96 0.11 1.01 50 0.19 0.12 0.16 0.19 0.28 0.75 0.23 0.38 0.27 0.34 60 0.23 0.88 0.16 0.17 0.25 0.43 0.20 0.79 0.29 -0.12 70 0.16 0.42 0.13 0.46 0.25 0.46 0.18 0.49 0.23 0.59 80 0.35 0.88 0.17 0.89 0.37 1.26 0.16 1.34 0.26 1.04 90 0.25 0.32 0.17 1.16 0.23 1.34 0.18 1.15 0.32 0.32 Average 0.21 0.52 0.15 0.47 0.25 0.71 0.17 0.76 0.23 0.48 Equal parts of original 1% inch by and % inch by coals. 6. EFFECT OF SIZE UPON FLY ASH The fly ash which collected in the boiler passages was removed and weighed after each test. It was found that a reduction in size of coal caused an increase in the amount of fly ash deposited (table 13). The average increase with the |4 inch by coal over the lj4 inch by coal was 0.04 percentage figures or 19 percent. The aver- age amount of fly ash deposited with the 1]4 inch by coal which was "loaded" with fines was 0.23 percent of the coal burned, compared with 0.21 and 0.25 percent for the 1]4 inch by and J4 inch by 0, respec- tively. Of course only a portion of the fly ash that leaves the fuel bed remains in the boiler passages. An appreciable quantity passes into the stack. The amount of fly ash leaving the boiler can be determined by subtracting the quantity of ash and clinker removed from the combustion chamber from the amount formed. Unfortunately the amount of ash formed can not be conven- iently determined with the precision re- quired. This fact will be readily appreciated by noting in table 41 (Appendix) that the percentages of moisture-free ash reported for coals 91 and 93 were 9.8 and 10.7 respec- tively, although the coals were presumably identical except in size. If 10.7 is the true average percentage of ash for coal 91, in- stead of the 9.8 reported, the calculated fly ash would be about three times greater than the 0.32 percent indicated in table 13. Obvi- ously very little reliance should be placed upon the calculated percentages of fly ash. 7. SUMMARY OF EFFECT UPON COMBUS- TION CHARACTERISTICS Table 14 gives the average effect of coal size upon the seven combustion characteris- tics previously discussed. No appreciable difference is shown for any of these charac- teristics with the possible exception of the improved uniformity with the smaller coal sizes, as reflected by the lower percent varia- tion from the average rate of heat release and the increase in ratio of minimum to average rates of heat release. Effect of Removing Minus 10-Mesh Coal upon Combustion Characteristics Most of the commercially prepared coals for domestic stokers have the finer coal par- ticles removed, which is commonly called "dedusting." Because it was considered de- sirable to test three coals (from each mine) that differed only in size composition, the fine coal caused by crushing was not re- moved from these coals. To gain informa- RESULTS 21 Table 14. — Summary of Effect of Coal Size upon Performance Characteristics Performance characteristic Heat obtained, B.t.u. per pound Uniformity, percent variation from average Responsiveness b Pickup Overrun d Clinker rating Minimum -f- average rate of heat release e . . Size code 3 6971 10.1 0.13 0.24 0.45 2.6 0.66 7255 6.5 0.22 0.23 0.47 2.7 0.86 7136 7.0 0.25 0.24 0.46 2.5 0.82 Average improvement 3 over 1 1 284 3.6 ■0.01 •0.01 ■0.02 0.1 0.20 5 over 1 ?165 3.1 0.02 0.00 ■0.01 ■0.1 0.16 3 over 5 119 0.5 -0.03 0.01 ■0.01 0.2 0.04 a No. 1 is the 1 % inch by coal; No. 3 is the % inch by coal; No. 5 has equal parts of No. 1 and No. 3 coals. b Ratio of rate of heat release during the first 30 minutes of stoker operation following the hold-fire period to the average rate during test with continuous stoker operation. c Ratio of rate of heat release during the first five minutes of stoker operation following a 45-minute off period to the aver- age rate during test with continuous stoker operation. d Ratio of rate of heat release during the first five minuter after stoker shut off, following the 15-minute on period to the average rate during test with continuous stoker operation. e With continuous stoker operation. Table 15. — Effect of Removing Minus 10-mesh Coal upon Heat Obtained (In B.t.u. per lb.) Size range and code Improve- ment, 2 over 1 Size range and code Coal Series \\i inch X (1) IK inch X 10 mesh (2) 34 inch X (3) 34 inch X 10 mesh (4) Improve- ment, 4 over 3 20 7030 6830 7670 7450 6480 6490 6880 6940 6971 6970 - 60 410 -170 - 40 320 200 90 -160 74 7140 7180 7750 7680 6970 6870 7160 7290 7255 7460 7320 7940 7720 7030 7080 7370 7290 7401 320 30 40 50 60 70 80 90 Average 7240 7500 7410 6800 6690 6970 6780 7045 140 190 40 60 210 210 146 400 ffl 200 Fig. 70 80 90 ■200 L 20 30 40 50 60 Coal series 13. — Effect of dedusting on heat obtained. (Removal of minus 10-mesh from 11/4 inch by coal.) 400 j 200 Fig. 40 50 60 Coal series 14. — Effect of dedusting on heat obtained. (Removal of minus 10-mesh from 14 inch by coal.) 22 DOMESTIC STOKER COMBUSTION Table 16. — Effect of Removing Minus 10-mesh Coal upon Heating Value (In B.t.u. per lb., as-flred basis) Size range and code Improve- ment, Size range and code Coal \}/i inch \\i inch \i inch x /i inch Improve- ment, Series X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 11,239 11,349 110 11,314 11,410 96 30 11,436 11,415 -21 11,499 11,460 -39 40 12,149 12,241 92 12,336 12,281 -55 50 12,246 12,136 -110 12,206 12,246 40 60 11,138 11,187 49 11,137 11,309 172 70 11,195 11,290 95 11,124 11,286 162 80 11,353 11,411 58 11.283 11,457 174 90 11,604 11,295 -309 11,411 11,391 -20 Average 11,545 11,540 -5 11,539 11,605 66 Table 17. — Effect of Removing Minus 10-mesh Coal upon Quantity of Ash (In percent, as-fired basis) Size range and code Improve- ment, Size range and code Coal \ l / A inch 1M inch x /i inch x /i inch Improve- ment, Series X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 8.7 8.6 0.1 9.3 8.6 0.7 30 10.9 10.5 0.4 10.6 10.5 0.1 40 9.5 8.7 0.8 8.8 9.1 -0.3 50 9.1 9.2 -0.1 9.7 9.3 0.4 60 11.3 9.8 1.5 10.9 10.2 0.7 70 9.5 9.4 0.1 9.5 9.5 0.0 80 8.9 8.3 0.6 9.1 8.4 0.7 90 8.8 9.6 -0.8 9.7 9.7 0.0 Average 9.6 9.3 0.3 9.7 9.4 0.3 tion regarding the effect of dedusting, the minus 10-mesh coal was removed from both the 1 j4 inch by and the ]/\ inch by coals, and comparative tests were made. 1. EFFECT UPON HEAT OBTAINED In four out of the eight comparative tests, the 1]4 mcn by 10-mesh coal furnished more heat per pound than the lj4 inch by coal (table 15 and fig. 13). The exception of the greatest magnitude was the 170 B.t.u. per pound with the Franklin County coal prepared from screenings (40 series), which should not be considered significant. The improvement of 410 and 320 B.t.u. per pound caused by dedusting the coals pre- pared from Vermilion County nut and Madison County screenings (30 and 60 series respectively) is considered significant. This improvement does not appear to be caused by a corresponding increase in heat- ing value (table 16). In fact the reported heating value of the Vermilion County 1 14 inch by 10-mesh coal was 21 B.t.u. per pound less than the corresponding I14 inch by coal. None of the 14 inch by coals furnished more heat per pound than the same coals after dedusting (table 15 and fig. 14). Although only the coal prepared from Ver- RESULTS 23 Table 18. — Effect of Removing Minus 10-mesh Coal upon Clinker Rating 8 Size range and code Improve- ment, 2 over 1 Size range and code Coal Series \ l A inch X (1) \}/i inch X 10 mesh (2) 3^ inch X (3) l /i inch X 10 mesh (4) Improve- ment, 4 over 3 20 30 40 SO 60 70 80 90 Average 3 3 2 2 3 2 3 3 2.6 3 3 2 2 3 3 3 3 2.7 1 0.1 3 3 2 3 3 2 3 3 2.7 3 3 3 2 3 3 3 4 3.0 1 -1 1 1 0.3 A subjective rating varying from (unsatisfactory) to 5 (ideal). mflion County screenings (20 series) fur- nished an appreciable improvement, the rather consistent trend appears to be one of very slight superiority for the dedusted coals. The average improvement caused by removing the minus 10-mesh from the j4 .inch by coal was 146 B.t.u. per pound. The average increase in heating value caused by dedusting was 66 B.t.u. per pound (table 16), which partially accounts for the increase in heat obtained. 2. EFFECT UPON ATTENTION REQUIRED The only significant change in the per- centage of ash which resulted from the removal of the minus 10-mesh coal was a reduction of 1.5 percentage points (13 per- cent) with the Madison County screenings (table 17). All other differences in ash between comparable coals could be caused by moisture variations and imperfect sam- pling and analysis. More precise informa- tion about the relative amount of ash in the various size fractions is given in table 37 (Appendix). The minus 10-mesh coal had a higher percentage of ash than the plus 10-mesh coal, although the difference was not great except with the Madison and La- Salle County screenings (60 and 80 series). Table 18 shows the effect of removing the fines upon the subjective clinker rating. The clinkers from both the 1|4 inch by 10- mesh and 14 inch by 10-mesh coals prepared from Madison County nut (70 series) ap- peared more suitable than the corresponding coals that were not dedusted. The |4 inch by 10-mesh coals appeared to be more suit- able from the clinkering standpoint for two other coals (70 and 90 series), but less suitable for another (50 series). In all other tests no change in clinker desirability re- sulted from dedusting. The present investigation was concerned only with effect of coal size upon its com- bustion properties, so no study of the rela- tive dustiness of the coals was made. It is obvious that the fine coal would tend to make more dust, and would be more diffi- cult to render dustless. 3. EFFECT UPON THE ABILITY TO MAINTAIN DESIRED HEAT OUTPUT a. Uniformity of heat release. — The re- moval of the minus 10-mesh coal did not have a consistent effect upon the uniformity of heat release. In nine out of 16 compara- tive tests, the dedusted coals burned more uniformly (table 19 and figs. 15 and 16). Of the seven comparative tests in which the dedusted coals burned less uniformly, the difference in uniformity was significant only with the Franklin County 1]4 inch coals (40 and 50 series). With these coals, the 1 14 inch by coals burned with about 25 percent less variation in rate of heat release (4.0 and 3.9 percentage figures) than the lj4 inch by 10-mesh coals. The greatest percentage point improvement caused by 24 DOMESTIC STOKER COMBUSTION Table 19. — Effect of Removing Minus 10-mesh Coal upon Uniformity of Heat Release (In percent variation from average rate of heat release) Size range and code Improve- ment, Size range and code Coal \\i inch 1M inch x /i inch M inch Improve- ment, Series X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 5.9 5.7 0.2 5.2 5.8 -0.6 30 6.4 3.8 2.6 5.4 5.5 -0.1 40 10.4 14.4 -4.0 9.5 8.0 1.5 50 11.6 15.5 -3.9 8.2 8.3 -0.1 60 12.6 8.6 4.0 6.5 7.3 -0.8 70 20.1 14.1 6.0 7.5 6.2 1.3 80 6.0 6.2 -0.2 5.1 4.1 1.0 90 7.4 6.0 1.4 4.3 4.2 0.1 Average 10.1 9.3 0.8 6.5 6.2 0.3 dedusting was 6.0 with the coal prepared from Madison County nut (70 series). However, the greatest percentage improve- ment was 41 with the coal prepared from Vermilion County nut (30 series). The 4.0 percentage figure improvement with the coal prepared from Madison County screenings (60 series) might be expected because of the reduction in ash caused by dedusting. However, no logical explana- tion can be given to account for the other changes in uniformity of combustion that are greater than might be obtained from duplicate tests on the same coal. b. Responsiveness. — The fire was usu- ally more responsive after a prolonged hold- fire period with the dedusted coals (table 20 and figs. 17 and 18). There were three exceptions, of minor magnitude, out of 16 comparative tests. In one case, no change in responsiveness ratio 10 was caused by de- dusting, and in several others the increase in responsiveness was not significant. c. Pickup. — Removing the minus 10- mesh coal from the 1]4 inch by coal did not appreciably affect the rate of pickup of the fire after a 45-minute off period (table 21 and fig. 19). The maximum change in pickup ratio 11 was 0.03. Removing the minus 10-mesh coal from the j4 i ncn D Y coal increased the pickup ratio for all the coals tested (table 21 and fig. 20). The maximum increase in ratio of 0.05 (20 to 24 percent) was obtained with three coals. The average increase in ratio was 0.04 ( 1 7 percent). Defined Defined 7, page IS. 8, page 16. 0.15 S - Fig. 40 50 60 70 80 90 Coal series 15. — Effect of dedusting on uniformity. (Removal of minus 10-mesh from 114 inch by coal.) . 2 i_ 20 30 40 50 60 70 80 90 Coal series Fig. 16. — Effect of dedusting on uniformity. (Removal of minus 10-mesh from !4 inch by coal.) Table 20. — Effect of Removing Minus 10-mesh Coal upon Responsiveness RATIO a Size range and code Improve- ment, Size range and code Coal Series 134 inch 134 inch 34 inch 34 inch Improve- ment, X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 0.33 0.28 -0.05 0.34 0.37 0.03 30 0.33 0.31 -0.02 0.21 0.33 0.12 40 0.16 0.17 0.01 0.16 0.23 0.07 50 0.22 0.22 0.00 0.17 0.25 0.08 60 0.22 0.25 0.03 0.24 0.40 0.16 70 0.20 0.21 0.01 0.19 0.40 0.21 80 0.18 0.27 0.09 0.23 0.20 -0.03 90 0.21 0.23 0.02 0.25 0.26 0.01 Average 0.23 0.24 0.01 0.22 0.30 0.08 a The ratio of the rate of heat release during the first 30 minutes of stoker operation following the hold-fire period, to the average rate with continuous stoker operation. 0.10 0.05 ■0.05 aver age L 20 90 30 40 50 60 70 80 Coal series Fig. 17. — Effect of dedusting on responsiveness ratio. (Removal of minus 10-mesh from 1J4 mc h by coal.) 0.20 \ 1 0.15 ■ 1 0.10 average 1 0.05 milt 0.05 - 20 30 40 50 60 70 80 90 Coal series Fig. 18. — Effect of dedusting on responsiveness ratio. (Removal of minus 10-mesh from 14 inch by coal.) Table 21. — Effect of Removing Minus 10-mesh Coal upon Pickup RATio a Size range and code Improve- ment, Size range and code Coal Series 134 i ncn 134 inch 34 inch 34 inch Improve- ment, X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 0.25 0.23 -0.02 0.25 0.29 0.04 30 0.23 0.24 0.01 0.21 0.26 0.05 40 0.26 0.23 -0.03 0.22 0.24 0.02 50 0.24 0.26 0.02 0.23 0.25 0.02 60 0.25 0.26 0.01 0.23 0.26 0.03 70 0.26 0.24 -0.02 0.21 0.26 0.05 80 0.24 0.24 0.00 0.25 0.27 0.02 90 0.22 0.24 0.02 0.24 0.29 0.05 Average 0.24 0.24 0.00 0.23 0.27 0.04 a The ratio of the average rate of heat release during the first five minutes of stoker operation following the 45-minute off period, to the average rate with continuous stoker operation. £ aver age -0.05 40 50 60 70 Coal series Fig. 19. — Effect of dedusting on pickup ratio. (Removal of minus 10-mesh from 1}4 inch by coal.) 0.05 aver age 20 30 40 50 60 Coal series 70 80 90 Fig. 20. — Effect of dedusting on pickup ratio. (Removal of minus 10-mesh from 34 inch by coal.) 26 DOMESTIC STOKER COMBUSTION Table 22.—] Effect of Removing Minus 10- mesh Coal upon Overrun R.ATio a Size range and code Improve- ment, Size range and code Coal Series \ l A inch \}/i inch }/i inch x /± inch Improve- ment, X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 0.51 0.48 0.03 0.48 0.49 -0.01 30 0.46 0.48 -0.02 0.44 0.51 -0.07 40 0.42 0.42 0.00 0.47 0.47 0.00 50 0.42 0.45 -0.03 0.47 0.45 0.02 60 0.44 0.51 -0,07 0.48 0.50 -0.02 70 0.43 0.43 0.00 0.47 0.50 -0.03 80 0.46 0.48 -0.02 0.49 0.49 0.00 90 0.44 0.44 0.00 0.48 0.51 -0.03 Average 0.45 0.46 -0.01 0.47 0.49 -0.02 The ratio of the average rate of heat release during the first five minutes after stoker shut-off following the 15-minute on periods, to the average rate with continuous stoker operation. A decrease in ratio is an improvement. d. Overrun. — Removing the minus 10- mesh coal increased the overrun ratio 12 in nine ouf of the 16 comparative tests (table 22, and figs. 21 and 22). In only two tests (30 and 60 series) was the increase more than might be expected from duplicate tests with the same coal. No change in overrun ratio was obtained with dedusted coals in five comparative tests, and a slight decrease was obtained with the other two tests. e. Heat output factor. — Removing the minus 10-mesh coal increased the ratio of the minimum to the average rate of heat release with continuous stoker operation in seven out of the 16 comparative tests (table 23). The increase was considered to be significant in only two cases. One of these was the 0.46 increase in ratio with the coal prepared from Madison County screenings (60 series). The ash in this coal was de- creased 1.5 percentage figures (13 percent), so an improvement in ratio of minimum to 12 Defined in footnote 9, page 16. S -o.io Fig 40 50 60 Coal series 21. — Effect of dedusting on overrun ratio. (Removal of minus 10-mesh from 11/; inch by coal.) average rate of heat release might be ex- pected. The other improvement considered significant was the increase of 0.22 in ratio for the LaSalle County coal (90 series). The reason for this improvement is not known. There is no significant difference in percentage of ash. However, this is the coal that heated slightly in the bins (reached a temperature of about 130°F.), and pos- sibly this "preoxidation" had some effect. No explanation can be given for the de- crease in ratio with the dedusted Vermilion and Franklin County coals (30 and 40 series). Possibly variations of this magni- tude could be expected from duplicate tests of the same coal and should be considered insignificant. 4. EFFECT UPON FLY ASH, SMOKE, APPEAR- ANCE OF THE FIRE, AND "HOLD- fire" ABILITY Although only a slight improvement in combustion characteristics was usually S 0.05 r Fig. ■ 0.05 •o.io rf *qr 20 70 90 40 50 60 Coal series 22. — Effect of dedusting on overrun ratio (Removal of minus 10-mesh from ^4 inch by coal.) RESULTS 27 Table 23. — Effect of Removing Minus 10-mesh Coal upon Ratio of Minimum to Average Rates of Heat Release with Continuous Stoker Operation Size range and code Improve- Size range and code Coal Improve- 134 inch \y± inch ment, 34 inch 34 inch ment, Series X X 2 over 1 X X 4 over 3 10 mesh 10 mesh (1) (2) (3) (4) 20 0.92 0.79 -0.13 0.83 0.91 0.08 30 0.78 0.86 0.08 0.92 0.72 -0.20 40 0.77 0.52 -0.25 0.80 0.78 -0.02 50 0.73 0.70 -0.03 0.82 0.81 -0.01 60 0.29 0.75 0.46 0.85 0.78 -0.07 70 0.39 0.42 0.03 0.85 0.82 -0.03 80 0.80 0.85 0.05 0.88 0.90 0.02 90 0.61 0.83 0.22 0.91 0.98 -0.04 Average 0.66 0.71 0.05 0.86 0.83 -0.03 caused by removing the minus 10-mesh coal, other important reasons will probably re- quire the continuance of this practice. One of the primary reasons appears to be the difficulty of rendering domestic stoker coal dustless without first removing the fines. Another reason for removing the fine coal is to reduce the amount of fly ash formed. Considerably less fly ash was deposited in the boiler passages when burning the de- dusted coals than when burning the corre- sponding single screened coal (table 13). The "calculated" fly ash did not show this trend, but the accuracy of these data are questionable for the reasons discussed on page 20. The removal of the minus 10-mesh coal did not appreciably affect the amount of smoke formed, the appearance of the fire, or the "hold-fire" ability. 5. SUMMARY OF EFFECT UPON COMBUS- TION CHARACTERISTICS Table 24 shows the average effect of re- moving the minus 10-mesh coal upon seven of the combustion characteristics measured. Table 24. — Summary of Effect of Removing Minus 10-mesh Coal upon Combustion Characteristics Combustion Characteristic Heat obtained, B.t.u. per pound Uniformity, percent variation from aver- age .. . Responsiveness 8, Pickup b Overrun Clinker rating Minimum -f- average rate of heat release d Size range and code IK inch X (1) 6971 10. 1 0.23 0.24 0.45 2.6 0.66 X 10 mesh (2) 7045 9.3 0.24 0.24 0.46 2.7 0.71 Improve- ment, 2 over 1 74 0.8 0.01 0.00 ■0.01 0.1 0.05 Size range and code x /i inch X (3) 7255 6.5 0.22 0.23 0.47 2.7 0.86 M i nc h X 10 mesh (4) 7401 6.2 0.30 0.27 0.49 3.0 0.83 Improve- ment, 4 over 3 146 0.3 0.08 0.04 -0.02 0.3 -0.03 Average Improve- ment 110 0.5 0.04 0.02 0.01 0.2 0.01 a Ratio of rate of heat release during the first 30 minutes of stoker operation following the hold-fire periods, to the average rate with continuous stoker operation. b Ratio of average rate of heat release during the first five minutes of stoker operation following the 45-minute off period to the average rate with continuous stoker operation. c Ratio of average rate of heat release during the first five minutes after stoker shut-off following the 15-minute on period, to the average rate with continuous stoker operation. d With continuous stoker operation/ 28 DOMESTIC STOKER COMBUSTION 400 r 200 ■200 I ,U — il I=A aver age I I T 21 22 23 24 25 41 42 43 44 45 61 62 63 64 65 81 82 83 84 85 31 32 33 34 35 51 52 53 54 55 71 72 73 74 75 91 92 93 94 95 Coal series Fig. 23. — Difference in heat obtained from stoker coals prepared from screenings and from nut coal. (Plus values — screenings superior; minus values — nut coal superior.) A slight improvement is indicated for ail these combustion characteristics except over- run, but the improvement is usually less than might be expected from normal fluctuations when burning the same coal, and would be undetectable in a household installation. Comparison of Combustion Charac- teristics of Stoker Coals Pre- pared from Screenings and Nut Coal 1. There was amount of heat obtained from the compara heat obtained very little difference in the tive tests on coals prepared from screenings and nut coal (table 25 and fig. 23). Most of the variations found might be expected from duplicate tests on the same coal. In 12 comparative tests out of 20, the coals prepared from screenings furnished more heat per pound than those prepared from nut coal. The average difference was only 54 B.t.u. per pound, which is certainly in- significant. The maximum difference was 290 B.t.u. per pound with the Franklin County I14 inch by coals which were loaded with fines (coals 45 and 55). The coals prepared from screenings had an average heating value of 43 B.t.u. per pound less than that prepared from nut coal Table 25. — Heat Obtained from Stoker Coals Prepared from Screenings and Nut Coals (In B.t.u. per pound) Size range and code Coal Series 11 \ l A inch X (1) l^ineh X 10 mesh (2) yi inch X (3) Y± inch X 10 mesh (4) \\i inch X b (5) Average 20 30 difference 40 50 difference 60 70 difference 80 90 difference Average difference 7030 6830 200 7670 7450 220 6480 6490 -10 6880 6940 -60 88 6970 7240 -270 7500 7410 90 6800 6690 110 6970 6780 190 30 7140 7180 -40 7750 7680 70 6970 6870 100 7160 7290 -130 7460 7320 140 7940 7720 220 7030 7080 -50 7370 7290 80 97 7240 7040 200 7690 7400 290 6790 6960 -170 6930 7040 -110 53 46 178 4 -6 54 a The 20, 40, 60, and 80 series were prepared from screenings and the others from nut coals. b Equal parts of No. 1 and No. 3 coals. RESULTS 29 Table 26. — Heating Values of Stoker Coals Prepared from Screenings and Nut Coals (In B.t.u. per pound, as-fired basis) Size range and code Coal Series* \\i inch X (1) \\i inch X 10 mesh (2) \i inch X (3) 3^ inch X 10 mesh (4) IMinch X b (5) Average 20 30 difference 40 50 difference 60 70 difference 80 90 difference Average difference 11,239 11,436. -197 12,149 12,246 -97 11,138 11,195 -57 11,353 11,604 -251 -151 11,349 11,415 -66 12,241 12,136 105 11,187 11,290 -103 11,411 11,295 116 13 11,314 11,499 -185 12,336 12,206 130 11,137 11,124 13 11,283 11,411 -128 -43 11,410 11,460 -50 12,281 12,246 35 11,309 11,286 23 11,457 11,391 66 19 11,370 11,509 -139 12,298 12,195 103 11,236 11,289 7 11,260 11,453 -193 -56 -127 55 -23 -78 -43 a The 20, 40, 60, and 80 series were prepared from screenings, and the others from nut coals. b Equal parts of No. 1 and No. 3 coals. (table 26), although the reverse trend was shown for heat obtained. This means that the average efficiency of combustion was higher with the coal prepared from screen- ings than with that prepared from nut coal. However, the increase indicated was only 0.7 percentage point, which is too small to be of practical significance. 2. ATTENTION REQUIRED In as far as the percentage of ash gov- erns the attention required, the stoker coals prepared from screenings were superior in 12 out of the 20 comparative tests (table 27 and fig. 24). The average difference in ash was only 0.4 percentage point which is cer- tainly insignificant. Only the stoker coals prepared from Madison County nut coal (70 series) were consistently lower in ash than the corresponding stoker coal prepared from screenings (60 series). There is no significant difference between the clinker ratings assigned to coals pre- pared from screenings and those prepared from nut coal (table 28). 3. ABILITY TO MAINTAIN DESIRED HEAT OUTPUT a. Uniformity of heat release. — The stoker coals prepared from screenings burned more uniformly than the corresponding coat prepared from nut coal for 13 out of the 20 comparative tests (table 29 and fig. 25). The average improvement was 0.9 percent- age point, which is not considered signifi- cant. The greatest improvement was 7.5 percentage points (37 percent) with the Madison County I14 inch by coals (coals 61 and 71). However, the 1]4 inch by 10-mesh coals from the same county had a greater percentage improvement (39 per- cent). This improved uniformity of burn- ing with the Madison County coals pre- pared from screenings is contrary to that expected, since the percentage of ash was lower in the coals prepared from the nut coal. One possible explanation is the differ- ence in the amounts of vitrain (table 30). Although the coal prepared from screenings (61) has only 4.6 percentage figures more vitrain than the coal prepared from nut 30 DOMESTIC STOKER COMBUSTION Table 27. — Quantity of Ash in Stoker Coals Prepared from Screenings and Nut Coals (Data are given in percent, as fired basis) Size range and code Coal Series a \y A inch X (1) \\i inch X 10 mesh (2) Minch X (3) x /i inch X 10 mesh (4) \ x /± inch X h (5) Average 20 difference 8.7 10.9 -2.2 8.6 10.5 -1.9 9.3 10.6 -1.3 8.6 10.5 -1.9 9.0 10.3 -1.3 -1.7 40 50 difference 9.5 9.1 0.4 8.7 9.2 -0.5 8.8 9.7 -0.9 9.1 9.3 -0.2 9.5 9.2 0.3 -0.2 60 70 difference 11.3 9.5 1.8 9.8 9.4 0.4 10.9 9.5 1.4 10.2 9.5 0.7 10.6 9.8 0.8 1.0 80 90 difference 8.9 8.8 0.1 8.3 9.6 -1.3 9.1 9.7 -0.6 8.4 9.7 -1.3 9.2 9.3 -0.1 -0.6 Average difference -0.8 -0.4 -0.7 -0.1 -0.4 a The 20, 40, 60, and 80 series were prepared from screenings, and the olhcrs from nut coals. b Equal parts of No. 1 and No. 3 coals. -2 |1»M"" ■ 1 ■ ■ . 3L 21 22 23 24 25 41 42 43 44 45 61 62 63 64 65 81 82 83 84 85 31 32 33 34 35 51 52 53 54 55 71 72 73 74 75 91 92 93 94 95 Coal series Fig. 24. — Difference in percentage of ash in stoker coals prepared from screenings and from nut coal. (Plus values — nut superior; minus values — screenings superior.) 01 u 3 OO 2 r 1 ■ 1 m O0 m ■_ -«-- H--M- -W- il 41 O -2 - \average J-i -4 - u C 0) u -6 «** -8 -21 22 23 24 25 41 42 43 44 45 61 62 63 64 65 81 82 83 84 85 Q 31 32 33 34 35 51 52 53 54 55 71 72 73 74 75 91 92 93 94 95 Coal Series Fig. 25. — Difference in uniformity of heat release with stoker coals prepared from screenings and from nut coal. (Plus values — nut superior; minus values — screenings superior.) RESULTS 31 Table 28. — Clinker Rating* 1 of Stoker Coals Prepared from Screenings and Nut Coals Size range and code Coal Series b \\i inch X (1) lli inch X 10 mesh (2) x /i inch X (3) x /i inch X 10 mesh (4) \ x /± inch X C (5) Average 20 30 difference 40 50 difference 60 70 difference 80 90 difference 3 3 2 2 3 2 1 3 3 3 3 2 2 3 3 3 3 3 3 2 3 -1 3 2 1 3 3 3 3 3 2 1 3 3 3 4 -1 3 3 2 2 2 2 3 3 0.4 -0.2 11 A subjective rating varying from (unsatisfactory) to 5 (ideal). 11 The 20, 40, 60, 80 teries were prepared from screenings, and the others from nut coals. c Equal parts of No. 1 and No. 3 coals. Table 29. — -Uniformity of Heat Release with Stoker Coals Prepared from Screenings and Nut Coals (In percent variation from average rate of heat release; thus lower values are superior) Size range and code Coal Series a \ x /i inch X (1) \\i inch X 10 mesh (2) y inch X (3) i^ inch X 10 mesh (4) iy inch X b (5) Average 20 30 difference 40 50 difference ' 60 70 difference 80 90 difference Average difference 5.9 6.4 -0.5 10.4 11.6 -1.2 12.6 20.1 -7.5 6.0 7.4 -1.4 -2.7 5.7 3.8 1.9 14.4 15.5 -1.1 8.6 14.1 -5.5 6.2 6.0 0.2 -1.1 5.2 5.4 - -0.2 9.5 8.2 1.3 6.5 7.5 -1.0 5.1 4.3 0.8 -0.2 5.8 5.5 0.3 8.0 8.3 -0.3 7.3 6.2 1.1 4.1 4.2 -0.1 0.3 4.4 5.2 -0.8 8.8 11.5 -2.7 7.8 9.3 -1.5 4.6 4.1 0.5 -1.1 5.4 5.3 0.1 10.2 11.0 -0.8 8.5 11.4 -2.9 5.2 5.2 -0.9 a The 20, 40, 60, and 80 series were prepared from screenings, the others from nut coals. b Equal parts of No. 1 and No. 3 coals. 32 DOMESTIC STOKER COMBUSTION Table 30. — Petrographic Analyses of Madison County Coals 1M inch X 2 inch X \\i screenings inch nut percent percent Vi train. Clarain. Durain. Fusain . Refuse . 19.3 14.7 76.1 73.6 2.3 9.9 1.7 1.6 0.6 0.2 (71), the increase is 3 1 percent, which may account for the more uniform combustion. Another possible explanation is the differ- ence in composition of the ash (table 44, Appendix). Stoker coal 61 prepared from screenings had 2.48 percentage figures (14 percent) less Fe 2 3 in the ash than stoker coal 71 prepared from nut. This explana- tion is not too reasonable, since no previous correlation was found between the Fe 2 ;J , and the uniformity of combustion. Neither do the tests in this investigation indicate 0.15 0.10 0.05 •0.05 21 22 ■0.10^-3! 32 I aver age aJ ■ ■ I J 23 24 25 41 42 43 44 45 61 62 63 64 65 81 82 83 84 85 33 34 35 51 52 53 54 55 71 12 73 74 75 91 92 93 94 95 Coal series Fig. 26. — Difference in responsiveness ratio with stoker coals prepared from screenings and from nut coal. (Plus values — screenings superior; minus values — nut coal superior.) Table 31. — Responsiveness Ratio 41 with Stoker Coals from Screenings and Nut Coals Prepared Size range and code Coal Series b 1^4 inch X (1) V/i inch X 10 mesh (2) Y± inch X (3) Y± inch X 10 mesh (4) \\i inch X C (5) Average 20 30 difference 0.33 0.33 0.00 0.28 0.31 -0.03 0.34 0.21 0.13 0.37 0.33 0.04 0.31 0.30 0.01 0.33 0.30 0.03 40 50 difference 0.16 0.22 -0.06 0.17 0.22 -0.05 0.16 0.17 -0.01 0.23 0.25 -0.02 0.18 0.21 -0.03 0.18 0.21 -0.03 60 70 difference 0.22 0.20 0.02 0.25 0.21 0.04 0.24 0.19 0.05 0.40 0.40 0.00 0.23 0.24 -0.01 0.27 0.25 0.02 80 90 difference 0.18 0.21 -0.03 0.27 0.23 0.04 0.23 0.25 -0.02 0.20 0.26 -0.06 0.33 0.24 0.09 0.24 0.24 0.00 Average difference -0.02 0.00 0.04 -0.01 0.01 0.00 a Ratio of the rate of heat release during the first 30 minutes of stoker operation following the hold-fire period, to the aver- age rate with continuous stoker operation. b The 20, 40, 60, and 80 series were prepared from screenings, the others from nut coals. c Equal parts of No. 1 and No. 3 coals. RESULTS 33 Table 32. — Pickup Ratio 3 - with Stoker Coals Prepared from Screenings and Nut Coals Size range and code Coal Series b \% inch X (1) l l /i inch X 10 mesh (2) }/i inch X (3) x /i inch X 10 mesh (4) 1M inch X C (5) Average 20 30 difference 40 50 difference 60 70 difference 80 90 difference Average difference 0.25 0.23 0.02 0.26 0.24 0.02 0.25 0.26 -0.01 0.24 0.22 0.02 0.01 0.23 0.24 -0.01 0.23 0.26 -0.03 0.26 0.24 0.02 0.24 0.24 0.00 -0.01 0.25 0.21 0.04 0.22 0.23 -0.01 0.23 0.21 0.02 0.25 0.24 0.01 0.02 0.29 0.26 0.03 0.24 0.25 -0.01 0.26 0.26 0.00 0.27 0.29 -0.02 0.00 0.25 0.23 0.02 0.24 0.24 0.00 0.25 0.23 0.02 0.25 0.27 -0.02 0.01 0.25 0.23 0.02 0.24 0.24 0.00 0.25 0.24 0.01 0.25 0.25 0.00 0.01 a The ralio of average rate of heat release during the first five minutes of stoker operation following periods, to the average rate with continuous stoker operation. b The 20, 40, 60, and 80 series were prepared from screenings, the others from nut coals. e Equal parts of No. 1 and No. 3 coals. the 45-minute off such a trend. For example, little or ho dif- ference in uniformity of combustion was ob- tained with the LaSalle County coals, al- though the ash from coal 81 had 6.93 per- centage figures (17 percent) less Fe 2 3 than the ash from coal 91. b. Responsiveness. — The responsiveness of the fire to a demand for heat after a pro- longed hold-fire period was about the same for the stoker coal prepared from screenings and as that prepared from the corresponding nut coal (table 31 and fig. 26). The maxi- mum difference in responsiveness ratio 13 was 0.13 with the }4 inch by coals from Vermilion County (series 2.3 and 33). The average difference with the Vermilion 13 Defined in footnote 7, page 15. County coals was only 0.03 which is not considered to be significant. c. Pickup. — There was no significant difference between the average pickup ratios 14 with the stoker coals prepared from screenings and from nut coal (table 32 and fig. 27). The maximum difference of 0.04 was with the ]4 inch by coals from Ver- milion County (coals 23 and 33). This dif- ference is greater than would be expected from duplicate tests on the same coal, and is particularly significant because the same relative tendency was exhibited with "re- sponsiveness." The cause of this significant difference in pickup and responsiveness with this particular size of coal is not known. 11 Defined in footnote 8, papge 16. 0.05 r -0.05 - !■ ■ ■ zz 32 23 33 24 34 25 35 41 51 Fig. 27. — Difference in pickup and from nut coal (Plus values — screenings superior; minus values average 42 43 44 45 61 52 53 54 55 71 Coal series atio with stoker coals prepared from screenings I ■ 1 62 63 64 65 81 82 83 84 85 I 72 73 74 75 91 92 93 94 95 •nut coal superior.) 34 DOMESTIC STOKER COMBUSTION Table 33. — Overrun Ratio* 1 with Stoker Coals Prepared from Screenings and Nut Coals Size range and code Coal Series 11 li^ inch X (1) \Ya inch X 10 mesh (2) x /i inch X (3) 34 inch X 10 mesh (4) \\i inch X C (5) Average 20 30 difference 40 50 difference 60 70 difference 80 90 difference Average difference 0.51 0.46 0.05 0.42 0.42 0.00 0.44 0.43 0.01 0.46 0.44 0.02 0.02 0.48 0.48 0.00 0.42 0.45 -0.03 0.51 0.43 0.08 0.48 0.44 0.04 0.02 0.48 0.44 0.04 0.47 0.47 0.00 0.48 0.47 0.01 0.49 0.48 0.01 0.02 0.49 0.51 -0.02 0.47 0.45 0.02 0.50 0.50 0.00 0.49 0.51 -0.02 -0.01 0.49 0.46 0.03 0.41 0.41 0.00 0.48 0.43 0.05 0.49 0.53 -0.04 0.01 0.49 0.47 0.02 0.44 0.44 0.00 0.48 0.45 0.03 0.48 0.48 0.00 0.01 a The ratio of average rate of heat release during the first five minute:, after rtoker shut off following the 15-minute periods, to the average rate with continuous stoker operation. b The 20, 40, 60, 80 series were prepared from screenings, the others from nut coals. c Equal parts of No. 1 and No. 3 coals. d. Overrun. — There were only a few comparable tests in which an appreciable difference in overrun was found between the stoker coals prepared from screenings and those prepared from nut coal (table 33 and fig. 28). The maximum difference in overrun ratio 15 was 0.08, with the 1*4 inch by 10-mesh Madison County coals (Nos. 62 and 72). The average difference for the 20 comparative tests was only 0.01 which is not significant. e. Heat output factor. — No consistent superiority was exhibited by stoker coals 15 Defined in footnote 9, page 16. prepared from screenings or nut coal in re- spect to the capacity of the heating plant during periods of poor fire. The greatest difference in ratio of minimum to maximum rates of heat release was 0.33 (table 34). The average difference for the 20 compara- tive tests was only 0.01, which is not sig- nificant. 4. SMOKE, APPEARANCE OF FIRE, AND "hold-fire" ABILITY No difference was observed between the stoker coals prepared from screenings and nut coal in the amount of smoke produced, 0.10 <0 .5 0.05 ~ ■ » 01 c 1 I 1 average J -■- I u ■ i * " i I Q -0.05 "21 22 23 24 25 41 42 43 44 45 61 62 63 64 65 81 82 83 84 85 31 32 33 34 35 51 52 53 54 55 71 72 73 74 75 91 92 93 94 95 Coal series Fig. 28. — Difference in overrun ratio with stoker coals prepared from screenings and from nut coal. (Plus values — nut superior; minus values — screenings superior.) RESULTS 3.5 Table 34. — Ratio of Minimum to Average Rates of Heat Release with Stoker Coals Prepared from Screenings and Nut Coals 8 - Size range and code Coal Series b 1M inch X (1) \ l /i inch X 10 mesh (2) Y± inch X (3) 14 inch X 10 mesh (4) \ x /i inch X C (5) Average 20 30 difference 40 50 difference 60 70 difference 80 90 difference Average difference 0.92 0.78 0.14 0.77 0.73 0.04 0.29 0.39 -0.10 0.80 0.61 0.19 0.07 0.79 0.86 -0.07 0.52 0.70 -0.18 0.75 0.42 0.33 0.85 0.83 0.02 0.03 0.83 0.92 -0.09 0.80 0.82 -0.02 0.85 0.85 0.00 0.88 0.91 -0.03 -0.04 0.91 0.72 0.19 0.78 0.81 -0.03 0.78 0.82 -0.04 0.90 0.87 0.03 0.04 0.89 0.89 0.00 0.71 0.84 -0.13 0.71 0.75 -0.04 0.90 0.90 0.00 -0.04 0.87 0.84 0.03 0.72 0.78 -0.06 0.68 0.65 0.03 0.86 0.82 0.04 0.01 a Data are from tests with continuous stoker operation. '' The 20, 40, 60, and 80 series were prepared from screenings, the others from nut coal. e Equal parts of No. 1 and No. 3 coals. the appearance of the fire, or the ability to maintain a fire at low rates of operation. 5. SUMMARY OF RELATIVE COMBUSTION CHARACTERISTICS Table 35 summarizes the differences in seven combustion characteristics which were found from the comparative tests of stoker coals prepared from screenings and those prepared from nut coal. The only signifi- cant difference shown is the more uniform rate of heat release (2.9 percentage points) with the stoker coals prepared from Madi- son County screenings than with those pre- pared from nut coal from the same mine. Table 35. -Summary of Combustion Characteristics of Stoker Coals Prepared from Nut Coals and Screenings Heat obtained, B.t.u. per pound. . . Uniformity, percent variation from average Responsiveness a Pickup b Overrun Clinker rating y . . Minimum -h average rate of heat release d Improvement of screenings over nut coal Vermilion County 50 -0.1 0.02 0.02 -0.02 0.0 0.03 Franklin County 180 0.8 -0.03 -0.01 0.00 0.0 -0.06 Madison County 2.9 0.02 0.01 -0.03 0.4 0.03 LaSalle County -10 0.0 0.00 0.00 0.00 -0.2 0.04 55 0.9 0.00 0.01 -0.01 0.1 0.01 a Ratio of rate of heat release during the first 30 minutes of stoker operation following the hold-fire period, to the aver- age rate with continuous stoker operation. ''Ratio of rate of heat release during the first five minutes of stoker operation following a 45-minute off period to the average rate with continuous stoker operation. c Ratio of rate of heat release during the first five minutes after stoker shut off following the 15-minute on periods, to the average rate with continuous stoker operation. d With continuous stoker operation. 36 DOMESTIC STOKER COMBUSTION CONCLUSIONS The performance characteristics of the stoker coals tested were not materially af- fected by the size range. The changes which occurred in responsiveness, pickup, overrun, and heat output were no more than might be expected from duplicate tests with the same coal. The average 14 mcn by coal did furnish slightly more heat per pound than the corresponding I14 inch by coal, although the difference would probably be undetectable with a normal installation in a house. The most significant difference in performance was in the more uniform rate of heat release with the smaller sized coal. The performance characteristics of the 1|4 inch by coals which were "loaded" with fines were equal or slightly superior to those of the corresponding natural lj4 inch by coals. The public rejection of coals with a large proportion of fines is evidently based upon prejudice, difference in quality of coal, or improper dust treat- ment. The latter two reasons are the most probable, since the fine sizes as hoisted from a mine frequently have higher ash, and they are much more difficult to render dustless. The removal of the minus 10-mesh coal resulted in a slight improvement in nearly all combustion characteristics, but the im- provement was usually less than might be expected from normal fluctuations with the same coal, and would probably be un- detectable in a household installation. Although only a slight change in com- bustion characteristics was caused by re- moving the fine coal, other important rea- sons will probably require the continuance of this practice. One of the primary reasons appears to be the difficulty of rendering domestic stoker coal dustless without first removing the fines. Coal was obtained from too few mines to furnish any conclusive data concerning the relative combustion characteristics of stoker coals prepared from screenings and nut coal. Little or no difference was found with the coals tested. APPENDIX Table 36. — Operating Schedule for Combustion Tests Tuesday 7:00 a.m. Start fire on clean hearth. Cause stoker to operate continuously. 10:00 a.m. Beginning of test period for continuous stoker operation. 3:45 p.m. Start taking motion pictures of fuel bed. 4:25 p.m. Stop taking motion pictures of fuel bed. 8:00 p.m. End of test period with continuous stoker operation. Remove clinker, fill hopper, and change stoker operating rate to 45 minutes on and 15 minutes off. 10:15 p.m. Beginning of test period with stoker operating 45 minutes out of each hour. Wednesday 10:50 a.m. Start taking motion pictures of fuel bed. 11:05 a.m. Stop taking motion pictures of fuel bed. 11:13 a.m. Start taking motion pictures of fuel bed. 11:40 a.m. Stop taking motion pictures of fuel bed. 1:15 p.m. End of test period with stoker operating 45 minutes out of each hour. Remove clinker, fill hopper, and change stoker operating rate to 30 minutes on and 30 minutes off. 4:30 p.m. Beginning of test period with stoker operating 30 minutes out of each hour. Thursday 10:45 a.m. Start taking motion pictures of fuel bed. 11:05 a.m. Stop taking motion pictures of fuel bed. 1 1 :28 a.m. Start taking motion pictures of fuel bed. 11:45 a.m. Stop taking motion pictures of fuel bed. 2:30 p.m. End of test period with stoker operating 30 minutes out of each hour. Remove clinker, fill hopper, and change stoker operating rate to 15 minutes on and 45 minutes off. 6:30 p.m. Beginning of test period with stoker operating 15 minutes out of each hour. Friday 8:43 a.m. Start taking motion pictures of fuel bed. 9:05 a.m. Stop taking motion pictures of fuel bed. 9:43 a.m. Start taking motion pictures of fuel bed. 9:55 a.m. Stop taking motion pictures of fuel bed. Saturday 10:30 a.m. End of test period with stoker operating 15 minutes out of each hour. Remove clinker and change stoker operating rate to hold-fire (3 minutes out of each 1% hours). Monday 11:45 a.m. Start stoker operating continuously. 1:45 p.m. Stop stoker. Quench fire, remove clinker and ash from hearth, and fiy ash from boiler passages. Remove coal from hopper, worm, and retort. APPENDIX 37 Table 37.— -Chemical Composition of Various Size Fractions of Te st Coals IMi tich by coal 3^ inch by coal Coal Series Size Ash, Heating value, B.t.u./lb Sulfur, Size Ash, Heating Sulfur, fraction a % % fraction % value, B.t.u./lb % 20 4- % inch 9.5 12927 1.69 4- 4 mesh 10.9 12764 1.68 % inch X % inch 9.8 12944 1.84 4 mesh X 6 mesh 10.5 12854 1.82 y% inch X 4 mesh 10.1 12912 1.78 6 mesh X 8 mesh 9.9 12967 1.74 4 mesh X 10 mesh 9.8 12943 1.86 8 mesh X 10 mesh 9.5 12949 1.73 10 mesh X 13.3 12442 2.13 10 mesh X 20 mesh 20 mesh X 10.0 12.2 12805 12401 1.79 2.16 30 + % inch 14.2 12316 1.56 4- 4 mesh 12.1 12620 1.56 ^ inch X V% inch 11.1 12788 1.63 4 mesh X 6 mesh 11.3 12797 1.58 ^8 inch X 4 mesh 9.9 13025 1.63 6 mesh X 8 mesh 11.4 12744 1.69 4 mesh X 10 mesh 9.9 12982 1.68 8 mesh X 10 mesh 11.2 12756 1.61 10 mesh X 13.3 12427 2.13 10 mesh X 20 mesh 20 mesh X 13.2 11.1 12498 12805 1.95 1.64 40 + % inch 9.7 13028 3.05 4- 4 mesh 10.0 13039 2.76 24 inch X Y% inch 9.0 13098 2.73 4 mesh X 6 mesh 8.9 13206 2.63 % inch X 4 mesh 8.5 13172 2.76 6 mesh X 8 mesh *8.8 13231 2.66 4 mesh X 10 mesh 8.9 13221 2.74 8 mesh X 10 mesh 19.0 13138 2.65 10 mesh X 13.0 12543 2.89 10 mesh X 20 mesh 20 mesh X 9.1 11.6 13115 12760 2.64 2.85 50 + % inch 11.0 12715 2.11 4- 4 mesh 11.3 12856 2.64 % inch X z /% inch 9.9 12942 2.24 4 mesh X 6 mesh 10.3 13001 2.56 Y% inch X 4 mesh 9.6 12971 2.26 6 mesh X 8 mesh 9.4 13087 2.36 4 mesh X 10 mesh 9.3 13053 2.41 8 mesh X 10 mesh 9.4 13129 2.34 10 mesh X 10.4 12838 2.58 10 mesh X 20 mesh 20 mesh X 9.4 10.8 13150 12902 2.35 2.49 60 4- % inch 10.9 12443 3.82 4- 4 mesh 11.0 12453 3.90 % inch X /^8 inch 10.4 12551 3.80 4 mesh X 6 mesh 10.8 12449 3.90 ^8 inch X 4 mesh 11.1 12537 3.79 6 mesh X 8 mesh 10.2 12514 3.87 4 mesh X 10 mesh 10.8 12513 3.58 8 mesh X 10 mesh 10.2 12504 3.91 10 mesh X 19.8 11103 3.83 10 mesh X 20 mesh 20 mesh X 11.1 16.1 12389 11631 3.90 4.03 70 + % inch 13.6 12201 3.66 4- 4 mesh 10.7 12529 4.17 % inch X Y% inch 9.8 12669 4.02 4 mesh X 6 mesh 10.6 12627 4.06 ^8 inch X 4 mesh 10.0 12718 3.81 6 mesh X 8 mesh 10.5 12593 3.92 4 mesh X 10 mesh 10.2 12643 3.91 8 mesh X 10 mesh 10.3 12647 3.87 10 mesh X 12.0 12329 3.91 10 mesh X 20 mesh 20 mesh X 10.3 10.8 12613 12526 3.93 3.94 80 4- % inch 8.9 13008 3.92 4- 4 mesh 9.2 12946 4.13 % inch X V% inch 9.6 12780 4.32 4 mesh X 6 mesh 8.9 12938 3.92 % inch X 4 mesh 9.3 12802 4.31 6 mesh X 8 mesh 8.9 13001 3.97 4 mesh X 10 mesh 9.2 12804 3.91 8 mesh X 10 mesh 9.2 13008 3.95 10 mesh X 15.0 11917 4.58 10 mesh X 20 mesh 20 mesh X 9.3 13.2 12891 12284 3.94 4.48 90 + z /i inch 7.1 13255 3.65 4- 4 mesh 10.5 12545 5.16 % inch X V% inch 8.2 13064 4.10 4 mesh X 6 mesh 9.6 12756 4.47 ^ inch X 4 mesh 9.9 12867 4.52 6 mesh X 8 mesh 9.2 12873 4.56 4 mesh X 10 mesh 9.5 12805 4.56 8 mesh X 10 mesh 9.3 12838 4.44 10 mesh X 12.8 12208 4.79 10 mesh X 20 mesh 20 mesh X 9.4 12.0 12737 12316 4.28 4.92 Determined with standard Tyler square-opening sieves. 38 DOMESTIC STOKER COMBUSTION Table 38. — Heat Obtained and Coal Burned for Each Operation Rati Heat obtained, M B.t.u./lb Average Coal burned, lb./hr. Coal effi- No. ciency, 60 a 45 a 30 a 15 a Average % 60 a 45 a 30 a 15 a 21 6.86 6.89 7.05 7.32 7.03 62.6 23.76 17.74 11.82 5.85 22 6.97 6.90 6.86 7.17 6.97 61.4 22.97 17.14 11.66 5.73 23 7.08 7.05 6.93 7.52 7.14 63.1 26.68 18.78 12.58 6.26 24 7.23 7.29 7.48 7.86 7.46 65.4 24.29 17.87 11.79 5.84 25 7.24 7.16 7.06 7.52 7.24 63.7 25.44 18.90 13.21 6.33 31 6.75 6.81 6.65 7.12 6.83 59.7 22.46 16.46 11.60 5.38 32 7.07 6.86 7.34 7.70 7.24 63.4 21.46 16.12 10.54 5.17 33 7.42 7.39 6.96 6.97 7.18 62.4 24.54 18.40 12.09 6.04 34 7.12 7.26 7.24 7.67 7.32 63.9 22.55 16.62 11.03 5.54 35 7.07 7.01 6.86 7.23 7.04 61.2 24.03 17.54 12.18 5.90 41 7.65 7.56 7.68 7.78 7.67 63.1 25.09 18.11 12.62 6.53 42 7.40 7.38 7.53 7.68 7.50 61.3 22.46 16.39 11.10 5.55 43 7.67 7.87 7.60 7.86 7.75 62.8 26.46 18.70 11.78 6.68 44 7.92 7.88 7.97 7.99 7.94 64.7 23.45 17.38 11.68 5.92 45 7.83 7.93 7.36 7.66 7.69 62.4 24.97 18.18 12.29 6.15 51 7.25 7.29 7.60 7.64 7.45 60.8 24.44 17.87 11.76 5.85 52 7.34 7.37 7.46 7.49 7.41 61.1 22.80 16.63 10.94 5.58 53 7.57 7.74 7.45 7.96 7.68 62.9 25.76 17.72 12.48 6.36 54 7.52 7.51 7.79 8.05 7.72 63.0 23.00 16.91 11.28 5.49 55 7.32 7.40 7.46 7.41 7.40 60.7 24.74 18.07 12.40 5.94 61 6.33 6.40 6.47 6.74 6.48 58.2 24.32 18.11 12.00 6.07 62 6.71 6.66 6.69 7.15 6.80 60.8 22.63 17.00 11.42 5.75 63 6.92 7.02 6.95 7.00 6.97 62.6 26.47 18.99 12.89 6.34 64 6.97 6.89 6.98 7.30 7.03 62.2 24.62 17.44 11.67 5.89 65 6.69 6.71 6.82 6.93 6.79 60.4 25.71 18.85 12.70 6.50 71 6.55 6.52 6.45 6.45 6.49 53.0 21.92 17.11 11.64 5.78 72 6.74 6.68 6.51 6.82 6.69 59.3 22.08 16.56 11.08 5.53 73 6.96 6.98 6.81 6.72 6.87 61.8 25.56 18.17 12.32 6.32 74 7.05 6.97 7.11 7.21 7.08 62.7 23.68 17.29 11.51 5.88 75 7.00 7.17 6.94 6.74 6.96 62.0 24.18 17.99 12.47 5.99 81 6.89 6.86 6.78 7.01 6.88 60.6 23.86 17.86 11 76 5.91 82 6.98 6.89 6.83 7.19 6.97 61.1 22.68 16.74 11.00 5.52 83 7.09 7.14 7.15 7.25 7.16 63.5 25.56 18.88 12.68 6.32 84 7.48 7.35 7.19 7.47 7.37 64.3 23.24 17.14 11.54 5.62 85 6.96 6.89 6.72 7.15 6.93 61.5 24.88 18.69 12.62 6.10 91 7.08 6.84 6.85 6.98 6.94 59.8 22.84 16.54 11.15 5.56 92 6.99 6.74 6.71 6.67 6.78 60.0 21.30 15.87 10.57 5.26 93 7.34 7.27 7.19 7.35 7.29 63.9 23.84 17.93 11.95 5.81 94 7.19 7.16 7.16 7.67 7.29 64.0 22.04 15.97 10.66 5.32 95 7.04 6.88 6.93 7.30 7.04 61.5 23.07 17.58 12.11 5.86 a Minutes of stoker operation per hour. APPENDIX 39 Table 39. — Miscellaneous Data on Combust ion Characteristics Boiler output with continuous stoker Uniformity Responsiveness Pickup Overrun operation Coal Ratio of No. Average Minimum Minimum Average mini- M B.t.u. M B.t.u. Average cycle M B.t.u. per hr. Mini- Average Maxi- M B.t.u./hr. M B.t.u./hr. ■£■ average vari- ation % mum to average heat first 30-min. first 60-min. mum cycle M B.t.u. cycle M B.t.u per hr. mum M B.t.u. per hr. output a per hr. 21 163 149 0.92 5.9 0.89 27 97 41 31 83 104 22 160 126 0.79 5.7 0.85 23 90 37 27 77 92 23 189 156 0.83 5.2 0.85 32 108 47 35 91 118 24 176 160 0.91 5.8 0.87 32 115 51 37 86 109 25 184 162 0.88 4.4 0.87 29 99 45 34 89 104 31 152 118 0.78 6.4 0.84 25 93 36 30 70 84 32 152 130 0.86 3.8 0.90 24 75 36 29 73 83 33 182 168 0.92 5.4 0.83 19 88 38 31 80 103 34 161 115 0.72 5.5 0.83 26 94 41 30 82 102 35 170 152 0.89 5.2 0.88 25 84 39 31 78 97 41 192 149 0.77 10.4 0.78 15 64 49 34 80 110 42 166 86 0.52 14.4 0.67 14 42 39 28 69 95 43 203 163 0.80 9.5 0.78 16 82 44 27 94 131 44 186 145 0.78 8.0 0.81 21 96 44 31 86 112 45 196 138 0.71 8.8 0.79 18 59 46 34 80 106 51 177 130 0.73 11.6 0.70 19 58 42 32 74 95 52 167 118 0.70 15.5 0.69 18 66 43 34 74 104 53 195 160 0.82 8.2 0.79 17 73 45 33 92 117 54 173 141 0.81 8.3 0.77 22 103 43 34 77 103 55 181 152 0.84 11.5 0.76 19 63 43 32 75 113 61 154 45 0.29 12.6 0.65 17 60 38 29 68 98 62 152 114 0.75 8.6 0.83 19 66 38 27 77 97 63 183 156 0.85 6.5 0.77 22 93 41 28 87 103 64 172 134 0.78 7.3 0.82 34 106 44 33 85 111 65 172 122 0.71 7.8 0.78 20 79 43 31 83 110 71 144 56 0.39 20.1 0.63 15 63 37 30 62 79 72 149 63 0.42 14.1 0.64 16 70 35 28 64 90 73 178 151 0.85 7.5 0.82 17 95 38 27 84 106 74 167 137 0.82 6.2 0.84 33 119 43 35 84 112 75 169 127 0.75 9.3 0.80 20 82 39 32 73 92 81 165 132 0.80 6.0 0.86 15 53 40 33 76 90 82 158 135 0.85 6.2 0.88 21 78 38 29 76 91 83 181 159 0.88 5.1 0.87 21 89 44 34 90 114 84 174 157 0.90 4.1 0.90 18 83 47 39 85 98 85 173 156 0.90 4.6 0.87 28 95 43 32 85 99 91 162 98 0.61 7.4 0.79 17 63 36 30 72 89 92 149 123 0.83 6.0 0.83 17 53 35 26 66 78 93 175 159 0.91 4.3 0.89 22 75 42 34 83 100 94 158 138 0.87 4.2 0.91 21 77 46 38 81 90 95 162 146 0.90 4.1 0.92 20 74 44 33 86 102 a Average of all operation rates except hold-fire. 40 DOMESTIC STOKER COMBUSTION OJ u C OJ 11 '•3 g ^ CO CN r- < OO CN CO W-) W) T^ oo co oo rt* I r-H VO TjH VO rf vO I CN CN r-H 1 oo vo i> 1 co rfri t— i co r^ ONvOt^vO PQ on r^- vo r^ oo cn O <— 1 r- vo ■^ CO ON r-l ObNO I O ON ON VO | CN TfH r^ rfi vo CO 1 1 r^ vo r^ 1 1 ^^O 1 OrON | 1 O VO GO 1 t^- o r^- on cn ON CO r- CN vo i— i oo vo co r~- Jo a O >. ^ OO 00 on oo oo CO co CO CO CO "rJH -hjh tJ-i tJh 1 ON ON ON ON ON CN CN Tf CO CO GO CO O ON ON CO CO CO CO CO Tt" 1 Tt* "^ "^ ^ CO CO ■<*! co co 3 co o r^ co r- CO CO co CO co r- CO CN O vo vo r-~ r- 1 tJ" 1 "^ "^t" 1 "^f 1 1 o co vo r^ o o oo vo vo r-~- CN O CO CN CN u~i io vo vo vo r^ on co vo o CN CN tJh CO -<*i tJ^ ^t^ ■ , ^ ^^ tJ^ c o rt — i ON vO OO (N M r) M cs CO CN r^ CN vo •* — i oo CN CN CN CN CN Tf OO VO O vO 1 CN CO CN CN vO vo vo r- vo 1 CN CN CN CN vo vo o r^ r^ r-^ vo vo oo CN CN Ol CN CN T3 c _o o 5 o o o o o CO N rH rH O ooosr^oort CN CN CN CN CO O O O O 1 r- r^ on co 1 CO CN CN CO OOO CO CN ^ 1 1 rHt^CO 1 CO co CO OOO 1 oo r^ t^ I 1 ^h co CN 1 CO CO co o o o o o co r- vo rp cn O O ON ON CN CO CO CN CN CO 3 C\hOO Stack temperature °F O vo vo O vo o r- co i— < cn On OO ON ON ON O O O vo O oo co t— i I ON CO ON ON 1 W-) i^-> u~) vo vo CO ^t 1 CN OO ON ON ON O ON ON O O O O vo co r^ co vo r~- ON OO O ON ON O O O O vo r^ co go cn vo CO GO ON ON ON d Z o U i— i CN co -^ io CN CN CN CN CN ^h CN CO ^ VO CO CO co co co r-H CN CO •'f VO '—t CN CO tJh vo uo vo vo vo vo i-H CN CO rfi vo vO vO vO vO vO APPENDIX 41 O i— i w-) u-> CO no r-^ cn vn w> OO CO oo CN oo ON w-i no vo r- cN co co <-n >0 O r-H r-l T-H no O oo CN O r-~ On On O oo (N rf | on oo oo no vc CN OO r-H O OO O CN O r-H CO ON CO Th t^ NO r- r- on oo on ON oo O On O CN CO co co co ^^^^^ co co ^ co ^* ■>*< --0 NO ^f »-0 no ■<*< Tti r^ cn no no r^ *o no OMNO\>0 Tt< CN u~> On CN on r^ oo >-o vo CN CN CN CN CN 26.2 26.3 25.9 26.7 w> on no r^ r^ CN CN CN CN (N OO o o o On r^ r- co ^f CN O i— i On On CO co co CN CN 2970 3000 2920 3000 o o o o o oo w-) u-> r~-- u~> On co O i-h i-h CN co co co co "Nt^NO^n l^ CN OO CO oo O On co i— i w-i oo On CN CN cN O i— i CN i—i NO NO NO NO NO i-H i-H TtH CO i-H NO NO NO NO NO OO O OO VT) ^ VO *n O o o o o o On oo on oo \o oo On O ^ On NONOt^-r^NO o OO o o OOON^O\^ O On co i-i O r^ no t^ r- r^ CN r- oo ^ On On On O r-i O 10.3 9.8 11.2 10.8 OO O OO CN CN O ON O O O O lo O O lo no rf vo co O oo oo On On On lo o o o o NO CO i—i ON O oo oo On oo On O O O O >-o OO Tf O ON OO oo oo On oo oo rH(N CO -^ vr> r- r- r- r- r^ i— l CN CO -f LO OO OO GO OO OO i— i CN co -of "-O On ON ON On On 42 DOMESTIC STOKER COMBUSTION c O O T-i O l ^~l ON O i— 1 CO ■<+< CN Tjn CN NO ■*^lOTt*CO o o no co r~- LO tJh -^ >-0 -^ t-H CN CN T-H t-< r_H *- H T-H r - 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