Steam, Its Generation and Use

by Babcock & Wilcox Company

Where capacity in the sense of overload is desired, the type of boiler selected will play a large part in the successful operation through such periods. A boiler must be selected with which there is possible a furnace arrangement that will give flexibility without undue loss in efficiency over the range of capacity desired. The heating surface must be so arranged that it will be possible to install in a practical manner, sufficient grate surface at or below the maximum combustion rate to develop the amount of power required. The design of boiler must be such that there will be no priming or foaming at high overloads and that any added scale formation due to such overloads may be easily removed. Certain boilers which deliver commercially dry steam when operated at about their normal rated capacity will prime badly when run at overloads and this action may take place with a water that should be easily handled by a properly designed boiler at any reasonable load. Such action is ordinarily produced by the lack of a well defined, positive circulation.

Relation of Efficiency and Capacity—The statement has been made that in general the efficiency of a boiler will decrease as the capacity is increased. Considering the boiler alone, apart from the furnace, this statement may be readily explained.

Presupposing a constant furnace temperature, regardless of the capacity at which a given boiler is run; to assure equal efficiencies at low and high ratings, the exit temperature in the two instances would necessarily be the same. For this temperature at the high rating, to be identical with that at the low rating, the rate of heat transfer from the gases to the heating surfaces would have to vary directly as the weight or volume of such gases. Experiment has shown, however, that this is not true but that this rate of transfer varies as some power of the volume of gas less than one. As the heat transfer does not, therefore, increase proportionately with the volume of gases, the exit temperature for a given furnace temperature will be increased as the volume of gases increases. As this is the measure of the efficiency of the heating surface, the boiler efficiency will, therefore, decrease as the volume of gases increases or the capacity at which the boiler is operated increases.

Further, a certain portion of the heat absorbed by the heating surface is through direct radiation from the fire. Again, presupposing a constant furnace temperature; the heat absorbed through radiation is solely a function of the amount of surface exposed to such radiation. Hence, for the conditions assumed, the amount of heat absorbed by radiation at the higher ratings will be the same as at the lower ratings but in proportion to the total absorption will be less. As the added volume of gas does not increase the rate of heat transfer, there are therefore two factors acting toward the decrease in the efficiency of a boiler with an increase in the capacity.
[Pg 280]

[TABLE 59]—Part 1 TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS Number of Test Name and Location of Plant Kind of Coal Kind of Furnace Rated Horse Power of Boiler Grate Surface Square Feet Duration of Test Hours Steam Pressure by Gauge Pounds Temperature Feed Water Degrees Fahrenheit Degrees of Superheat Degrees Fahrenheit Factor of Evaporation Draft In Furnace Inches At Boiler Damper Inches 1 Susquehanna Coal Co., Shenandoah, Pa. No. 1 Anthracite Buckwheat Hand Fired 300 84 8 68 53.9 1.1965 +.41 .21 2 Balbach Smelting & Refining Co., Newark, N. J. No. 2 Buckwheat and Bird’s-eye Wilkenson Stoker 218 51.6 7 136.3 203 150 1.1480 +.65 .47 .56 3 H. R. Worthington, Harrison N. J. No. 2 Anthracite Buckwheat Hand Fired 300 67.6 8 139 139.6 139 1.1984 .70 .96 4 Raymond Street Jail, Brooklyn, N. Y. Anthracite Pea Hand Fired 155 40 8 110.2 137 1.1185 .33 .43 5 R. H. Macy & Co., New York, N. Y. No. 3 Anthracite Buckwheat Hand Fired 293 59.5 10 133.2 75.2 1.1849 .19 .40 6 National Bureau of Standards, Washington, D.C. Anthracite Egg Hand Fired 119 26.5 18 132.1 70.5 1.1897 .33 7 Fred. Loeser & Co., Brooklyn, N. Y. No. 1 Anthracite Buckwheat Hand Fired 300 48.9 7 101 121.3 1.1333 +.51 -.20 .30 8 New York Edison Co., New York City No. 2 Anthracite Buckwheat Hand Fired 374 59.5 6 191.8 88.3 1.1771 .50 9 Sewage Pumping Station, Cleveland, O. Hocking Valley Lump, O. Hand Fired 150 27 24 156.3 58 1.2051 .10 .24 10 Scioto River Pumping Sta., Cleveland, O. Hocking Valley, O. Hand Fired 300 24 145 75 1.1866 .26 .46 11 Consolidated Gas & Electric Co., Baltimore, Md. Somerset, Pa. Hand Fired 640 118 8 170 186.1 66.7 1.1162 .34 .42 12 Consolidated Gas & Electric Co., Baltimore, Md. Somerset, Pa. Hand Fired 640 118 7.92 173 180.2 75.2 1.1276 .44 .58 13 Merrimac Mfg. Co., Lowell, Mass. Georges Creek, Md. Hand Fired 321 52 24 75 53.3 1.1987 .25 .35 14 Great West’n Sugar Co., Ft. Collins, Col. Lafayette, Col., Mine Run Hand Fired Extension 351 59.5 8 105 35.8 1.2219 .17 .38 15 Baltimore Sewage Pumping Station New River Hand Fired 266 59.5 24 170.1 133 1.1293 .12 .43 16 Tennessee State Prison, Nashville, Tenn. Brushy Mountain, Tenn. Hand Fired 300 51.3 10 105 75.1 1.1814 .21 .42 17 Pine Bluff Corporation, Pine Bluff, Ark. Arkansas Slack Hand Fired 298 59.5 8 149.2 71 1.1910 .35 .59 18 Pub. Serv. Corporation of N. J., Hoboken Valley, Pa., Mine Run Roney Stoker 520 103.2 10 133.2 65.3 65.9 1.2346 .05 .49 19 Pub. Serv. Corporation of N. J., Hoboken Valley, Pa., Mine Run Roney Stoker 520 103.2 9 139 64 80.2 1.2358 .18 .57 20 Frick Building, Pittsburgh, Pa. Pittsburgh Nut and Slack American Stoker 300 53 9 125 76.6 1.1826 +1.64 .64 21 New York Edison Co., New York City Loyal Hanna, Pa. Taylor Stoker 604 75 8 198.5 165.1 104 1.1662 +3.05 .60 22 City of Columbus, O., Dept. Lighting Hocking Valley, O. Detroit Stoker 300 9 140 67 180 1.2942 .22 .35 23 Edison Elec. Illum. Co., Boston, Mass. New River Murphy Stoker 508 90 16.25 199 48.4 136.5 1.2996 .23 1.27 24 Colorado Springs & Interurban Ry., Col. Pike View, Col., Mine Run Green Chain Grate 400 103 8 129 56 1.2002 .23 .30 25 Pub. Serv. Corporation of N. J., Marion Lancashire, Pa. B.&W. Chain Grate 600 132 8 200 57.2 280.4 1.3909 +.52 +.19 .52 26 Pub. Serv. Corporation of N. J., Marion Lancashire, Pa. B.&W. Chain Grate 600 132 8 199 60.7 171.0 1.3191 +.15 .04 .52 27 Erie County Electric Co., Erie, Pa. Mercer County, Pa. B.&W. Chain Grate 508 90 8 120 69.9 1.1888 .31 .58 28 Union Elec. Lt. & Pr. Co., St. Louis, Mo. Mascouth, Ill. B.&W. Chain Grate 508 103.5 8 180 46 113 1.2871 .62 1.24 29 Union Elec. Lt. & Pr. Co., St. Louis, Mo. St. Clair County, Ill. B.&W. Chain Grate 508 103.5 8 183 53.1 104 1.2725 .60 1.26 30 Commonwealth Edison Co., Chicago, Ill. Carterville, Ill., Screenings B.&W. Chain Grate 508 90 7 184 127.1 180 1.2393 .68 1.15

[Pg 281]

TABLE 59—Part 2 TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS Number of Test Temperature of Flue Gases degrees Fahrenheit Coal Water Total Weight of Coal as Fired Pounds Moisture Per Cent Total Dry Coal Pounds Ash and Refuse Per Cent Total Combustible Pounds Dry Coal Per Square Foot of Grate Surface per Hour Pounds Actual Evaporation per Hour Pounds Equivalent Evaporation @ >=212° per Hour Pounds Equivalent Evaporation @ >=212° per Square Foot of Heating Surface per Hour Pounds 1 11670 4.45 11151 26.05 8248 16.6 10268 12286 4.10 2 487 8800 7.62 8129 29.82 5705 19.71 8246 9466 4.34 3 559 10799 6.42 10106 20.02 8081 21.77 9145 10959 3.65 4 427 5088 4.00 4884 19.35 3939 15.26 5006 5599 3.61 5 414 9440 2.14 9238 11.19 8204 15.52 7434 8809 3.06 6 410 8555 3.62 8245 15.73 6948 17.28 2903 3454 2.91 7 480 7130 7.38 6604 18.35 5392 19.29 7464 8459 2.82 8 449 7500 2.70 7298 27.94 5259 14.73 9164 10787 2.88 9 410 15087 7.50 13956 11.30 12379 21.5 4374 5271 3.51 10 503 29528 7.72 27248 24.7 8688 10309 3.44 11 487 20400 2.84 19821 7.83 18269 21.00 24036 26829 4.19 12 494 21332 2.29 20843 8.23 19127 22.31 25313 28544 4.46 13 516 24584 4.29 23529 7.63 21883 18.85 9168 10990 3.42 14 523 15540 18.64 12643 28.59 11202 13689 3.91 15 474 18330 2.03 17958 16.36 16096 12.57 7565 8543 3.21 16 536 12243 2.14 11981 23.40 9512 11237 3.74 17 534 10500 3.04 10181 21.40 9257 11025 3.70 18 458 18600 3.40 17968 18.38 14665 17.41 15887 19614 3.77 19 609 23400 2.56 22801 16.89 18951 24.55 21320 26347 5.06 20 518 10500 1.83 10308 12.22 9048 21.56 9976 11978 3.93 21 536 25296 2.20 24736 41.0 28451 33066 5.47 22 511 14263 8.63 13032 10467 13526 4.51 23 560 39670 4.22 37996 4.32 36355 25.98 20700 26902 5.30 24 538 23000 23.73 17542 21.36 14650 17583 4.40 25 590 32205 4.03 30907 15.65 26070 29.26 28906 40205 6.70 26 529 24243 4.09 23251 12.33 20385 22.01 23074 30437 5.07 27 533 22328 4.42 21341 16.88 17739 29.64 20759 24678 4.85 28 523 32163 13.74 27744 33.50 21998 28314 5.67 29 567 36150 14.62 30865 37.28 24386 31031 6.11 30 30610 11.12 27206 14.70 23198 43.20 30505 37805 7.43

TABLE 59—Part 3 TESTS OF BABCOCK & WILCOX BOILERS WITH VARIOUS FUELS Number of Test Per Cent of Rated Capacity Developed Per Cent Flue Gas Analysis Proximate Analysis Dry Coal Equivalent Evaporation @ >=212° per Pound of Dry Coal Pounds Combined Efficiency Boiler and Grate Per Cent CO2 Per Cent O Per Cent CO Per Cent Volatile Matter Per Cent Fixed Carbon Per Cent Ash Per Cent B.t.u. per Pound Dry Coal B.t.u. 1 118.7 26.05 11913 8.81 71.8 2 125.7 11104 8.15 72.1 3 105.9 5.55 80.60 13.87 12300 8.67 68.4 4 104.7 12.26 7.88 0.0 7.74 77.48 14.78 12851 9.17 69.2 5 87.2 13138 9.53 69.6 6 84.4 6.13 84.86 9.01 13454 9.57 69.0 7 81.7 12224 8.97 71.2 8 83.5 0.55 86.73 12.72 12642 8.87 68.1 9 101.8 11.7 7.3 0.07 39.01 48.08 12.91 12292 9.06 71.5 10 99.6 12.9 5.0 0.2 38.33 46.71 14.96 12284 9.08 71.7 11 121.5 12.5 6.4 0.5 19.86 73.02 7.12 14602 10.83 72.0 12 129.3 13.3 5.1 0.5 20.24 72.26 7.50 14381 10.84 73.2 13 99.3 9.6 8.8 0.4 14955 11.21 72.7 14 113.5 9.1 9.9 0.0 39.60 54.46 5.94 11585 8.66 72.5 15 93.1 10.71 9.10 0.0 17.44 76.42 5.84 15379 11.42 72.1 16 108.6 33.40 54.73 11.87 12751 9.38 71.4 17 107.2 15.42 62.48 22.10 12060 8.66 69.6 18 108.7 11.7 7.7 0.0 14.99 75.13 9.88 14152 10.92 74.88 19 146.7 11.9 7.8 0.0 14.40 74.33 11.27 14022 10.40 71.97 20 112.0 11.3 7.5 0.0 32.44 56.71 10.85 13510 10.30 74.6 21 158.6 12.3 6.4 0.7 19.02 72.09 8.89 14105 10.69 73.5 22 130.7 11.9 7.2 0.04 32.11 53.93 13.96 12435 9.41 73.4 23 153.5 11.1 19.66 75.41 4.93 14910 11.51 74.9 24 127.4 43.57 46.22 10.21 11160 8.02 69.7 25 194.2 10.5 8.3 0.0 22.84 69.91 7.25 13840 10.41 72.6 26 147.0 10.1 9.0 0.0 32.36 60.67 6.97 14027 10.47 72.1 27 140.8 10.1 9.1 0.0 33.26 54.03 12.71 12742 9.25 70.4 28 161.5 8.7 10.6 0.0 28.96 46.88 24.16 10576 8.16 74.9 29 177.1 8.9 10.7 0.2 36.50 41.20 22.30 10849 8.04 71.9 30 [Pg 282] 215.7 10.4 9.4 0.2 10.24 13126 9.73 71.9