Part 39 (1/2)
Capacity--Capacity, as already defined, is the ability of a definite aenerate steam Boilers are ordinarily purchased under a manufacturer's specification, which rates a boiler at a nominal rated horse power, usually based on 10 square feet of heating surface per horse power Such a builders' rating is absolutely arbitrary and i a surface will evaporate It does not imply that the evaporation of 345 pounds of water fro surface is the limit of the capacity of the boiler Further, from a statement that a boiler is of a certain horse power on the manufacturer's basis, it is not to be understood that the boiler is in any state of strain when developing more than its rated capacity
Broadly stated, the evaporative capacity of a certain aned boiler, that is, the boiler horse power it is capable of producing, is limited only by the amount of fuel that can be burned under the boiler While such a statement would imply that the question of capacity to be secured was siement by which sufficient fuel could be burned under a definite aenerate the required ahed against the advantages of high capacity developed fro surfaces Briefly stated, these factors are as follows:
1st Efficiency As the capacity increases, there will in general be a decrease in efficiency, this loss above a certain pointit inadvisable to try to secure iven boiler This loss of efficiency with increased capacity is treated below in detail, in considering the relation of efficiency to capacity
2nd Grate Ratio Possible or Practicable All fuels have a maximum rate of combustion, beyond which satisfactory results cannot be obtained, regardless of draft available or whichthe case, it is evident that with thisadded capacity will be through the addition of grate surface There is obviously a point beyond which the grate surface for a given boiler cannot be increased This is due to the irates above a certain h a boiler resulting froh the heating surface and to innun and ement wholly unfeasible
3rd Feed Water The difficulties that h the use of poor feed water or that are liable to happen through the use of practically any feed water have already been pointed out This question of feed is frequently the li factor in the capacity obtainable, for with an increase in such capacity coredients in the feed water as will cause pri or rapid scale forive no trouble that cannot be readily overcos will cause difficulties at higher ratings entirely out of proportion to any advantage secured by an increase in the power that a definite a surface may be made to produce
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 eive flexibility without undue loss in efficiency over the range of capacity desired The heating surface ed that it will be possible to install in a practical rate surface at or below the maximum combustion rate to develop the an of boiler h 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 stateeneral the efficiency of a boiler will decrease as the capacity is increased Considering the boiler alone, apart from the furnace, this state a constant furnace teiven boiler is run; to assure equal efficiencies at low and high ratings, the exit temperature in the two instances would necessarily be the sa, to be identical with that at the low rating, the rate of heat transfer fro surfaces would have to vary directly as the weight or voluases Experiment has shown, however, that this is not true but that this rate of transfer varies as soas less than one As the heat transfer does not, therefore, increase proportionately with the voluiven furnace teases increases As this is thesurface, the boiler efficiency will, therefore, decrease as the voluases 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 fro a constant furnace teh radiation is solely a function of the amount of surface exposed to such radiation
Hence, for the conditions assuher ratings will be the sas but in proportion to the total absorption will be less As the added voluas 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
TABLE 59
TESTS OF BABcock & WILcox BOILERS WITH VARIOUS FUELS
______________________________________________________________________ |Number| | | | Rated | | of | Name and Location | Kind of Coal | Kind of | Horse | | Test | of Plant | | Furnace |Power of| | | | | | Boiler | | | | | | | |______|___________________________|________________|_________|________| | |Susquehanna Coal Co, |No 1 Anthracite|Hand | | | 1 |Shenandoah, Pa |Buckwheat |Fired | 300 | |______|___________________________|________________|_________|________| | |Balbach S Co, Newark, N J|and Bird's-eye | Stoker | 218 | |______|___________________________|________________|_________|________| | |H R Worthington, |No 2 Anthracite|Hand | | | 3 |Harrison N J |Buckwheat |Fired | 300 | |______|___________________________|________________|_________|________| | |Raymond Street Jail, |Anthracite Pea |Hand | | | 4 |Brooklyn, N Y | |Fired | 155 | |______|___________________________|________________|_________|________| | |R H Macy & Co, |No 3 Anthracite|Hand | | | 5 |New York, N Y |Buckwheat |Fired | 293 | |______|___________________________|________________|_________|________| | |National Bureau of |Anthracite Egg |Hand | | | 6 |Standards, Washi+ngton, DC| |Fired | 119 | |______|___________________________|________________|_________|________| | |Fred Loeser & Co, |No 1 Anthracite|Hand | | | 7 |Brooklyn, N Y |Buckwheat |Fired | 300 | |______|___________________________|________________|_________|________| | |New York Edison Co, |No 2 Anthracite|Hand | | | 8 |New York City |Buckwheat |Fired | 374 | |______|___________________________|________________|_________|________| | |Sewage Pu Valley |Hand | | | 9 |Cleveland, O |Lump, O |Fired | 150 | |______|___________________________|________________|_________|________| | |Scioto River Pu Valley, |Hand | | | 10 |Cleveland, O |O |Fired | 300 | |______|___________________________|________________|_________|________| | |Consolidated Gas & Electric|Somerset, Pa |Hand | | | 11 |Co, Baltimore, Md | |Fired | 640 | |______|___________________________|________________|_________|________| | |Consolidated Gas & Electric|Somerset, Pa |Hand | | | 12 |Co, Baltimore, Md | |Fired | 640 | |______|___________________________|________________|_________|________| | |Merries Creek, |Hand | | | 13 |Lowell, Mass |Md |Fired | 321 | |______|___________________________|________________|_________|________| | |Great West'n Sugar Co, |Lafayette, Col,|HandFired| | | 14 |Ft Collins, Col |Mine Run |Extension| 351 | |______|___________________________|________________|_________|________| | |Balti |New River |Hand | | | 15 | Station | |Fired | 266 | |______|___________________________|________________|_________|________| | |Tennessee State Prison, |Brushy Mountain,|Hand | | | 16 |Nashville, Tenn |Tenn |Fired | 300 | |______|___________________________|________________|_________|________| | |Pine Bluff Corporation, |Arkansas Slack |Hand | | | 17 |Pine Bluff, Ark | |Fired | 298 | |______|___________________________|________________|_________|________| | |Pub Serv Corporation |Valley, Pa, |Roney| | | 18 |of N J, Hoboken |Mine Run |Stoker | 520 | |______|___________________________|________________|_________|________| | |Pub Serv Corporation |Valley, Pa, |Roney | | | 19 |of N J, Hoboken |Mine Run |Stoker | 520 | |______|___________________________|________________|_________|________| | |Frick Building, |Pittsburgh Nut |Ah, Pa |and Slack |Stoker | 300 | |______|___________________________|________________|_________|________| | |New York Edison Co, |Loyal Hanna, Pa|Taylor | | | 21 |New York City | |Stoker | 604 | |______|___________________________|________________|_________|________| | |City of Colu |O |Stoker | 300 | |______|___________________________|________________|_________|________| | |Edison Elec Illum Co, |New River |Murphy | | | 23 |Boston, Mass | |Stoker | 508 | |______|___________________________|________________|_________|________| | |Colorado Springs & |Pike View, Col,|Green Chn| | | 24 |Interurban Ry, Col |Mine Run |Grate | 400 | |______|___________________________|________________|_________|________| | |Pub Serv Corporation |Lancashi+re, Pa |B&WChain| | | 25 |of N J, Marion | |Grate | 600 | |______|___________________________|________________|_________|________| | |Pub Serv Corporation |Lancashi+re, Pa |B&WChain| | | 26 |of N J, Marion | |Grate | 600 | |______|___________________________|________________|_________|________| | |Erie County Electric Co, |Mercer County, |B&WChain| | | 27 |Erie, Pa |Pa |Grate | 508 | |______|___________________________|________________|_________|________| | |Union Elec Lt & Pr Co, |Mascouth, Ill |B&WChain| | | 28 |St Louis, Mo | |Grate | 508 | |______|___________________________|________________|_________|________| | |Union Elec Lt & Pr Co, |St Clair |B&WChain| | | 29 |St Louis, Mo |County, Ill |Grate | 508 | |______|___________________________|________________|_________|________| | |Como, Ill |Ill, Screenings|Grate | 508 | |______|___________________________|________________|_________|________|
________________________________________________________________ |Nurees|Factor| Draft | | of |Surf | tion|Pres | ature | Super | of | In | At | | Test |Square|Test | By | Water | -heat |Evapo-|Furnace|Boiler| | | Feet |Hours|Gauge |Degrees|Degrees|ration|Inches |Damper| | | | |Pounds| Fahr | Fahr | |Upr/Lwr|Inches| |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 1 | 84 | 8 | 68 | 539 | |11965| +41 | 21 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | +65 | | | 2 | 516 | 7 | 1363| 203 | 150 |11480| 47 | 56 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 3 | 676 | 8 | 139 | 1396 | 139 |11984| 70 | 96 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 4 | 40 | 8 | 1102| 137 | |11185| 33 | 43 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 5 | 595 | 10 | 1332| 752 | |11849| 19 | 40 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 6 | 265 | 18 | 1321| 705 | |11897| 33 | | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | +51 | | | 7 | 489 | 7 | 101 | 1213 | |11333| -20 | 30 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 8 | 595 | 6 | 1918| 883 | |11771| 50 | | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 9 | 27 | 24 | 1563| 58 | |12051| 10 | 24 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 10 | | 24 | 145 | 75 | |11866| 26 | 46 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 11 | 118 | 8 | 170 | 1861 | 667 |11162| 34 | 42 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 12 | 118 | 792| 173 | 1802 | 752 |11276| 44 | 58 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 13 | 52 | 24 | 75 | 533 | |11987| 25 | 35 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 14 | 595 | 8 | 105 | 358 | |12219| 17 | 38 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 15 | 595 | 24 | 1701| 133 | |11293| 12 | 43 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 16 | 513 | 10 | 105 | 751 | |11814| 21 | 42 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 17 | 595 | 8 | 1492| 71 | |11910| 35 | 59 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 18 | 1032| 10 | 1332| 653 | 659 |12346| 05 | 49 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 19 | 1032| 9 | 139 | 64 | 802 |12358| 18 | 57 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 20 | 53 | 9 | 125 | 766 | |11826| +164 | 64 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 21 | 75 | 8 | 1985| 1651 | 104 |11662| +305 | 60 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 22 | | 9 | 140 | 67 | 180 |12942| 22 | 35 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 23 | 90 |1625| 199 | 484 | 1365 |12996| 23 | 127 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 24 | 103 | 8 | 129 | 56 | |12002| 23 | 30 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | +52 | | | 25 | 132 | 8 | 200 | 572 | 2804 |13909| +19 | 52 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | +15 | | | 26 | 132 | 8 | 199 | 607 | 1710 |13191| 04 | 52 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 27 | 90 | 8 | 120 | 699 | |11888| 31 | 58 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 28 | 1035| 8 | 180 | 46 | 113 |12871| 62 | 124 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 29 | 1035| 8 | 183 | 531 | 104 |12725| 60 | 126 | |______|______|_____|______|_______|_______|______|_______|______| | | | | | | | | | | | 30 | 90 | 7 | 184 | 1271 | 180 |12393| 68 | 115 | |______|______|_____|______|_______|_______|______|_______|______| ______________________________________________________________ |Number|Temper-| Coal | | of | ature | Total | Moist-| Total |Ash and| Total |DryCoal| | Test |FlueGas|Weight:| ure | dry | Refuse|Corees| Fired | Per | Coal | Per | tible | Grate | | | Fahr |Pounds | Cent | Pounds| Cent | Pounds|/HrLb| |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 1 | | 11670 | 445 | 11151 | 2605 | 8248 | 166 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 2 | 487 | 8800 | 762 | 8129 | 2982 | 5705 | 1971 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 3 | 559 | 10799 | 642 | 10106 | 2002 | 8081 | 2177 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 4 | 427 | 5088 | 400 | 4884 | 1935 | 3939 | 1526 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 5 | 414 | 9440 | 214 | 9238 | 1119 | 8204 | 1552 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 6 | 410 | 8555 | 362 | 8245 | 1573 | 6948 | 1728 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 7 | 480 | 7130 | 738 | 6604 | 1835 | 5392 | 1929 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 8 | 449 | 7500 | 270 | 7298 | 2794 | 5259 | 1473 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 9 | 410 | 15087 | 750 | 13956 | 1130 | 12379 | 215 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 10 | 503 | 29528 | 772 | 27248 | | | 247 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 11 | 487 | 20400 | 284 | 19821 | 783 | 18269 | 2100 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 12 | 494 | 21332 | 229 | 20843 | 823 | 19127 | 2231 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 13 | 516 | 24584 | 429 | 23529 | 763 | 21883 | 1885 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 14 | 523 | 15540 | 1864 | 12643 | | | 2859 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 15 | 474 | 18330 | 203 | 17958 | 1636 | 16096 | 1257 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 16 | 536 | 12243 | 214 | 11981 | | | 2340 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 17 | 534 | 10500 | 304 | 10181 | | | 2140 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 18 | 458 | 18600 | 340 | 17968 | 1838 | 14665 | 1741 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 19 | 609 | 23400 | 256 | 22801 | 1689 | 18951 | 2455 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 20 | 518 | 10500 | 183 | 10308 | 1222 | 9048 | 2156 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 21 | 536 | 25296 | 220 | 24736 | | | 410 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 22 | 511 | 14263 | 863 | 13032 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 23 | 560 | 39670 | 422 | 37996 | 432 | 36355 | 2598 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 24 | 538 | 23000 | 2373 | 17542 | | | 2136 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 25 | 590 | 32205 | 403 | 30907 | 1565 | 26070 | 2926 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 26 | 529 | 24243 | 409 | 23251 | 1233 | 20385 | 2201 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 27 | 533 | 22328 | 442 | 21341 | 1688 | 17739 | 2964 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 28 | 523 | 32163 | 1374 | 27744 | | | 3350 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 29 | 567 | 36150 | 1462 | 30865 | | | 3728 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 30 | | 30610 | 1112 | 27206 | 1470 | 23198 | 4320 | |______|_______|_______|_______|_______|_______|_______|_______|
______________________________________________________________ |Number| Water | | Flue Gas analysis | | of |Actual | Equiv|ditto /| Rated|CO_{2} | O | CO | | Test |Evapor-|Evap |sqft |Cap'ty| Per | Per | Per | | | ation |>=212 |Heating|Develpd| Cent | Cent | Cent | | |/HrLb|/HrLb|Surface|PerCent| | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 1 | 10268 | 12286 | 410 | 1187 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 2 | 8246 | 9466 | 434 | 1257 | | || |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 3 | 9145 | 10959 | 365 | 1059 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 4 | 5006 | 5599 | 361 | 1047 | 1226 | 788 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 5 | 7434 | 8809 | 306 | 872 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 6 | 2903 | 3454 | 291 | 844 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 7 | 7464 | 8459 | 282 | 817 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 8 | 9164 | 10787 | 288 | 835 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 9 | 4374 | 5271 | 351 | 1018 | 117 | 73 | 007 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 10 | 8688 | 10309 | 344 | 996 | 129 | 50 | 02 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 11 | 24036 | 26829 | 419 | 1215 | 125 | 64 | 05 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 12 | 25313 | 28544 | 446 | 1293 | 133 | 51 | 05 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 13 | 9168 | 10990 | 342 | 993 | 96 | 88 | 04 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 14 | 11202 | 13689 | 391 | 1135 | 91 | 99 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 15 | 7565 | 8543 | 321 | 931 | 1071 | 910 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 16 | 9512 | 11237 | 374 | 1086 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 17 | 9257 | 11025 | 370 | 1072 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 18 | 15887 | 19614 | 377 | 1087 | 117 | 77 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 19 | 21320 | 26347 | 506 | 1467 | 119 | 78 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 20 | 9976 | 11978 | 393 | 1120 | 113 | 75 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 21 | 28451 | 33066 | 547 | 1586 | 123 | 64 | 07 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 22 | 10467 | 13526 | 451 | 1307 | 119 | 72 | 004 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 23 | 20700 | 26902 | 530 | 1535 | 111 | || |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 24 | 14650 | 17583 | 440 | 1274 | | | | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 25 | 28906 | 40205 | 670 | 1942 | 105 | 83 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 26 | 23074 | 30437 | 507 | 1470 | 101 | 90 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 27 | 20759 | 24678 | 485 | 1408 | 101 | 91 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 28 | 21998 | 28314 | 567 | 1615 | 87 | 106 | 00 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 29 | 24386 | 31031 | 611 | 1771 | 89 | 107 | 02 | |______|_______|_______|_______|_______|_______|_______|_______| | | | | | | | | | | 30 | 30505 | 37805 | 743 | 2157 | 104 | 94 | 02 | |______|_______|_______|_______|_______|_______|_______|_______|
_______________________________________________________ |Number| Proximate analysis Dry Coal | Equiv|Combnd| | of |Volatl| Fixed | Ash |Btu/|Evap |Efficy| | Test |Matter |Carbon | Per | Pound |>=212/|Boiler | | | Per | Per | Cent | Dry | Pound |& Grate| | | Cent | Cent | | Coal |DryCoal|PerCent| |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 1 | | | 2605 | 11913 | 881 | 718 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 2 | | | | 11104 | 815 | 721 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 3 | 555 | 8060 | 1387 | 12300 | 867 | 684 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 4 | 774 | 7748 | 1478 | 12851 | 917 | 692 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 5 | | | | 13138 | 953 | 696 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 6 | 613 | 8486 | 901 | 13454 | 957 | 690 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 7 | | | | 12224 | 897 | 712 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 8 | 055 | 8673 | 1272 | 12642 | 887 | 681 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 9 | 3901 | 4808 | 1291 | 12292 | 906 | 715 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 10 | 3833 | 4671 | 1496 | 12284 | 908 | 717 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 11 | 1986 | 7302 | 712 | 14602 | 1083 | 720 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 12 | 2024 | 7226 | 750 | 14381 | 1084 | 732 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 13 | | | | 14955 | 1121 | 727 | |______|_______|_______|_______|_______|_______|_______| | | | || | | | | 14 | 3960 | 5446 | 594 | 11585 | 866 | 725 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 15 | 1744 | 7642 | 584 | 15379 | 1142 | 721 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 16 | 3340 | 5473 | 1187 | 12751 | 938 | 714 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 17 | 1542 | 6248 | 2210 | 12060 | 866 | 696 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 18 | 1499 | 7513 | 988 | 14152 | 1092 | 7488 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 19 | 1440 | 7433 | 1127 | 14022 | 1040 | 7197 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 20 | 3244 | 5671 | 1085 | 13510 | 1030 | 746 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 21 | 1902 | 7209 | 889 | 14105 | 1069 | 735 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 22 | 3211 | 5393 | 1396 | 12435 | 941 | 734 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 23 | 1966 | 7541 | 493 | 14910 | 1151 | 749 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 24 | 4357 | 4622 | 1021 | 11160 | 802 | 697 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 25 | 2284 | 6991 | 725 | 13840 | 1041 | 726 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 26 | 3236 | 6067 | 697 | 14027 | 1047 | 721 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 27 | 3326 | 5403 | 1271 | 12742 | 925 | 704 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 28 | 2896 | 4688 | 2416 | 10576 | 816 | 749 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 29 | 3650 | 4120 | 2230 | 10849 | 804 | 719 | |______|_______|_______|_______|_______|_______|_______| | | | | | | | | | 30 | | | 1024 | 13126 | 973 | 719 | |______|_______|_______|_______|_______|_______|_______|
[Illustration: 15400 Horse-power Installation of Babcock & Wilcox Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate Stokers at the Plant of the Twin City Rapid Transit Co, Minneapolis, Minn]
This increase in the efficiency of the boiler alone with the decrease in the rate at which it is operated, will hold to a point where the radiation of heat frooverning factor in the total aiven above for a decrease of boiler efficiency with increase of capacity, viz, the effect of radiant heat, is to a greater extent than the first reason dependent upon a constant furnace temperature Any increase in this temperature will affect enormously the amount of heat absorbed by radiation, as this absorption will vary as the fourth power of the te body In this way it is seen that but a slight increase in furnace te the proportional part, due to absorption by radiation, of the total heat absorbed, up to its proper proportion at the higher ratings This factor of furnace tes to the consideration of furnace efficiency than of boiler efficiency There is a point, however, in any furnace above which the combustion will be so poor as to actually reduce the furnace temperature and, therefore, the proportion of heat absorbed through radiation by a given a surface
Since it is thus true that the efficiency of the boiler considered alone will increase with a decreased capacity, it is evident that if the furnace conditions are constant regardless of the load, that the combined efficiency of boiler and furnace will also decrease with increasing loads This fact was clearly proven in the tests of the boilers at the Detroit Edison Coreat care hich the tests were run ood furnace conditions irrespective of load, and here the maximum efficiency was obtained at a point somewhat less than the rated capacity of the boilers
In some cases, however, and especially in the ordinary operation of the plant, the furnace efficiency will, up to a certain point, increase with an increase in power This increase in furnace efficiency is ordinarily at a greater rate as the capacity increases than is the decrease in boiler efficiency, with the result that the combined efficiency of boiler and furnace will to a certain point increase with an increase in capacity This makes the ordinary point of maximum combined efficiency somewhat above the rated capacity of the boiler and in many cases the combined efficiency will be practically a constant over a considerable range of ratings The features li of the point ofare the sarate surface that can be installed under a boiler The relative efficiency of different cos depends so largely upon the furnace conditions that what ht hold for one combination would not for another
In view of the above, it is impossible to make a statement of the efficiency at different capacities of a boiler and furnace which will hold for any and all conditions Fig 40 shows in a general form the relation of efficiency to capacity This curve has been plotted froreat nu them to approximately the same conditions The curve represents test conditions
The efficiencies represented are those which eneral direction of the curve, however, will be found to hold approxiuide to what may be expected
[Graph: Coainst Per Cent of Boiler's Rated Capacity Developed
Fig 40 Approximate Variation of Efficiency with Capacity under Test Conditions]
Economical Loads--With the effect of capacity on economy in mind, the question arises as to what constitutes the econo on the economical load for an individual plant, the broader econoainst the boiler efficiency, there is to be weighed the plant first cost, returns on such investment, fuel cost, labor, capacity, etc, etc This matter has been widely discussed, but unfortunately such discussion has been largely lienerated in such stations, while representing an enorer proportion of the total power generated throughout the country