Document NN2N3pqGkLkZDvnmGk91VvgYE

310 CHAPTER 16 1946 Guide fuel beds on the grate increase the effective combustion space in the . furnace, supply more air for combustion, and are sometimes effective in reducing the smoke emitted, but care should be taken that holes are not formed in the fire. A lower volatile coal or a higher A.P.I. gravity oil always produces less smoke than a high volatile coal or low A.P.I. gravity oil used in the same furnace and fired in the same manner. The installation of more modern or better designed fuel burning equip ment, or a change in the construction of the furnace, will often reduce smoke. The installation of a Dutch oven which will increase the furnace "volume and raise the furnace temperature often produces satisfactory results. In the case of new installations, the problem of smoke abatement can be solved by the selection of the. proper fuel-burning equipment and furnace design for the particular fuel to be burned and by the proper operation of that equipment. Constant vigilance is necessary to make certain that the equipment is properly operated. In old installations the solution of the problem presents many difficulties, and a considerable investment in special apparatus is often necessary. Lower rates of combustion per square foot of grate area will reduce the quantity of solid matter discharged from the chimney with the gases of combustion. The burning of coke, coking coal, and sized coal from which the extremely fine coal has been removed will not as a general rule produce as much dust and cinders as will result from the burning of non-coking coals and slack coals when they are burned on a grate. Modem boiler installations are usually designed for high capacity per square foot of ground area because such designs give the lowest cost of construction per unit of capacity. Designs of this type discharge a large quantity of dust and cinders with the gases of combustion, and if pollution of the atmosphere is to be prevented, some type of catcher must be installed. FIRING METHODS FOR SEMI-BITUMINOUS COAL The Pocahontas Operators' Association recommends the central cone method of firing, in which the coal is heaped on to the center of the bed forming a cone, the top of which should be level with the middle of the firing door. This allows the larger lumps to fall to the sides, and the fines to remain in the center and be coked. The poking should be limited to breaking down the coke without stirring, and to gently rocking the grates. It is recommended that the slides in the firing door be kept closed, as the thinner fuel bed around the sides allows enough air to get through. FIRING METHODS FOR COKE Coke ignites less readily than bituminous coal and more readily than anthracite and burns rapidly with little draft. In order to control the air admitted to the fuel it is very important that all openings or leaks into the ashpit be closed tightly. A coke fire.responds rapidly to the opening of the dampers. This is an advantage in warming up the system, but it also makes it necessary to watch the dampers more closely in order to prevent the fire from burning too rapidly. In order to obtain the same interval of attention as with other fuels a deep fuel bed always should.be maintained when burning coke. The grates should be shaken only. slightly in mild weather and should be shaken only until the first red particles drop from the grates in cold weather. The best size of coke for T a b le 7. D e ta ile d Requirements for F uel Oil s 0 ' Fuels and Combustion. \ 311 2S"SaR52a I-SS r .X S'"-- v 3 S,, Sill |31=1 sitHS ;rilTrr^ S|03v :5 k %O ] .o'*O* SS .33 J c a3 > 8*5 *iXll9 Mi ll!' t! i 3:P 0 4-1! Se8 an O v St |sl. U M * 33C S-> 4< li'gO c c6**7 3: j3 sc. SgJ'o; Min I HJj