GB769538A - Improvements in or relating to tubulous vapour generating and vapour heating units - Google Patents

Abstract

769,538. Combustion apparatus. BABCOCK & WILCOX, Ltd. Jan. 24, 1955 [Jan. 25, 1954], No. 2070/55. Class 51 (1). [Also in Group XIII] A steam &c. boiler has a furnace 10 which is lined with steam generating tubes extending from lower headers 16, 26, 48 to a steam and water drum 20 and fired by an upper row 216 of oil or gas burners and lower spaced rows 60 ... 63 of pulverized fuel burners, the latter discharging into a combustion space which is lined with refractory material to maintain the fluidity of the slag formed during combustion, the slag flowing over the furnace floor 15 to a pit (not shown). Gases leave the furnace through an outlet between an arch 32 and the burner wall and flow between widely spaced, dependent tube platens of a radiant, secondary superheater section 116 and then laterally through the more closely-spaced tube platens of the convection section 118 of this superheater into three parallel downpasses the middle of which locates reheater sections 138, 140, 142, 144 whilst in the two outer passes are disposed similarly arranged sections of primary superheater. The three gas streams unite at the bottom of the downpasses for flow through a breeching 90 to a single downpass including an economizer 92 and air heater 230. Steam from drum 20 flows to the primary superheater inlet headers through tubes lining the three downpasses, upwardly through the two primary superheaters and through cross-over connections including attemperators to the diagonally opposite section of the secondary superheater which is divided into two sections by a vertical, tubular mid-partition. To reduce the temperature of the furnaces gases contacting superheaters 116, 118 below that at which entrained slag particles will adhere to the tube surfaces and to provide the primary means for regulating superheat, cool flue gas is withdrawn from breeching 90 by a fan 84 which delivers it through ducts 100, 102, 104 provided with control dampers to each end of chambers 80, 82 which extend horizontally on the burner wall, the gas entering the furnace chamber through a number of slots 114, 112, which are of the construction described in Specification 726,244, [Group XIII], and which may each be provided with multi-louvred deflectors so that the gas can be directed upwardly or downwardly into the furnace chamber. The flue gas flows from chamber 80 at high velocity into the stream of furnace gas deflected forwardly by the arch 32, the gases mixing efficiently so that entrained, sticky, slag particles solidify before the mixed gases reach superheater 118. At high loads, the major proportion or all of the recycled gas is injected through ports 114 to ensure that superheater 116 is not contacted by gas at excessive temperature. As the rate of firing decreases and the final steam temperature consequently tends to drop, an increasing percentage of flue gas is directed through the lower velocity ports 112, these ports being disposed between burner rows 60 and 216 so that the flue gas mixes directly with freshly-generated combustion gas to reduce the amount of heat radiated to the furnace wall tubes and thereby increase that available for superheating. At low load the superheat temperature may be maintained by operation of the burners 216. Specification 769,539, [Group XIII], also is referred to.