GB840728A - Improvements in tubulous vapour generating and vapour heating units and a method of operation thereof - Google Patents

Abstract

840,728. Controlling steam temperature in boilers. BABCOCK & WILCOX Ltd. Aug. 16, 1956 [Aug. 16, 1955], No. 25108/56. Classes 123(2) and 123(3) A water-tube boiler comprises two radiation chambers 12, 14 from which gases pass upwardly through parallel passes 16, 18, the chambers and passes being separated by a tube wall 10. The chambers 12, 14 are respectively supplied with hot gases from cyclone furnaces 20, 22, for example of the type described in Specification 598,141, the furnaces firing into secondary furnaces 42, 24 from which the gases discharge into the radiation chambers 12, 14 respectively through screens 86, 84. The chambers 12, 14 and the passes 16, 18 are lined with steam generating tubes which, with the tubes of the wall 10 and of the secondary furnace walls 50, 52, extend between headers 60, 70, 80 and 68, 76, 110, the latter being connected to a steam and water drum (not shown). The pass 16 locates an economizer section 124, a primary superheater 136 and a section 148 of secondary superheater whilst in the pass 18 are disposed other economizer sections 128, 130, a reheater 160 and the other section 152 of the secondary superheater. An attemperator 142, preferably of the spray type described in Specification 656,551, is inserted in the line between the superheaters 136, 148. The unit includes a gas recirculation system for regulation of the superheat and reheat temperatures, cooled flue gases being withdrawn through openings 26, 28 at the tops of passes 16, 18 by a fan 32 which delivers them through ducts 36, 46 controlled by dampers 202, 200 to wind boxes 34, 44 provided with openings into the secondary furnaces 24, 42 distributed across the entire width thereof and also through ducts 224, 226 controlled by dampers 220, 222 to windboxes 228, 230 located within noses projecting from the division wall 10 into the chambers 12, 14 respectively, the noses having openings 96, 104 distributed across the width of the chambers through which the flue gas is injected into a region adjacent the inlets to the respective passes 16, 18. In the operation of the unit, as the rate of steam generation decreases, the dampers 200, 202 are automatically or manually adjusted according to changes in load or superheat temperature to increase the flow of flue gas into the furnaces 42, 24 and thereby to maintain the superheat temperature at the required value and the dampers 220, 222 are simultaneously adjusted to proportion the flow of recirculated gas as tempering gas between the passes 16, 18 to maintain the reheat temperature at the required value. The latter control may be supplemented in the lower load range by adjustment of dampers 204, 210 at the outlets of the passes. At and near full load these dampers are kept wide open thus reducing draught loss in the unit whilst superheat and reheat temperatures are regulated by the gas recirculation system.