GB778712A - Improved tubulous vapour generating and superheating units - Google Patents

Abstract

778,712. Regulating superheat in steam boilers. BABCOCK & WILCOX, Ltd. Aug. 4, 1955 [Aug. 5 1954], No. 1113/57. Divided out of 778,711. Class 123(3) In a water-tube steam boiler comprising a vertical steam generating tube-lined furnace 10 from the upper part of which hot gases flow through a lateral pass 32 locating a secondary superheater 40 and then downwardly in a pass 46 containing a primary superheater 115 and an economizer 133 and wherein steam temperature is regulated at loads below the design load by recirculating cooled flue gas at an appropriate rate from the bottom of the-downpass 46 into the bottom of the furnace, the flue gas is withdrawn through a duct 142 controlled by a damper 143 by a fan 144 which delivers it through a duct 146 controlled by a damper 145 to two ports 148 formed by off-setting some of the tubes lining the rear wall 28 of the hopperbottom of the furnace. To give uniform gas distribution between the ports 148 the duct 146 is divided into two branches 160, 162 leading to the respective ports, division plates 172, 174 being disposed within the branches. In order to prevent the reverse flow of furnace gases through the recirculating system when the latter is inoperative, the four flow paths through the duct branches 160, 162 are connected by respective conduits 155 with the cold air inlet of the air heater of the boiler, i.e. with the outlet of a forced draught fan, the control of air flow from each conduit being effected by a damper 157 normally closed when the gas recirculation system is in operation.