GB773107A - Improvements in tubulous vapour generating and vapour heating units - Google Patents

Abstract

773,107. Water-tube steam boilers; regulating superheat. BABCOCK & WILCOX, Ltd. June 22, 1955 [June 22, 1954], No. 18073/55. Classes 123(2) and 123(3) In a water-tube boiler comprising a furnace 10 lined with'steam generating tubes which extend from a water drum 62 to a steam and water drum 60 and fired at a temperature above ash-melting temperature by rows of pulverised fuel burners 12, the molten ash passing through a slag tap 174 in the furnace floor 74 and the combustion gases passing through a gas outlet 14 into an open pass 16 in which they flow downwardly to a gas turning space 18 within a hopper bottom below the open pass and thence upwardly in a pass 20 locating successively secondary superheater tube-banks 22, 24, reheater banks 25...27, primary superheater banks 28...30 and an economiser 32 to discharge to the boiler stack through a flue 36 and air heater 38, superheat temperature is controlled by withdrawing cooled combustion gases from flue 36 through ducts 40...42 by means of a fan 44 which delivers the gas via ducts 46...50 to an inlet chamber 52 at the top of the open pass into which the gases flow through ports provided in the wall of the chamber. The rate of gas recirculation is varied as the load varies, for example in response to changes of steam temperature, steam flow and air flow in the manner described in Specification 675,410, to maintain the final steam temperature at a constant value. The recirculated gas also assists in preventing adherence of molten slag particles to the superheater surfaces by lowering the temperature of the gases in the downpass so that the particles carried by the combustion gas passing through outlet 14 solidify in downpass 16 and are deposited in hopper 18 from which they fall into a collection pit 112. Specification 526,825 also is referred to .