GB862183A - Improvements in tubulous vapour generating and superheating units - Google Patents

Abstract

862,183. Forced-Sow steam boilers; regulating steam temperature. BABCOCK & WILCOX Ltd. July 1, 1957 [July 2, 1956]. No. 20722/57. Classes 123(2) and 123(3) A forced-flow, once-through steam boiler operating at supercritical pressure has a vertical tube-lined setting of rectangular cross-section providing a furnace chamber A and a superjacent convection, gas-cooling chamber B. The furnace A has a small volume lower portion 14 the lining tubes of which are refractory covered and into which discharge combustion gases and molten slag from eight cyclone furnaces 10 arranged four on each side, the cyclone furnaces being generally as described in Specification 552,747. Molten slag flows from the furnace portion 14 through openings 21 into a tank 21a whilst hot gases rise into an upper furnace portion 26 of larger volume, the lining tubes of the upper portion being bare. The convection, gas cooling chamber B is separated from the upper furnace 26 by tube screens 27, 27a, which rise vertically to divide the chamber into three passes 30, 31, 32 containing respectively a second stage reheater 37 and economizer 38, a first stage reheater 36 and economizer 39 and a primary superheater 35 and economizer 40. A secondary superheater 28 spans the entire setting below the three gas passes, the gas flows through which are respectively controlled by outlet dampers 41, 42, 43. The three gas streams unite above the dampsrs for flow through an air heater 45 to. a stack, some of the cooled gases being withdrawn by a fan 47 and recirculated to the furnace through ducts 49 leading to distributing chambers 50, 51 from which gas nozzles open into the furnace adjacent the junction of the lower and upper portions 14, 26. The recycled gas mixes with and tempers the fresh ,gases from the lower furnace 14 to control the gas temperature entering the chamber B to a value below the ash fusion temperature and to lower the heat input rate to the bare wall tubes of the upper furnace so that the transition zone may be located in these tubes. Water at 4,500 lbs./sq. in. passes from the econmizers 38, 39, 40 through the cyclone furnace wall tubes and the wall tubes of the furnace portion 14 into the wall tubes lining the portion 26, where it is converted into steam. The steam passes successively through support tubes 60, see below, the primary superheater 35, an interstage attemperator, preferably of the type disclosed in Specincatiion 656,551, and the secondary superheater to the point of use. Superheat is controlled by regulating the gas recirculation and attemperation rates and reheat by adjustment of the proportioning dampers 41, 42, 43. The unit is top supported by upright girders 57 and upper and lower cross beams 58, 59. The heavy cyclone furnaces are not supported by the wall lining tubes however, but by the support tubes 60 which are hung from the cross beams 59 and carry cross beams 61 on which the furnaces are mounted on ball bearing supports to allow for their transverse movement. The support tubes 60 carry steam at a temperature near the mean temperature of the furnace walls so that the downward expansions of support tubes and walls are approximately equal. This method of supporting the unit is also described and is claimed in Specification 862,184.