GB739489A - Improvements in or relating to tubulous vapour generating and vapour heating units and a method of operating such units - Google Patents

Abstract

739,489. Water-tube steam boilers; steam superheaters. BABCOCK & WILCOX, Ltd. Jan. 14, 1954 [Jan. 16, 1953], No. 1368/53. Classes 123 (2) and 123 (3). In a steam boiler as described in Specification 738,092 comprising a vertical furnace chamber 1 from the top of which combustion gases flow through a lateral opening 19 and then successively through a horizontal pass 60 locating convection superheater sections and three parallel, damper-controlled downpasses 61a ... 61c locating, in the middle pass 61b a reheater and in the outer passes 61a, 61c, further superheater sections, slagging and overheating of the tubes in the middle regions of the superheater sections in pass 60, which would otherwise occur due to the high temperature of the central part of the furnace gas stream flowing through opening 19, which central part has been screened whilst in the furnace chamber by the outer, partially opaque, parts of the flame, is prevented by mixing with this high-temperature central part cooled, recirculated flue gas in sufficient quantity to lower its temperature to that at which the gas may be allowed safely to impinge on the tubes. The flue gas is withdrawn from the bottom of the downpass extension 85 through a flue 206 and delivered by a fan 330 through two ducts 301 leading one into each end of a windbox 300 disposed on the front wall 3 of chamber 1 opposite the opening 19. As shown in Fig. 3, the windbox is divided internally into seven sections 310 ... 316, the admission of gas to each section being controlled by a damper 320. Each section has an aperture group, numbered 303 ... 309 respectively, through which the flue gas flows to mix with the stream of furnace gas entering pass 60 at 19. In operation, excessive temperature of the core of the furnace gas stream is corrected by admission of flue gas firstly through aperture 306 and then, if necessary, because for example of an increased firing rate, through apertures 305, 307; 304, 308 and finally 303, 309. The distribution of flue gas between the apertures and regulation of the quantity of gas recirculated may also be used in conjunction with the adjustment of dampers at the bottoms of the three downpasses 61a ... 61c to control reheat and superheat temperatures.