GB1306659A - Steam generators - Google Patents

Abstract

1306659 Steam generator SULZER BROS Ltd 31 Dec 1971 [31 Dec 1970] 61047/71 Heading F4A A steam generator employs both forced flow and natural circulation of water which is first circulated by forced flow through a set of evaporator tubes in a hot gas flue and is then allowed to flow by natural circulation through the vertical tubes which form, at least in the region of the hot gas inlet, the walls of the flue. Hot gases pass through the flue 34 from muffle burners 70 to outlet 75 and a feed pump 17 supplies water, via economizer 3, header G, and support tubes 8, to a first evaporator surface 12. The steam water mixture passes along 14 to separator drum 15, and the water flows by natural circulation through downcomer 20 and, via headers 31, 41, up through the welded tubes forming the walls 31, 33, 42. Steam passes from the drum 15, via 50, through super-heaters 51, 55, 59 before being discharged through 60, and water from the downcomer 20 is injected between the stages at 53, 58 to produce more steam. Alternatively feedwater may be employed in the superheater injectors. The forced flow section produces at least 30% and preferably about 50% of the steam, the natural circulation section less than 40% and the injectors can produce at least 20%. As shown the water from downcomer 20 is passed by a circulating pump 22 to header 6 for recirculation downstream of the economizer 3, but in a further embodiment (Fig. 2, not shown) this water is fed to a reservoir (4) and then pumped to the inlet of the economizer, The water entering and leaving the reservoir are passed through a heat exchanger (2) so that the former may heat the latter. Moreover a level sensing device in the drum, and a flow rate sensing device in the reservoir outlet can operate valves to adjust the rate of flow into and out of the reservoir.