GB1008792A - Forced flow, once through vapour generators - Google Patents

Abstract

1,008,792. Forced flow steam boilers; regulating steam temperature. SULZER FRERES S.A. July 27, 1962 [July 27, 1961], No. 29026/ 62. Heading F4A. In a forced-flow, once-through steam boiler operating with reheat and at subcritical or supercritical pressure and having two independently-fired furnaces the outer walls of which are lined with parallel-connected heat exchange tubes and which are separated by a tubulous partition of parallel-connected heat exchange tubes, the furnaces discharging gases into a common pass, the wall lining tubes and partition tubes and further heat exchange surfaces in the gas pass are serially connected for flow of the working medium and the or each reheater is exposed primarily to the gases produced in one of the two furnaces. As shown in Fig. 1 the boiler has a pair of furnaces 12, 14 respectively fired by tangential tilting burners 16, 18 and discharging gases into a common gas pass 20. Water is supplied by a pump 22 through a regulator valve 24 to an economizer 26 in the gas pass. From the economizer it flows through a mixing vessel 30, a recirculating pump 32 and a lower header 34 to enter the tubes 38 lining the outer walls of the furnaces. The tubes are diametrically finned and welded together. Steam or steam-water mixture flows from the tubes into a header 40 and thence through lines 42 and a header 44 to enter the partition tubes 48 which may also be welded together or may be contiguous and unwelded. From these tubes steam flows serially through superheaters 54, 58 to a turbine 62. First and second stage reheaters 66, 72 are disposed in the gas pass 20 so as to be substantially wholly in the flow of gases from the furnaces 12 and 14 respectively. Reheat temperature is controlled by independently adjusting burner tilt in or gas recirculation to the two furnaces and the range of control may be extended by differentially firing the furnaces. When starting or at low loads when the flow velocity in the wall lining tubes 38 and partition tubes 48 is below a critical value, a recirculation of working medium through these tubes is superimposed on the through-flow system by starting the pump 32. In a modification, Fig. 9 (not shown) there is a single stage of reheat, the reheater being aligned with the gas flow from the furnace 14. In this installation the major portion of the superheater is aligned with the gas flow from the furnace 12.