GB1005172A - A forced flow once-through vapor generator and method for starting the same - Google Patents

Abstract

1,005,172. Forced flow steam boilers. COMBUSTION ENGINEERING Inc. Nov. 12, 1963 [Nov. 20, 1962], No. 44583/63. Heading F4A. A method for starting a forced-flow oncethrough vapour generator, having means for recirculating heated fluid through the vapour generating section, comprises initially maintaining a liquid level in a primary superheater and thereby obtaining low pressure vapour. In starting a vapour generator comprising economizer 20, vapour generating tubes 24, boiler throttling valves 56, 57, convection superheater 32 and finishing superheater 36 arranged in series together with turbine 40, condenser 14, feed pump 12 and feed valve 18 and having a recirculating circuit 46 containing valve 52, a mixing vessel 48 and a pump 50 for recirculating fluid through the tubes 24, fluid is first pumped through the economizer 20 and tubes 24 and, with valves 56, 57 closed, discharged through a boiler extraction valve 55. When this cleaning operation is completed valve 55 is closed or set to open at a predetermined high pressure, the furnace is fired and when a given pressure is reached valve 18 is closed and liquid is recirculated through tubes 24 to maintain a minimum safe velocity through them. When a given temperature, determined at a point such as 72, is reached, valve 57 is gradually opened by an actuator 62 permitting fluid to flow into superheater 32 which is maintained at a low pressure by a relief valve 75. Some of the fluid vaporizes, cooling the final superheater 36 whilst the remainder establishes a liquid level 58. When a suitable pressure and temperature has been reached as indicated by devices 74, 76, a turbine flow control valve 42 is opened permitting vapour to commence heating and rolling the turbine. Valve 57 is then controlled, to maintain the level 58, by a pressure differential indicating device 60 connected hydraulically or electrically to pressure sensing means 64, 66 until as the temperature in the vapour generating portion rises and normal operating conditions are approached the liquid level 58 falls until no liquid remains in the superheater 32 and the pressure drop across valves 56, 57 as indicated by devices 73 becomes negligible when these valves are fully opened.