GB993146A - Improvements relating to turbine power plants incorporating forced flow once throughsteam generating units - Google Patents

Abstract

993,146. Forced flow steam boilers. RILEY STOKER CORPORATION. June 26, 1961 [June 27, 1960], No. 23066/61. Heading F4A. In a steam power plant having a forced-flow, once through boiler supplying steam to a high-pressure turbine and a low-pressure turbine of greater capacity than the H.P. turbine, separate feedwater lines connect to the inlets of the boiler economizer and evaporator and the outlet of the economizer has a normally closed valved connection to the inlet of the reheater, the valve being opened at peak load so that additional steam is generated for the low-pressure turbine. In the form shown the generator has a radiation chamber lined with evaporator tubes 28 and primary superheater tubes 29 and locates in its upper part pendant platens of secondary superheater tubes 30 and secondary reheater tubes 31. Gases from the chamber flow downwardly in a divided pass the sections of which respectively contain the low temperature section 19 of an economizer and a primary reheater 14. Two feedwater pumps 11 are connected through a valve 24 to a spray attemperator 23 between superheaters 14 and 30, and through a feed regulator 13 to the economizer inlet header 18 and to the evaporator inlet header 17, the latter connection being made through a pipe controlled by a throttling valve 16. The economizer which has a high-temperature section in the boiler furnace, discharges into a collecting header 21 whence a pipe 25 with a non-return valve 27 conveys the heated water to the evaporator inlet header 17 and through a branch pipe to an intermediate part of the evaporator 28. Steam from the evaporator discharges into a mixer 26 whence it flows through the superheaters 29, 30 and pipe 32 to the H.P. turbine 35. Partially expanded steam returns through the reheaters 14, 31 and flows to the L.P. turbine 36, the turbines driving an electric generator 37. The header 21 is connetted to a header in the pipe between the reheaters 14, 31 by a pipe controlled by a valve 22. In operation under normal load conditions the boiler performs as a conventional reheat unit, superheat temperature being controlled by spray attemperation at 23 according to indications of temperature in pipe 32 whilst reheat temperature is controlled by proportioning dampers controlling gas flow through the downpasses according to indications of temperature in the pipe 33. A controller 15 maintains the ratio of water supplied to the economizer and water supplied to the attemperator constant in the manner described in Specification 993,145 whilst steam output is controlled according to fuel input, the latter being controlled in response to signals received from a wattmeter 38. When a higher than normal load demand is encountered, the wattmeter 38 calls for an increased firing rate. The resulting increase in steam temperature causes an increase in feedwater flow and simultaneously the valve 16 is opened permitting a portion of the feedwater to flow directly to the evaporator. The economizer now acts as an evaporator and when steam generated therein reaches a predetermined temperature, the valve 22 opens admitting the steam to the reheater 31, the valve 22 acting as a reducing valve to give the appropriate pressure. When the valve 22 opens the pressure drop in the pipe 25 causes the non- return valve 27 to close. Thus at peak loads the reheater flow is increased by steam generated in the economizer.