GB1052385A - - Google Patents

Abstract

1,052,385. Steam generators. COMBUSTION ENGINEERING Inc. Nov. 12, 1963 [Nov. 20, 1962], No. 44585/63. Heading F4A. In a method of starting a forced flow once through vapour generator in which initially fluid is recirculated through the vapour generating section and a primary superheater, pressure and temperature conditions at the outlet of the primary superheater are accurately measured in a section of the recirculation circuit and the flow to a finishing superheater commenced and controlled in accordance with said conditions to ensure that all the fluid flashes to vapour before entering the finishing superheater. The vapour generator heated by combustion gases consists of a feed pump 12, Fig. 1 (not shown), supplying fluid from a deaerator 14 through a preheater 18 and an economizer 22 to a vapour generating section 24 and primary and finishing superheaters 26, 28 from which vapour passes through a turbine 30 to a condenser 32 with a shut-off valve 55 and a throttling valve 56 arranged in parallel to control the flow between the superheaters 26 and 28. The starting method consists of closing valves 55, 56 opening boiler extraction valves 51, 52 in an extraction line 50 to the condenser, supplying vapour from an auxiliary source 38 to the deaerator 14 and circulating fluid through section 24 and superheater 26 whilst the generator is being fired until the clean-up operation is completed. A feed valve 20 is then closed and with valve 51 set to open only at a given relief pressure, fluid is recirculated by pump 48 through section 24 via conduit 44 and through the superheater 26 via conduit 60. At the same time the turbine is heated and rolled by vapour from the source 38 which first cools the superheater 28. The flow through conduit 60 allows the temperature and pressure before valves 55, 56 to be accurately measured. When conditions ensure the complete flashing to vapour of the fluid, the control element 68 commences to open valve 56, feed valve 20 is opened to pass an equivalent flow to section 24 and the auxiliary vapour flow is reduced by closing valve 42. This continues until the pressure drop across valve 56 becomes negligible when valve 55 is opened and valve 42 closed to establish normal operating conditions. In another embodiment, Fig. 2 (not shown). auxiliary vapour is not used, vapour for cooling superheater 28 and starting turbine 30 being produced by flashing liquid leaving superheater 26 through valve 56.