Patent GB-1052418-A (GB)
IPC: F01K3/22
Abstract: 1,052,418. Forced flow steam generators. COMBUSTION ENGINEERING Inc. March 24, 1964 [March 25, 1963], No. 12503/64. Heading F4A. A combined recirculation supercritical forced through flow steam generator and method of starting and hot restarting the generator, comprises a through flow circuit having first and second heating portions with valve means between them, a recirculation system superimposed on at least the first heating portion having the highest heat absorption during start up, a steam turbine driven main feed pump in series with and downstream of a L.P. motor driven booster pump and a flash tank connected to the pump turbine and to the through flow circuit by a conduit containing throttle means. The steam generator comprises a generating portion 12 (drawings not shown), consisting of economizer 14, centre and outer furnace walls tubes 16, 18, rear gas pass tubes 20 which preferably act as an initial superheater, a superheating portion 10 consisting of sections 22, H.P. and L.P. turbines. 26, 28 and condenser 30 from which pump 32 circulates condensate through demineralizer 34 and de-aerator 38 to booster pump 40 and the main feed pump 46, low, intermediate and high pressure heaters 36, 42, 46 being interspersed in the feedwater circuit. Fluid is recirculated through the tubes 16, 18, 20 via conduit 52 by pump 58 as described .in Specification 1,008,795, and these tubes are separated from the superheating portion 10 by valves 62 across which is connected, in parallel, a flash tank 64 via conduit 66 containing throttle valve 68 and valved conduit 70 connected to the upper part of the tank. The method of starting the generator comprises starting the recirculation pump 58, starting the booster pump to provide a minimum amount of through flow at low pressure, commencing firing, closing valves 62 and adjusting valve 68 to maintain greater than saturation pressure in the generating portion 12, the through flow passing to tank 64 in which the level is maintained by a valve 84 in a return line to the condenser 30. As the temperature rises fluid flashes to steam which is conveyed from tank 64 to the pump turbine 67 thereby starting pump 44 and increasing the fluid pressure until the desired supercritical pressure is reached, the firing rate being gradually increased and more steam produced. When sufficient steam is available it is passed through conduit 70 to the superheater portion 10 and is then used for heating and rolling the turbines 26, 28. When the desired pressure and temperature are attained upstream of valves 62, valves 68, 62 are operated to control the pressure in the generating portion and the flow to the superheating sections 22 as described in Specification 1,052,417, the steam for the pump turbine 67 being transferred first to the superheater outlet and, when a predetermined load is reached, to an extraction point of the H.P. turbine 26. In a hot restart, valves 62 are closed to maintain the high working pressure, e.g. 3500 P.S.I. existing in the generating portion 12, starting recirculation pump 58 and booster pump 40 and passing H.P. steam from the superheater portion 10 to pump turbine 67 to start pump 44 and to lower the pressure in the superheater. Firing is commenced and the fluid being already hot, a portion flashes immediately to steam in tank 64 to replace in turbine 67 steam from the superheater portion 10. The start up procedure is then as described for a cold start up.