Patent GB-997549-A (GB)
Title: Combined circulation steam generator and method of initiating its operation
IPC: F22B29/02
Filed: 1964-02-18
Abstract: 997,549. Forced flow steam boilers. COMBUSTION ENGINEERING Inc. Feb. 18, 1964 [March 25, 1963], No. 6691/64. Heading F4A. A once through forced flow steam generator having a main fuel pump driven by steam from an auxiliary boiler during start up and fluid recirculation through the portion of the generator having the highest heat absorption comprises an economizer 12, tube lined furnace centre and outer walls 14, 16, gas pass walls 18 and a series of fluid heaters 20 consisting of sinuous inter-nested tubular panels. Steam passes from the heaters 20 through H.P. and L.P. turbines 28, 34 to condenser 38 from which condensate passes to a demineralizer 44, L.P. feedwater heaters 46, de-aerator 48, motor driven feedwater booster pump 50, intermediate pressure heaters 52, main feed pump 54 driven by steam turbine 88, H.P. feedwater heaters 56 and re-enters the generator via feedwater control valve 10. Fluid is recirculated through the furnace wall sections 14, 16, 18 and conduit 58 connected to a mixing vessel 60 downstream of economizer 12 by a pump 62. Suitable valves 64 are placed upstream and downstream of the pump which is bypassed by conduit 66 containing a check valve 68. Boiler throttle and boiler throttle bypass valves 70, 72 are provided immediately before the heaters 20 and a flash tank 76 is connected up and downstream of these valves by conduits 74, 80 containing reducing valve 78 and control valve 82, the lower portion of the tank being connected to the hot well of the condenser by conduit 84. The method of starting comprises filling the generator by means of pump 50 to the level of valves 70, 72 which are closed, starting the recirculating pump 62 and circulating about 10% of maximum flow through the portion of the generator upstream of valves 70, 72 and through conduits 74, 84 with pump 54 and commencing heating. Pump 54 is driven by turbine 88 supplied with steam from an auxiliary boiler 90 normally provided to supply steam for turbine sealing (through conduit 94), soot blowing, air preheating &c. The valve 78 maintains a relatively high pressure in the generator and as the fluid heats up a portion flashes to steam in the tank 76. This is passed through conduit 80 to the fluid heaters 20 and when the quantity and pressure is sufficient is admitted to the turbine to heat, roll and synchronize the turbine. As the fluid temperature rises valves 70, 72 are opened and valve 78 is closed. The turbine 88 is supplied with steam from boiler 90 until the temperature and pressure of the steam produced by the generator are at least equal to those of the auxiliary boiler steam. Generator steam is initially supplied through conduit 104 until the main generator load exceeds, for example, one third of maximum load, when for greater efficiency H.P. steam extracted from the turbine 28 is used, being conveyed to the pump turbine via conduit 108. Normally, at loads below one third of maximum, steam is supplied to the turbine through conduits 104, 112 in parallel. The turbine 88 may be of the condensing or non-condensing type with exhausted steam returned to the de-aerator.