GB1028509A - Apparatus and method for operating a vapor generator at subcritical and supercritical pressures - Google Patents

Abstract

1,028,509. Steam generators operable at subcritical and supercritical pressures. COMBUSTION ENGINEERING Inc. Dec. 14, 1964 [Dec. 23, 1963], No. 50892/64. Heading F4A. A vapour generator is adapted to be operated as a combined circulation or once through forced flow generator at supercritical pressure and alternatively as a controlled or natural circulation generator at subcritical pressure. In the embodiment shown, under supercritical operating conditions at high load, feedwater from condenser 30 is delivered by feed pump 33 into economizer 12a to pass into steam and water drum 14a, which in this case acts only as a mixing vessel, to mingle with a small recirculated quantity of a working medium from furnace radiant tubes 18a returned through conduit 26a. From the steam and water drum 14a the medium flows through the furnace tubes 18a under the action of recirculating pump 16a, after which the small recirculated portion passes back to the steam and water drum 14a via conduit 26a, while the remaining through flow quantity passes through open valve 34 in conduit 19a to the superheater 21a and turbine generators 36. Under these conditions valve 35 in conduit 38a is kept closed to prevent medium flow from steam and water drum 14a direct to superheater 21a. Under subcritical operating conditions the generator acts a controlled circulation steam generator, valve 34 being shut and valve 35 opened, so that feed water from economizer 12a passes into the steam and water drum 14a, the water from the drum 14a being circulated by pump 16a through evaporator tubes 18a, the resultant steam/water mixture all passing via line 26a back to the steam and water drum 14a. The separated steam then passes via line 28a to the superheater 21a whilst the water mixes with the incoming feed water to be recirculated through the evaporator tubes 18a. In the embodiment of Fig. 3 (not shown), a valve is included in the line from the furnace tubes outlet to the steam and water drum which valve is kept closed during supercritical pressure operation to give a forced-flow once through circulation. Also no recirculating pump is included in the circuitry so that during subcritical pressure operation a natural circulation of the steam/water mixture occurs. A single three-way valve (Fig. 1, not shown), may replace the combinations of valves used in the preceding embodiments.