GB816765A - Steam power plants - Google Patents

Abstract

816,765. Forced-flow steam boilers. SULZER FRERES S. A. Nov. 6, 1957 [Nov. 22, 1956], No. 34640/57. Class 123(2) In a steam power plant comprising a once-through boiler 1 having an economizer 8, an evaporating section 9 and a superheater 12 supplying steam to a turbine having two stages 2, 3 between which is a reheater 5 and from which the exhaust steam flows into a condenser 6 whence condensate is pumped into a feed water tank 19 from which a feed pump 7 returns the water to the economizer, salts removal from the working medium is achieved without much loss of thermal efficiency by providing for multiple stage evaporation of the water withdrawn from the system with return of heat from each evaporation stage to an appropriate point in the system. Under normal working conditions wet steam from the evaporator 9 flows into a separator 10 in which a low level of separated water is maintained by a measuring device 23 which controls a water outlet valve 22, the device being set so that about 4 per cent of the working medium flows through the valve and via a line 20 to a second separator 21. In the separator 21, which is at a lower pressure, steam is evolved and flows through a pipe 30 to the reheater inlet. Water, representing about 2.5 per cent of the working medium flow passes through a valve 31 controlled by a low level measuring device 34 and through a pipe 32 to a lower pressure separator 33 where the final stage evaporation occurs, steam passing through a line 41 to the tank 19 whilst water, representing about 0.5 to 1.0 per cent of the working medium flow and containing dissolved salts, passes to a total salts removal plant through an orifice plate 42. The arrangement also provides for the withdrawal of the large amounts of water from the boiler which is necessary when starting up or during no-load operation. For this purpose, valves 27, 38 of larger diameter than the valves 22, 31 are provided in pipes 37, 26 respectively branching from the separator outlet pipes 20, 32. The valves 27, 38 are respectively controlled by measuring devices 28, 39 to maintain a high level in the separators 10, 21. The pipes 37, 26 unite in a common connection to a cooler 26a whence steam and water flow to the condenser 6. In a modification, the invention, which is described above in its application to a boiler operating at sub-critical pressure, is applied to a boiler designed for operation at supercritical pressure, the amount of working medium withdrawn from the tube system being regulated in dependence on the temperature of the medium at an appropriate point instead of the height of a water level.