GB753825A - Feed systems for steam generators - Google Patents

Abstract

753,825. Centrifugal pumps. SULZER FRERES, SOC. ANON. Nov. 5,1954 [Nov. 20, 1953], No. 32086/54. Class 110(1) [Also in Group XXIX] A feed system for a steam generator comprises at least one centrifugal pump, a control valve on the delivery side of the for the control valve arranged to close the control valve when pumping ceases and to re-open the control valve after a time delay when the pumping is restarted. In the system shown, centrifugal feed water pumps 8, 9 driven by electric motors 2, 5 respectively, discharge through respective non-return valves 13, 17 and stop valves 14, 18 to a pipe 15 and thence by way of a delivery pressure control valve 19 and a flow-metering valve 20 to a steam generator 21. After driving a turbine 22, the steam is condensed in a condenser 24 and returned to the feed water tank 10. Valve 20 is controlled by means (not shown) from a measuring point located after, and preferably adjacent, a heating surface of the steam generator 21. During normal operation, valve 19 is controlled in accordance with the pressure drop across valve 20. For this purpose, the pressures upstream and downstream of the valve 20 are communicated through pipes 26 to a servomotor 27 to determine the position of a spring-loaded piston 28 in relation to a pressure fluid supply pipe 31 and a discharge pipe 30, thereby controlling the pressure applied by way of pipes 32, 34 to a servomotor 35 to control the position of a spring-loaded piston 36 relative to a pressure fluid supply pipe 38 and discharge pipe 39, whereby a control pressure is applied through a pipe 40 to a servomotor 41 which actuates the valve 19. The valve 19 may be manually adjusted by a means 43, independently of the automatic regulation. If both pumps 8, 9 are put out of operation by opening both of the switches 3, 6 which control their driving motors, auxiliary switches 44, 45 associated with the switches 3, 6 are closed. Current is then supplied from a transformer 47 through the switches 44, 45 in series to energise a solenoid 46 which raises the piston 48 of a valve 33 to disconnect the pipe 34 from pipe 32 and connect it instead to a pressure fluid supply pipe 49, thereby closing the valve 19. If one of the pumps, say pump 8, is started up, the switch 44 opens to de-energize the solenoid 46. The resultant drop of the piston 48 is retarded by an oil dashpot comprising a piston 50 and a by-pass 53 containing a restricted orifice 54. There is thus a time delay which permits the pump 8 to run up to full speed before the valve 19 opens, thereby preventing overloading of the pump. If the second pump 9 is later brought into operation, the non-return valve 17 remains closed so long as the discharge pressure of pump 8 is greater than that of pump 9, so that overloading of pump 9 is prevented. A non-return valve 52 in a by-pass 51 opens during upward movement of piston 50, so that actuation of valve 33 to close the valve 19 is not subject to the aforementioned time delay. The oil dashpot may be replaced by a time delay relay in the electrical circuit, and the whole control could be worked electrically, the valve 33 being replaced by a relay. Alternatively, the solenoid 46 and the associated electrical circuit could be replaced by a hydraulic circuit for operating the piston 48. The electric motors 2, 5 could be replaced by turbines, the starting and stopping of the pumps being done by a coupling such as a hydraulic coupling between a driving turbine and a pump. There may be more than two feed pumps. Valve 20 may be replaced by a fixed orifice.