GB861583A - Improvements relating to forced recirculation steam generators - Google Patents

Abstract

861,583. Valves. VORKAUF, H. Jan. 13, 1958 [June 24, 1957], No. 1176/58. Class 135. [Also in Groups XIII, XXVI and XXXV] A forced recirculation steam generator of the type (not illustrated) in which the working medium is circulated through the heating surface in quantities in excess of the evaporation by means of a constant-speed centrifugal pump which draws water from a steam and water drum and delivers it to the heated boiler tubes, is provided with a regulating or throttling device arranged in a suction or delivery pipe of the water circulating pump and adapted to operate in response to variation in " water condition," so to regulate the water flow as to maintain the power consumption of the pump at an approximately constant level, the term " water condition " being defined as the pressure and/or corresponding temperature of the water in circulation at any operating condition from cold start-up until full boiler operating pressure is reached. Three forms of the device are shown in Figs. 1, 2 and 3, respectively. In Fig. 1, a throttling gate member 4 in the suction or delivery pipe 1 of the pump is spring-loaded in the direction to throttle the flow and the water pressure has direct access past this member to an actuating-piston 3, so that the throttling effect is lessened and flow increased as the boiler pressure rises, thereby maintaining the power consumption of the pump approximately constant. At full boiler pressure, the piston 3 can seat itself on a seat 7 and prevent the leak-off of boiler water through a pipe 6 which otherwise functions as a drain connection. In Fig. 2, a butterfly throttle valve 9 in a pipe 8 of the pump is responsive to water temperature, being actuated by an expansion bar 11 pivoted to the valve 9 at 12 and to the pipe 8 at 13, this bar having a higher linear expansion than the pipe so that on rise of temperature the valve opens to lessen the throttling effect, and again the power consumption of the pump is kept constant. It is stated that the valve 9 and expansion bar 11 may be fitted in separate pipes through which the working medium is circulated, the two members being connected together through a linkage. In Fig. 3, the pump is driven by an electric motor (not shown) and a throttling- member 14 in the suction or delivery pipe is actuated through gearing 16 by a reversible electric motor 17, in response to variations of power current supplied to the pump driving motor, this current acting through a coil 18 on an armature 20 against a spring 19 to make and break alternately contacts 21, 24 and 22, 23, respectively, in the circuit of the motor 17 so that a fall in power consumption as the boiler temperature or pressure rises results in a reduction of throttling by the member 14 to increase the flow, and vice versa, whereby the power consumption is again maintained at an approximately constant level.