GB758833A - Improvements relating to forced flow, once-through tubulous vapour generating and superheating units and to a method of regulating temperature of superheat - Google Patents

Abstract

758,833. Fluid-pressure servomotor control systems. BABCOCK & WILCOX, Ltd. Sept. 29, 1954 (Sept. 30, 1953], No. 26850/53. Class 135. A forced flow, once-through tubulous vapour generating and superheating unit comprising a plurality of parallel vapour generating and superheating circuits each provided with a spray attemperator automatically regulating superheated vapour temperature in the circuit is provided with means for comparing the rates of flow of attemperating liquid to the different attemperators and with means for controlling the relationship between the rates of flow of feed liquid to the parallel circuits. In an embodiment, the feed pipe 1 is branched to two parallel circuits, each of which includes an economizer 4, steam generator 5, 6, superheater 7 receiving its heat by radiation, spray attemperator 22, and convention superheater 8, and the outputs from the two circuits are combined in a single pipe 2. Control impulses representative of the pressure and temperature of the steam at the outlet are derived from measuring devices 9, 10, respectively, and utilized in the actuation of valves 13, 15, controlling, respectively the total supply of feed water and the rate of firing. The water supply 21 to each attemperator is branched from the feed line to the circuit in which the attemperator is situated. The final temperature of steam in each circuit is measured and applied to the actuation of a control valve 24, of the type described in Specification 425,507, [Group XII], and this valve controls a servomotor actuating a valve 23 which regulates the supply of water to the attemperator. The flow of water in each circuit of the unit, less the flow branched to the attemperator along line 21, is measured and applied to a pilot valve 31, and the two pneumatic pressures produced by the pilot valves are applied to separate bellows 33, 33<SP>1</SP>. The latter act on levers 34, 34<SP>1</SP>, respectively, and the resultant differential movement of the levers actuates a pilot valve 41 of which the output pressure is applied to a relay 43 of the kind described in Specification 461,389. The relay controls the adjustment of a valve 46 regulating the total flow of water fed to one of the parallel circuits. The flow in the other circuit is controlled by a preset valve 46<SP>1</SP>. The flow of water in each attemperator line 21 is measured and, by means of pilot valves 17, two pneumatic pressures indicative of the flows are obtained and applied to separate bellows 47, 47<SP>1</SP>, and also to separate needles on an indicator 28. The differential of the pressures in bellows 47, 47<SP>1</SP> is applied through a pilot valve 49 and relay 51 to a spring-loaded bellows 53 which varies the position of. an abutment movable between levers 34, 34<SP>1</SP> to adjust the relationship between the flows of feed water to the two parallel circuits in the generator. Specification 744,797, [Group XII], also is referred to.