GB793341A - Improvements in or relating to apparatus for regulating a forced-flow, once-through boiler - Google Patents

Abstract

793,341. Forced-flow steam boilers; controlling superheat. SIEMENS-SCHUCKERTWERKE AKT.-GES. June 27, 1956, No. 19943/56. Classes 123(2) and 123(3) A forced-flow, once-through steam-boiler comprising an evaporating section from which steam flows through successive superheaters 1, 2 to a turbine 4 driving a generator G is regulated under sharplychanging loads by variation of the firing rate and of the settings of the main feedwater valve 9, of a valve E1 which controls the amount of water injected into the boiler tubing at a point e1 between the superheaters 1, 2 and a valve E2 which controls the amount of water inpected at e2 between the evaporating section and the superheater 1. The setting of the valve E2 is controlled according to changes in boiler load, whilst valve E1 is controlled through a regulator device f according to changes in steam temperature measured at points t2, t3 located respectively before and after the superheater 2. If, for example, the demand on the generator G suddenly increases, the main turbine regulator h causes a valve 3 to open to admit more steam to the turbine. Impulses r, x representative of steam pressure variation and generator output respectively are transmitted through a boiler load setting device g to regulating devices, a, b, c which respectively effect appropriate increases in the amounts of air, feedwater and fuel fed to the boiler. To satisfy the demand for extra steam during the time when the increased supply is traversing the evaporating tubes, and thus to avoid a temporary drop in pressure at the boiler outlet, the load setting device g also causes the valve E2 to open further to admit an increased quantity of water to the superheater 1 wherein it evaporates by adsorption of heat from the tube system to supply the extra steam required. The resulting reduction in steam temperature is offset by the closing of the valve E1 to reduce the amount of water injected at the point e1. When the increased quantity of feed- - water has advanced to the injection point e2, a time delay element Z3 cancels the control order to the valve E2 and the boiler operates normally at the higher load.