Improvements in or relating to steam power installations including forced-flow, once-through boilers

摘要

946,406. Controlling forced flow steam boilers. SIEMENS - SCHUCKERTWERKE A.G. July 4, 1960 [July 3, 1959], No. 23373/60. Heading F4A. In a steam power plant including a forced-flow, once through boiler of which the supply of fuel and air to the boiler furnace and the supply of feedwater are separately controlled, there being automatic means for ensuring that the rate of supply of feedwater corresponds to the rate at which steam is withdrawn from the superheater as required by the load on the boiler, no direct measure of the rate of flow of superheated steam is made but means are provided to give controlling signals dependent on said rate, for example, signals which are derived from outlet superheater pressure, turbine regulating oil pressure or from the electrical output of the turbo-generator. As shown in the drawing, a feed pump 11 forces water through a regulator valve 12 and rate-offlow constriction 13 into the boiler tubing which consists of economizers 14, 15, evaporators 16, 17, and a superheater 18. At a point 52 between the evaporators 16, 17 the pressure is measured and a pressure dependent signal P 1 is obtained. Feedwater is injected into the tubing after the evaporator 17 under the control of a valve 33 the setting of which is controlled by steam temperature signals obtained at points T 1 , T 2 at the inlet and outlet respectively of the superheater 18. The steam pressure is also measured at the superheater outlet at 53 and a signal P 2 is obtained, this signal acting to correct the signal P 1 when load variations occur. The steam passes through a valve 20 to the high-pressure stage 21 of a turbine and then to the low-pressure stage 23 by way of a reheater 20A and the valve 20. The steam exhausts into a condenser 24 whence condensate is pumped into an accumulator 30. A pump 31 draws water from the accumulator and returns it to the boiler through a bled steam heater 25. The valve 20 is controlled by a load dependent signal u derived from the turbine regulator 65 to which is applied a signal representative of turbine speed derived at 67. A signal e derived from changes in the pressure of the oil in the turbine regulating system passes to the boiler load-setting device 35. The load-setting device emits a load-dependent signal a which is passed to a control device 36 controlling the speed of the feed pump 11, the control device also receiving a signal representative of the ratio between the rate of flow of injected water measured at an orifice 61 and the rate of flow of the main feedwater stream measured at 13. The coal feed to the furnace is regulated according to variations in the steam pressure P 1 as corrected by P 2 , the air supply being adjusted either manually or automatically according to measures of O 2 or CO 2 . A load variation limiter 62 is provided to prevent unallowably high temperature changes in the turbine. Specification 896,502 is referred to.