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

摘要

896,502. Controlling forced-flow steam boilers. SIEMENS-SCHUCKERTWERKE A.G. July 31, 1958 [July 31, 1957(2); Nov. 16, 1957], No. 24776/58. Class 123(2) In a forced-flow, once-through steam generator comprising a feedwater pump 2 supplying water through an external high pressure preheater 3 to a preheater 4 whence it flows through and is evaporated in tube sections 6, 7, the steam being superheated in sections 8, 9, 10 and passing through a stop valve 12 to a turbine 11, the rate of flow of feed supply is controlled to correspond with the rate of steam output whilst the rate of firing of the boiler is separately controlled according to other variables such as steam pressure at the boiler outlet or at a point between the superheaters. As shown in Fig. 1, flow-measuring constrictions M 1 , M 4 are situated at points 27, 28 and give rise to signals M 1 1, M 4 1 which are compared in a device 30. The output signal from this device, corrected by temperature-dependent signals taken from points 32, 33, which signals are increased as the flow measured at point 34 and represented by a signal M 2 1 increases and vice versa, is passed to the feed pump 2 through a line 31, the signal being effective to increase or decrease the pump speed to bring the signals M 1 , M 4 into correspondence. Steam temperature is maintained constant by automatic interstage water injection at points 36, 37 in dependence on temperature indications at points T 4 , T 5 , T 6 . The furnace chamber shown at 16 receives fuel from a distributer 15 and air from a compressor 18 and discharges gases along a path 19 terminating in an induced draught fan 20. The firing rate is controlled according to signals L 1 , L 2 representative of turbine speed and steam pressure respectively measured at the speed control device 23 of the turbine and at a point 26 at the outlet of the final superheater 10. The distributer 15 is additionally controlled according to the oxygen content of the gases entering the fan 20. In a modification, the steam pressure is measured between the superheaters 9, 10 or 8, 9. In a further modification, the interstage water injection is controlled by superheater temperature and by the throughflow of steam or the rate of flow of feedwater to the preheater 4.