Patent GB-998831-A (GB)
Title: Supercritical vapor generator and method for operating the same
IPC: F01K7/24
Filed: 1963-12-13
Abstract: 998,831. Regulating steam temperature In boilers. COMBUSTION ENGINEERING Inc. Dec. 13, 1963 [Dec. 28, 1962 (3)], No. 49274/63. Heading F4A. The reheat vapour temperatures in a supercritical forced flow once through vapour generator supplying a 3-stage turbine, operating on a double reheat cycle, are maintained constant throughout a substantial load range by regulating the flow of recirculation gases and by varying the furnace gases outlet temperature. The generator comprises a furnace 10 tangentially fired by an assembly of burners having nozzles 24 vertically adjustable to move the combustion zone from A to B and horizontal and vertical gas passes 14, 16. A fan 82 passes exhaust gases through duct 88 containing damper 94 into the bottom of the furnace for recirculation and through duct 86 containing damper 92 into the top of the combustion zone for temperating the furnace gases. The working fluid is circulated by a pump 40 in series flow through an economizer 32, a mixing vessel 44, furnace-cooling tubes 34, tubes lining gas pass 16 and superheater sections 36, 38 containing bundles of sinuously or otherwise bent tubes connected in parallel, before passing through the high, intermediate and low pressure stages 64, 70, 80 of a turbine 64 and through high and low pressure convection heated reheaters 66, 70 immediately upstream of the intermediate and low-pressure turbine stages respectively. With respect to the flow of combustion gases the low-pressure reheater is downstream of the high pressure reheater and separated from it by superheater section 36. A recirculation circuit for providing adequate flow through the furnace cooling tubes at low loads and during start-up connectsthe upper header 48 of the tubes through pump 119 and valve 120 to the mixing vessel 44. The pressure and temperature of the primary vapour entering the first turbine stage are maintained constant by temperature and pressure responsive means 108, 109 controlling, via actuators 114, the air and fuel flow control valves 28, 31 of the burners and, via actuator 116, the feed water control valve 81. The outlet temperature of the high-pressure reheater 66 is maintained constant by temperature sensing means 96 which varies the furnace gases outlet temperature by first controlling via actuator 100 and damper 92 the flow of the tempering gases and when this flow is completely stopped, tilting the burner nozzles upwards by operating actuators 122. The output temperature of the low-pressure reheater is -maintained constant by the temperature-sensing means 102 controlling the flow of recirculation gases via actuator 106 and damper 94. In a second embodiment the positions and methods of temperature control of the reheaters are interchanged, in this case the nozzles are tilted downwards. In another embodiment with the reheaters positioned as in Fig. 1, the highpressure reheater is heated mainly by radiation. As this has different heat exchange characteristics, regulation of the low-pressure reheat temperature by control of the recirculation flow results in a high pressure reheat temperature close to the desired value and it can be maintained constant by tilting up or down the burner nozzles, no tempering gases being required. Alternatively, control of tempering gases can be used in lieu of burner tilt control.