GB1488594A - Htgr power plant hot reheat system pressure control syste - Google Patents

Abstract

1488594 Steam turbine plant WESTINGHOUSE ELECTRIC CORP 21 April 1975 [22 April 1974] 16360/75 Heading FIT [Also in Divisions F3 and F4] In a system in which the coolant gas (e.g. helium) from a high temperature gas-cooled reactor 100 generates super-heated steam (in generators 101 A, B, C) to drive high 108, intermediate 111, and low 112 pressure turbines of a power plant, steam from the turbine 108 is re-heated in re-heaters RHA, RHB, RHC and delivered via hot re-heat header 125 and turbines 111, 112 to a condenser 130 with a condenser by-pass 131 (valved at 132) provided between the header 125 and condenser 130, an intercept valve 127 being controlled by a device 139 to allow the desired flow to pass to the turbines, and a control system 146 being responsive to this device 139 to operate valve 132 so that the steam flow through the re-heater is equal to a predetermined minimum when the flow through valve 127 is less than that minimum and when the pressure in header 125 (detected at 144) is equal to the desired header pressure (as represented by device 142) - in addition the control system 146 operates on the valve 132 when the desired and actual header pressures are not equal to reduce the difference between them. Although a single turbine set can be used, in the arrangement shown in Fig. 1 two sets of turbines and associated control systems are employed each set of intermediate/low pressure turbines and their by-pass lines being arranged to take half the steam flow from the re-heater. Auxiliary turbines ASTA, ASTB, ASTC at the inlets to the re-heaters drive circulators for the reactor coolant gases. Alternate by-pass lines (e.g. 133 controlled by valve 134) are provided from the re-heat headers to discharge to an alternate steam receiving means (as shown they discharge to the atmosphere) and each control system controls a condenser by-pass line and an alternate by-pass line (e.g. by means 135, 137). The control system 146 (identical to control system 165) is shown in more detail in Fig. 2: signals from the devices 142, 144 (representing the desired and actual pressure in the re-heat header 125) are fed to a comparator 201 and their difference, along with a signal from turbine demand device 139, and a bias signal from generator 207 is passed to a summing device 206, which signals on line 210 how much steam is to be by-passed. When the outputs of 142, 144 are equal and valve 127 is fully open the by-pass demand is zero, and as valve 127 closes the by-pass demand increases to maintain the predetermined minimum flow of steam through the re-heater. In addition only a limited flow is allowed through the condenser by-pass 131 and a device 211 will not signal to valve 132 a value exceeding the limit; however a comparator 216 receives the signal output by device 211 and the by-pass demand signal from line 210 and actuates the valve 134 to put any flow required above the limit through the alternate by-pass line 133. The device 211 is controlled by a function generator which responds to the pressure in header 125 to ensure an inverse relationship exists between that pressure and the limit set by device 211. When the signals from devices 142, 144 are different the difference signal is passed by device 204 and causes the output of comparator 206 to be such as to reduce the difference. In the embodiment described the above features of the control system operate only from 0-25% load -- above 25% load the valve 127 receives signals from device 139 to cause it to be fully open, valves 132, 134 are closed, and device 142 puts out a signal equal to that from detector 144. If, when operating at above 25% load, one of the two turbine sets trips, the load on that turbine set drops to zero and the control system reverts to the 0-25% mode, however device 142 will represent the header pressure level immediately prior to the trip and will cause the control system to operate the by-pass lines of the tripped turbine set to maintain header pressure at that level thereby causing the least inconvenience to the untripped set. If both sets trip then both sets of by-pass lines operate to hold header pressure at the pre-trip value.