GB1509743A - Power producing units - Google Patents

Abstract

1509743 Automatic control BABCOCK & WILCOX CO 30 April 1975 [30 April 1974] 17970/75 Heading G3N [Also in Division F4] A conventional power-producing unit comprises a steam generator and HP, IP and LP turbines, separately driving electric generators feeding into a common bus, or, a single electric generator. Primary and secondary superheaters, and a reheater, are provided. The unit is automatically controlled during "cold start" and "hot start" to bring the unit on line in the minimum time. As shown, a load demand signal is fed from a dispatch system 29 to a signal generator 30 providing a feed-forward signal representative of load demand. This signal is modified, in dependence on actual load, in a unit 32 and also fed to a unit 35, to modify the development of a ramp signal related to control parameters 36-38. The modified feedforward signal is used to positionally control turbine steam flow control valves 42, a fuel valve 40 and a damper 41 in parallel, and flue gas temperature in dependence on a control programme 56. The ramp signal, on a line 39, is 1) used through a control 43 to position a superheater division valve in dependence on deviation of sensed throttle pressure 44 and 2) fed to a boiler pressure programme 47 and used to determine deviation of sensed primary superheater outlet pressure 48. The sensed deviation, through a sequence 58, control a superheater valve 67 and affects a "high select" unit 52. During "start-up" the unit 52 selects the highest deviation, from boiler pressure deviation 51 and flue gas temperature 53 and throttle pressure 54, which is then used to modulate 50 the demand signal to valve 40 and damper 41. A unit 59 is responsive to manually set criteria of steam temperature 60, rate-of-increase 61 and on-line temperature 62 to derive a rate-of-change ramp signal, for a control 64, whereby the difference between steam temperature and turbine metal temperature is maintained within prescribed limits. The control unit 64 also receives a comparison superheater temperature 63 and a modifying furnace air-flow 65 and controls at low load, by a valve 66, the flow of saturated steam into the superheated steam, and at higher load, by a valve 68, water. The unit 64 also modulates the firing rate through a unit 77 when. during start-up and on low-load, the programmed steam temperature is not attained. Reheat steam temperature is controlled by a unit 69, responsive to the ramp signal from unit 59 and actual air-flow 65 and steam reheat temperature 70, operating via a sequence control 72 a steam attemperator valve 73, a flue-gas recirculating control damper 74 and a reheat water attemperator valve 75.