Patent GB-826835-A (GB)
Title: Improvements relating to power plant and to the operation of power plant and to tubulous boilers suitable for use in power plant
IPC: F22G5/00
Filed: 1956-03-08
Abstract: 826,835. Steam and gas turbine plant. BABCOCK & WILCOX Ltd. March 8, 1956 [March 10, 1955], No. 7278/56. Class 110 (3). [Also in Groups XIII and XXIX] A binary elastic fluid power plant comprises a pressure-fired, once-through steam generating and superheating unit, a steam turbine receiving superheated steam from the unit and a gas turbine driven by the combustion gases from the unit, the pressure, temperature and rate of flow of these gases being held substantially constant over a wide range of rate of steam generation. The steam generating and superheating unit (see also Group XIII) consists of two pressureresisting casings B, S individually fired by cyclone furnaces 16. The casing B contains tubes 396 in which steam generation and some superheating occurs whilst the casing S contains in one vertical pass a final superheater 402 receiving steam from the tubes 396 through a line 398 and in another vertical pass a reheater 428. Steam from the superheater 402 flows successively through a high-pressure turbine 380, the reheater 428 and a low-pressure turbine 368. Combustion gases from the casing B are in part recirculated to the lower part of the casing by a fan 434, the remainder being passed by the fan into the lower part of the casing S wherein they mix with the fresh combustion gases from the cyclone furnace 16 of this casing and flow through the steam heating passes between which they are proportioned by dampers 200, 202 to an outlet 350. From the outlet the gases flow through a line 340 to a gas turbine 354, 442, the exhaust from which passes through a line 448 into a casing E containing an air heater 318 and an economizer 382. The steam turbines 380, 368 respectively drive electric generators 424, 440 whilst the gas turbine drives an electric generator 446 and an air compressor 314 supplying combustion air via the air heater to the cyclone furnaces 16. During starting the compressor 314 is driven by an auxiliary steam turbine 312 supplied with steam from an external source. Feed-water is pumped by a pump 360 from the main condenser 366 through bled steam heaters and the economizer 382 to the lining tubes of the furnaces 16 and thence through the evaporating section 396 of the casing B. During operation the feed-water flow is controlled to maintain a constant steam temperature at the inlet to the turbine 380. The air flow to the cyclone furnace of the B unit is controlled according to variations in steam pressure at that point. The air flow to the furnace controls the fuel supply thereto so that, for example, an increased steam demand with consequent slight drop in pressure is effective appropriately to increase the firing rate and hence the rate of steam generation in the B unit. The increased firing rate tends to increase the gas temperature in the B unit but this change immediately causes the rate of gas recirculation to the B unit to increase to restore the temperature to its predetermined value. The proportioning dampers 200, 202 are adjusted to maintain a constant reheat temperature. At all loads the gas turbines 354, 442 operate at full rating and, at boiler loads at which the air compressor 314 delivers an excess of air over that required for combustion, this excess is delivered through lines 334, 338 respectively controlled by valves 343, 342 into the furnace of the S unit. If the temperature of the gas leaving the S unit should rise above the predetermined value, about 1450‹ F., a valve 344 in a line 339 opens to admit sufficient air directly into the main 340 to restore the temperature to the required value. Moreover, if the gas turbine exhaust temperature rises to an abnormal value a valve 454 opens to permit a percentage of the gas flow from the main 340 to by-pass the turbine and flow directly into its exhaust line 448; the valve 454 is also responsive to overspeeding of the turbine. An increase in the gas temperature at the turbine inlet is also immediately effective to decrease the air and fuel flow to the cyclone furnace of the S unit. The control, which may be by fluid-pressure servomotors (see Group XXIX), involving the variable rate of flow of tempering gases and the control of the rate of firing of the S unit in combination with excess air variation is effective to maintain the desired conditions of gas temperature and flow at the gas turbine inlet over a wide range of power output of the steam turbine. Specifications 461,389, [Group XXIX], 598,141, [Groups XII and XIII], and 826,836, [Group XIII], are referred to.