GB871063A - Sub-atmospheric gas turbine circuits - Google Patents

Abstract

871,063. Fluid pressure servomotor control systems. AMERICAN MACHINE & FOUNDRY CO. July 2, 1957, No. 20911/57. Class 135. [Also in Group XXVI] A gas turbine plant comprises a compressor supplying gas to a combustion chamber feeding a turbine driving the compressor, the turbine exhausting through a cooler and aspirator valve, for admitting fresh air into the circuit, to the intake of the compressor, a load turbine connected to the outlet of the compressor and discharging to atmosphere and means for controlling the aspirator valve so as to create a progressively increasing partial vacuum at the compressor intake as the external load decreases. A compressor 10, driven by a turbine 11 through a shaft 12, receives air from a duct 13 connected to an aspirator 14, which includes a fresh air duct 15 and a gas duct 16. The aspirator 14 is controlled by a needle valve 18. The duct 16 is connected through a cooler 20 to the discharge of the turbine 11. The output of the compressor 10 is divided. Part flows through the combustion chamber 23 to the turbine 11 and part flows through a duct containing a bypass valve 24 to a combustion chamber 49 feeding a turbine 47. The power plant is controlled by a throttle pedal 65 which controls an orifice 64. At full load, the throttle 65 is released and orifice 64 thereby closed. Full oil pressure is then exerted on the servo-controlled valves 31, 28 and 67 so that the fuel valve 32 is open, the aspirator valve 14 fully open and the by-pass valve 24 shut off. As the valve 14 is fully open the pressure at the intake of the compressor will be approximately atmospheric. Fuel valve 54 which is controlled by a thermocouple 62 will also be fully open. The fuel valve 32 is controlled by the speed governor 34 to maintain the speed of the turbine-compressor unit 10, 11 constant. At partial load, the throttle valve 63 and pedal 65 are at an intermediate position. The pressure in the pipes 40, 44, 41 and 43 is lowered so that the valves 31, 67 and 54 will be at an intermediate position. The by-pass valve 24 will still be closed. The pressure at the intake of the compressor will be lower and the discharge pressure also will be lower. The amount of working fluid supplied to the turbine 47 and its power output will be correspondingly reduced. At idling, the orifice 64 is opened and the pressures in the pipes 40, 44, 41 and 43 reduced so that the fuel valve 31 and aspirator valves 67 are closed to a preset value. The drop in the pipe 43 allows the valve 28 to open so that duct 22 is connected to atmosphere. Under these conditions the pressure in the duct 13 will only be a small fraction of the atmospheric pressure. The load turbine is by-passed and therefore supplies no power. The pressure in the pipe 39 falls so low that the servomotor 56 closes the fuel valve 54. If desired, the by-pass valve 24 may be omitted. In a modification, Fig. 5 (not shown), the fuel supply to the combustion chamber 49 is controlled by a speed governor driven by the turbine 47. In another modification, the air supply to the combustion chambers 23, 49 is preheated in heat exchangers by the exhaust gases from the turbines 11, 47. In another modification two compressors with an intercooler between them are provided. In this case the air supply to the combustion chambers is preheated by the turbine exhaust gases and provision is made to by-pass the heat exchanger in the exhaust of the turbine 47 at full load. In another modification, the combustion chamber 49 is omitted.