Patent GB-760240-A (GB)
Title: Improvements in and relating to power control systems for gas turbines
Inventor: BOLTER JOHN REGINALD
IPC: F02C1/06
Filed: 1953-11-02
Abstract: 760,240. Gas-turbine plant. PARSONS & CO., Ltd., C. A. Dec. 10, 1954 [Nov. 2, 1953], No. 30185/53. Class 110 (3). A control means for a gas-turbine plant comprises a bleed valve situated at the outlet of the compressor or compressors, a venturi tube in the duct conveying the working fluid from the heating apparatus to the turbine or turbines and a second bleed valve connected to the heated working fluid duct downstream of the venturi tube. The invention is described with reference to a coal-fired gas-turbine plant in which air compressed in a compressor b is heated in a heat exchange d having two heating coils, namely a preheater e and a main heater f. The heated air passes through a flowlimiting venturi or convergent divergent nozzle g to a high pressure turbine h which drives the compressor b. The exhaust of the turbine h is led to a low-pressure turbine i which drives an alternator k. The exhaust of the turbine i is fed to a combustion chamber l fed with fuel from a mixing chamber m to which fuel and air are fed at n and o. Additional tempering air is fed to the chamber m by a fan q. The resulting combustion gases heat the coils e and f and exhausts to atmosphere through a pipe u which, if desired, may lead to a dust extractor plant. Exhaust air from the turbine i may be led to the heat exchange d through a pipe a. A bleed valve v is provided at the compressor outlet and a second bleed valve x at the turbine inlet. The air bled through these valves may pass direct to atmosphere through the duct w or to some convenient point in the cycle, for example, the exhaust gases leaving the air heater d. A third bleed valve y is provided between the outlet of the compressor and the inlet of the heater d. This valve allows air to be led to the low-pressure side of the heater d. The arrangement is such that for small reductions in load, a governor on the shaft j of the low-pressure turbine i would cause the bleed valve v to open. If the load on the alternator k falls suddenly, the opening of the valve v would be insufficient to control the rise of speed of the low-pressure turbine. This increased speed would cause the governor to open also the bleed valves x and y. The flow of air from the heater d to the high-pressure turbine h would be limited by the venturi tube g causing the pressure at the inlet to the turbine h to fall and the speed of the low-pressure turbine i to stop rising. These operations take place quicker than the fall in temperature of the combustion gases from the combustion chamber l. The opening of the valve y prevents overheating of the air heater tubes. To prevent overheating of the valve x during normal running, cooling air is led to the valve from the compressor outlet through a pipe z. As an alternative the valves x and y may be controlled by a governor responsive to the acceleration of the turbine i. The bleed valves and venturi tube are so designed that when the bleed valves are opened the pressure on the high pressure side of the air heater falls at such a rate that surging or choking of the compressor is avoided. The invention may be applied to gas turbine plants not having a heat exchanger or air heater but in which a large combustion chamber having a high thermal inertia is used.