GB774391A - Improvements in or relating to gas turbine plant and control arrangements therefor - Google Patents

Abstract

774,391. Centrifugal compressors; gas-turbine plant. POWER JETS (RESEARCH & DEVELOPMENT), Ltd. Feb. 24, 1955 [Feb. 24, 1954], No. 5397/54. Classes 110 (1) and 110 (3). [Also in Group XXIX] A gas-turbine plant supplying a gaseous output comprises separate low and highpressure compressors for the gas, separate turbines driving the compressors, a minor part only of the gaseous delivery of the lowpressure compressor being passed through the high-pressure compressor to the output, and a major part being passed through a heating system and the turbines to exhaust. In the plant shown in Fig. 4, a two-stage high-pressure turbine 12A drives a centrifugal compressor 10 which supplies air to the combustion chamber 15 of the plant. High-pressure compressors 11A, 11B, connected in series with one another and with the low-pressure compressor 10, are driven through step-up gearing 28 by a lowpressure turbine 13A and supply air to a delivery duct 20. The speed of the highpressure compressors is maintained substantially constant by means of a centrifugal governor which controls the fuel supply. Fuel and oil pumps are driven through a shaft 29. Surging in the compressors 11A, 11B at low outputs is prevented by by-passing air from the delivery duct 20 to the combustion chamber 15 through a by-pass 25 under the control of a valve 26. The valve 26 is operated through a rod 72 by a servomotor piston 69, Fig. 6. The static pressures P2 and P1 at opposite sides of a diffuser vane 40 are sensed through pipes 60 and 59 respectively and applied to chambers 44, 45 on opposite sides of a piston 43. As the surge condition is approached, the angle a between the direction of the air flow V and the radial direction increases, causing the ratio P2/P1 to increase. When the ratio reaches a predetermined upper value, piston 43 moves to the right to open valves 46, 47, thereby allowing oil from the oil pump to enter a chamber 70 and to escape from a chamber 71. The resultant movement of piston 69 opens the valve 26 to avert surging. Piston 43 also moves a valve 54 to the right, closing a passage 57 through which a chamber 73 has been subjected to the pressure P1 and opening a port 58 which vents the chamber 73 to atmosphere, thereby preventing a piston 55 from moving to the left as the ratio P2/P1, in response to the opening of valve 26, begins to fall. When the ratio has fallen to a predetermined lower value, piston 43 moves to the left, valves 46, 47 are closed and piston 69 stops moving. Piston 54 closes the port 58 and opens the passage 57, and piston 55, under the influence of pressure P2 in chamber 74 and pressure P1 in chamber 73, moves to the left in response to the decreased value of P2/P1. This opens valves 61, 62, allowing oil to enter chamber 71 and escape from chamber 70; piston 69 moves to the left to reduce the opening of valve 26. When the ratio P2/P1 has increased again to a chosen design value, between the upper and lower values, the piston 55 moves to the right, closing valves 61, 62 and piston 69 stops moving. When the output exceeds 50 per cent of the maximum output, the ratio P2/P1 is below the above-mentioned lower value, and piston 55 is moved to the left, valves 61, 62 open, and piston 69 is moved to the left to shut the valve 26. Rapid movement of piston 43 is ensured by the construction shown in Fig. 7. When the piston 43 is in the normal position shown, an area A3 is subjected to the pressure P2. As soon as the piston begins to move to the right, an additional annular area A2 becomes subject to the pressure P2. A similar construction is used for piston 55. The turbines may be in parallel instead of series, and may have separate combustion chambers and the by-pass may be taken to atmosphere or to a separate turbine instead of to the combustion chamber. The centrifugal governor 18 may be replaced by a device responsive to the pressure in the delivery duct 20 and operable to maintain the pressure constant. Alternatively, the device may be responsive to the overall pressure ratio of the low and high pressure compressors and operable to maintain that ratio constant. The plant may be provided with intercoolers and heat exchangers. Speceification 612,414 is referred to.