Patent GB-596698-A (GB)
Title: Improvements in or relating to gas turbine plants
Filed: 1945-10-30
Abstract: 596,698. Fluid-pressure servomotor systems. SULZER FRERES SOC. ANON. Oct. 30, 1945, No. 28778. Convention date, May 26. [Class 135] [Also in Group XXVI] The invention relates to a gas turbine plant of the type in which air flows in a circuit containing a turbine and a compressor and in which air is withdrawn from the circuit and passed through another turbine which drives a further compressor for supplying compressed air to the circuit, at least at high outputs, to replace the air withdrawn from the circuit. The invention consists in the provision of a control device for adjusting the output of the plant which control device also adjusts the ratio of the pressure in a part of the circuit to the pressure of the make-up air in such a manner that this ratio is increased as the output of the plant is increased. In the gas turbine plant shown, Fig. 1, the working medium flows in a circuit formed by a compressor 1, a preheater 5, a heater for the working fluid 10, a turbine 12 driving the compressor 1 and back to the compressor 1 through the preheater 5 and cooler 15. Part of the working medium is extracted from the circuit through a pipe 6 to act as combustion air for the burner 17 of the heater 10, the combustion gases from which are used to drive a useful output turbine 19 and a turbine 23 driving a compressor 31 supplying air to the circuit, at least at high outputs from the plant to replace that extracted through the pipe 6. The plant is controlled by a regulator 46 which regulates the pressures at the inlet to the turbine 12 and the discharge of the compressor 3 so that, for any given output, the ratio between them is maintained at a predetermined value. This ratio is increased as the output is increased. These pressures and the useful output from the plant, are preset by the hand lever 61. The regulator, shown in detail in Fig. 2, comprises a hand lever 61 connected through a bell-crank 68 to a pilot valve 72 and a bar 69 provided with two cams 70, 71 which control the position of two spring- loaded pistons 76, 77. When the lever 61 is in the minus position corresponding to no load, the plungers 76 and 77 are at their highest position and the valve 72 at its lowest position so that pressure oil from the supply pipe 65 is supplied to the pipe 66 and the pipe 67 is open to drain. This causes the pistons of the servomotors 38, 39, 40 and 41 to rise so that the valves 22 and 28 are closed and the valves 21 and 27 are opened. The exhaust gases from the turbine 19 then byepass the turbine 23 and the compressor 31 is shut off from the circuit, the make-up air-being drawn from the atmosphere past the non-return valve 62 and valve 27. If now the lever 61 is moved towards the left, the plunger 76 is moved downwards whilst the plunger 77 remains in the original position. At first, the valve 72 does not move over the control edges so that the valves 21, 22, 27 and 28 remain unmoved. The spring 80 is compressed by the movement of the plunger 76 and this causes the left-hand end of the lever 78 and valve 88 to move against the action of the dashpot 96 and pressure fluid to be supplied to the underside of the piston 90 which moves upwards and relieves the compression stress in the spring 92. This allows the valve 94 to rise under the action of the pressure in the pipe 50 and open the pipe 50 to drain until the pressure in the pipe falls sufficiently to balance the reduced stress in the .spring 92. The fall in pressure in the pipe 50 allows the spring in the servomotor 49 to open the valve 48 in the byepass pipe 47 of the turbine 12. A larger quantity of working fluid passes through the turbine which speeds up and consequently increases the discharge pressure of the compressor 1. This causes an increased pressure at the inlet of the turbine 12 which is transmitted through the pipe 56 to the underside of the piston 84 which rises against the action of the spring 82 to lift the valve 88 and cut off the supply of pressure medium to the underside of the piston 90. The regulating action continues until the spring 80 is unstressed and the valve 88 is in the neutral position, i.e. when the pressure on the underside of the piston 84 corresponds to a particular value. The increased pressure in the pipe 56 also increases the fuel supply to the burner 17 by opening the valve 100 against the action of the spring 101. Further movement of the -lever 61 towards the left will cause the plunger 76 to be pushed further downwards resulting in an additional rise in the circuit pressure and also cause the plunger 77 to be pushed downwards and this, by means of a servomotor system similar to that described with reference to the action of the plunger 76, actuates a ring 52 which moves the inlet guide blades 51 of the turbine 23 so as to increase its speed and output. The resulting increase of pressure at the discharge 59 of the make-up compressor 31 acts through the pipe 58 on the piston 85. The regulating action continues until the spring 81 is unstressed and the valve 89 is in a neutral position, i.e. when the pressure on the piston 85 corresponds to a particular value. At any desired position between the minimum and maximum output from the plant, the valve 72 passes over the control edges and the pipe 66 is open to drain and the pipe 67 connected to the pressure fluid supply pipe 65. At this point, the valves 27 and 21 are closed and the valves 22 and 28 opened and the make-up compressor 31 and driving turbine 23 brought into operation. The pressure in the circuit and at the discharge of the compressor 31 and the relationship of these pressures to one another depends upon the shapes of the cams 70 and 71 which are so chosen that the ratio of these pressures is increased as the output of the plant is increased. An electric motor 34 is used for starting the plant.