Patent GB-612414-A (GB)
Title: Improvements relating to rotary compressors and their control, and applications thereof in combustion turbine power plant
IPC: F02C7/04
Filed: 1945-03-05
Abstract: 612,414. Compressors and gas-turbine plant. POWER JETS (RESEARCH & DEVELOPMENT) Ltd., McLEOD, R. C., and HODGE, J. March 5, 1945, No. 5519. [Classes 110 (i) and 110 (iii)] In an axial flow or centrifugal compressor or an internal combustion turbine plant comprising such a rotary compressor, controlling means for the compressor comprise a device giving a response which is a measure of the instantaneous deviation of the ratio of rotational speed to fluid velocity or of the ratio of whirl velocity to axial velocity from a prescribed value, and means controlled by the device in accordance with the response to restore said ratio to its prescribed value. The said device may comprise means giving responses proportional to rotational speed and to fluid velocity respectively, together with further means sensitive to changes. in the ratio of the responses; or may comprise a device giving a direct response to changes in the said ratio. A gas-turbine plant, Fig. 2, comprises a turbine 32, a compressor 20 driven by the turbine and supplying air to combustion chambers 25 and a variable pitch propeller 37 driven through reduction gearing within a housing 34. The sun-wheel 55 of a bevel differential gear is driven through bevel gears 51, 52 and 48, 49 from an anemometer consisting of a fixed-pitch screw-type windmill 47 located in the fluid passage through the compressor. Sun-wheel 54 is driven through bevel gears 43, 44 and further gearing within the housing 34 from shaft 33. The wheels 54, 55 are connected by the usual planet wheels 56, and the gearing between shaft 33 and wheel 54 and between windmill 47 and wheel 55 is such that when the ratio of rotational speed N to fluid velocity V is of the prescribed value, the wheels 54, 55 revolve at equal and opposite speeds, so that no rotation of the planetary cage 57 takes place. Any deviation of the ratio N/V from the prescribed value causes rotation, in one direction or the other, of the planetary cage, and hence through gearing 58, 59 of a shaft 60 which operates the control valve 29 of the fuel supply to burners 26. The resultant variation of the fuel supply causes variation of the back pressure on the compressor and hence causes such variation of the fluid velocity as will tend to restore the ratio N/V to its prescribed value. Since the optimum value of the ratio N/V may vary with the operating conditions, provision is made for varying the value at which the system stabilizes. The stator blades 61, Fig. 3, of the windmill 47 are pivotally mounted on axes 111 and have pins 62 which engage a grooved ring 63 which can slide axially of the windmill and carries a rack 64 engaged by a pinion 65. The latter is operable by a lever 66 connected to the rodding 40, so that movement of the manual speed control lever 41 simultaneously varies the setting of the rotational speed governor 38 through the speed selector 39 and, by varying the angle of the windmill stator blades 61 varies also the value of the ratio N/V at which the system stabilizes. In the arrangement shown in Fig. 4, a yawmeter head 22 detects directly changes in the ratio N/V. The yawmeter head consists of a compressor stator blade 22 which is provided with two orifices located near the leading edge in such relative positions that at the prescribed value of the ratio N/V they experience equal pressures. Alternatively, each orifice may be located in a separate stator blade. Any variation in the ratio N/V causes a corresponding variation in the ratio of whirl velocity to axial velocity and hence of the angle of attack between the fluid and the yawmeter blade, resulting in a differ. ence of pressure between the two orifices. The latter are connected by pressure tubes 70, 71 to a control device 72 which is sensitive to the pressure difference and controls an electric motor 83 which drives the fuel supply control shaft 60. A slidable "bullet" 90 operated from the shaft 60 by suitable gearing enables the area of the exhaust jet nozzle 89 to be varied simultaneously with the fuel supply. The yawmeter head may be of the known type, Fig. 8, in which the tubes 70, 71 are bent so that their open ends face .one another and make equal angles (usually 45 degrees) with the direction of the air stream. The strut 67, which supports the tubes may be pivotally supported at 68 with a pin 69, which corresponds to pin 62 of Fig. 3, engaging the grooved sliding ring 63. The control device 72 comprises a sealed chamber 73, Fig. 9, with the interior of which the tube 70 communicates and which contains a bellows-type capsule with the interior of which .the tube 71 communicates. The free end of the capsule carries a moving contact bar 75 connected to lead 76 and which can make contact with one of two fixed contacts 77, 78 connected to leads 79, 80, whereby one or other of two field coils 81, 82 can be energized to drive the motor 83 in one direction or the other. There may be a relay between the control device 72 and the field coils. As an alternative to varying the fuel supply or jet nozzle area, the control may be effected by means of a throttle valve at the compressor intake or discharge or by a blow-off valve at the compressor discharge or by a variable angle turbine stator blade. It is stated that the invention may be applied to fixed speed compressors and gas turbine plants to control some geometrical parameter of the compressor. The compressor may be of the axial flow or centrifugal types, or a combination of the two types in series. Servomotors may be used for the operation of the various control means.