GB807071A - Improvements in or relating to gas compressing plant - Google Patents

Abstract

807,071. Centrifugal compressors; gas turbine plant POWER JETS (RESEARCH & DEVELOPMENT) Ltd. Aug. 3, 1956 [Aug. 26, 1955], No. 24552/55. Addition to 774,391. Classes 110 (1) and 110 (3). [Also in Group XXIX] A compressor plant comprises separate low and high-pressure compressors connected in series and driven by separate turbines, the low-pressure compressor also supplying gas to the turbines by way of a heating system, and surging is prevented by a by-pass at the outlet of the high-pressure compressor, the by-pass valve being controlled by a pneumatic differential relay responsive to two gas pressures sensed by tappings at the high-pressure compressor. In the gas turbine plant described in the parent Specification, wherein the output from a lowpressure centrifugal air compressor is divided, part of it going through a two-stage highpressure centrifugal air compressor to the output and part directly to the combustion chamber and from there to the two separate turbines which separately drive the compressors; the surge-preventing by-pass valve 17, Fig. 4, is actuated pneumatically instead of hydraulically. The high-pressure compressor runs at a constant governor-controlled speed. Pressure tappings 28, 29 at the inlet and throat of a venturi flow meter situated at the intake or delivery of the high-pressure compressor communicate with corrugated diaphragms or, as shown, bellows 32, 33 of differing diameters, connected in opposition to a lever 40 pivoted about a fulcrum 41. A valve 37 carried by the lever 40 throttles the escape of air through a nozzle at the end of a pipe 38. Variations in the leak-off result in corresponding variations in the pressure in an air supply pipe 21 downstream of a restriction 39. This pressure is applied to a diaphragm 44 to operate the by-pass valve 17. A device 35 can alter the pressure to provide compensation for temperature variations sensed at 36. At normal rates of flow, the venturi is partly bypassed by a valve 31 which lifts at a load value just above the operating range of the surgepreventing control. The pipe 21 is connected to the outlet of the low-pressure compressor, and may incorporate a cooler. The venturi may be omitted, the flow measuring tappings then being taken from static points in an outlet duct wall or from a yawmeter. The yawmeter tapping points may comprise sensing holes 26, 27, Fig. 2, in small diameter tubes 25 in the leading edges of separate diffuser vanes 24 of the second-stage high-pressure compressor. The tubes 25 are adjustable to bring the holes 26, 27 to the required positions. A number of such pairs of holes may be disposed around the circumference of the compressor. A second and larger pneumatic relay may be interposed between the pneumatic relay and the by-pass valve 17. Mechanical or pneumatic feedback may be used.