GB798477A - Improvements in and relating to centrifugal compressors - Google Patents

Abstract

798,477. Centrifugal compressors. BRITISH THOMSON-HOUSTON CO., Ltd. June 11, 1956 [June 14, 1955; Dec. 23, 1955], Nos. 17138/55 and 36900/55. Class 110 (1). A plant for extracting a gaseous medium, as from a steam condenser, comprises a number of centrifugal compressors, each directly driven by an alternating current electric motor, and one or several frequency changer or alternator sets to supply current to the motors at a frequency or frequencies substantially higher than conventional power frequency to produce a motor speed as required for operation at favourable efficiency of each of the compressors. Fig. 1 shows a two-stage centrifugal compressor driven by a high-frequency alternating current motor 2. The casing 13 is of one-piece construction, the impellers, diffusers and interstage diaphragm being arranged for endwise assembly. Air admitted through a valve 20 circulates through the motor and enters the compressor inlet past a shaft gland 21. The motor is surrounded by a cooling water-jacket 8. A lubricant.pump 17 is driven through gearing 18. The plant shown in Fig. 3 comprises six such compressors mounted on a common baseplate, the two low-pressure compressors 23 being connected in parallel, and the remaining compressors being connected in series. Intercoolers 24, an inlet 25 with a butterfly valve, and a discharge 27 with a non-return valve are provided in the base-plate. All the motors are supplied at the same high frequency. Connections for by-passing any compressor becoming faulty may be provided in the base-plate. Fig. 5 shows a plant in which the high-pressure compressors 103, 104 are supported by the lowpressure compressors 101, 102. Intercoolers 105, 106 and 107 and a curved duct 108 are provided. The outlet 116 is adjacent the inlet 115 and has a non-return valve 117. Preferably, the supply frequency of the motors driving the compressors 103, 104 is higher, at say 275 cycles per second, than the supply frequency of the motors driving the compressors 101, 102, which may be 200 cycles per second.