Multi-stage compressor having first and second passages for cooling a

Abstract

A multi-stage compressor having at least two compressor stages comprises an inter-cooler provided between the stages for cooling a gas being discharged from a compressor in the preceding stage. The compressor stages are driven by a common electric motor, of which a rotating shaft is supported by magnetic bearings. A part of the gas cooled by the inter-cooler and a part of the work gas discharged from a bleed valve provided down-stream of a rear stage of the compressor are selectively introduced into the electric motor or the magnetic bearings. Thus, at the time of load operation the gas discharged from the inter-cooler is introduced into the motor or the magnetic bearings to cool them, and at the time of non-load operation the gas discharged from the bleed valve is introduced into the motor or the magnetic bearings to cool them. It is possible to ensure a flow rate of gas required for cooling the motor during non-load operation with economy during load operation.