Multi-stage centrifugal compressor and return channels therefor

Abstract

A multi-stage impeller is configured in a multi-stage centrifugal compressor by fixing and attaching a plurality of centrifugal impellers to one rotating shaft. Diffusers and return channels are provided in order downstream from each impeller. The centrifugal impellers, the diffusers and the return channel are housed within a compressor casing. The return channels have a plurality of vanes positioned at intervals from one another in a circumferential direction, and at least two stages are provided. The vane exit angles monotonically increase toward the downstream stage.

1 . A multi-stage centrifugal compressor comprising:
 a multi-stage impeller configured by fixing and attaching a plurality of centrifugal impellers to one rotating shaft, diffusers and return channels formed in order downstream from each impeller, and a casing housing the centrifugal impellers, the diffusers and the return channels,   wherein the return channels have a plurality of vanes circumferentially arranged with spacing, and wherein the vanes have exit angles monotonically increased toward the downstream stage.   
     
     
         2 . A multi-stage centrifugal compressor according to  claim 1 , wherein the more downstream impeller has the larger or equal blade angle with respect to a radial direction at an exit of the impeller. 
     
     
         3 . A multi-stage centrifugal compressor comprising:
 a multi-stage impeller configured by fixing and attaching a plurality of centrifugal impellers to one rotating shaft, diffusers and return channels provided in order downstream from each impeller, and a casing which houses the centrifugal impellers, the diffusers and the return channels and in which a plurality of compressor groups are configured by forming a plurality of inlet channels,   wherein in at least one of the plural compressor groups, the return channels have a plurality of vanes circumferentially arranged with spacing and are provided at least in two stages, and wherein the vanes have exit angles monotonically increased toward the downstream stage.   
     
     
         4 . The multi-stage centrifugal compressor according to  claim 3 , wherein in each group, the more downstream impeller has the larger or equal blade angle with respect to a radial direction at an exit of the impeller. 
     
     
         5 . A return channel for use in multi-stage centrifugal compressor which is used in at least more than one stage of the multi-stage centrifugal compressor having a plurality of impellers attached to one shaft and which includes a plurality of vanes circumferentially arranged with spacing and attached in a channel formed between opposite flat plates, wherein of the plural vane exit angles with respect to a radial direction, an exit angle of the vane used in an upstream stage is equal to or less than an exit angle of the vane used in a downstream stage. 
     
     
         6 . The return channel according to  claim 5 , wherein the vane of the uppermost return channel has an exit angle substantially equal to zero.