Multi-stage screw compressor

Abstract

A multi-stage screw compressor includes at least two stages of compression, each compressor stage including a pair of rotors driven to effect gas compression. Each compression stage is provided with independent variable speed drive means and a control unit for controlling the speeds of the independent drive means. The control unit includes processing means for processing signals generated by a plurality of devices monitoring operating parameters of the compressor, and adjusting the speed of the drive means to provide a required gas flow delivery rate and pressure, at least one of the monitoring devices monitoring the torque and at least one of the monitoring devices monitoring the speed of each drive means.

1 . A multi-stage screw compressor ( 30 ) comprising at least two stages of compression; a control unit ( 33 ) comprising processing means for processing signals generated by a plurality of devices monitoring operating parameters of the compressor; each compressor stage ( 10 , 11 ) comprising a pair of rotors driven to effect gas compression; characterised in that each compression stage ( 10 , 11 ) is provided with independent variable speed drive means ( 31 , 32 ); and the control unit ( 33 ) controls the speeds of the independent drive means ( 31 , 32 ), and adjust the speeds of the drive means ( 31 , 32 ) to provide a required gas flow delivery rate and pressure, wherein at least one of said monitoring devices monitors the torque and at least one of said monitoring devices monitors the speed of each drive means.  
     
     
         2 . A screw compressor ( 30 ) as claimed in  claim 1  in which monitoring devices monitor the delivery temperatures of the gas at each compressor stage ( 10 , 11 ).  
     
     
         3 . A screw compressor ( 30 ) as claimed in any one of the preceding claims in which at least one monitoring device monitors the ambient temperature.  
     
     
         4 . A screw compressor ( 30 ) as claimed in any one of the preceding claims further comprising cooling means provided between adjacent stages, wherein at least one monitoring device monitors the temperature of the gas after passing through the cooling means.  
     
     
         5 . A screw compressor ( 30 ) as claimed in any one of the preceding claims in which at least one monitoring device monitors the delivery pressure of the gas at each compression stage ( 10 , 11 ).