Multi-stage compression system including variable speed motors

Abstract

A multi-stage fluid compression system includes a first centrifugal compressor stage having a first inlet and a first outlet and a second centrifugal compressor stage having a second inlet and a second outlet. The second inlet receives a flow of compressed fluid from the first outlet. A first variable-speed motor is coupled to the first centrifugal compressor stage and is operable to drive the first centrifugal compressor stage at a first speed. A second variable speed motor is coupled to the second centrifugal compressor stage and is operable to drive the second centrifugal compressor stage at a second speed. The first speed and the second speed are each independently variable.

1 . A multi-stage fluid compression system comprising: 
 a first centrifugal compressor stage having a first inlet and a first outlet;    a second centrifugal compressor stage having a second inlet and a second outlet, the second inlet receiving a flow of compressed fluid from the first outlet;    a first variable-speed motor coupled to the first centrifugal compressor stage and operable to drive the first centrifugal compressor stage at a first speed; and    a second variable speed motor coupled to the second centrifugal compressor stage and operable to drive the second centrifugal compressor stage at a second speed, the first speed and the second speed each being independently variable.    
   
   
       2 . The multi-stage fluid compression system of  claim 1 , wherein one of the first centrifugal compressor stage and the second centrifugal compressor stage includes a first shaft that supports a first impeller and a second impeller, and the other of the first centrifugal compressor stage and the second centrifugal compressor stage includes a second shaft that supports a single third impeller.  
   
   
       3 . The multi-stage fluid compression system of  claim 1 , wherein the first centrifugal compressor stage includes a first shaft that supports a first impeller and a second impeller, and the second centrifugal compressor stage includes a second shaft that supports a third impeller and a fourth impeller.  
   
   
       4 . The multi-stage fluid compression system of  claim 1 , further comprising a heat exchanger configured to receive the flow of compressed fluid from the first outlet and deliver the flow to the second inlet.  
   
   
       5 . The multi-stage fluid compression system of  claim 1 , further comprising a control system operable to control the speed of each of the motors independently.  
   
   
       6 . The multi-stage fluid compression system of  claim 5 , further comprising at least one sensor associated with the first centrifugal compressor stage and at least one sensor associated with the second centrifugal compressor stage, the control system operable to determine an output flow rate and an output pressure of the first centrifugal compressor stage and the second centrifugal compressor stage based at least partially on the data sensed by the sensors.  
   
   
       7 . The multi-stage fluid compression system of  claim 6 , wherein at least one of the sensors measures a pressure and at least one of the sensors measures a velocity.  
   
   
       8 . The multi-stage fluid compression system of  claim 1 , further comprising a first motor controller operable to control the speed of the first motor and a second motor controller operable to control the speed of the second motor.  
   
   
       9 . The multi-stage fluid compression system of  claim 1 , further comprising an active magnetic thrust bearing coupled to the first centrifugal compressor and operable to support the thrust load of the first centrifugal compressor.  
   
   
       10 . The multi-stage compression system of  claim 1 , wherein each motor includes a shaft that rotates at a speed that is greater than or equal to about 50,000 RPM.  
   
   
       11 . A multi-stage compression system comprising: 
 a plurality of centrifugal compressor units, each compressor unit having an inlet and an outlet, a first of the compressor units drawing in a fluid at a first pressure and a last of the compressor units discharging the fluid at a second pressure;    a plurality of variable-speed motors, each of the motors directly driving one of the plurality of compressor units, each motor operable at a speed between a motor minimum and a motor maximum independent of the other motors; and    a control system operable to vary the speed of each motor independently at least partially in response to the second pressure.    
   
   
       12 . The multi-stage compression system of  claim 11 , wherein each of the plurality of centrifugal compressor units includes a shaft that supports a first impeller for rotation, and wherein at least one of the shafts supports a second impeller in addition to the first impeller.  
   
   
       13 . The multi-stage fluid compression system of  claim 11 , further comprising a plurality of heat exchangers, each heat exchanger disposed between the outlet and the inlet of adjacent centrifugal compressor units.  
   
   
       14 . The multi-stage fluid compression system of  claim 11 , further comprising a control system operable to control the speed of each of the motors independently.  
   
   
       15 . The multi-stage fluid compression system of  claim 14 , further comprising a plurality of sensors, each sensor associated with at least one of the centrifugal compressor units, the control system operable to determine an output flow rate and an output pressure of each of the centrifugal compressor units based at least partially on the data sensed by the sensors.  
   
   
       16 . The multi-stage fluid compression system of  claim 15 , wherein at least one of the sensors associated with each compressor unit measures a pressure and at least one of the sensors associated with each compressor unit measures a velocity.  
   
   
       17 . The multi-stage fluid compression system of  claim 11 , further comprising a plurality of motor controllers, each operable to control the speed of one of the plurality of motors.  
   
   
       18 . The multi-stage compression system of  claim 11 , further comprising a plurality of active magnetic thrust bearings, each magnetic thrust bearing coupled to one of the plurality of centrifugal compressor units and operable to support the thrust load of the associated centrifugal compressor unit.  
   
   
       19 . The multi-stage compression system of  claim 11 , wherein each motor includes a shaft that rotates at a speed that is greater than or equal to about 50,000 RPM.  
   
   
       20 . The multi-stage compression system of  claim 19 , further comprising a plurality of impellers, each impeller coupled to one of the shafts, each shaft supported for rotation by at least two active magnetic bearings.