Multi-stage compression system and method of operating the same

Abstract

A multi-stage compression system includes a plurality of centrifugal compression stages. Each stage includes an impeller and a variable speed motor coup led to the impeller. Each variable speed motor is operable at a speed between a (test speed and a second speed. The multi-stage compression system also includes a control system that is connected to each of the variable speed motors and is operable to vary the speed of each motor. The speed of each motor is varied simultaneously such that a ratio of the speed of any two variable speed motors remains constant.

What is claimed is: 
     
         1 . A multi-stage compression system comprising:
 a plurality of centrifugal compression stages, each stage including an impeller and a variable speed motor coupled to the impeller, each variable speed motor operable at a speed between a first speed and a second speed; and   a control system connected to each of the variable speed motors and operable to vary the speed of each motor, the speed of each motor being varied simultaneously such that a ratio of the speed of any two variable speed motors remains constant.   
     
     
         2 . The multi-stage compression system of  claim 1 , wherein a fluid flow passes through the plurality of centrifugal compression stages sequentially. 
     
     
         3 . The multi-stage compression system of  claim 1 , wherein the plurality of centrifugal compression stages are mechanically de-coupled from each other. 
     
     
         4 . The multi-stage compression system of  claim 1 , further comprising at least one heat exchanger, the at least one heat exchanger positioned to receive a fluid flow from at least one of the plurality of centrifugal compression stages. 
     
     
         5 . The multi-stage compression system of  claim 1 , wherein the control system includes at least one sensor positional to measure a parameter of a fluid flow passing through the plurality of centrifugal compression stages. 
     
     
         6 . The multi-stage compression system of  claim 5 , further comprising a valve disposed between the plurality of centrifugal compression stages and a gas utilization system, the valve operable to discharge a portion of the fluid flow from the multi-stage compression system. 
     
     
         7 . The multi-stage compression system of  claim 6 , wherein the control system varies the speed of the variable speed motor and operates the valve at least partially in response to the measured parameter. 
     
     
         8 . The multi-stage compression system of  claim 5 , wherein the parameter is at least one of a pressure, a temperature, and a mass flow rate. 
     
     
         9 . The multi-stage compression system of  claim 1 , wherein a mass How rate of the plurality of centrifugal compression stages is substantially constant. 
     
     
         10 . The multi-stage compression system of  claim 1 , wherein a mass flow rate of the plurality of centrifugal compression stages is variable in response to use of a fluid flow at a gas utilization system. 
     
     
         11 . The multi-stage compression system of  claim 1 , wherein a first variable speed motor operates at a different speed than a second of the variable speed motors. 
     
     
         12 . A multi-stage compression system comprising:
 a first centrifugal compressor stage including a first impeller and a first variable speed motor, the first variable speed motor operable at a first speed between a low speed and a high speed;   a second centrifugal compressor stage including a second impeller and a second variable speed motor, the second variable speed motor operable at a second speed between a low speed and a high speed, the first speed and the second speed defining a first ratio;   a third centrifugal compressor stage including a third impeller and a third variable speed motor, the third variable speed motor operable at a third speed between a low speed and a high speed, the first speed and the third speed defining a second ratio and the second speed and the third speed defining a third ratio; and   a control system operable to synchronously vary the first speed, the second speed, and the third speed such that the first ratio, the second ratio, and the third ratio remain constant.   
     
     
         13 . The multi-stage compression system of  claim 12 , wherein the first centrifugal compressor stage, the second centrifugal compressor stage, and the third centrifugal compressor stage are arranged in series. 
     
     
         14 . The multi-stage compression system of  claim 12 , wherein the centrifugal compressor stages are mechanically de-coupled from each other. 
     
     
         15 . The multi-stage compression system of  claim 12 , further comprising a first heat exchanger positioned between the first centrifugal compression stage and the second centrifugal compression stage, a second heat exchanger positioned between the second centrifugal compression stage and the third centrifugal compression stage, and a third heat exchanger positioned between the third centrifugal compression stage and an air utilization system. 
     
     
         16 . The multi-stage compression system of  claim 12 , wherein the control system includes at least one sensor positioned to measure a parameter of a fluid flow passing through the centrifugal compression stages. 
     
     
         17 . The multi-stage compression system of  claim 16 , further comprising a valve disposal between the third centrifugal compression stage and an air utilization system, the valve operable to discharge a portion of the fluid flow from the multi-stage compression system. 
     
     
         18 . The multi-stage compression system of  claim 17 , wherein the control system varies the speed of the first variable speed motor, the second variable speed motor, and the third variable speed motor and operates the valve in response to the measured parameter. 
     
     
         19 . The multistage compression system of  claim 16 , wherein the parameter is at least one of a temperature, a pressure, and a mass flow rate. 
     
     
         20 . The multistage compression system of  claim 12 , wherein a mass flow rate of the centrifugal compression stages is substantially constant.