Method for compressing an incoming feed air stream in a cryogenic air separation plant

Abstract

A method for compression of an incoming feed air stream using at least two variable speed compressor drive assemblies controlled in tandem is provided. The first variable speed driver assembly drives at least one compression stage in the lower pressure compressor unit driven while the second variable speed driver assembly drives higher pressure compression stage disposed either in the common air compression train or the split functional compression train of the air separation plant. The first and second variable speed driver assemblies are preferably high speed, variable speed electric motor assemblies each having a motor body, a motor housing, and a motor shaft with one or more impellers directly and rigidly coupled to the motor shaft via a sacrificial rigid shaft coupling.

What is claimed is: 
     
         1 . A method for compression of an incoming feed air stream to a cryogenic air separation plant, the method comprising the steps of:
 (a) compressing at least a portion of the incoming feed air stream in a lower pressure single stage or multi-stage compressor of a common air compression train, at least one compression stage in the lower pressure single stage or multi-stage compressor driven directly by a first variable speed driver assembly;   (b) further compressing the compressed feed air stream in one or more higher pressure or intermediate pressure single stage or multi-stage compressors of the common air compression train;   (c) purifying the further compressed feed air stream to remove impurities either after step (a); after step (b) or between compression stages of step (b);   (d) directing two or more portions of the compressed and purified feed air stream to a split functional air compression train having one or more compression stages driven by a second variable speed driver assembly;   (e) directing one or more of the portions of the compressed and purified feed air stream in the split functional air compression train to a primary heat exchanger in order to cool the one or more portions to temperatures suitable for rectification in a distillation column system of the cryogenic air separation plant; and   (f) directing some or all of the one or more of the portions of the cooled, compressed and purified feed air stream to the distillation column system of the cryogenic air separation plant to produce liquid and gaseous products.   
     
     
         2 . The method of  claim 1  wherein the first variable speed driver assembly and the second variable speed driver assembly are high speed electric motor assemblies each having a motor body, a motor housing, and a motor shaft with one or more impellers directly and rigidly coupled to the motor shaft. 
     
     
         3 . The method of  claim 1  wherein the lower pressure single stage or multi-stage compressor further comprises two compression stages arranged in parallel and driven directly by a double ended variable speed driver assembly, wherein the two compression stages are configured to receive and compress ambient pressure air to produce a first compressed air stream. 
     
     
         4 . The method of  claim 1  wherein the lower pressure single stage or multi-stage compressor further comprises a first compression stage and a second compression stage arranged in series and driven directly a double ended first variable speed driver assembly, wherein the first compression stage is configured to receive and compress ambient pressure air and produce a first compressed air stream and the second compression stage is configured to receive and compress the first compressed air stream to produce a second compressed air stream. 
     
     
         5 . The method of  claim 1  wherein the lower pressure single stage or multi-stage compressor further comprises a single stage compressor driven directly by a single ended first variable speed driver assembly, wherein the single compression stage is configured to receive and compress ambient pressure air and produce a first compressed air stream. 
     
     
         6 . The method of  claim 1  wherein the compression stages of the split functional air compression train further comprises at least two compression stages arranged in series and driven by a double ended second variable speed driver assembly. 
     
     
         7 . The method of  claim 1  wherein the compression stages of the split functional air compression train further comprises a single compression stage driven by a single ended second variable speed driver assembly. 
     
     
         8 . The method of  claim 1  wherein the compression stages of the split functional air compression train further comprises one or more boiler air compressors arranged in series. 
     
     
         9 . The method of  claim 1  wherein the compression stages of the split functional air compression train further comprises one or more compressors selected from the group consisting of an upper column turbine circuit compressor, a lower column turbine circuit compressor, a warm recycle circuit compressor, a warm lower column circuit compressor, a partial lower column turbine circuit compressor, and combinations thereof. 
     
     
         10 . The method of  claim 1  further comprising the step of directing portions of the compressed and purified feed air stream to one or more further compression stages of the common air compression train configured as an integrally geared compressor. 
     
     
         11 . The method of  claim 1  further comprising the step of directing portions of the compressed and purified feed air stream to one or more further compression stages of the common air compression train driven by another variable speed drive assembly. 
     
     
         12 . The method of  claim 1  wherein a volumetric flow of the incoming feed air stream is controlled by adjusting the speed of the first variable speed driver assembly in response to changes in the operating conditions of the cryogenic air separation plant and wherein a discharge pressure from the common air compression train is a variable discharge pressure that changes by adjusting the speed of the first variable speed driver assembly in response to changes in the operating conditions of the cryogenic air separation plant. 
     
     
         13 . The method of  claim 1  wherein the speed of the first variable speed driver assembly is set in response to a measured flow rate of air in the common air compression train and wherein the speed of the second variable speed driver assembly is set in response to a measured pressure of at least one of the portions of purified, compressed air streams in the split functional air compression train and the speed of the first variable speed driver assembly. 
     
     
         14 . The method of  claim 1  wherein the speed of the first variable speed driver assembly is set in response to a measured flow rate of air in the common air compression train and wherein the speed of the second variable speed driver assembly is set in response to a discharge pressure in the common air compression train and the speed of the first variable speed driver assembly. 
     
     
         15 . The method of  claim 1  wherein the speed of the first variable speed driver assembly is set in response to the measured flow rate of air in the common air compression train and one or more process limits and wherein the speed of the second variable speed driver assembly is set in response to the one or more one or more process limits and the speed of the first variable speed driver assembly. 
     
     
         16 . The method of  claim 1  wherein the speed of the first variable speed driver assembly is set in response to the measured flow rate of air in the common air compression train and one or more a compression stage limits and wherein the speed of the second variable speed driver assembly is set in response to the one or more compression stage limits and the speed of the first variable speed driver assembly. 
     
     
         17 . The method of  claim 1  wherein the speed of the first variable speed driver assembly is set in response to the measured flow rate of air in the common air compression train and one or more driver assembly limits and wherein the speed of the second variable speed driver assembly is set in response to the one or more one or more driver assembly limits and the speed of the first variable speed driver assembly. 
     
     
         18 . The method of  claim 1  wherein the speed of the first variable speed driver assembly or the speed of the second variable speed driver assembly or both are further adjusted periodically in response to the diversion or venting of a portion of the compressed air from the common air compression train. 
     
     
         19 . The method of  claim 1  wherein the speed of the first variable speed driver assembly or the speed of the second variable speed driver assembly or both are further adjusted in response to changes in ambient air conditions. 
     
     
         20 . The method of  claim 1  wherein the two or more portions of the purified, compressed air stream in the split functional air compression train further comprise a first portion of a boiler air stream and a second portion of an upper column turbine air stream. 
     
     
         21 . The method of  claim 1  wherein the two or more portions of the purified, compressed air stream in the split functional air compression train further comprise a first portion of a boiler air stream and a second portion of a lower column turbine air stream. 
     
     
         22 . The method of  claim 1  wherein the two or more portions of the purified, compressed air stream in the split functional air compression train further comprise a first portion of a boiler air stream, a second portion of an upper column turbine air stream, and a third portion of a warm recycle turbine air stream. 
     
     
         23 . The method of  claim 1  wherein the portions of the purified, compressed air stream in the split functional air compression train further comprise a first portion of a boiler air stream, a second portion of a lower column turbine air stream, and a third portion of a warm recycle turbine air stream. 
     
     
         24 . The method of  claim 1  further comprising the step of cooling the compressed feed air stream in one or more intercoolers disposed between consecutive compression stages in the common air compression train wherein each intercooler is configured to cool the compressed air stream exiting the first of the consecutive compression stages prior to further compression in the second of the consecutive compression stages. 
     
     
         25 . The method of  claim 1  further comprising the step of cooling the compressed feed air stream in an aftercooler disposed between a compression stage in the common air compression train and a pre-purification unit wherein the aftercooler is configured to cool the compressed air stream exiting the compression stage prior to purification of the compressed feed air stream. 
     
     
         26 . The method of  claim 1  wherein the step of purifying the further compressed feed air stream to remove impurities further comprises purifying the further compressed feed air stream in an adsorptive pre-purification unit. 
     
     
         27 . The method of  claim 26  further comprising the steps of:
 periodically diverting a portion of the compressed feed air stream from the common air compression train; and 
 repressurizing the adsorptive pre-purification unit with the portion of diverted air from the common air compression train. 
 
     
     
         28 . The method of  claim 1  further comprising the step of discharging a portion of the compressed air out of the common air compression train via a vent. 
     
     
         29 . The method of  claim 1  wherein at least one stage of compression in the common air compression train or the split functional air compression train comprises a centrifugal compressor having inlet guide vanes wherein the inlet guide vanes are adjusted to control the flow rate of the stream to the at least one stage of compression.