System and method for integrated air separation and liquefaction

Abstract

A high efficiency and high volume air liquefaction system and method is disclosed wherein the cryogenic air separation plant includes a warm gas turbo-expansion cycle to supply the supplemental refrigeration required to produce liquid products in excess of about 15% of the incoming feed air.

What is claimed is: 
     
         1 . A method of separating a feed mixture comprised of air components in a cryogenic separation plant to produce liquid products, the cryogenic separation plant having a main heat exchanger and a distillation column system, the method comprising the steps of:
 producing a pressurized and purified feed stream;   directing a first portion of the compressed and purified feed stream to the main heat exchanger to cool the first portion of the compressed and purified feed stream;   liquefying the cooled first portion of the compressed and purified feed stream to produce a liquid feed stream suitable for rectification in the distillation column system;   diverting a second portion of the compressed and purified feed stream to a turbo- expander section of the cryogenic separation plant;   partially cooling at least a portion of the second compressed and purified feed stream in the main heat exchanger;   expanding the partially cooled second portion of the compressed and purified feed stream in a turbo-expander to produce work and a gaseous exhaust stream at a pressure suitable for the rectification in the distillation column system;   conducting a cryogenic distillation process to separate the first and second portions in the distillation column system thereby producing at least one liquid product stream;   compressing a working fluid in a supplemental refrigeration circuit using the work produced by the turbo-expansion of the partially cooled second portion of the compressed and purified feed stream;   cooling and expanding the compressed working fluid in a turbo-expander disposed within the supplemental refrigeration circuit;   warming the expanded working fluid by way of heat exchange with at least a portion of the feed stream to impart a portion of the refrigeration required by the cryogenic separation plant; and   recirculating at least a portion of the warmed working fluid to a compressor section within the supplemental refrigeration circuit after having been warmed by way of said heat exchange.   
     
     
         2 . The method of  claim 1  wherein the working fluid is selected from the group consisting of air, nitrogen, or a mixture of air constituents having an oxygen content not greater than air. 
     
     
         3 . The method of  claim 1  wherein the step of cooling the compressed working fluid further comprises cooling the compressed working fluid in one or more stages of cooling prior to expanding the compressed working fluid in the turboexpander. 
     
     
         4 . The method of  claim 1  wherein the step of cooling the compressed working fluid further comprises partially cooling the compressed working fluid in the main heat exchanger. 
     
     
         5 . The method of  claim 1  wherein the step of compressing the working fluid in a compressor section within the supplemental refrigeration circuit further comprises:
 compressing the working fluid in a first booster compressor coupled to the turboexpander section of the cryogenic separation plant; and 
 further compressing the working fluid in a second booster compressor coupled to the turboexpander disposed within the supplemental refrigeration circuit. 
 
     
     
         6 . The method of  claim 1  wherein the compressed and purified feed stream is at a pressure of greater than the critical pressure of the feed stream. 
     
     
         7 . The method of  claim 1  wherein the first portion of the compressed and purified feed stream directed to the main heat exchanger is less than about 35 percent by volume of the compressed and purified feed stream. 
     
     
         8 . The method of  claim 1  wherein the second portion of the compressed and purified feed stream diverted to the turboexpander section of the cryogenic separation plant is greater than about 65 percent by volume of the compressed and purified feed stream. 
     
     
         9 . The method of  claim 1  wherein the step of producing a compressed and purified feed stream further comprises the steps of:
 compressing an air feed stream in a multistage main air compression section of the cryogenic separation plant to produced a compressed feed air stream; and 
 purifying the compressed feed air stream in a pre-purification unit of the cryogenic separation plant to produce the compressed and purified feed stream. 
 
     
     
         10 . The method of  claim 9  wherein the working fluid comprises a portion of the compressed feed air stream diverted from within the multistage main air compression section of the cryogenic separation plant. 
     
     
         11 . The method of  claim 1  wherein the distillation column system comprises at least two columns wherein the feed mixture is fractionally distilling into their component parts to produce a plurality of product streams and waste streams, including the at least one liquid product stream. 
     
     
         12 . A supplemental refrigeration system for producing liquefied products in a cryogenic separation plant comprising:
 an intake conduit configured to receive a working fluid;   a first compressor coupled to the intake conduit and configured to compress the working fluid, the first compressor mechanically coupled to a first turboexpander of the cryogenic separation plant and using the work produced by the first turboexpander of the cryogenic separation plant;   a second compressor coupled to the first compressor and configured to further compress the compressed working fluid;   a second turboexpander operatively coupled to the second compressor configured to expand the further compressed working fluid to generate an expanded working fluid;   a heat exchanger configured to receive the expanded working fluid from the second turboexpander and warm the expanded working fluid to impart a portion of the refrigeration required by the cryogenic separation plant; and   a recirculating conduit configured to return the warmed expanded working fluid from the heat exchanger to the first compressor section.   
     
     
         13 . The supplemental refrigeration system of  claim 12  wherein the heat exchanger is a main heat exchanger of the cryogenic separation plant and the expanded working fluid imparts the portion of the refrigeration required by the cryogenic separation plant via the main heat exchanger. 
     
     
         14 . The supplemental refrigeration system of  claim 12  wherein the heat exchanger is an auxiliary heat exchanger and the expanded working fluid is warmed via indirect heat exchange with a boosted compressed stream from the cryogenic separation plant. 
     
     
         15 . The supplemental refrigeration system of  claim 12  further comprising one or more aftercoolers configured to cool the compressed working fluid and/or the further compressed working fluid. 
     
     
         16 . The supplemental refrigeration system of  claim 12  wherein the first compressor further comprises a booster compressor coupled to a lower column turboexpander of the cryogenic separation plant. 
     
     
         17 . The supplemental refrigeration system of  claim 12  further comprising a supplemental cooling circuit and wherein the further compressed working fluid is cooled via indirect heat exchange with expanded working fluid. 
     
     
         18 . The supplemental refrigeration system of  claim 17  wherein the supplemental cooling circuit further comprises passages within the main heat exchanger of the cryogenic separation plant.