Air separation method and apparatus

Abstract

A method and apparatus for separating air by cryogenic rectification in which cooled, compressed and purified air is separated in a distillation column system having higher and lower pressure columns operatively associated with one another in a heat transfer relationship to produce an oxygen-rich liquid stream from the lower pressure column. The oxygen-rich liquid stream is pumped and heated through indirect heat exchange with a compressed heat exchange stream to form a pressurized oxygen product stream. Part of the air is sequentially and successively compressed in booster compressors driven by turboexpanders to form the compressed heat exchange stream while other parts of the air are expanded in turboexpanders driving the booster compressors to form exhaust streams that are introduced into both the higher and lower pressure columns to generate refrigeration.

I claim: 
     
         1 . A method of separating air within a cryogenic rectification process, said method comprising:
 separating the air in the cryogenic rectification process by cooling the air, after having been compressed and purified and rectifying the air in a distillation column system having a higher pressure column and a lower pressure column operatively associated within one another in a heat transfer relationship to produce return streams enriched in components of the air that are warmed through indirect heat exchange with the air to help cool the air and to produce product streams;   one of the product streams formed by withdrawing an oxygen-rich liquid stream from a bottom region of the lower pressure column, pumping at least part of the oxygen-rich liquid stream to produce a pumped liquid oxygen stream and heating at least part of the pumped liquid oxygen stream to form a pressurized oxygen product stream, the at least part of the pumped liquid oxygen stream constituting one of the return streams and the at least part of the pumped liquid oxygen stream heated through indirect heat exchange with a compressed heat exchange stream composed of part of the air to be cooled and rectified in the distillation column system;   forming the compressed heat exchange stream, a first exhaust stream and a second exhaust stream with the use of a first booster loaded expander and a second booster loaded expander having booster compressors driven by turboexpanders by sequentially compressing the part of the air within the booster compressors of the first booster loaded expander and the second booster loaded expander to form the compressed heat exchange stream and partially cooling and then expanding other parts of the air within the turboexpanders to produce a first exhaust stream and a second exhaust stream from expansion of the other parts of the air within in the first booster loaded expander and the second booster loaded expander, respectively; and   introducing the first exhaust stream into lower pressure column and the second exhaust stream into the higher pressure column, thereby to impart refrigeration into the cryogenic rectification process.   
     
     
         2 . The method of  claim 1 , wherein:
 a first compressed air stream, a second compressed air stream and a third compressed air stream are formed, at least in part, by compressing and purifying the air to produce a compressed and purified air stream and dividing the compressed and purified air stream into the first compressed air stream, the second compressed air stream and the third compressed air stream, thereby to form the part of the air from the first compressed air stream and the other parts of the air from the second compressed air stream and the third compressed air stream;   the first compressed air stream is sequentially compressed within a first and second booster compressor of the first booster loaded expander and the second booster loaded expander to form the compressed heat exchange stream;   the second compressed air stream is partially cooled and introduced into a first turboexpander of the first booster loaded expander, thereby to produce the first exhaust stream;   the third compressed air stream is partially cooled and introduced into a second turboexpander of the second booster loaded expander, thereby to produce the second exhaust stream; and   the first compressed air stream and the second compressed air stream is partially cooled in a main heat exchanger and the compressed heat exchange stream condensed in the main heat exchanger through indirect heat exchange with the at least part of the pumped liquid oxygen stream to form a liquid air stream;   the liquid air stream is divided into first and second subsidiary liquid air streams that are introduced into the higher pressure column and the lower pressure column after having been reduced in pressure compatible with the higher pressure column and the lower pressure column.   
     
     
         3 . The method of  claim 2 , wherein:
 the first compressed stream is further compressed in a third booster compressor located upstream of the first and second booster compressor; and   the third compressed air stream is further compressed in a forth booster compressor located upstream of the second turboexpander.   
     
     
         4 . The method of  claim 1  or  claim 2 , wherein:
 the oxygen-rich liquid stream is divided into a first oxygen-rich liquid subsidiary stream and a second oxygen-rich liquid subsidiary stream; 
 the first oxygen-rich liquid subsidiary stream is pumped by a pump to produce the pumped liquid oxygen stream; and 
 the second oxygen-rich liquid subsidiary stream is taken as a liquid product. 
 
     
     
         5 . The method of  claim 4 , wherein:
 a nitrogen-rich liquid stream is pumped to produce a pumped liquid nitrogen stream and is warmed through indirect heat exchange with the compressed heat exchange stream to produce another of the product streams; and   the pumped liquid oxygen stream is divided into a first pumped oxygen stream and a second pumped oxygen stream which are warmed through indirect heat exchange with the compressed heat exchange stream and the second pumped oxygen stream is passed through a valve prior to being warmed so that pressurized oxygen products at two different pressures are produced.   
     
     
         6 . The method of  claim 5 , wherein:
 the higher pressure column and the lower pressure column are thermally linked by a condenser reboiler condensing nitrogen-rich vapor column overhead in the higher pressure column through indirect heat exchange with the oxygen-rich liquid column bottoms of the lower pressure column, thereby producing nitrogen-rich reflux streams introduced, at least in part, into the higher pressure column and the lower pressure column as reflux;   the distillation column system also has an argon column connected to the lower pressure column to separate argon from oxygen containing in a crude argon feed stream withdrawn from the lower pressure column and fed to the argon column for rectification;   a kettle liquid stream composed of a crude liquid oxygen column bottoms of the higher pressure column is partially vaporized in an argon condenser connected to the argon column to produce reflux for the argon column and a liquid argon-rich liquid stream;   liquid and vapor phase streams produced as a result of partially vaporizing the kettle liquid stream are introduced into the lower pressure column for further refinement;   one of the nitrogen-rich reflux streams and the kettle liquid streams are subcooled in a subcooling heat exchanger; and   a lower pressure column, nitrogen-rich vapor column overhead stream and a waste nitrogen stream are partially warmed in the subcooling heat exchanger and further warmed within the main heat exchanger to help cool the incoming air.   
     
     
         7 . An air separation apparatus comprising:
 an air separation plant having a main heat exchanger for cooling the air, after having been compressed and purified and a distillation column system connected to the main heat exchanger and having a higher pressure column and a lower pressure column operatively associated within one another in a heat transfer relationship and producing return streams enriched in components of the air that are warmed within the main heat exchanger through indirect heat exchange with the air to help cool the air and to produce product streams;   the air separation plant having a pump connected to a bottom region of the lower pressure column to pump at least part of an oxygen-rich liquid stream to produce a pumped liquid oxygen stream and the pump also connected to the main heat exchanger so that at least part of the pumped liquid oxygen stream is heated within the main heat exchanger as one of the return streams to form a pressurized oxygen product stream constituting one of the product streams;   the main heat exchanger configured so that the at least part of the pumped liquid oxygen stream is heated through indirect heat exchange with a compressed heat exchange stream composed of part of the air to be cooled and rectified in the distillation column system; and   the air separation plant also having a first booster loaded expander and a second booster loaded expander comprising first and second booster compressors connected to one another and to the main heat exchanger so that part of the air is sequentially compressed within the first and second booster compressors to form the compressed heat exchange stream and first and second turboexpanders drive the first and second booster compressors, respectively;   the first and second turboexpanders connected to the main heat exchanger so that other parts of the air are expanded after having been partially cooled in the main heat exchanger, thereby producing a first exhaust stream and a second exhaust stream, respectively; and   the first and second turboexpanders connected to the distillation column system so that the first exhaust stream is introduced into lower pressure column and the second exhaust stream is introduced into the higher pressure column, thereby to impart refrigeration into the air separation plant.   
     
     
         8 . The apparatus of  claim 7 , wherein:
 the air separation plant has a main air compressor connected to a pre-purification unit to produce a compressed and purified air stream;   the first of the booster compressors in flow communication with the pre-purification unit so that the first compressed air stream is formed from part of the compressed and purified air stream and is sequentially compressed within a first and second booster compressors to form the compressed heat exchange stream;   the main heat exchanger is in flow communication with the pre-purification unit so that the second compressed air stream and the third compressed air stream are formed from other parts of the compressed and purified air stream and are partially cooled in the main heat exchanger;   the higher pressure column and the lower pressure column connected to the main heat exchanger so that a liquid air stream, formed from the compressed heat exchange stream indirectly exchanging heat with the at least part of the pumped liquid oxygen stream, divides into first and second subsidiary liquid air streams that are introduced into the higher pressure column and the lower pressure column; and   expansion valves are positioned so that the first and second subsidiary liquid air streams are reduced in pressure compatible with that the higher pressure column and the lower pressure column.   
     
     
         9 . The apparatus of  claim 7 , wherein:
 a third booster compressor is located between the pre-purification unit and the first of the booster compressors so that the first compressed air stream is further compressed in the third booster compressor; and   a forth booster compressor is located between the main heat exchanger and pre-purification unit so that the third compressed air stream is further compressed in the forth booster compressor prior to being partially cooled in the main heat exchanger.   
     
     
         10 . The apparatus of  claim 7  or  claim 8 , wherein:
 a piping juncture is located between the pump and the bottom region of the lower pressure column so that the oxygen-rich liquid stream is divided into a first oxygen-rich liquid subsidiary stream and a second oxygen-rich liquid subsidiary stream; and 
 the pump connected to the piping juncture so that first oxygen-rich liquid subsidiary stream is pumped by a pump to produce the pumped liquid oxygen stream and the second oxygen-rich liquid subsidiary stream is able to be taken as a liquid product. 
 
     
     
         11 . The apparatus of  claim 10 , wherein:
 the main heat exchanger also has passages to warm a pumped liquid nitrogen stream and a first pumped oxygen stream and a second pumped oxygen stream through indirect heat exchange with the compressed heat exchange stream to produce other of the product streams and   the pump is connected to the passages so that pumped liquid oxygen stream is divided into the first pumped oxygen stream and the second pumped oxygen stream;   an expansion valve is located between the pump and one of the passages so that the second pumped oxygen stream is passed through a valve prior to being warmed and pressurized oxygen products at two different pressures are produced; and   another pump is located between the higher pressure column and the main heat exchanger to pump a liquid nitrogen stream and thereby form the pumped liquid nitrogen stream.   
     
     
         12 . The apparatus of  claim 11 , wherein:
 the higher pressure column and the lower pressure column are thermally linked by a condenser reboiler condensing nitrogen-rich vapor column overhead in the higher pressure column through indirect heat exchange with the oxygen-rich liquid column bottoms of the lower pressure column, thereby producing nitrogen-rich reflux streams;   the higher pressure column and the lower pressure column are connected to the condenser reboiler so that the nitrogen-rich reflux streams are introduced, at least in part, into the higher pressure column and the lower pressure column as reflux;   the distillation column system also has an argon column connected to the lower pressure column so that a crude argon feed stream from the lower pressure column is rectified in the argon column to separate argon from oxygen contained in the crude argon feed stream;   an argon condenser is connected to the argon column to produce reflux for the argon column and a liquid argon-rich liquid stream;   the argon condenser is connected to the higher pressure column so that a kettle liquid stream composed of a crude liquid oxygen column bottoms of the higher pressure column is partially vaporized in the argon condenser;   the argon condenser connected to the lower pressure column so that liquid and vapor phase streams produced as a result of partially vaporizing the kettle liquid stream are introduced into the lower pressure column for further refinement;   a subcooling heat exchanger in flow communication with the condenser reboiler and the higher pressure column so that one of the nitrogen-rich reflux streams and the kettle liquid streams are subcooled in a subcooling heat exchanger; and   the subcooling heat exchanger positioned between the lower pressure column and the main heat exchanger so that a lower pressure column, nitrogen-rich vapor column overhead stream and a waste nitrogen stream are partially warmed in the subcooling heat exchanger and further warmed within the main heat exchanger to help cool the incoming air.