Air separation method and apparatus

Abstract

A cryogenic air separation method and apparatus in which a lower pressure distillation column is configured to receive, at successively higher locations of the lower pressure column and at successively lower temperatures, crude oxygen derived from a crude liquid oxygen stream discharged from a higher pressure column, an intermediate reflux stream and a nitrogen-rich reflux stream. All of the streams are subcooled and depressurized. The subcooling is conducted such that the intermediate reflux stream and the nitrogen-rich liquid stream cocurrently, indirectly exchange heat to a nitrogen-rich vapor stream withdrawn from the lower pressure column and the intermediate reflux stream is subcooled to a temperature between the temperatures over which the nitrogen-rich liquid stream is subcooled. Additionally, the crude liquid oxygen stream and the intermediate reflux stream can, cocurrently, indirectly exchange heat to a pressurized liquid stream used in forming an oxygen product and the nitrogen-rich vapor stream.

I claim: 
     
         1 . An air separation method comprising:
 separating air by a cryogenic rectification process to produce at least an oxygen product stream;   the cryogenic rectification process using a distillation column unit having a higher pressure column and a lower pressure column operatively associated with the higher pressure column in a heat transfer relationship and configured to receive, at successively higher locations of the lower pressure column, crude oxygen formed from a crude liquid oxygen stream discharged from the higher pressure column, an intermediate reflux stream and at least part of a nitrogen-rich reflux stream;   the cryogenic rectification process including depressurizing the crude liquid oxygen stream, the intermediate reflux stream and the at least part of the nitrogen-rich reflux stream and subcooling the crude liquid oxygen stream, the intermediate reflux stream and the nitrogen-rich reflux stream to successively lower temperatures prior to depressurization and through indirect heat exchange with at least a nitrogen-rich vapor stream withdrawn from the lower pressure column; and   the intermediate reflux stream and the nitrogen-rich reflux stream cocurrently, indirectly exchanging heat to the at least the nitrogen-rich vapor stream such that the intermediate reflux stream is subcooled to a temperature between the temperatures over which the nitrogen-rich liquid stream is subcooled.   
     
     
         2 . An air separation method comprising:
 separating air by a cryogenic rectification process to produce at least an oxygen product stream and such that the oxygen product stream is formed by warming a pressurized liquid stream;   the cryogenic rectification process using a distillation column unit having a higher pressure column and a lower pressure column operatively associated with the higher pressure column in a heat transfer relationship and configured to receive, at successively higher locations of the lower pressure column, crude oxygen formed from a crude liquid oxygen stream discharged from the higher pressure column, an intermediate reflux stream and at least part of a nitrogen-rich reflux stream;   the cryogenic rectification process including depressurizing the crude liquid oxygen stream, the intermediate reflux stream and the at least part of the nitrogen-rich reflux stream and subcooling the crude liquid oxygen stream, the intermediate reflux stream and the nitrogen-rich reflux stream to successively lower temperatures prior to depressurization and through indirect heat exchange with at least a nitrogen-rich vapor stream withdrawn from the lower pressure column; and   the crude liquid oxygen stream or both the crude liquid oxygen stream and the intermediate reflux stream cocurrently, indirectly exchanging heat to the pressurized liquid stream and the at least the nitrogen-rich vapor stream.   
     
     
         3 . The method of  claim 1 , wherein the crude liquid oxygen stream is subcooled to a further temperature that is equal to or greater than that of the nitrogen-rich reflux prior to the subcooling of the nitrogen-rich reflux stream and that lies within a temperature range over which the intermediate reflux stream is subcooled. 
     
     
         4 . The method of  claim 3 , wherein the crude liquid oxygen stream is subcooled from a yet further temperature, higher than that of the intermediate reflux stream prior to the subcooling of the intermediate reflux stream. 
     
     
         5 . The method of  claim 1  or  claim 2 , wherein:
 the distillation column unit also has an argon column; 
 a crude argon vapor stream is withdrawn from the lower pressure column and rectified in the argon column to produce an argon-rich vapor column overhead and an oxygen containing column bottoms; 
 an oxygen containing stream composed of the oxygen containing column bottoms is introduced into the lower pressure column; 
 at least part of the crude liquid oxygen stream, after having been subcooled, is expanded and is passed in indirect heat exchange with an argon-rich vapor stream composed of the argon-rich vapor column overhead, thereby partially vaporizing the at least part of the crude liquid oxygen stream and condensing the argon-rich vapor stream to form an argon-rich liquid stream and liquid and vapor phases of the at least part of the crude liquid oxygen stream; 
 part of the argon-rich liquid stream is discharged as an argon product stream and another part of the argon-rich liquid stream is introduced into the argon column as an argon column reflux stream; and 
 liquid and vapor phase streams composed of the crude liquid oxygen, respectively, are introduced into the lower pressure column and form at least part of the crude oxygen introduced into the lower pressure column. 
 
     
     
         6 . The air separation method of  claim 1 , wherein:
 the air is compressed and purified to form a compressed and purified air stream;   part of the compressed and purified air stream is cooled through indirect heat exchange with the nitrogen-rich vapor stream and thereafter, introduced into the higher pressure column;   the oxygen product stream is formed by further compressing another part of the compressed and purified air stream to form a boosted pressure compressed and purified air stream, pumping the at least part of the oxygen-rich liquid stream to form a pressurized liquid stream and warming at least part of the pressurized liquid stream through indirect heat exchange with the boosted pressure compressed and purified air stream, thereby producing the oxygen product from the pressurized liquid stream and a liquid air stream from at least part of the boosted pressure compressed and purified air stream; and   the intermediate reflux stream is composed of at least part of the liquid air stream.   
     
     
         7 . The air separation method of  claim 6 , wherein the crude liquid oxygen stream or both the crude liquid oxygen stream and the intermediate reflux stream cocurrently, indirectly exchanges heat to the pressurized liquid stream and at least the nitrogen-rich vapor stream and the pressurized liquid stream. 
     
     
         8 . The air separation method of  claim 2 , wherein:
 the air is compressed and purified to form a compressed and purified air stream;   part of the compressed and purified air stream is cooled through indirect heat exchange with the nitrogen-rich vapor stream and thereafter, introduced into the higher pressure column;   the oxygen product stream is formed by further compressing another part of the compressed and purified air stream to form a boosted pressure compressed and purified air stream, pumping the at least part of the oxygen-rich liquid stream to form the pressurized liquid stream and warming at least part of the pressurized liquid stream through indirect heat exchange with the boosted pressure compressed and purified air stream, thereby producing the oxygen product from the pressurized liquid stream and a liquid air stream from at least part of the boosted pressure compressed and purified air stream; and   the intermediate reflux stream is composed of at least part of the liquid air stream.   
     
     
         9 . The air separation method of  claim 6  or  claim 8 , wherein:
 a first part of the boosted pressure compressed and purified air stream is fully cooled and forms the liquid air stream; 
 a second part of the boosted pressure compressed and purified air stream is partially cooled and introduced into a turboexpander to form an exhaust stream; and 
 the exhaust stream is introduced into one of the higher pressure column and the lower pressure column to impart refrigeration into the cryogenic rectification process. 
 
     
     
         10 . An air separation apparatus comprising:
 an air separation plant configured to separate air by cryogenic rectification to at least produce an oxygen product stream;   the air separation plant having a distillation column unit comprising a higher pressure column and a lower pressure column operatively associated with the higher pressure column in a heat transfer relationship and configured to receive, at successively higher locations of the lower pressure column, crude oxygen formed from a crude liquid oxygen stream discharged from the higher pressure column, an intermediate reflux stream and at least part of nitrogen-rich reflux stream, a set of expansion valves and a subcooling heat exchanger;   the expansion valves positioned to depressurize the crude liquid oxygen stream, the intermediate reflux stream and the at least part of the nitrogen-rich reflux stream;   the subcooling heat exchanger positioned upstream of the expansion valves and connected to the lower pressure column to receive at least a nitrogen-rich vapor stream from the lower pressure column; and   the subcooling heat exchanger configured such that the crude liquid oxygen stream, the intermediate reflux stream and the nitrogen-rich liquid stream are subcooled to successively lower temperatures through indirect heat exchange with at least the nitrogen-rich vapor stream, the intermediate reflux stream and the nitrogen-rich liquid stream cocurrently, indirectly exchange heat to the at least the nitrogen-rich vapor stream and the intermediate reflux stream is subcooled to a temperature between the temperatures over which the nitrogen-rich liquid stream is subcooled.   
     
     
         11 . An air separation apparatus comprising:
 an air separation plant configured to separate air by cryogenic rectification to at least produce an oxygen product stream from a pressurized liquid stream;   the air separation plant having a distillation column unit comprising a higher pressure column and a lower pressure column operatively associated with the higher pressure column in a heat transfer relationship and configured to receive, at successively higher locations of the lower pressure column, crude oxygen formed from a crude liquid oxygen stream discharged from the higher pressure column, an intermediate reflux stream and at least part of nitrogen-rich reflux stream, a set of expansion valves and a subcooling heat exchanger;   the expansion valves positioned to depressurize the crude liquid oxygen stream, the intermediate reflux stream and the at least part of the nitrogen-rich reflux stream;   the subcooling heat exchanger positioned upstream of the expansion valves and connected to the lower pressure column to receive at least a nitrogen-rich vapor stream from the lower pressure column; and   the subcooling heat exchanger configured such that the crude liquid oxygen stream, the intermediate reflux stream and the nitrogen-rich liquid stream are subcooled to successively lower temperatures through indirect heat exchange with the at least the nitrogen-rich vapor stream and the crude liquid oxygen stream or both the crude liquid oxygen stream and the intermediate reflux stream, cocurrently, indirectly exchanges heat to the pressurized liquid stream and the at least the nitrogen-rich vapor stream.   
     
     
         12 . The air separation apparatus of  claim 10 , wherein the subcooling heat exchanger is also configured such that the crude liquid oxygen stream is subcooled to a further temperature that is equal to or greater than that of the nitrogen-rich liquid stream prior to the subcooling of the nitrogen-rich liquid stream and that lies within a temperature range over which the intermediate reflux stream is subcooled. 
     
     
         13 . The air separation apparatus of  claim 12 , wherein the subcooling heat exchanger is also configured such that the crude liquid oxygen stream is subcooled from a yet further temperature that is higher than that of the intermediate reflux stream prior to the subcooling of the intermediate reflux stream. 
     
     
         14 . The air separation apparatus of  claim 10  or  claim 11 , wherein:
 the distillation column unit also has an argon column; 
 the argon column connected to the lower pressure column such that a crude argon vapor stream is withdrawn from the lower pressure column and rectified in the argon column to produce an argon-rich vapor column overhead and an oxygen containing column bottoms and an oxygen containing stream composed of the oxygen containing column bottoms is introduced into the lower pressure column; 
 an argon condenser; 
 an expansion valve of the set of expansion valves is positioned between the subcooling unit and the argon condenser such that at least part of the crude liquid oxygen stream is expanded after having been subcooled; 
 the argon condenser is connected to the argon column and to the expansion valve, and configured such that at least part of the crude liquid oxygen stream, after having been subcooled and expanded, is passed in indirect heat exchange with an argon-rich vapor stream composed of the argon-rich vapor column overhead, thereby partially vaporizing the at least part of the crude liquid oxygen stream and condensing the argon-rich vapor stream to form an argon-rich liquid stream and liquid and vapor phases of the at least part of the crude liquid oxygen stream, part of the argon-rich liquid stream is discharged from the argon condenser to form an argon product stream and another part of the argon-rich liquid stream is introduced from the argon condenser into the argon column as an argon column reflux stream; and 
 the argon condenser is connected to the lower pressure column such that liquid and vapor phase streams composed of the liquid and vapor phases, respectively, are introduced into the lower pressure column to form at least part of the crude oxygen introduced into the lower pressure column. 
 
     
     
         15 . The air separation apparatus of  claim 10 , wherein:
 the air separation plant has a main heat exchanger, a main air compressor to compress the air, a purification unit connected to the main air compressor to purify the air after having been compressed and thereby to form a compressed and purified air stream and a booster compressor connected to the purification unit to form a further compressed and purified air stream;   the main heat exchanger is connected between the purification unit and the higher pressure column and configured such that part of the compressed and purified air stream is cooled through indirect heat exchange with the nitrogen-rich vapor stream and introduced into the higher pressure column;   a pump is connected to the distillation column unit to pump the at least part of the oxygen-rich liquid stream to form a pressurized liquid stream and the main heat exchanger connected to the booster compressor and also configured to warm at least part of the pressurized liquid stream through indirect heat exchange with the boosted pressure compressed and purified air stream, thereby producing the oxygen product from the pressurized liquid stream and a liquid air stream from at least part of the boosted pressure compressed and purified air stream; and   the main heat exchanger is in flow communication with the lower pressure column and another expansion valve of the set of expansion valves positioned between the subcooling unit and the lower pressure column such that at least part of the liquid air stream is subcooled within the subcooling heat exchanger, expanded and introduced into the lower pressure column and thereby forms the oxygen and nitrogen containing intermediate liquid reflux stream.   
     
     
         16 . The air separation apparatus of  claim 15 , wherein the subcooling heat exchanger is connected between the lower pressure column and the main heat exchanger and also configured such that the crude liquid oxygen stream or both the crude liquid oxygen stream and the intermediate reflux stream cocurrently, indirectly exchanges heat to the pressurized liquid stream and at least the nitrogen-rich vapor stream. 
     
     
         17 . The air separation apparatus of  claim 11 , wherein:
 the air separation plant has a main heat exchanger, a main air compressor to compress the air, a purification unit connected to the main air compressor to purify the air after having been compressed and thereby to form a compressed and purified air stream and a booster compressor connected to the purification unit to form a further compressed and purified air stream;   the main heat exchanger is connected between the purification unit and the higher pressure column and configured such that part of the compressed and purified air stream is cooled through indirect heat exchange with the nitrogen-rich vapor stream and introduced into the higher pressure column;   a pump is connected to the distillation column unit to pump the at least part of the oxygen-rich liquid stream to form the pressurized liquid stream and the main heat exchanger connected to the booster compressor and also configured to warm at least part of the pressurized liquid stream through indirect heat exchange with the boosted pressure compressed and purified air stream, thereby producing the oxygen product from the pressurized liquid stream and a liquid air stream from at least part of the boosted pressure compressed and purified air stream; and   the main heat exchanger is in flow communication with the lower pressure column and another expansion valve of the set of expansion valves positioned between the subcooling unit and the lower pressure column such that at least part of the liquid air stream is subcooled within the subcooling heat exchanger, expanded and introduced into the lower pressure column and thereby forms the intermediate liquid reflux stream.   
     
     
         18 . The air separation apparatus of  claim 15  or  claim 17 , wherein:
 the air separation plant has a turboexpander connected to one of the lower pressure column and the higher pressure column such that an exhaust stream generated by the turboexpander is introduced into the one of the lower pressure column and the higher pressure column to impart refrigeration into the air separation plant; and 
 the main heat exchanger is configured such that a first part of the boosted pressure compressed and purified air stream is fully cooled and forms the liquid air stream and a second part of the boosted pressure compressed and purified air stream is partially cooled and discharged from the main heat exchanger; and 
 the turboexpander is connected to the main heat exchanger such that the second part of the boosted pressure compressed and purified air stream is expanded in the turboexpander to generate the exhaust stream.