Separation method and apparatus

Abstract

A method and apparatus for producing an oxygen product in which air is separated in an installation including one or more air separation units having higher and lower pressure columns. An exhaust stream produced from a turboexpander and optionally an impure oxygen stream such as that derivable from higher pressure column bottoms is rectified within an auxiliary column to produce an oxygen containing stream that is introduced into the lower pressure column of each of the air separation units to increase the capacity of such columns. The pressure within the auxiliary column is set by the pressure of the exhaust stream such that a nitrogen-rich vapor stream extracted from the top of the auxiliary column can be used in regenerating adsorbent within a pre-purification unit utilized in connection with the installation.

1 . A method of separating air, said method comprising:
 separating a compressed and purified air stream in a cryogenic rectification process employing a pre-purification unit to purify the air of higher boiling impurities and at least one air separation unit having a higher pressure column and a lower pressure column configured to produce oxygen and nitrogen-rich fractions;   generating refrigeration within the cryogenic rectification process by further compressing and partially cooling part of the compressed and purified air stream and work expanding the part of the compressed and purified air stream, after having been further compressed, within a turboexpander to produce an exhaust stream;   introducing the exhaust stream into a bottom region of an auxiliary column and rectifying the exhaust stream within the auxiliary column to form an oxygen containing liquid as a column bottoms and an auxiliary column nitrogen-rich vapor column overhead;   withdrawing at least one oxygen containing stream from the auxiliary column having a lower nitrogen content than that of the exhaust stream and introducing the at least one oxygen containing stream into the at least one air separation unit for rectification within the lower pressure column;   withdrawing and warming an auxiliary column nitrogen-rich stream, composed of the auxiliary column nitrogen-rich vapor column overhead and introducing at least a portion of the auxiliary column nitrogen-rich vapor stream into the pre-purification unit so as to regenerate adsorbent within the pre-purification unit with the auxiliary column nitrogen-rich vapor stream; and   the work expanding of the part of the compressed and purified air stream within the turboexpander being conducted such that the exhaust stream pressure of the exhaust stream sets the pressure within the auxiliary column at a level that the auxiliary column nitrogen-rich vapor stream is able to be introduced into the pre-purification unit without further compression.   
     
     
         2 . The method of  claim 1 , wherein the auxiliary column nitrogen-rich vapor stream is at a higher pressure than that of at least one lower pressure nitrogen-rich vapor stream composed of lower pressure column nitrogen-rich vapor column overhead produced in the lower pressure column of the at least one air separation unit. 
     
     
         3 . The method of  claim 1 , wherein:
 the cryogenic rectification process generates at least one impure oxygen stream containing oxygen and nitrogen and having an oxygen content no less than that of the air;   the at least one impure oxygen stream, along with the exhaust stream, is introduced into a bottom region of an auxiliary column and rectified along with the exhaust stream within the auxiliary column to form the oxygen containing liquid as a column bottoms and the auxiliary column nitrogen-rich vapor column overhead; and   the at least one oxygen containing stream withdrawn from the auxiliary column has a lower nitrogen content of that of the at least one impure oxygen stream and the exhaust stream and is introduced into the lower pressure column of the at least one air separation unit.   
     
     
         4 . The method of  claim 3 , wherein the at least one impure oxygen stream is composed of a crude liquid oxygen column bottoms produced in the higher pressure column of the at least one air separation unit. 
     
     
         5 . The method of  claim 3  or  claim 4 , wherein:
 at least part of the at least one oxygen-rich liquid stream of high purity and composed of an oxygen-rich liquid column bottoms produced in the lower pressure column of the at least one air separation unit is pumped to form a pumped liquid oxygen stream; 
 another part of the compressed and purified air stream is further compressed to form a compressed air stream; 
 the compressed air stream indirectly exchanges heat with at least part of the pumped liquid oxygen stream, thereby forming a liquid air stream from the compressed air stream and an oxygen product from the at least part of the pumped liquid oxygen stream; and 
 intermediate reflux streams composed of the liquid stream are introduced into the lower pressure column of the at least one air separation unit above locations at which the at least one oxygen containing stream is introduced into the low pressure column and also, into the auxiliary column above the bottom region thereof. 
 
     
     
         6 . The method of  claim 5 , wherein:
 a higher pressure nitrogen-rich column overhead produced in the higher pressure column of the at least one air separation unit is condensed into a nitrogen-rich liquid against vaporizing part of the oxygen-rich liquid column bottoms;   reflux liquid streams composed of the nitrogen-rich liquid are introduced as reflux into the higher pressure column and the lower pressure column of the at least one air separation unit and into the auxiliary column;   the nitrogen-rich liquid that is used in forming the reflux liquid streams that are fed as the reflux to the lower pressure column of the at least one air separation unit and the auxiliary column is subcooled through indirect heat exchange with the at least one lower pressure nitrogen-rich vapor stream and the nitrogen-rich auxiliary column vapor stream; and   at least one lower pressure nitrogen-rich vapor stream composed of nitrogen-rich vapor column overhead produced in the lower pressure column and the auxiliary column nitrogen-rich vapor stream are fully warmed in the main heat exchanger used in cooling the air to a temperature suitable for its rectification within the at least one air separation unit.   
     
     
         7 . The method of  claim 6 , wherein the intermediate reflux streams are also introduced into the higher pressure column of the at least one air separation unit. 
     
     
         8 . An apparatus for separating air comprising:
 a cryogenic rectification installation configured to separate the air and including a main compressor and a pre-purification unit in flow communication with the main compressor to produce a compressed and purified air stream, a main heat exchanger configured to cool the compressed and purified air stream to a temperature suitable for its rectification, at least one air separation unit connected to the main heat exchanger and having a higher pressure column and a lower pressure column configured to produce oxygen and nitrogen-rich fractions, a refrigeration generation system and an auxiliary column;   the refrigeration generation system comprising a booster compressor in flow communication with the main compressor to further compress part of the compressed and purified air stream, the booster compressor connected to the main heat exchanger and the main heat exchanger configured to partially cool the part of the compressed and purified air stream after having been further compressed in the booster compressor and a turboexpander connected to the main heat exchanger to work expand the part of the compressed and purified air stream, after having been further compressed and partially cooled and thereby produce an exhaust stream;   the auxiliary column connected to the turboexpander so as to receive the exhaust stream in a bottom region thereof and configured to rectify the exhaust stream, thereby form an oxygen containing liquid as a column bottoms and an auxiliary column nitrogen-rich vapor column overhead;   the at least one air separation unit connected to the auxiliary column so that at least one oxygen containing stream is withdrawn from the auxiliary column having a lower nitrogen content of that of the exhaust stream and is introduced into the at least one air separation unit;   the pre-purification unit and the auxiliary column are connected to the main heat exchanger such that an auxiliary column nitrogen-rich vapor stream, composed of the auxiliary column nitrogen-rich vapor column overhead, after having been warmed in the main heat exchanger is introduced into the pre-purification unit so as to regenerate adsorbent within the pre-purification unit with the auxiliary column nitrogen-rich stream; and   the refrigeration system configured such that exhaust stream pressure of the exhaust stream sets pressure within the auxiliary column at a level that the auxiliary column nitrogen-rich stream is able to be introduced into the pre-purification unit without further compression.   
     
     
         9 . The apparatus of  claim 8 , wherein the auxiliary column nitrogen-rich vapor stream is at a higher pressure than that of at least one lower pressure nitrogen-rich vapor stream composed of lower pressure column nitrogen-rich vapor column overhead produced in the lower pressure column of the at least one air separation unit. 
     
     
         10 . The apparatus of  claim 8 , wherein:
 the auxiliary column is connected to the at least one air separation unit so as to receive at least one impure oxygen stream, together with the exhaust stream in the bottom region thereof, the at least one impure oxygen stream containing oxygen and nitrogen and having an oxygen content that is no less than that of the air;   the auxiliary column configured to rectify the at least one impure oxygen stream along with the exhaust stream, thereby forming the oxygen containing liquid as a column bottoms and the auxiliary column nitrogen-rich vapor column overhead; and   the lower pressure column of the at least one air separation unit is connected to the auxiliary column so that the at least one oxygen containing stream is withdrawn from the auxiliary column having a lower nitrogen content of that of the impure oxygen stream and the exhaust stream and is introduced into the lower pressure column for rectification within the lower pressure column of the at least one air separation unit.   
     
     
         11 . The apparatus of  claim 10 , wherein the auxiliary column is connected to the higher pressure column of the at least one air separation unit such that the at least one impure oxygen stream is composed of a crude liquid oxygen column bottoms produced in the higher pressure column of the at least one air separation unit. 
     
     
         12 . The apparatus of  claim 10  or  claim 11 , wherein:
 a pump is connected to the lower pressure column of the at least one air separation unit so that at least part of at least one oxygen-rich stream of high purity and composed of an oxygen-rich liquid column bottoms produced in the lower pressure column of the at least one air separation unit, is pumped to form a pumped liquid stream; 
 the main heat exchanger is connected to the pump so that the at least part of the pumped liquid stream is introduced into the main heat exchanger and warmed to form an oxygen product; 
 a further booster compressor compresses another part of the compressed and purified air stream, thereby to form a compressed air stream, the further booster compressor is connected to the main heat exchanger such that the pressurized liquid stream warms within the main heat exchanger through indirect heat exchange with the compressed air stream and the compressed air stream is thereby liquefied to form a liquid air stream; and 
 the lower pressure column of the at least one air separation unit and the auxiliary column are connected to the main heat exchanger such that intermediate reflux streams composed of the liquid air stream are introduced into the lower pressure column of the at least one air separation unit and the auxiliary column above locations at which the at least one oxygen containing stream is introduced into the lower pressure column and above the bottom region of the auxiliary column. 
 
     
     
         13 . The apparatus of  claim 12 , wherein:
 a heat exchanger is connected to the higher pressure column and the lower pressure column of the at least one air separation unit so that a higher pressure nitrogen-rich column overhead produced in the higher pressure column is condensed into a nitrogen-rich liquid against vaporizing part of the oxygen-rich liquid column bottoms;   the higher pressure column and the lower pressure column of the at least one air separation unit and the auxiliary column are connected to the heat exchanger so that reflux liquid streams composed of the nitrogen-rich liquid are introduced as reflux into the higher pressure column and the lower pressure column of the at least one air separation unit and into the auxiliary column; and   a subcooling unit is positioned between the lower pressure column of the at least one air separation unit and the main heat exchanger so that the nitrogen-rich liquid that is used in forming the reflux liquid streams, that are fed as the reflux to the lower pressure column of the at least one air separation unit and the auxiliary column, is subcooled through indirect heat exchange with a lower pressure nitrogen-rich vapor stream, composed of a nitrogen-rich vapor column overhead produced in the lower pressure column and the auxiliary column nitrogen-rich vapor stream.   
     
     
         14 . The apparatus of  claim 13 , wherein the higher pressure column of the at least one air separation unit is connected to the main heat exchanger so that the intermediate reflux streams are also introduced into the higher pressure column of the at least one air separation unit.