Nitrogen and argon producing air separation unit

Abstract

A nitrogen liquefier configured to be integrated with an argon and nitrogen producing cryogenic air separation unit and method of nitrogen liquefaction are provided. The integrated nitrogen liquefier and associated methods may be operated in at least three distinct modes including: (i) a nil liquid nitrogen mode; (ii) a low liquid nitrogen mode; and (iii) a high liquid nitrogen mode. The present systems and methods are further characterized in an oxygen enriched stream from the lower pressure column of the air separation unit is an oxygen enriched condensing medium used in the argon condenser.

What is claimed is: 
     
         1 . An air separation unit comprising:
 a main air compression system configured for receiving a stream of incoming feed air and producing a compressed air stream;   an adsorption based pre-purifier unit configured for removing water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream and producing a compressed and purified air stream;   a main heat exchange system configured to cool the compressed and purified air stream to temperatures suitable for fractional distillation;   a distillation column system having a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser-reboiler, the distillation column system further includes an argon column arrangement operatively coupled with the lower pressure column, the argon column arrangement having at least one argon column and an argon condenser, the distillation column system configured for receiving the cooled, compressed and purified air stream and produce at least two or more oxygen enriched streams from the lower pressure column; a crude argon stream, and a gaseous nitrogen stream;   wherein the argon column is configured to receive an argon-oxygen enriched stream from the lower pressure column and to produce an oxygen enriched bottoms that is returned to the lower pressure column and an argon-enriched overhead that is directed to the argon condenser;   wherein the argon condenser is configured to condense the argon-enriched overhead against a condensing medium comprised of all or a portion of one of the oxygen enriched streams taken from the lower pressure column and a source of nitrogen taken from the distillation column system to produce the crude argon stream, an argon reflux stream and an oxygen enriched waste stream.   wherein the source of nitrogen in the condensing medium directed to the argon condenser is taken from the lower pressure column; or the condenser-reboiler; or a combination of nitrogen taken from the lower pressure column and nitrogen taken from the condenser-reboiler.   
     
     
         2 . The air separation unit of  claim 1 , wherein the source of nitrogen in the condensing medium directed to the argon condenser is a portion of the gaseous nitrogen stream taken from the lower pressure column, and wherein the portion of the gaseous nitrogen stream is diverted to a nitrogen liquefier and liquified prior to being directed to the argon condenser. 
     
     
         3 . The air separation unit of  claim 2 , wherein the portion of the gaseous nitrogen stream diverted to the nitrogen liquefier is between 5% and 10% of the gaseous nitrogen stream. 
     
     
         4 . The air separation unit of  claim 1 , wherein the source of nitrogen in the condensing medium directed to the argon condenser is a liquid nitrogen stream taken from the condenser-reboiler in the lower pressure column. 
     
     
         5 . The air separation unit of  claim 1 , wherein the source of nitrogen in the condensing medium directed to the argon condenser is a combination of a first liquid nitrogen stream taken from the condenser-reboiler and a second liquid nitrogen stream from a nitrogen liquefier. 
     
     
         6 . The air separation unit of  claim 1 , wherein the oxygen enriched stream in the condensing medium directed to the argon condenser is a lower purity oxygen enriched stream taken from the lower pressure column several stages above the condenser-reboiler. 
     
     
         7 . The air separation unit of  claim 1 , wherein the oxygen enriched stream in the condensing medium directed to the argon condenser is a higher purity oxygen enriched stream taken from near the base of the lower pressure column. 
     
     
         8 . The air separation unit of  claim 1 , wherein the oxygen enriched waste stream is warmed in the main heat exchange system and used to regenerate the adsorption based pre-purification unit. 
     
     
         9 . The air separation unit of  claim 6 , wherein the oxygen enriched waste stream is further compressed upstream of the adsorption based pre-purification unit. 
     
     
         10 . A method of producing a liquid nitrogen product stream from an air separation unit, the method comprising the steps of:
 compressing a stream of incoming feed air in a main air compression system to produce a compressed air stream;   purifying the compressed air stream in an adsorption based pre-purifier unit to produce a compressed and purified air stream;   cooling the compressed and purified air stream in a main heat exchange system to temperatures suitable for fractional distillation;   fractionally distilling the cooled, compressed and purified air stream in a distillation column system having a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser-reboiler, the distillation column system further comprising an argon column arrangement operatively coupled with the lower pressure column, the argon column arrangement having at least one argon column and an argon condenser,   wherein the argon column is configured to receive an argon-oxygen enriched stream from the lower pressure column and to produce an oxygen enriched bottoms that is returned to the lower pressure column and an argon-enriched overhead that is directed to the argon condenser;   wherein the distillation column system is further configured to produce two or more oxygen enriched streams from the lower pressure column; a crude argon stream, and a gaseous nitrogen stream;   directing a condensing medium comprised of all or a portion of one of the oxygen enriched streams from the lower pressure column and a source of nitrogen to the argon condenser; and   condensing the argon-enriched overhead against the condensing medium to produce the crude argon stream, an argon reflux stream and an oxygen enriched waste stream;   wherein the source of nitrogen in the condensing medium directed to the argon condenser is taken from the lower pressure column; or the condenser-reboiler; or a combination of nitrogen taken from the lower pressure column and nitrogen taken from the condenser-reboiler.   
     
     
         11 . The method of  claim 10 , wherein the source of nitrogen in the condensing medium directed to the argon condenser is a portion of the gaseous nitrogen stream taken from the lower pressure column, and the method further comprises the steps of:
 diverting the portion of the gaseous nitrogen stream from the lower pressure column to a nitrogen liquefier;   liquefying the diverted portion of the gaseous nitrogen stream to produce a liquid nitrogen stream; and   mixing the liquid nitrogen stream with all or the portion of one of the oxygen enriched streams from the lower pressure column to form the condensing medium.   
     
     
         12 . The method of  claim 11 , wherein the portion of the gaseous nitrogen stream from the lower pressure column diverted to the nitrogen liquefier is between 5% and 10% of the gaseous nitrogen stream. 
     
     
         13 . The method of  claim 10 , wherein the source of nitrogen in the condensing medium directed to the argon condenser is a liquid nitrogen stream taken from the condenser-reboiler. 
     
     
         14 . The method of  claim 10 , wherein the source of nitrogen in the condensing medium directed to the argon condenser is a combination of a first liquid nitrogen stream taken from the condenser-reboiler and a second liquid nitrogen stream from a nitrogen liquefier. 
     
     
         15 . The method of  claim 10 , wherein the oxygen enriched stream in the condensing medium directed to the argon condenser is a lower purity oxygen enriched stream taken from the lower pressure column several stages above the condenser-reboiler. 
     
     
         16 . The method of  claim 10 , wherein the oxygen enriched stream in the condensing medium directed to the argon condenser is a higher purity oxygen enriched stream taken from near the base of the lower pressure column. 
     
     
         17 . The method of  claim 10 , further comprising the steps of: warming the oxygen enriched waste stream in the main heat exchange system; and regenerating the adsorption based pre-purification unit with the warmed oxygen enriched waste stream. 
     
     
         18 . The method of  claim 17 , further comprising the step of compressing the oxygen enriched waste stream upstream of the adsorption based pre-purification unit.