Enhancements to a moderate pressure nitrogen and argon producing cryogenic air separation unit

Abstract

Enhancements to the distillation column system and cycles for an argon and nitrogen producing cryogenic air separation unit are provided. The enhancements include systems and methods for: (i) recovery of xenon and krypton; (ii) production of oxygen product substantially free of hydrocarbons; and (iii) improvement in the design and performance of the super-stage argon column. 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; an argon product stream, a gaseous nitrogen product stream; and   wherein the distillation column system further comprises a rare gas rectification system configured to receive an argon-oxygen enriched stream from the lower pressure column and to produce a crude rare gas stream.   
     
     
         2 . The air separation unit of  claim 1 , wherein at least one of the oxygen enriched streams from the lower pressure column is an oxygen product stream and at least one of the oxygen enriched streams from the lower pressure column is an oxygen enriched condensing medium directed to the argon condenser. 
     
     
         3 . The air separation unit of  claim 1 , wherein the rare gas rectification system further comprises between 2 and 6 theoretical stages of separation. 
     
     
         4 . The air separation unit of  claim 1 , wherein the rare gas rectification system is configured to recover between about 90% to 99% of the xenon and between about 10% to 90% of the krypton in the compressed and purified air stream. 
     
     
         5 . The air separation unit of  claim 1 , wherein the rare gas rectification system further comprises an additional separation section of trays disposed in the lower pressure column just above the condenser-reboiler and the crude rare gas stream is extracted from the bottom of the lower pressure column. 
     
     
         6 . The air separation unit of  claim 1 , wherein the rare gas rectification system further comprises an additional separation section of trays disposed in an argon condenser vessel just above the argon condenser and the crude rare gas stream is extracted from the bottom of the argon condenser vessel. 
     
     
         7 . The air separation unit of  claim 1 , wherein the rare gas rectification system further comprises a bifurcated separation section of trays with a first part of the separation section disposed in an argon condenser vessel just above the argon condenser and a second part of the of the separation section disposed in the lower pressure column just above the condenser-reboiler and the crude rare gas stream is extracted from the bottom of the lower pressure column. 
     
     
         8 . The air separation unit of  claim 1 , wherein the rare gas rectification system further comprises a bifurcated separation section of trays with a first part of the separation section disposed in an argon condenser vessel just above the argon condenser and a second part of the of the separation section disposed in a stand-alone rare gas column and the crude rare gas stream is extracted from the bottom of the stand-alone rare gas column. 
     
     
         9 . The air separation unit of  claim 8 , wherein the crude rare gas stream is bifurcated into a first crude rare gas stream directed to an upper location of the stand-alone rare gas column and a second crude rare gas stream directed to an intermediate location of the stand-alone rare gas column. 
     
     
         10 . 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 an argon column, an argon condenser, and a reboiler;   wherein the distillation column system configured for receiving the cooled, compressed and purified air stream and produce a first oxygen enriched stream from the bottom of the lower pressure column; an argon product stream, a gaseous nitrogen product stream;   wherein the argon column arrangement is configured to receive an argon-oxygen enriched stream from the lower pressure column at the reboiler and produce a condensed argon-oxygen enriched stream that is let down in pressure and directed to an intermediate location of the argon column;   wherein the argon column arrangement is further configured to produce another oxygen enriched stream that is returned to or released into the lower pressure column and an argon-enriched overhead that is directed to the argon condenser; and   wherein the argon condenser is configured to condense the argon-enriched overhead against the oxygen enriched stream taken from the bottom of the lower pressure column to produce a crude argon stream, an argon reflux stream and an oxygen enriched waste stream.   
     
     
         11 . The air separation unit of  claim 10 , wherein the argon condenser is configured to condense the argon-enriched overhead against a mixture of the oxygen enriched stream taken from the bottom of the lower pressure column and a source of liquid nitrogen to produce the crude argon stream, the argon reflux stream and the oxygen enriched waste stream. 
     
     
         12 . The air separation unit of  claim 10 , wherein the oxygen enriched waste stream is warmed in the main heat exchange system and used to regenerate the adsorption based pre-purification unit. 
     
     
         13 . 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 an argon column and an argon condenser, the distillation column system configured for receiving the cooled, compressed and purified air stream and a first oxygen enriched stream from the lower pressure column; an argon product stream, a gaseous nitrogen product stream;   wherein the argon column arrangement is configured to receive an argon-oxygen enriched stream from the lower pressure column and produce a second oxygen enriched stream that is returned to or released into the lower pressure column and an argon-enriched overhead that is directed to the argon condenser;   wherein the distillation column system further comprises a supplemental oxygen column configured to receive another oxygen enriched stream from the argon column and rectify the received another oxygen enriched stream to produce an oxygen enriched overhead stream that is returned to the argon column and a hydrocarbon-free oxygen liquid stream;   wherein the supplemental oxygen column includes a reboiler disposed proximate the bottom of the supplemental oxygen column and configured to boil oxygen in the supplemental oxygen column against a stream of nitrogen received from the higher pressure column or a portion of the compressed and purified air stream to produce an ascending oxygen vapor in the supplemental oxygen column and a condensed nitrogen stream; and   wherein all or a portion of the first oxygen enriched stream from the lower pressure column is an oxygen enriched condensing medium directed to the argon condenser.   
     
     
         14 . The air separation unit of  claim 13 , wherein the another oxygen enriched stream from the argon column received by the supplemental oxygen column is a diverted portion of the second oxygen enriched stream and the oxygen enriched overhead stream is returned to the argon column. 
     
     
         15 . The air separation unit of  claim 13 , wherein the another oxygen enriched stream from the argon column received by the supplemental oxygen column is taken from an intermediate location of the argon column and the oxygen enriched overhead stream is returned to another intermediate location of the argon column just below the intermediate location of the argon column where the oxygen enriched stream is taken.