System and method for enhanced recovery of argon and oxygen from a nitrogen producing cryogenic air separation unit

Abstract

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon, an overall nitrogen recovery of 98 percent or greater and limited gaseous oxygen production. The air separation is configured to produce a first high purity oxygen enriched stream and a second lower purity oxygen enriched stream from the lower pressure column, one of which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption pre-purifier unit. All or a portion of the first high purity oxygen enriched stream is vaporized in the main heat exchanger to produce the gaseous oxygen products.

1 - 21 . canceled 
     
     
         22 . 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, wherein the compressed and purified air stream is split into at least a boiler air stream and a turbine air stream;   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;   a main heat exchange system configured to cool the boiler air stream against a pumped oxygen stream received from the distillation column system to produce a cooled boiler air stream that is directed to the distillation column system and a gaseous oxygen product stream;   a turboexpander arrangement configured to expand the turbine air stream to form an exhaust stream;   the distillation column system is configured to receive the cooled boiler air stream and the exhaust stream and to produce a first oxygen enriched stream from the lower pressure column having a first oxygen concentration greater than or equal to 99.5 percent oxygen, a second oxygen enriched stream from the lower pressure column having a second oxygen concentration greater than 93 percent and lower than the first oxygen concentration, an oxygen enriched kettle stream from the bottom of the higher pressure column, and a nitrogen overhead stream from the lower pressure column;   an oxygen pump configured to pump the first oxygen enriched stream or the second oxygen enriched stream to produce the pumped oxygen stream;   wherein the argon column is configured to receive an argon-oxygen enriched stream from the lower pressure column and to produce a third 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 argon condenser is configured to condense the argon-enriched overhead against: (i) all or a portion of the first oxygen enriched stream from the lower pressure column, or (ii) all or a portion of the second oxygen enriched stream from the lower pressure column, to produce a crude argon stream, an argon reflux stream and an oxygen enriched waste stream;   wherein the air separation unit is configured to produce one or more nitrogen products, the gaseous oxygen product stream, and the crude argon stream and wherein the argon recovery in the crude argon stream is greater than 30 percent of the argon contained in the compressed air stream.   
     
     
         23 . The air separation unit of  claim 22 , further comprising a subcooler arrangement operatively coupled with the distillation column system and configured to subcool the oxygen enriched kettle stream from the higher pressure column and a nitrogen stream from the condenser-reboiler via indirect heat exchange with the nitrogen overhead stream from the lower pressure column. 
     
     
         24 . The air separation unit of  claim 23 , wherein the subcooler arrangement is further configured to subcool the first oxygen enriched stream from the lower pressure column or the second oxygen enriched stream from the lower pressure column via indirect heat exchange with the oxygen enriched waste stream. 
     
     
         25 . The air separation unit of  claim 22 , wherein the adsorption based pre-purifier unit is a multi-bed temperature swing adsorption unit configured for purifying the compressed air stream, the multi-bed temperature swing adsorption unit is further configured such that each bed alternates between an on-line operating phase adsorbing the water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream and an off-line operating phase where the bed is being regenerated with a purge gas taken from the air separation unit and having greater than 90.0 percent oxygen content; and
 wherein the air separation unit is configured to produce one or more high purity nitrogen products and have a nitrogen recovery of 98 percent or greater of the nitrogen contained in the compressed air stream.   
     
     
         26 . The air separation unit of  claim 25 , wherein the purge gas is the oxygen enriched waste stream. 
     
     
         27 . The air separation unit of  claim 26 , wherein the adsorption based pre-purifier unit further comprises a steam heater, electric heater, or other non-fired heater configured to heat the oxygen enriched waste stream to a temperature less than or equal to about 450° F., for use in regenerating the adsorbent beds in the temperature swing adsorption unit. 
     
     
         28 . The air separation unit of  claim 23 , further comprising a booster compressor configured to further compress the turbine air stream. 
     
     
         29 . The air separation unit of  claim 28 , wherein the turboexpander arrangement further comprises a booster loaded turbine configured to expand the further compressed turbine air stream to form the exhaust stream and the booster loaded turbine is operatively coupled to drive the booster compressor. 
     
     
         30 . The air separation unit of  claim 28 , wherein the subcooler arrangement is further configured to subcool the exhaust stream via indirect heat exchange with the waste oxygen enriched stream. 
     
     
         31 . The air separation unit of  claim 22 , wherein the higher pressure column is configured to operate at a pressure between 6.0 bar(a) and 10.0 bar(a), the lower pressure column is configured to operate at a pressure between 1.5 bar(a) and 2.8 bar(a), and the argon column is configured to operate at a pressure of between about 1.3 bar(a) and 2.8 bar(a). 
     
     
         32 . The air separation unit of  claim 22 , wherein the argon column in the argon column arrangement is a superstaged column having between 180 and 260 stages of separation or an ultrasuperstaged column having between 185 and 270 stages of separation. 
     
     
         33 . The air separation unit of  claim 22  wherein the argon column arrangement further comprises a first argon column configured as a superstaged argon column, a second argon column configured as a high ratio column. 
     
     
         34 . The air separation unit of  claim 23 , wherein the one or more nitrogen products further comprise a high purity gaseous nitrogen product stream produced by warming the nitrogen overhead stream in the subcooler arrangement and the main heat exchanger system and a high purity liquid nitrogen product stream produced by diverting a portion of the subcooled nitrogen from the condenser-reboiler.