System and method for flexible recovery of argon from a cryogenic air separation unit

Abstract

A system and method for flexible production of argon from a cryogenic air separation unit is provided. The cryogenic air separation unit is capable of operating in a ‘no-argon’ or ‘low-argon’ mode when argon demand is low or non-existent and then switching to operating in a ‘high-argon’ mode when argon is needed. The recovery of the argon products from the air separation unit is adjusted by varying the percentages of dirty shelf nitrogen and clean shelf nitrogen in the reflux stream directed to the lower pressure column. The cryogenic air separation unit and associated method also provides an efficient argon production/rejection process that minimizes the power consumption when the cryogenic air separation unit is operating in a ‘no-argon’ or ‘low-argon’ mode yet maintains the capability to produce higher volumes of argon products at full design capacity to meet argon product demands.

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         30 . An air separation unit comprising:
 a main air compression system configured for producing a compressed and purified air stream;   a main heat exchange system configured to cool the compressed and purified air stream;   a distillation column system comprising a plurality of columns including a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser-reboiler and an argon column arrangement operatively coupled with the lower pressure column, the distillation column system configured to receive the compressed and purified air stream and produce a clean shelf nitrogen stream, a dirty shelf nitrogen stream from the plurality of columns, one or more oxygen products from the lower pressure column, and an argon product from the argon column;   a nitrogen subcooler system having a plurality of valves and a plurality of discrete passages through one or more heat exchanging cores, the nitrogen subcooler system configured to subcool the clean shelf nitrogen stream and the dirty shelf nitrogen stream via indirect heat exchange with one or more nitrogen streams from the lower pressure column and produce a first nitrogen reflux stream comprised of the clean shelf nitrogen stream, and a second nitrogen reflux stream comprised of the dirty shelf nitrogen stream; and   a plurality of reflux conduits configured to directing the first nitrogen reflux stream to an uppermost location of the lower pressure column and directing the second nitrogen reflux stream to a location of the lower pressure column at or below the uppermost location;   wherein the plurality of valves are configured to regulate flow of the clean shelf nitrogen stream and the dirty shelf nitrogen stream through the plurality of discrete passages in the one or more heat exchange cores of the nitrogen subcooler system and wherein at least one of the plurality of discrete passages in the one or more heat exchange cores is configured to subcool the dirty shelf nitrogen stream when the plurality of valves are in a first operating mode and subcool the clean shelf nitrogen stream when the plurality of valves are in a second operating mode;   wherein a ratio of subcooled clean shelf nitrogen directed to the lower pressure column to subcooled dirty shelf nitrogen directed to the lower pressure column is less than 1.5 in the first operating mode and wherein the ratio of subcooled clean shelf nitrogen directed to the lower pressure column to subcooled dirty shelf nitrogen directed to the lower pressure column is greater than or equal to 1.5 in the second operating mode; and   wherein the argon recovery within the air separation unit when the plurality of valves are in the second operating mode is higher than the argon recovery within the air separation unit when the plurality of valves are in the second operating mode and a power consumption of the air separation unit is lower when the plurality of valves are in the first operating mode than when the plurality of valves are in the second operating mode.   
     
     
         31 . The air separation unit of  claim 30 , wherein the distillation column system is further configured to produce a liquid nitrogen product stream comprised of a portion of the clean shelf nitrogen and wherein the recovery of the one or more oxygen products, nitrogen product, and argon product from the air separation unit is adjusted by varying the percentage of dirty shelf nitrogen in the total nitrogen reflux stream. 
     
     
         32 . The air separation unit of  claim 31 , wherein a portion of a nitrogen overhead from the lower pressure column is diverted from the distillation column system to the main heat exchanger system, and wherein the diverted portion of the nitrogen overhead is warmed in the main heat exchange system to form a gaseous nitrogen product stream. 
     
     
         33 . The air separation unit of  claim 32 , wherein argon recovery within the air separation unit is also adjusted via varying the amount of nitrogen overhead diverted from the from the distillation column system to the main heat exchanger system. 
     
     
         34 . The air separation unit of  claim 30 , further comprising a pump configured to pump the oxygen-rich liquid from the lower pressure column to produce a pumped liquid oxygen stream, and wherein at least part of the pumped liquid oxygen stream is warmed in the main heat exchange system to form a gaseous oxygen-rich product. 
     
     
         35 . The air separation unit of  claim 34 , wherein a portion of the pumped liquid oxygen stream is taken as a liquid oxygen product stream. 
     
     
         36 . The air separation unit of  claim 30 , wherein the nitrogen subcooler system further comprises:
 a first inlet configured to receive the dirty shelf nitrogen stream;   a second inlet configured to receive the clean shelf nitrogen stream;   a header conduit coupled to the first inlet and the second inlet and configured to receive the dirty shelf nitrogen stream from the first inlet and the clean shelf nitrogen stream from the second inlet;   one or more heat exchanger cores coupled to the header conduit configured to cool portions of the clean shelf nitrogen stream and the dirty shelf nitrogen stream via indirect heat exchange with one or more nitrogen streams from the lower pressure column;   one or more valves disposed in the header conduit configured to separate the dirty shelf nitrogen stream from the clean shelf nitrogen stream such that each heat exchanger core receives a portion of the dirty shelf nitrogen stream and a portion of the clean shelf nitrogen streams in discrete passages, or a portion of the dirty shelf nitrogen stream, or a portion of the clean shelf nitrogen stream;   a clean shelf outlet circuit configured to receive the clean shelf nitrogen from the heat exchanger cores cooling the clean shelf nitrogen, the clean shelf outlet circuit having one or more valves operatively configured to direct the clean shelf nitrogen stream to the lower pressure column at the uppermost location; and   a dirty shelf outlet circuit configured to receive the dirty shelf nitrogen from the heat exchanger cores cooling the dirty shelf nitrogen, the dirty shelf outlet circuit having one or more valves operatively configured to direct the dirty shelf nitrogen stream to the lower pressure column at the first location at the uppermost location or at the second location below the uppermost location.   
     
     
         37 . The air separation unit of  claim 36 , wherein the nitrogen subcooler system further comprises between one heat exchanger core and twelve heat exchanger cores. 
     
     
         38 . The air separation unit of  claim 30 , wherein the argon column arrangement further comprises an argon rejection column disposed adjacent to a portion of the lower pressure column and within a lower pressure column structure. 
     
     
         39 . The air separation unit of  claim 30 , wherein the argon column arrangement further comprises:
 an argon distillation column configured to rectify an oxygen-argon containing stream drawn from the lower pressure column and produce a crude argon stream;   an argon condenser configured to condense an argon-rich vapor stream using a condensing stream of subcooled kettle oxygen from the higher pressure column to produce an argon-rich liquid as reflux to the argon distillation column while releasing or directing the vaporized or partially vaporized condensing medium to an intermediate location of the lower pressure column; and   an argon refining system configured to receive the crude argon stream from the argon distillation column and produce an argon product stream.   
     
     
         40 . The air separation unit of  claim 39 , wherein the argon refining system further comprises a liquid phase argon adsorption system. 
     
     
         41 . The air separation unit of  claim 39 , wherein the argon refining system further comprises a gaseous phase argon pressure swing adsorption system. 
     
     
         42 . The air separation unit of  claim 39 , wherein the argon refining system further comprises a superstaged argon distillation column and the argon-rich vapor stream condensed in the argon condenser is an argon-rich vapor overhead stream from the superstaged argon distillation column.