Method for flexible recovery of argon from a cryogenic air separation unit

Abstract

A method for flexible production of argon from a cryogenic air separation unit is provided. The disclosed 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.

What is claimed is: 
     
         1 . A method of producing an argon product in an air separation unit, the method comprising the steps of:
 producing a stream of compressed and purified air;   cooling the compressed and purified air stream in a main heat exchanger system;   rectifying the cooled, compressed and purified air stream in a distillation column system configured to produce a plurality of products including one or more oxygen products and the argon product, wherein the distillation column system comprises a higher pressure column and a lower pressure column linked in a heat transfer relationship via a condenser-reboiler and an argon column,   extracting a clean shelf nitrogen stream and a dirty shelf nitrogen stream from the distillation column system   subcooling the clean shelf nitrogen stream and the dirty shelf nitrogen stream in one or more nitrogen subcoolers;   directing the subcooled clean shelf nitrogen stream to an uppermost location of the lower pressure column and the subcooled dirty shelf nitrogen stream to another location of the lower pressure column at or below the uppermost location;   wherein the air separation unit operates in a first operating mode having a ratio of subcooled clean shelf nitrogen directed to the lower pressure column to subcooled dirty shelf nitrogen directed to the lower pressure column of less than 1.5 and the argon recovery within the air separation unit is less than a predetermined recovery level; and   wherein the air separation unit operates in a second operating mode having a ratio of subcooled clean shelf nitrogen directed to the lower pressure column to subcooled dirty shelf nitrogen directed to the lower pressure column of greater than or equal to 1.5 and the argon recovery within the air separation unit is higher than the predetermined recovery level;   opening and/or closing one or more valves configured to regulate flow of the clean shelf nitrogen stream and the dirty shelf nitrogen stream through a plurality of discrete passages in the one or more nitrogen subcoolers to switch the flow of the clean shelf nitrogen stream and the dirty shelf nitrogen stream through the plurality of discrete passages, wherein one or more of the plurality of discrete passages switches between sub cooling the dirty shelf nitrogen stream and sub cooling the clean shelf nitrogen stream;   wherein the air separation unit switches between the first operating mode and the second operating mode by such opening and/or closing of the one or more valves resulting in an adjustment in the recovery of the argon product from the distillation column system; and   wherein a power consumption of the air separation unit is lower in the first operating mode than in the second operating mode.   
     
     
         2 . The method of  claim 1 , further comprising the steps of:
 pumping an oxygen-rich liquid from the lower pressure column to produce a pumped liquid oxygen stream;   warming at least part of the pumped liquid oxygen stream in the main heat exchange system to produce an oxygen-rich gaseous product stream; and   taking a portion of the pumped liquid oxygen stream to produce a liquid oxygen product stream;   wherein the one or more oxygen products further comprise the oxygen-rich gaseous product stream and the liquid oxygen product stream.   
     
     
         3 . The method of  claim 1 , wherein the distillation column system is further configured to produce a liquid nitrogen product stream comprised of a portion of the clean shelf nitrogen stream. 
     
     
         4 . The method of  claim 3 , further comprising the steps of:
 diverting a portion of a nitrogen overhead from the higher pressure column to the main heat exchanger system; and   warming the diverted portion of the nitrogen overhead in the main heat exchange system to form a gaseous nitrogen product stream;   wherein the recovery of the one or more oxygen products, the one or more nitrogen products, and the argon product from the distillation column system is adjusted when the at least one of the plurality of discrete passages in the plurality of heat exchange cores switches between sub cooling the dirty shelf nitrogen stream and subcooling the clean shelf nitrogen stream and a flow of the diverted portion of the nitrogen overhead to the main heat exchanger system is varied; and   wherein the one or more nitrogen products further comprise the gaseous nitrogen product stream and the liquid nitrogen product stream.   
     
     
         5 . The method of  claim 1 , further comprising the steps of:
 splitting the stream of compressed and purified air into at least a first part of the compressed and purified air stream and a second part of the compressed and purified air stream;   further compressing the first part of the compressed and purified air stream in a booster compressor arrangement to produce a boosted pressure air stream; and   cooling the boosted pressure air stream in the main heat exchange system; and   directing the boosted pressure air stream to the distillation column system.   
     
     
         6 . The method of  claim 5 , further comprising the steps of expanding a portion of the second part of the compressed and purified air stream or a portion of the boosted pressure air stream in a turboexpander arrangement to form an exhaust stream and directing the exhaust stream to the distillation column system; 
     
     
         7 . The method of  claim 1 , wherein the argon column arrangement further comprises an argon distillation column, an argon condenser, and an argon refining system and wherein the method further comprises the steps of:
 directing an oxygen-argon containing stream from the lower pressure column to the argon distillation column;   rectifying the oxygen-argon containing stream in the argon distillation column to produce an argon-rich vapor stream and an oxygen-rich bottoms stream;   returning the oxygen-rich bottoms stream from the argon distillation column to an intermediate location of the lower pressure column;   condensing the argon-rich vapor stream in the argon condenser against a subcooled liquid oxygen to produce a crude argon stream; and   refining the crude argon stream in the argon refining system to produce the argon product.   
     
     
         8 . The method of  claim 7 , wherein the argon refining system further comprises a liquid phase argon adsorption system. 
     
     
         9 . The method of  claim 7 , wherein the argon refining system further comprises a gaseous phase argon pressure swing adsorption system. 
     
     
         10 . The method of  claim 7 , wherein the argon distillation column further comprises a superstaged argon distillation column.