Method and installation for production of noble gases and oxygen by means of cryrogenic air distillation

Abstract

A method and an apparatus for producing oxygen and noble gases by cryogenic distillation. A first stream of cooled and purified air is sent to a medium pressure column where it is separated. A first nitrogen enriched stream is withdrawn from the medium pressure column, and part of this stream is sent to a low pressure column. An intermediate stream is withdrawn from an intermediate level of the medium pressure column. This intermediate stream is then sent to the low pressure column. A stream, which is enriched in oxygen relative to the intermediate stream, is withdrawn from the bottom of the medium pressure column and sent to an auxiliary column. The auxiliary column also receives at liquid stream of nitrogen which is used for reflux. A second nitrogen rich stream is withdrawn from the top of the low pressure column. A second oxygen rich liquid stream, which is suitable for use as a product, is withdrawn from the low pressure column. Finally, a final oxygen enriched stream which is also enriched with krypton and xenon, is withdrawn from the auxiliary column.

1 - 12 . (canceled)  
   
   
       13 . A method which may be used producing oxygen and rare gases by distillation, said method comprising: 
 a) separating at least one stream of cooled and purified air in a medium pressure column;    b) withdrawing at least a first nitrogen enriched stream from said medium pressure column;    c) sending at least part of said first nitrogen enriched stream to a low pressure column;    d) withdrawing an intermediate stream from an intermediate level of said medium pressure column;    e) withdrawing a first oxygen enriched stream from the bottom of said medium pressure column, wherein said first oxygen enriched stream is richer in oxygen than said intermediate stream;    f) sending said first oxygen enriched stream to the bottom of at least one auxiliary column;    g) withdrawing a second nitrogen rich stream from the top of said low pressure column;    h) withdrawing a second oxygen rich liquid stream from said low pressure column;    i) withdrawing a third oxygen enriched stream from said auxiliary column, wherein said third oxygen enriched stream is also enriched with xenon and krypton as compared to said second oxygen rich stream;    j) sending said intermediate stream to said low pressure column; and    k) sending at least one liquid reflux stream to said auxiliary column, wherein said reflux stream comprises about 78 mol % nitrogen.    
   
   
       14 . The method of  claim 13 , further comprising vaporizing said second oxygen rich liquid stream to obtain a gaseous product.  
   
   
       15 . The method of  claim 13 , further comprising indirectly sending at least part of said first nitrogen enriched stream to said low pressure column.  
   
   
       16 . The method of  claim 13 , further comprising: 
 a) sending said third oxygen enriched stream to the top of a purification column; and    b) withdrawing a final oxygen enriched stream from a final location on said purification column, wherein: 
 1) said final oxygen enriched stream comprises a mixture enriched with krypton and xenon; and  
 2) said final location is at least about three theoretical stages down from the top of said purification column.  
   
   
   
       17 . The method of  claim 13 , wherein said liquid reflux stream comprises at least one member selected from the group consisting of: 
 a) liquefied air; and    b) a liquid stream richer in nitrogen than a liquid air stream which is sent to said medium pressure column.    
   
   
       18 . The method of  claim 13 , wherein the bottom of said auxiliary column is heated by an overhead gas from an argon column.  
   
   
       19 . The method of  claim 17 , further comprising producing said liquid reflux stream by heat exchange with said second oxygen rich liquid stream.  
   
   
       20 . The method of  claim 19 , wherein said heat exchange takes place after a pressurization step.  
   
   
       21 . The method of  claim 17 , wherein said reflux stream comprises at least about 80 mol % nitrogen.  
   
   
       22 . The method of  claim 17 , wherein said liquefied air does not originate from said medium pressure column.  
   
   
       23 . The method of  claim 13 , wherein said reflux stream is richer in nitrogen than said intermediate stream.  
   
   
       24 . The method of  claim 13 , further comprising withdrawing at least about 10% of all the oxygen produced by said method from said low pressure column.  
   
   
       25 . An apparatus which may be used for producing oxygen and rare gases by distillation, said apparatus comprising: 
 a) at least one medium pressure column;    b) a low pressure column;    c) an auxiliary column;    d) a first distribution means for sending at least one stream of cooled and purified air to said medium pressure column, wherein said cooled and purified stream is then separated;    e) a first withdrawing means for withdrawing at least a first nitrogen enriched stream from said medium pressure column;    f) a second distribution means for sending at least a portion of said first nitrogen enriched stream to said low pressure column;    g) a second withdrawing means for withdrawing a second nitrogen rich stream from the top of said low pressure column;    h) a third withdrawing means for withdrawing an intermediate stream from an intermediate level of said medium pressure column;    i) a third distribution means for sending a first oxygen enriched stream from said medium pressure column to said auxiliary column, wherein said first oxygen enriched stream is richer in oxygen than said intermediate stream;    j) a fourth distribution means for sending a liquid reflux stream to said auxiliary column;    k) a fourth withdrawing means for withdrawing a second oxygen rich stream from the bottom of said low pressure column, wherein said second oxygen rich stream is withdrawn as a liquid and is suitable for use as product;    l) a fifth withdrawing means for withdrawing a third oxygen enriched stream from said auxiliary column, wherein: 
 1) said third oxygen enriched stream is richer in krypton and xenon than said second oxygen rich stream; and  
 2) said fifth withdrawing means comprises a fifth distribution means for sending a second reflux stream to said auxiliary column, wherein said second reflux stream comprises at least one member selected from the group consisting of: 
 i) liquefied air; and  
 ii) a liquid stream richer in nitrogen than a liquid air stream which is sent to said medium pressure column.  
 
   
   
   
       26 . The apparatus of  claim 25 , wherein said second oxygen rich liquid stream is vaporized prior to withdrawal in order to obtain a gaseous product.  
   
   
       27 . The apparatus of  claim 25 , wherein said second distribution means indirectly sends at least a portion of said first nitrogen enriched stream to said low pressure column.  
   
   
       28 . The apparatus of  claim 25 , further comprising: 
 a) a purification column;    b) a purification distribution means for sending said third oxygen enriched stream into the top of said purification column;    c) a purification withdraw means for withdrawing a final oxygen enriched stream, wherein: 
 1) said final oxygen enriched stream comprises a mixture enriched with krypton and xenon; and  
 2) said final oxygen enriched stream is withdrawn at least about three theoretical stages down from the top of said purification column.  
   
   
   
       29 . The apparatus of  claim 25 , further comprising an exchange line, wherein said second reflux stream is produced in said exchange line by heat exchange with fourth oxygen rich stream.  
   
   
       30 . The apparatus of  claim 29 , wherein said second reflux stream is produced after a pressurization step.