Method and apparatus for separating air by cryogenic distillation

Abstract

The invention concerns a method for separating air by cryogenic distillation in an installation comprising a medium pressure column ( 3 ), a low pressure column ( 4 ) and a mixing column ( 6 ). According to the method: air is compressed in a compressor (C 01 ); is cooled in an exchange line ( 1 ); a first portion ( 2 ) of the air is fed to the vessel of the mixing column; a second portion of the air is fed to the medium pressure column where it separates; an oxygen-enriched liquid ( 19 ) and a nitrogen-enriched liquid ( 11 ) are fed from the medium pressure column to the low pressure column; an oxygen-rich liquid ( 26 ) is fed from the low pressure column to the top of the mixing column; at least one flow of liquid ( 27, 29 ) is drawn off from the medium or low pressure column; the second portion of air is boosted in a booster ( 8 ); this air is cooled in the exchange line; it is divided into a first fraction and second fraction; the first fraction of air is cooled in the exchange line; it is at least partially liquefied and then sent to the medium pressure column and/or the low pressure column; the second fraction of air is expanded in a Claude turbine ( 9 ) and is fed to the medium pressure column, and; an oxygen-rich flow ( 18 ) is drawn off from the mixing column and is heated in the exchange line.

1 - 10 . (canceled)  
   
   
       11 : A method for separating air by cryogenic distillation in an installation comprising a medium-pressure column, a low-pressure column and a mixing column in which: 
 a) air is compressed in a compressor, cooled in a heat exchange line and a first portion of the air is sent to the vessel of the mixing column;    b) a second portion of the air is sent to the medium-pressure column where it is separated;    c) an oxygen-enriched liquid and a nitrogen-enriched liquid are sent from the medium-pressure column to the low-pressure column;    d) an oxygen-enriched liquid is sent from the low-pressure column to the top of the mixing column;    e) at least one flow of liquid is drawn off from the medium or low-pressure column;    f) the second portion of the air is boosted in a booster, cooled in the heat exchange line, and divided into a first fraction and a second fraction;    g) the first fraction of the air is cooled in the heat exchange line, at least partially liquefied, and sent to the medium-pressure column and/or the low-pressure column;    h) the second fraction of the air is expanded in a Claude turbine and sent to the medium-pressure column; and    i) an oxygen-rich flow is drawn off from the mixing column and heated in the heat exchange line.    
   
   
       12 : The method of  claim 11 , in which the liquid drawn off from the medium or low-pressure column is an end product.  
   
   
       13 : The method of  claim 11 , in which the booster is coupled to the Claude turbine.  
   
   
       14 : The method of  claim 11 , in which the booster is a cold booster.  
   
   
       15 : The method of  claim 11 , in which the mixing column operates at between 8 and 20 bar abs.  
   
   
       16 : The method of  claim 11 , in which all the air sent for distillation is compressed to between 8 and 20 bar abs.  
   
   
       17 : The method of  claim 11 , in which between 40 and 90% of the air sent for distillation is boosted.  
   
   
       18 : The method of  claim 11 , in which the boosted air is boosted to between 12 and 30 bar abs.  
   
   
       19 : An installation for separating air by cryogenic distillation in an apparatus comprising a medium-pressure column, a low-pressure column and a mixing column, a Claude turbine, a booster, means for compressing air, means for sending a portion of the compressed air of the air to the mixing column, means for sending another portion of the compressed air to the booster, means for sending a fraction of the boosted air to the Claude turbine and for sending the expanded air to the medium-pressure column, means for sending the rest of the boosted air to the medium pressure and/or low-pressure column after liquefaction and expansion, and means for drawing off at least one liquid from the medium-pressure column and/or the low-pressure column as end product.  
   
   
       20 : The installation of  claim 19 , in which the booster is coupled to the Claude turbine.