Process and apparatus for producing a pressurized product by low-temperature fractionation of air

Abstract

For producing a pressurized product by low-temperature producing a pressurized product by low-temperature fractionation of air in a rectification system which has a high-pressure column ( 13 ) and a low-pressure column ( 14 ), a first feed airstream ( 12 ) is introduced into the high-pressure column ( 13 ), and an oxygen-rich fraction ( 38 ) from the low-pressure column ( 14 ) is brought ( 39 ) to pressure in the liquid state and introduced ( 41 ) into a mixing column ( 16 ). A second feed airstream ( 6, 15 ) is introduced into the lower region of the mixing column ( 16 ) and brought into countercurrent contact with the oxygen-rich fraction ( 41 ). The mixing column ( 16 ) is operated at a pressure (P M1S ) which is lower than the operating pressure (p HDS ) of the high-pressure column ( 13 ). A total airstream ( 1 ) which comprises the first and second feed airstreams is compressed ( 2 ) to a first pressure (p 1 ) which is lower than the operating pressure (p HDS ) of the high-pressure column ( 13 ) and is purified ( 3 ) at about this first pressure (p 2 ) . The purified total airstream ( 4 ) is divided into the first ( 5 ) and the second (6) feed airstream. The first feed airstream ( 5 ) is further compressed ( 8 ) separately from the second feed airstream to a second pressure (P 2 ) which is at least equal to the operating pressure (P HDS ) of the high-pressure column ( 13 ).

1 . A process for producing a pressurized product by low-temperature fractionation of air in a rectification system which has a high-pressure column ( 13 ) and a low-pressure column ( 14 ), in which 
 a first feed airstream ( 12 ) is introduced into the high-pressure column ( 13 ),    an oxygen-rich fraction ( 38 ) from the low-pressure column ( 14 ) is brought ( 39 ) to pressure in the liquid state and introduced ( 41 ) into a mixing column ( 16 ),    a second feed airstream ( 6 ,  15 ,  306 ,  406 ) is introduced into the lower region of the mixing column ( 16 ) and brought into countercurrent contact with the oxygen-rich fraction ( 41 ),    with the mixing column ( 16 ) being operated at a pressure (p MIS ) which is lower than the operating pressure (p HDS ) of the high-pressure column ( 13 ), and in which    a gaseous top product ( 51 ) is taken off from the upper region of the mixing column ( 16 ) and produced as pressurized product ( 52 ),    characterized in that    a total airstream ( 1 ) which comprises the first and second feed airstreams is compressed ( 2 ) to a first pressure (p 1 ) which is lower than the operating pressure (p HDS ) of the high-pressure column ( 13 ),    the total airstream ( 4 ) is divided into the first ( 5 ) and the second ( 6 ,  306 ,  406 ) feed airstreams and in that    the first feed airstream ( 5 ) is further compressed ( 8 ,  108 ) separately from the second feed airstream to a second pressure (p 2 ) which is at least equal to the operating pressure (p HDS ) of the high-pressure column ( 13 ).    
     
     
         2 . Process according to    claim 1   , characterized in that the first pressure (p 1 ) is about equal to the operating pressure (p M1S ) of the mixing column ( 16 ).  
     
     
         3 . Process according to    claim 1   , characterized in that the first pressure is lower than the operating pressure (p M1S ) of the mixing column ( 16 ) and in that the second feed airstream ( 306 ,  406 ) is further compressed ( 317 ,  417 ) separately from the first feed airstream to a third pressure (p 3 ) which is at least equal to the operating pressure (p M1S ) of the mixing column ( 16 ).  
     
     
         4 . Process according to one of    claims 1    to    3   , characterized in that the oxygen-rich fraction brought to pressure in the liquid state, before the introduction ( 41 ) into the mixing column ( 16 ), is warmed in indirect heat exchange ( 40 ) with a superheated airstream ( 42 ).  
     
     
         5 . Process according to one of    claims 1    to    4   , characterized in that a third feed airstream ( 7 ,  50 ,  207 ,  407 ,  450 ) is work-expanded ( 20 ,  420 ) and introduced ( 21 ) into the low-pressure column ( 14 ).  
     
     
         6 . Process according to one of claims l to  5 , characterized in that the third feed airstream ( 7 ), before the work expansion ( 20 ) , is recompressed ( 17 ) with, in particular, mechanical energy produced during the work expansion ( 20 ) being used for the recompression ( 17 ).  
     
     
         7 . Process according to one of    claims 1    to    6   , characterized in that the third feed airstream is formed downstream of the purification ( 3 ) by a portion of the total airstream ( 4 ) and is fed ( 7 ,  207 ) directly, or after joint recompression ( 108 ) with the first feed airstream, to the recompression ( 17 ).  
     
     
         8 . Process according to one of    claims 1    to    4   , characterized in that the second feed airsteam ( 306 ,  349 ,  350 ) is work-expanded ( 320 ) before its introduction into the mixing column.  
     
     
         9 . Apparatus for producing a pressurized product by low-temperature fractionation of air by a rectification system which has a high-pressure column ( 13 ) and a low-pressure column ( 14 ) and having 
 a first feed air line ( 5 ,  11 ,  12 ) which leads into the high-pressure column ( 13 ),    a liquid line ( 38 ,  41 ) for taking off an oxygen-rich fraction from the low-pressure column ( 14 ), which comprises means ( 39 ) for pressure elevation and leads to a mixing column ( 16 ),    a second feed air line ( 6 ,  15 ) which leads to the lower region of the mixing column ( 16 ), and having    an oxygen product line which is connected to the upper region of the mixing column ( 16 ),    characterized by    a total air line which leads via an air compressor ( 2 ) and a purification device ( 3 ) and is connected downstream to the first and second feed air lines and by    a recompressor ( 8 ,  108 ) which is disposed in the first feed air line ( 5 ,  11 ,  12 ).