Method and device for obtaining pure nitrogen and pure oxygen by low-temperature separation of air

Abstract

Feed air is compressed to a first pressure in a main air compressor. A first sub-stream of the air compressed to the first pressure is cooled and fed at least in part to the distillation column system. A second sub-stream of the air compressed to the first pressure is cooled and at least partially liquefied in a low-pressure column bottom evaporator. The at least partially liquefied second sub-stream is introduced at least in part into the distillation column system. A liquid oxygen-enriched fraction is introduced into the evaporation chamber of a high-pressure top condenser. An argon-containing oxygen stream from an intermediate point in the low-pressure column is introduced into an argon column. The second sub-stream is introduced at least in part into an argon top condenser and partially evaporated therein. The second sub-stream is then introduced at least in part into the high-pressure column and/or into the low-pressure column.

1 . A process for producing pure nitrogen and oxygen by cryogenic fractionation of air in a distillation column system having a high-pressure column ( 20 ) and a low-pressure column ( 21 ) and also a high-pressure column top condenser ( 23 ) and a low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ), both of which take the form of condenser-evaporators, wherein
 the entirety of the feed air is compressed to a first pressure in a main air compressor ( 1 ),   a first substream ( 10 ,  6 ,  15 ,  16 ;  209 ,  246 ,  247 ) of the air compressed to the first pressure is cooled in a main heat exchanger ( 26 ) and at least partly fed ( 18 ;  249 ) to the distillation column system,   a second substream ( 7 ) of the air compressed to the first pressure is cooled in the main heat exchanger ( 26 ) and then at least partly liquefied in the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ),   the at least partly liquefied second substream ( 31 ,  33 ,  19 ) is at least partly introduced into the distillation column system,   a liquid, oxygen-enriched fraction ( 62 ,  86 ) is introduced ( 63 ,  64 ,  65 ) into the evaporation space of the high-pressure column top condenser ( 23 ),   the distillation column system also has an argon column ( 22 ) with an argon top condenser ( 25 ) which takes the form of a condenser-evaporator, and   an argon-containing oxygen stream ( 70 ) is drawn off from an intermediate point in the low-pressure column ( 21 ) and introduced into the argon column ( 22 ),   
       characterized in that
 the second substream ( 31 ), downstream of the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ), is at least partly introduced into the argon top condenser ( 25 ) where it is partly evaporated and 
 the second substream ( 33 ), downstream of the argon top condenser ( 25 ), is at least partly introduced into the high-pressure column ( 20 ) and/or into the low-pressure column ( 21 ). 
 
     
     
         2 . The process as claimed in  claim 1 , characterized in that the first substream ( 16 ;  247 ), upstream of its introduction into the high-pressure column ( 20 ) or into the low-pressure column ( 21 ), is expanded to perform work in a first expansion machine ( 17 ;  248 ). 
     
     
         3 . The process as claimed in  claim 2 , characterized in that the first substream, upstream of its expansion to perform work, is recompressed ( 11 ,  13 ;  244 ) to a second pressure higher than the first pressure. 
     
     
         4 . The process as claimed in  claim 1 , characterized in that
 a liquid fraction ( 58 ;  78 ) from the distillation column system in the liquid state is brought ( 59 ,  79 ) to an elevated product pressure, warmed in the main heat exchanger ( 26 ) under this elevated product pressure and finally drawn off as a gaseous compressed product (GAN-IC; GOX-IC),   a third substream ( 10 ,  8 ) of the feed air compressed to the first pressure is recompressed ( 11 ,  34 ) to a third pressure higher than the first pressure and especially higher than the second pressure, and is cooled in the main heat exchanger ( 26 ), and   the cooled third substream ( 37 ) is expanded ( 38 ,  938 ) and introduced ( 40 ,  41 ,  43 ) into the high-pressure column ( 20 ) and/or the low-pressure column ( 21 ).   
     
     
         5 . The process as claimed in  claim 1 , characterized in that
 the liquid fraction is formed by a liquid oxygen stream ( 78 ) from the low-pressure column ( 21 ) or from the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ),   the liquid fraction is formed by a liquid nitrogen stream ( 58 ) from the high-pressure column ( 20 ) or from the high-pressure column top condenser ( 23 ;  323 ) or   a first liquid fraction is formed by a liquid oxygen stream ( 78 ) from the low-pressure column ( 21 ) or from the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ) and a second liquid fraction is formed by a liquid nitrogen stream ( 58 ) from the high-pressure column ( 20 ) or from the high-pressure column top condenser ( 23 ;  323 ).   
     
     
         6 . The process as claimed in  claim 4 , characterized in that the first substream ( 37 ) is expanded to perform work downstream of the main heat exchanger ( 26 ) in a liquid expander ( 38 ,  938 ). 
     
     
         7 . The process as claimed in  claim 1 , characterized in that a fourth substream ( 9 ) of the feed air compressed to the first pressure is expanded to perform work in a second expansion machine ( 48 ) and then introduced ( 49 ) into the low-pressure column ( 21 ). 
     
     
         8 . The process as claimed in  claim 1 , characterized in that the liquid oxygen-enriched fraction ( 63 ,  65 ) which is introduced into the evaporation space of the high-pressure column top condenser ( 23 ) is formed by bottoms liquid ( 62 ) from the high-pressure column ( 20 ) and/or from the remaining liquid  86  from the evaporation space of the argon top condenser  25 . 
     
     
         9 . The process as claimed in  claim 1 , characterized in that the liquid oxygen-enriched fraction which is introduced into the evaporation space of the high-pressure column top condenser ( 323 ) is formed by an intermediate liquid from the low-pressure column ( 21 ). 
     
     
         10 . The process as claimed in  claim 1 , characterized in that
 the low-pressure column ( 21 ) has an intermediate evaporator which takes the form of a condenser-evaporator, and   at least a portion of the second substream ( 489 ) is introduced into the liquefaction space of the intermediate evaporator ( 488 ) downstream of the low-pressure column reboiler ( 424 ) and upstream of the argon top condenser ( 25 ).   
     
     
         11 . The process as claimed in  claim 1 , characterized in that the evaporation space of the low-pressure column reboiler ( 524 ) takes the form of a dephlegmator. 
     
     
         12 . The process as claimed in  claim 1 , referring back to  claim 2 , characterized in that the expansion machine is formed by two series-connected turbines ( 617   a ,  617   b ) and especially the first substream ( 618 ,  616 ) is introduced between the two turbines ( 617   a ,  617   b ) into the main heat exchanger ( 26 ), where it is cooled or warmed. 
     
     
         13 . The process as claimed in  claim 12 , characterized in that the two turbines ( 617   a ,  617   b ) are decelerated by one of the following methods:
 one recompressor ( 613   a ,  613   b ) each, where the two recompressors are connected in series,   a common recompressor ( 813 ) mechanically coupled to both turbines ( 617   a ,  617   b ),   one electrical generator each.   
     
     
         14 . The process as claimed in  claim 6 , characterized in that the first substream ( 37 ), downstream of the main heat exchanger ( 26 ) and upstream of the liquid expander ( 938 ), is cooled in a countercurrent subcooler ( 42 ). 
     
     
         15 . An apparatus for production of pure nitrogen and oxygen by cryogenic fractionation of air, comprising
 a distillation column system having a high-pressure column ( 20 ) and a low-pressure column ( 21 ) and also a high-pressure column top condenser ( 23 ) and a low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ), both of which take the form of condenser-evaporators,   a main air compressor ( 1 ) for compression of the entirety of the feed air to a first pressure,   a main heat exchanger ( 26 ) for cooling of feed air,   means of supplying ( 18 ;  249 ) a first substream ( 10 ,  6 ,  15 ,  16 ;  209 ,  246 ,  247 ), cooled in the main heat exchanger ( 26 ), of the air compressed to the first pressure to the distillation column system,   means of supplying a second substream ( 7 ), cooled in the main heat exchanger ( 26 ), of the air compressed to the first pressure into the liquefaction space of the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ),   means of introducing the second substream ( 31 ,  33 ,  19 ) liquefied liquefaction space of the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ) into the distillation column system and comprising   means of introducing ( 63 ,  64 ,  65 ) a liquid oxygen-enriched fraction ( 62 ,  86 ) into the evaporation space of the high-pressure column top condenser ( 23 ),   wherein the distillation column system also includes an argon column ( 22 ) with an argon top condenser ( 25 )   and means of introducing an argon-containing oxygen stream ( 27 ) from an intermediate point in the low-pressure column ( 21 ) into the argon column ( 22 ),   
       characterized by
 means of introducing the second substream ( 31 ) downstream of the low-pressure column reboiler ( 24 ,  424 ,  488 ,  524 ) into the evaporation space of the argon top condenser ( 25 ) and 
 means of introducing the second substream ( 33 ) downstream of the argon top condenser ( 25 ) into the high-pressure column ( 20 ) and/or into the low-pressure column ( 21 ).