Process for low-temperature separation of air

Abstract

In a low-temperature separation of air in a distillation system, having at least one high-pressure column ( 11 ) and one low-pressure column ( 12 ), process air ( 20, 32 ) is introduced into the high-pressure column ( 11 ). A liquid product stream ( 42; 46 ) is removed from the distillation system, brought in the liquid state to an elevated pressure ( 43; 47 ), evaporated or pseudo-evaporated under this elevated pressure by indirect heat exchange ( 6 ), and finally drawn off as a gaseous product stream ( 45; 49 ). All of the process air ( 1 ) is compressed in a main air compressor to a first pressure, which is at least equal to the operating pressure of the high-pressure column ( 11 ) and then is purified in a purification device. A first partial stream ( 2, 7 ) of the process air is fed under approximately the first pressure to a first expander ( 8 ), actively depressurized there to approximately the operating pressure of the low-pressure column ( 12 ), and then introduced ( 10 ) into the low-pressure column ( 12 ). A second partial stream ( 3 ) of the process air is compressed in a first secondary compressor ( 14 ) to a second pressure that is higher than the first pressure. At least one portion ( 17 ) of the second partial stream ( 16 ) downstream from the compression is further compressed in a second secondary compressor ( 18 ) to a third pressure, which is higher than the second pressure, fed to the indirect heat exchange ( 6 ) for evaporation or pseudo-evaporation of the liquid product stream, and then introduced ( 20 ) into the distilling-column system. The second secondary compressor ( 18 ) is designed as a cold compressor. At least a portion of the mechanical energy that is produced in the active depressurization ( 8 ) of the first partial stream ( 7 ) is used to drive the second secondary compressor ( 18 ).

1 . A process for low-temperature separation of air in a distillation system ( 20 ) that has at least one high-pressure column ( 11 ) and one low-pressure column ( 12 ), in which
 a branched stream of process air ( 20 ,  32 ,  132 ) after compression and purification is introduced into the high-pressure column ( 11 ),   a liquid product stream ( 42 ;  46 ;  346 ) is removed from the distillation system, brought in the liquid state to an elevated pressure ( 43 ;  47 ;  347 ) and evaporated or pseudo-evaporated under said elevated pressure by indirect heat exchange ( 6 ), and then drawn off as a gaseous product stream ( 45 ;  49 ;  349 ),   all of the process air ( 1 ) is compressed in a main air compressor to a first pressure, which is at least equal to the operating pressure of the high-pressure column ( 11 ),   and then the resultant compressed process air ( 1 ) is purified in a purification device,   a first partial stream ( 2 ,  7 ) of the resultant purified process air ( 1 ) is fed under approximately the first pressure to a first expander ( 8 ), actively depressurized therein to approximately the operating pressure of the low-pressure column ( 12 ), thereby producing mechanical energy and then introduced ( 10 ) into the low-pressure column ( 12 ),   a second partial stream ( 3 ) of the compressed purified process air ( 1 ) is compressed in a first secondary compressor ( 14 ) to a second pressure that is higher than the first pressure, and   at least one portion ( 17 ) of the second partial stream ( 16 ) downstream from the compression in a second secondary compressor ( 18 ) is further compressed to a third pressure, which is higher than the second pressure, fed to the indirect heat exchange ( 6 ) for evaporation or pseudo-evaporation of the liquid product stream, and then introduced into the distillation system ( 20 ), the second secondary compressor ( 18 ) being a cold compressor, and wherein   at least a portion of the mechanical energy produced in the active depressurization ( 8 ) of the first partial stream ( 7 ) drives the second secondary compressor ( 18 ).   
   
   
       2 . A process according to  claim 1 , wherein a third partial stream ( 4 ) of the process air is actively depressurized in a second expander ( 30 ,  130 ). 
   
   
       3 . A process according to  claim 2 , wherein the actively depressurized third partial stream ( 31 ) is introduced ( 10 ) into the low-pressure column ( 12 ). 
   
   
       4 . A process according to  claim 2 , wherein the actively depressurized third partial stream ( 131 ) is introduced ( 132 ) into the high-pressure column ( 11 ). 
   
   
       5 . A process according to  claim 1  wherein all of the process air is compressed to a pressure of more than 1 bar higher than the operating pressure of the high pressure column. 
   
   
       6 . A process according to  claim 1  wherein all of the process air is compressed to a pressure of more than 3 bars higher than the operating pressure of the high pressure column.