Process and device for low-temperature separation of air

Abstract

The process and the device are used for low-temperature separation of air with a distilling-column system for nitrogen-oxygen separation ( 20 ), which has at least one separation column ( 21, 22 ). A main air stream ( 1, 5 ) is compressed in an air compressor ( 2 ) and purified in a purification device ( 4 ). A first air stream ( 7 ) and a second air stream ( 8 ) are diverted from the main air stream ( 5 ). The first air stream ( 7 ) is further compressed in two secondary compressors ( 10, 13 ) that are connected in series. The further compressed first air stream ( 15 ) is cooled by indirect heat exchange ( 16 ), and at least partially liquefied or pseudo-liquefied, and then introduced into the distilling-column system for nitrogen-oxygen separation ( 20 ). The second air stream ( 8 ) is cooled by indirect heat exchange ( 16 ) and then, divided into two partial streams ( 24, 27 ), is actively depressurized in two expanders ( 25, 28 ), whereby the two expanders have essentially the same inlet pressure. The actively depressurized partial streams ( 26, 29 ) of the second air stream are introduced ( 30, 129 ) at least in part into the distilling-column system for nitrogen-oxygen separation ( 20 ). The mechanical energy that is produced in the active depressurization ( 25, 28 ) of the second air stream is used at least partially in the driving of the two secondary compressors ( 10, 13 ) that are connected in series. A liquid product stream ( 31 ) is removed from the distilling-column system for nitrogen-oxygen separation ( 20 ), brought to an elevated pressure in the liquid state ( 32 ), and evaporated or pseudo-evaporated under this elevated pressure by indirect heat exchange ( 16 ) with the first air stream ( 15 ), and finally removed as a gaseous product stream ( 34 ). Both secondary compressors ( 10, 13 ) are operated with an inlet temperature that is higher than 250 K, in particular higher than 270 K.

1 . Process for low-temperature separation of air with a distilling-column system for nitrogen-oxygen separation ( 20 ), which has at least one separation column ( 21 ,  22 ), in which
 A main air stream ( 1 ,  5 ) is compressed in an air compressor ( 2 ) and purified in a purification device ( 4 ),   A first air stream ( 7 ) and a second air stream ( 8 ) are diverted from the main air stream ( 5 ),   The first air stream ( 7 ) is further compressed in two secondary compressors ( 10 ,  13 ) that are connected in series,   The further compressed first air stream ( 15 ) is cooled by indirect heat exchange ( 16 ) and at least partially liquefied or pseudo-liquefied, and then introduced into the distilling-column system for nitrogen-oxygen separation ( 20 ),   The second air stream ( 8 ) is cooled by indirect heat exchange ( 16 ) and then, divided into two partial streams ( 24 ,  27 ), is actively depressurized in two expanders ( 25 ,  28 ), whereby the two expanders have essentially the same inlet pressure,   The actively depressurized partial streams ( 26 ,  29 ) of the second air stream are introduced ( 30 ,  129 ) at least in part into the distilling-column system for nitrogen-oxygen separation ( 20 ),   The mechanical energy that is produced in the active depressurization ( 25 ,  28 ) of the second air stream is used at least partially in the driving of the two secondary compressors ( 10 ,  13 ) that are connected in series,   A liquid product stream ( 31 ) is removed from the distilling-column system for nitrogen-oxygen separation ( 20 ), brought to an elevated pressure in the liquid state ( 32 ), and evaporated or pseudo-evaporated under this elevated pressure by indirect heat exchange ( 16 ) with the first air stream ( 15 ), and finally removed as a gaseous product stream ( 34 ),   
     characterized in that both secondary compressors ( 10 ,  13 ) are operated at an inlet temperature that is higher than 250 K, in particular higher than 270 K. 
   
   
       2 . Process according to  claim 1 , wherein the distilling-column system for nitrogen-oxygen separation ( 20 ) has a high-pressure column ( 21 ) and a low-pressure column ( 22 ). 
   
   
       3 . Process according to  claim 2 , wherein a first ( 26 ) of the two partial streams of the second air stream is introduced ( 30 ) at least in part into the high-pressure column ( 21 ). 
   
   
       4 . Process according to  claim 3 , wherein the second ( 29 ) of the two partial streams of the second air stream is introduced ( 30 ) at least in part into the high-pressure column ( 21 ). 
   
   
       5 . Process according to  claim 2 , wherein the second of the two partial streams of the second air stream is introduced ( 129 ) at least in part into the low-pressure column ( 22 ). 
   
   
       6 . Process according to  claim 1 , wherein the distilling-column system for nitrogen-oxygen separation has a high-pressure column, a medium-pressure column, and a low-pressure column, whereby the first partial stream is introduced at least in part into the high-pressure column and the second partial stream is introduced at least in part into the medium-pressure column and/or the low-pressure column. 
   
   
       7 . Process according to  claim 1 , wherein the first air stream upstream from the first secondary compressor and the first air stream downstream from the second secondary compressor are brought together in indirect heat exchange ( 9 ). 
   
   
       8 . Process according to  claim 1 , wherein only the first secondary compressor, only the second secondary compressor, or both secondary compressors in each case have a secondary condenser ( 11 ,  14 ). 
   
   
       9 . Device for low-temperature separation of air for low-temperature separation of air with a distilling-column system for nitrogen-oxygen separation ( 20 ), which has at least one separation column ( 21 ,  22 ), with
 An air compressor ( 2 ) for compressing a main air stream ( 1 ),   Purification device ( 4 ) for purifying the compressed main air stream,   Means for diverting a first and second air stream ( 7 ,  8 ) from the main air stream ( 5 ),   Two secondary compressors ( 10 ,  13 ) that are connected in series for further compression of the first air stream ( 7 ),   Means ( 16 ,  20 ) for cooling and liquefaction or pseudo-liquefaction of the further compressed first air stream ( 15 ) by indirect heat exchange and for introduction thereof into the distilling-column system for nitrogen-oxygen separation ( 20 ),   Means ( 16 ) for cooling the second air stream ( 8 ) by indirect heat exchange ( 16 ) to an intermediate temperature,   Two expanders ( 25 ,  28 ) that are connected in parallel on the inlet side for active depressurization of the cooled second air stream in two partial streams ( 24 ,  27 ),   Means ( 26 ,  29 ,  30 ,  129 ) for introducing the actively depressurized partial streams ( 26 ,  29 ) of the second air stream into the distilling-column system for nitrogen-oxygen separation ( 20 ),   Means for transfer of the mechanical energy that is produced in the active depressurization ( 25 ,  28 ) of the second air stream to the two secondary compressors ( 10 ,  13 ) that are connected in series,   Means ( 31 ,  32 ,  33 ,  16 ,  34 ) for removing a liquid product stream ( 31 ) from the distilling-column system for nitrogen-oxygen separation ( 20 ), for increasing the pressure of the liquid product stream that is brought to an elevated pressure in the liquid state ( 32 ), for evaporation or pseudo-evaporation under this elevated pressure by indirect heat exchange with the first air stream ( 15 ), and for drawing off as a gaseous product stream ( 34 ),   
     wherein both secondary compressors ( 10 ,  13 ) are connected to means for feeding the first air stream under an inlet temperature that is higher than 250 K, in particular higher than 270 K.