Three-column system for the low-temperature fractionation of air

Abstract

The process and the apparatus are used for the low-temperature fractionation of air in a three-column system which has a high-pressure column ( 5 ), a low-pressure column ( 7 ) and a medial column ( 6 ). Charge air ( 1, 2, 4 ) is introduced into the high-pressure column ( 5 ), where it is separated into a first oxygen-enriched liquid and a first nitrogen fraction ( 16 ). At least a part ( 19 ) of the first nitrogen fraction ( 16 ) is condensed in a first condenser/evaporator ( 8 ) to form a first liquid nitrogen fraction ( 20 ). A first oxygen-enriched fraction ( 22 ) from the high-pressure column ( 5 ) is introduced into the medial column ( 6 ), where it is separated into a second oxygen-enriched liquid and a second nitrogen fraction ( 24 ). At least a part of the second nitrogen fraction ( 24 ) is condensed in a second condenser/evaporator ( 25 ) to form a second liquid nitrogen fraction ( 26 ) and is added as reflux to one of the columns of the three-column system and/or is obtained as liquid product ( 64 ). A second oxygen-enriched fraction ( 29, 31 ) from the high-pressure column or from the medial column ( 6 ) is introduced into the low-pressure column ( 7 ), where it is separated into a third oxygen-enriched liquid and a third nitrogen fraction. Liquid reflux nitrogen ( 54, 60 ), which has not been formed in the second condenser/evaporator ( 25 ), is introduced into the medial column ( 6 ).

Patent claims  
     
         1 . Process for the low-temperature fractionation of air in a three-column system, which has a high-pressure column ( 5 ), a low-pressure column ( 7 ) and an medial column ( 6 ), in which process 
 (a) charge air ( 1 ,  2 ,  4 ,  1080 ,  1083 ,  1084 ,  1085 ,  1104 ,  1113 ,  1183 ,  1184 ,  1190 ,  1191 ) is introduced into the high-pressure column ( 5 ), where it is separated into a first oxygen-enriched liquid and a first nitrogen fraction ( 16 ),    (b) at least a part ( 19 ) of the first nitrogen fraction ( 16 ) is condensed in a first condenser/evaporator ( 8 ) to form a first liquid nitrogen fraction ( 20 ),    (c) a first oxygen-enriched fraction ( 22 ) from the high-pressure column ( 5 ) is introduced into the medial column ( 6 ), where it is separated into a second oxygen-enriched liquid and a second nitrogen fraction ( 24 ),    (d) at least a part of the second nitrogen fraction ( 24 ) is condensed in a second condenser/evaporator ( 25 ) to form a second liquid nitrogen fraction ( 26 ) and is added as reflux to one of the columns of the three-column system and/or is obtained as liquid product ( 64 ), and in which process    (e) at least a second oxygen-enriched fraction ( 29 ,  31 ,  870 ,  871 ,  1270 ,  1271 ) from the high-pressure column or from the medial column ( 6 ) is introduced into the low-pressure column ( 7 ), where it is separated into a third oxygen-enriched liquid and a third nitrogen fraction,    characterized in that liquid reflux nitrogen ( 54 ,  60 ,  860 ), which has not been formed in the second condenser/evaporator ( 25 ), is introduced into the medial column ( 6 ).    
     
     
         2 . Process according to  claim 1 , characterized in that at least a part ( 60 ) of the liquid reflux nitrogen for the medial column is formed by at least a part of the first liquid nitrogen fraction ( 20 ,  21 ).  
     
     
         3 . Process according to  claim 1  or  2 , characterized in that no part or no significant part of the second liquid nitrogen fraction ( 26 ) formed in the second condenser/evaporator ( 25 ) is introduced into the medial column ( 6 ).  
     
     
         4 . Process according to one of  claims 1  to  3 , characterized in that at least a part of the second liquid nitrogen fraction ( 26 ) is introduced into the low-pressure column ( 7 ) by means of static pressure.  
     
     
         5 . Process according to one of  claims 1  to  4 , characterized in that a liquid fraction ( 36 ,  38 ,  39 ) is removed from the low-pressure column ( 7 ) and is evaporated in the second condenser/evaporator ( 25 ).  
     
     
         6 . Process according to one of  claims 1  to  5 , characterized in that the second oxygen-enriched liquid is boiled by means of a third condenser/evaporator ( 28 ).  
     
     
         7 . Process according to  claim 6 , characterized in that the third condenser/evaporator is heated by means of gaseous nitrogen ( 49 ,  449 ,  549 ), which has been compressed in particular in a circulation compressor ( 46 ,  346 ,  446 ).  
     
     
         8 . Process according to  claim 7 , characterized in that nitrogen ( 50 ,  54 ) which has liquefied in the third condenser/evaporator is introduced into the medial column ( 6 ) as liquid reflux nitrogen.  
     
     
         9 . Process according to one of  claims 1  to  8 , characterized in that the medial column ( 6 ) is operated at a pressure which is higher than the operating pressure of the high-pressure column ( 5 ).  
     
     
         10 . Apparatus for the low-temperature fractionation of air, having a three-column system which has a high-pressure column ( 5 ), a low-pressure column ( 7 ) and a medial column ( 6 ), and having 
 (a) a charge-air line ( 1 ,  2 ,  4 ,  1080 ,  1083 ,  1084 ,  1085 ,  1104 ,  1113 ,  1183 ,  1184 ,  1190 ,  1191 ), which leads into high-pressure column ( 5 ),    (b) a first condenser/evaporator ( 8 ) for condensing at least a part ( 19 ) of a first nitrogen fraction ( 16 ) from the high-pressure column ( 5 ) to form a first liquid nitrogen fraction ( 20 ),    (c) a line ( 22 ) for introducing a first oxygen-enriched fraction from the high-pressure column ( 5 ) into the medial column ( 6 ),    (d) a second condenser/evaporator ( 25 ) for condensing at least a part of a second nitrogen fraction ( 24 ) from the medial column ( 6 ) to form a second liquid nitrogen fraction ( 26 ), the liquefaction space of which is connected, via a reflux line, to one of the columns of the three-column system or to a liquid product line ( 64 ), and having    (e) a charge line ( 29 ,  31 ,  870 ,  871 ,  1270 ,  1271 ) for introducing a second oxygen-enriched fraction from the high-pressure column or from the medial column ( 6 ) into the low-pressure column ( 7 ),    characterized by a liquid line ( 54 ,  60 ,  860 ) for introducing liquid reflux nitrogen into the medial column ( 6 ), which is not in flow communication with the liquefaction space of the second condenser/evaporator ( 25 ).    
     
     
         11 . Apparatus according to  claim 10 , characterized in that the second condenser/evaporator ( 25 ) is arranged at a higher geodetic level than the top of the low-pressure column ( 7 ).