Process for the recovery of krypton and/or xenon by low-temperature separation of air

Abstract

The process is used for the recovery of krypton and/or xenon by low-temperature separation of air. Compressed and purified feed air ( 1, 1 A, 1 B, 29 ) is introduced into a rectification system for nitrogen-oxygen separation, which has a high-pressure column ( 2 ) and a low-pressure column ( 3 ). An oxygen-rich liquid ( 42 ) is removed at a first point from the low-pressure column ( 3 ). At least a first portion ( 43 ) of the oxygen-rich liquid ( 42 ) is re-introduced in the low-pressure column at a second point, whereby a mass exchange section ( 44 ) is arranged between the first and second points on the low-pressure column. An additional liquid ( 35 ) is drawn off from a third point of the low-pressure column ( 3 ), which is arranged at the level of the second point or below it, said liquid introduced into the evaporation chamber of a first condenser-evaporator ( 4 ) and partially evaporated there. A krypton- and xenon-containing fraction ( 138 ) is drawn off from the evaporation chamber of a first condenser-evaporator and introduced into the evaporation chamber of a second condenser-evaporator ( 27 ). A krypton-xenon concentrate ( 125 ) is drawn off from the second condenser-evaporator ( 27 ).

1 . A process for the recovery of krypton and/or xenon by low-temperature separation of air, which comprises: 
 introducing compressed and purified feed air ( 1 ,  1 A,  1 B,  29 ) into a rectification system for nitrogen-oxygen separation, which has at least a high-pressure column ( 2 ) and a low-pressure column ( 3 ),    removing an oxygen-rich liquid ( 42 ) at a first point from the low-pressure column ( 3 ),    re-introducing at least a first portion ( 43 ) of the oxygen-rich liquid ( 42 ) in the low-pressure column at a second point, whereby a mass exchange section ( 44 ) is arranged between the first and second points on the low-pressure column,    drawing off a liquid ( 35 ) from a third point of the low-pressure column ( 3 ), which is arranged at the level of the second point or below it, and introducing it into the evaporation chamber of a first condenser-evaporator ( 4 ) and partially evaporating it there, and    drawing off a krypton- and xenon-containing fraction ( 138 ) from the evaporation chamber of the first condenser-evaporator ( 4 ),    introducing the krypton- and xenon-containing fraction ( 138 ) into the evaporation chamber of a second condenser-evaporator ( 27 ), and    drawing off a krypton-xenon concentrate ( 125 ) from the second condenser-evaporator ( 27 ).    
     
     
         2 . A process according to  claim 1 , wherein the second condenser-evaporator ( 27 ) is heated with a gas ( 1 B) that has a pressure that is approximately equal to the operating pressure of the high-pressure column.  
     
     
         3 . A process according to  claim 1 , wherein the second condenser-evaporator is heated with a partial stream ( 1 B) of the charging air ( 1 ).  
     
     
         4 . A process according to  claim 1 , wherein a second portion ( 45 ,  48 ) of the oxygen-rich liquid ( 42 ) from the first point on the low-pressure column ( 3 ) and/or another oxygen fraction from above the first point of the low-pressure column is removed as product.  
     
     
         5 . A process according to  claim 1 , wherein the first condenser-evaporator ( 4 ) is designed as a bath evaporator.  
     
     
         6 . A process according to  claim 1 , wherein another krypton- and xenon-containing stream ( 13 ) is drawn off from the high-pressure column ( 3 ) and is introduced ( 121 ) into the evaporation chamber of the second condenser-evaporator ( 27 ).  
     
     
         7 . A process according to  claim 6 , wherein the additional krypton- and xenon-containing stream ( 13 ,  26 ) is directed upstream from its introduction into the evaporation chamber of the second condenser-evaporator ( 27 ) through its purification stage.  
     
     
         8 . A process according to  claim 7 , wherein the purification stage is designed as a stripping column ( 120 ).  
     
     
         9 . A process according to  claim 8 , wherein gas ( 30 ,  31 ) that is formed in the evaporation chamber of the second condenser-evaporator ( 27 ) is introduced into the stripping column ( 120 ) at least partly as rising steam.  
     
     
         10 . A process according to  claim 6 , wherein the additional krypton- and xenon-containing stream ( 13 ) is partially evaporated upstream from its introduction into the evaporation chamber of the second condenser-evaporator.  
     
     
         11 . A process according to  claim 8 , wherein the additional krypton- and xenon-containing stream ( 13 ) is partially evaporated upstream from the purification stage ( 120 ) in a third condenser-evaporator ( 17 ).  
     
     
         12 . A process according to  claim 11 , wherein the third condenser-evaporator ( 17 ) is a top condenser of a crude argon column ( 19 ).