Process and apparatus for cryogenic air separation

Abstract

The process and the apparatus in accordance with the invention relate to cryogenic separation of air in a distillation column system that has at least one single column ( 12 ). A compressed feed air stream ( 6, 8 ) is cooled in a main heat exchanger ( 9 ) in counter-current flow to a first return stream ( 16, 23 ) from the distillation column system. Cooled feed air stream ( 11 ) is fed into the distillation column system. A nitrogen-rich fraction ( 15 ) is produced in the upper region of the single column ( 12 ). At least part ( 16 b ) of the nitrogen-rich fraction ( 15 ) is condensed in a top condenser ( 13 ), which is constructed as a condenser-evaporator. At least part ( 54 ) of the liquid nitrogen-rich fraction ( 52 ) produced in the top condenser ( 13 ) is fed into the single column ( 12 ) as reflux. An oxygen-containing recycle fraction ( 18 a ) is drawn off from the single column ( 12 ) in liquid form. The liquid recycle fraction ( 18 a ) is cooled in a counter-current subcooler ( 100 ). The cooled recycle fraction ( 18 b ) is evaporated in the top condenser ( 13 ). The evaporated recycle fraction ( 29 ) is re-compressed in a re-compressor ( 30 ). The re-compressed recycle fraction ( 31, 32 ) is fed to the lower region of the single column ( 12 ). The main heat exchanger ( 9 ) and the counter-current subcooler ( 100 ) are formed as an integrated heat exchanger ( 102 ). The first return stream ( 16, 23 ) is fed into a group of passages ( 102 ) within the integrated heat exchanger which extend from the cold end thereof to the warm end thereof, and, in the process, the first return stream is brought into indirect heat exchange with both the liquid recycle fraction ( 18 a ) and the feed air stream ( 8 ).

1 . A process for cryogenic air separation in a distillation column system comprising at least one single column ( 12 ), said process comprising:
 cooling a compressed feed air stream ( 6 ,  8 ) in a main heat exchanger ( 9 ) in counter-current to a first return stream ( 16 ,  23 ) from the distillation column system,   introducing the cooled feed air stream ( 11 ) into said single column ( 12 ),   removing a nitrogen-rich fraction ( 15 ) from the upper region of said single column ( 12 ),   condensing at least part ( 16   b ) of the nitrogen-rich fraction ( 15 ) in a top condenser-evaporator ( 13 ),   introducing at least part ( 54 ) of the condensed liquid nitrogen-rich fraction ( 52 ) from the top condenser-evaporator ( 13 ) into said single column ( 12 ) as reflux,   withdrawing an oxygen-containing recycle fraction ( 18   a ) from said single column ( 12 ) in liquid form,   cooling the oxygen-containing recycle liquid fraction ( 18   a ) in a counter-current subcooler ( 100 ),   evaporating the cooled oxygen-containing recycle fraction ( 18   b ) in the top condenser-evaporator ( 13 ),   re-compressing the evaporated oxygen-containing recycle fraction ( 29 ) in a re-compressor ( 30 ), and   introducing the re-compressed recycle fraction ( 31 ,  32 ) into the lower region of said single column ( 12 ),   
       wherein
 the main heat exchanger ( 9 ) and the counter-current subcooler ( 100 ) are formed as an integrated heat exchanger ( 101 ), 
 the integrated heat exchanger ( 101 ) having a first group of passages for said first return stream ( 16 ,  23 ), which extend from the cold end of said integrated heat exchanger ( 101 ) to the warm end of said integrated heat exchanger ( 101 ), 
 said first return stream ( 16 ,  23 ) being introduced into said first group of passages ( 102 ) at the cold end of said integrated heat exchanger ( 101 ), and flowing through said integrated heat exchanger ( 101 ) to the warm end said integrated heat exchanger ( 101 ) and, 
 during passage through said integrated heat exchanger ( 101 ), said first return stream is brought into indirect heat exchange with both said liquid recycle fraction ( 18   a ) and said the feed air stream ( 8 ), and 
 the cooled feed air stream ( 11 ) is withdrawn from said integrated heat exchanger ( 101 ) in completely gaseous form and is fed into said single column ( 12 ) in completely gaseous form. 
 
     
     
         2 . A process according to  claim 1 , wherein said integrated heat exchanger is a single plate-type heat exchanger block. 
     
     
         3 . A process according to  claim 1 , wherein said single column is the only distillation column of said distillation column system. 
     
     
         4 . A process according to  claim 1 , further comprising
 withdrawing a further oxygen-containing fraction ( 14   a ) from said single column ( 12 ) in liquid form,   cooling the further oxygen-containing liquid fraction ( 14   a ) in said integrated heat exchanger ( 101 ),   evaporating the cooled further oxygen-containing liquid fraction in the top condenser-evaporator ( 13 ),   warming the evaporated further oxygen-containing fraction ( 19 ) in said integrated heat exchanger ( 101 ) in counter-current flow to air, and   expanding the warmed evaporated further oxygen-containing fraction in an expansion machine ( 21 ) to produce work,   wherein the temperature of the further oxygen-containing liquid fraction ( 14   a ) as introduced into said integrated heat exchanger ( 101 ) is higher than the temperature of the cooled feed air stream ( 11 ) withdrawn off from said integrated heat exchanger ( 101 ).   
     
     
         5 . A process according to  claim 4 , wherein, before the work-producing expansion, the warmed evaporated further oxygen-containing fraction is warmed up in counter-current flow to air in said integrated heat exchanger. 
     
     
         6 . A process according to  claim 4 , wherein said oxygen-containing recycle fraction is removed from said single column at an intermediate point which is located at least one theoretical or practical plate above the point at which said further oxygen-containing fraction is removed from said single column ( 12 ). 
     
     
         7 . A process according to  claim 4 , wherein said expansion machine ( 21 ) is coupled mechanically to said re-compressor ( 30 ). 
     
     
         8 . A process according to  claim 1 , wherein said re-compressor ( 30 ) is constructed as a cold compressor. 
     
     
         9 . A process according to  claim 1 , wherein said re-compressed recycle fraction ( 31 ) is cooled in said integrated heat exchanger ( 101 ) before being introduced into the lower region of said single column ( 12 ), and said re-compressed recycle fraction ( 32 ) is withdrawn from said integrated heat exchanger ( 101 ) in completely gaseous form and fed into said single column ( 12 ) in completely gaseous form. 
     
     
         10 . An apparatus for cryogenic air separation in a distillation column system, comprising:
 at least one single column ( 12 ),   a main heat exchanger ( 9 ) for cooling a compressed feed air stream ( 6 ,  8 ) in counter-current flow to a first return stream ( 16 ,  23 ) from the distillation column system,   means for introducing a cooled feed air stream ( 11 ) into said single column ( 12 ),   means for removing a nitrogen-rich fraction ( 15 ) from the upper region of said single column ( 12 ),   a top condenser-evaporator for condensing at least part of the nitrogen-rich fraction,   means for introducing condensed nitrogen-rich fraction ( 52 ) from said top condenser-evaporator ( 13 ) into said single column ( 12 ) as reflux,   means for withdrawing an oxygen-containing liquid recycle fraction ( 18   a ) from said single column ( 12 ),   a counter-current subcooler ( 100 ) for cooling down liquid recycle fraction ( 18   a ),   means for introducing cooled recycle fraction ( 18   b ) into said top condenser-evaporator ( 13 ),   a re-compressor ( 30 ) for compressing evaporated recycle fraction ( 29 ) from said top condenser-evaporator ( 13 ), and   means for introducing re-compressed recycle fraction ( 31 ,  32 ) into the lower region of said single column ( 12 ),   
       wherein
 said main heat exchanger ( 9 ) and said counter-current subcooler ( 100 ) are formed as an integrated heat exchanger ( 101 ), 
 said integrated heat exchanger ( 101 ) having a first group of passages ( 102 ) for the first return stream ( 16 ,  23 ), which extends from the cold end of said integrated heat exchanger to the warm end of said integrated heat exchanger, 
 the cold end of said integrated heat exchanger ( 101 ) being connected to means for introducing the first return stream ( 16 ,  23 ) into said first group of passages, 
 the warm end of said integrated heat exchanger ( 101 ) being connected to means for withdrawing the first return stream ( 16 ,  23 ) from said first group of passages, 
 the integrated heat exchanger ( 101 ) being constructed so that, during operation, the first return stream ( 16 ,  23 ) is brought into indirect heat exchange with both liquid recycle fraction ( 18   a ) and feed air stream ( 8 ), and 
 the passages in the integrated heat exchanger ( 101 ) are arranged so that, during operation, cooled feed air stream ( 11 ) is withdrawn from said integrated heat exchanger ( 101 ) in completely gaseous form and is fed into said single column ( 12 ) in completely gaseous form.