Low Temperature Air Fractionation with External Fluid

Abstract

In low-temperature air fractionation, feed air ( 8 ) is cooled in a main heat exchanger ( 9 ) and introduced into a distillation column system for nitrogen-oxygen separation ( 11, 43 ), which system has at least one single column ( 12 ). At least one nitrogen-enriched or oxygen-enriched product stream ( 15, 16, 17; 53; 51, 56, 57; 19, 60 ) is withdrawn from the distillation column system for nitrogen-oxygen separation and warmed in the main heat exchanger ( 9 ). A fluid from an external source is passed at least at times into a liquid tank ( 70 ). At least at times fluid ( 71 ) is withdrawn in the liquid state from the liquid tank ( 70 ), vaporized in the main heat exchanger ( 9 ) and is obtained as gaseous additional product ( 72, 73 ).

1 . A process for low temperature air fractionation in which
 feed air ( 8 ) is cooled in a main heat exchanger ( 9 ) and introduced into a distillation column system for nitrogen-oxygen separation ( 11 ,  43 ), which system has at least one single column ( 12 ) for obtaining nitrogen,   at least one nitrogen-enriched or oxygen-enriched product stream ( 15 ,  16 ,  17 ;  53 ;  51 ,  56 ,  57 ;  19 ,  60 ) is withdrawn from the distillation column system for nitrogen-oxygen separation and warmed in the main heat exchanger ( 9 ),   the single column ( 12 ) has a top condenser ( 13 ) in which vapor from the upper region of the single column is at least in part condensed,   a first residual fraction ( 14 ,  19 ) is withdrawn in the liquid state from the lower region of the single column ( 12 ) and at least in part vaporized in the top condenser ( 13 ),   at least a first part ( 20 ) of the first residual fraction ( 19 ) is expanded downstream of the top condenser ( 13 ) in an expansion machine ( 21 ) to produce work and in which   a second residual fraction ( 18 ,  29 ) is withdrawn from the lower or intermediate region of the single column ( 12 ), recompressed ( 30 ) and subsequently at least a first part is passed ( 32 ) back to the single column ( 12 )   
     characterized in that
 a fluid from an external source is passed at least at times into a liquid tank ( 70 ) and 
 at least at times fluid ( 71 ) is withdrawn in the liquid state from the liquid tank ( 70 ), vaporized in the main heat exchanger ( 9 ) and is obtained as gaseous additional product ( 72 ,  73 ), wherein neither the fluid from the external source nor the gaseous additional product ( 72 ,  73 ) is mixed with a product from the distillation column system. 
 
   
   
       2 . A process according to  claim 1 , characterized in that the fluid ( 71 ) is not increased in pressure between liquid tank ( 70 ) and main heat exchanger ( 9 ). 
   
   
       3 . A process according to  claim 1 , characterized in that the fluid ( 71 ) is introduced into the main heat exchanger ( 9 ) at a pressure which is not higher than the operating pressure of the liquid tank ( 70 ). 
   
   
       4 . A process according to  claim 1 , characterized in that the operating pressure of the liquid tank ( 70 ) is at least 1 bar above atmospheric pressure. 
   
   
       5 . A process according to  claim 1 , characterized in that the second residual fraction ( 18 ,  29 ) is recompressed by means of a cold compressor ( 30 ). 
   
   
       6 . A process according to  claim 1 , characterized in that mechanical energy generated in the work-producing expansion ( 21 ) is at least in part applied to recompressing ( 30 ) the second residual fraction. 
   
   
       7 . A process according to  claim 1 , characterized in that a second part of the first residual fraction ( 19 ) is not introduced downstream of the top condenser ( 13 ) into the expansion machine ( 21 ), but is taken off as gaseous impure oxygen product ( 60 ) and/or a second part of the second residual fraction is taken off as gaseous impure oxygen product ( 160 ) downstream of the recompression ( 30 ). 
   
   
       8 . A process according to  claim 1 , characterized in that
 an oxygen-containing stream ( 36 ) is withdrawn from the single column ( 12 ) at an intermediate point and passed ( 39 ) to a pure oxygen column ( 38 ) and   a pure oxygen product stream ( 41 ) is withdrawn in the liquid state from the lower region of the pure oxygen column ( 38 ),   the pure oxygen product stream ( 41 ,  56 ), after optional pressure elevation ( 55 ) in the liquid state, is vaporized and warmed against feed air ( 8 ) in the main heat exchanger ( 9 )   and is thus obtained as gaseous product ( 57 ).   
   
   
       9 . A process according to  claim 1 , characterized in that the first residual fraction ( 14 ) is taken off at the bottom of the single column ( 12 ). 
   
   
       10 . A process according to  claim 1 , characterized in that the second residual fraction ( 18 ) is taken off from an intermediate point arranged above the bottom of the single column ( 12 ), in particular above the point at which the first residual fraction ( 14 ) is withdrawn. 
   
   
       11 . A process according to  claim 1 , characterized in that the main heat exchanger ( 9 ) and the top condenser ( 13 ) are separate from one another. 
   
   
       12 . Apparatus for low temperature air fractionation having
 distillation column system for nitrogen-oxygen separation which has at least one single column ( 12 ) for obtaining nitrogen,   a main heat exchanger ( 9 ) for cooling feed air ( 8 )   a feed air line ( 11 ,  43 ) for introducing cooled feed air into the distillation column system for nitrogen-oxygen separation,   means for feeding a nitrogen-enriched or oxygen-enriched product stream ( 15 ,  16 ,  17 ;  53 ;  51 ,  56 ,  57 ;  19 ,  60 ) from the distillation column system for nitrogen-oxygen separation to the main heat exchanger ( 9 ),   a top condenser ( 13 ) for the at least partial condensation of vapor from the upper region of the single column,   means for feeding a first liquid residual fraction ( 14 ,  19 ) from the lower region of the single column ( 12 ) to the top condenser ( 13 ),   an expansion machine ( 21 ) for work-producing expansion of at least a first part ( 20 ) of the first residual fraction ( 19 ) downstream of the top condenser ( 13 ),   a recompressor ( 30 ) for recompressing a second residual fraction ( 18 ,  29 ) from the lower or intermediate region of the single column ( 12 )   and having means for introducing at least a first part of the recompressed second residual fraction into the single column ( 12 ),   
     characterized by
 a liquid tank for storage of a fluid from an external source and 
 means for withdrawing at least at times fluid ( 71 ) in the liquid state from the liquid tank ( 70 ) vaporizing it in the main heat exchanger ( 9 ) and obtaining it as gaseous additional product ( 72 ,  73 ) 
 wherein the device does not have an appliance for mixing the fluid from the external source or the gaseous additional product ( 72 ,  73 ) with a product from the distillation column system.