Process and apparatus for low-temperature air fractionation

Abstract

The process and the apparatus are used for low-temperature air fractionation. Input air ( 8 ) is cooled in a main heat exchanger ( 9 ) and introduced into a single column ( 12 ) for obtaining nitrogen ( 11, 43 ). A nitrogen product stream ( 15, 16, 17 ) is removed from the upper region of the single column ( 12 ). A first residual fraction ( 18, 29 ) is removed from the lower or central region of the single column ( 12 ), re-compressed ( 30 ) and then fed to the single column ( 12 ) again ( 32 ). An oxygen-containing stream ( 36 ) is removed from the single column ( 12 ) at an intermediate point and fed to a pure oxygen column ( 38 ) ( 39 ). A pure oxygen product stream ( 41 ) in the liquid state is removed from the lower region of the pure oxygen column ( 38 ). The pure oxygen product stream ( 41, 56 ) is evaporated and warmed with respect to input air ( 8 ) in the main heat exchanger ( 9 ) and finally obtained as a gaseous product ( 57 ).

1 . A Process for low-temperature air fractionation, in which
 input air ( 8 ) is cooled in a main heat exchanger ( 9 ) and introduced into a single column ( 12 ) for obtaining nitrogen ( 11 ,  43 ),   a nitrogen product stream ( 15 ,  16 ,  17 ) is removed from the upper region of the single column ( 12 ),   a first residual fraction ( 18 ,  29 ) is removed from the lower or central region of the single column ( 12 ), re-compressed ( 30 ) and then fed to the single column ( 12 ) again ( 32 ),   an oxygen-containing stream ( 36 ) is removed from the single column ( 12 ) at an intermediate point and fed to a pure oxygen column ( 38 ) ( 39 ) and   a pure oxygen product stream ( 41 ) in a liquid state is removed from the lower region of the pure oxygen column ( 38 ),   
     characterized in that
 the pure oxygen product stream ( 41 ,  56 ) is evaporated and warmed with respect to input air ( 8 ) in the main heat exchanger ( 9 ) 
 and is finally obtained as a gaseous product ( 57 ). 
 
   
   
       2 . A Process according to  claim 1 , characterized in that the pure oxygen product stream ( 41 ) prior to evaporation is brought to an increased pressure ( 55 ) in the liquid state. 
   
   
       3 . A Process according to  claim 1 , characterized in that the re-compression ( 30 ) of the first residual fraction ( 18 ,  29 ) is performed in a cold compressor. 
   
   
       4 . A Process according to  claim 1 , characterized in that a second residual fraction ( 14 ,  19 ) is removed from the lower region of the single column ( 12 ) and is depressurized in a depressurizing machine ( 21 ), providing work, the mechanical energy produced during the depressurization providing work being used at least to some extent for the re-compression of the first residual fraction. 
   
   
       5 . A Process according to  claim 4 , characterized in that the single column ( 12 ) has a top condenser ( 13 ), in which vapour from the upper region of the single column is at least partly condensed, the first residual fraction ( 18 ) being at least partly evaporated in the top condenser before its re-compression ( 30 ) and/or the second residual fraction ( 14 ) being at least partly evaporated in the top condenser before its depressurization providing work ( 21 ). 
   
   
       6 . A Process according to  claim 4 , characterized in that the second residual fraction ( 14 ) is drawn off at the bottom of the single column ( 12 ). 
   
   
       7 . A Process according to  claim 4 , characterized in that the first residual fraction ( 18 ) is drawn off from an intermediate point of the single column ( 12 ) which is arranged above the bottom, in particular above the point at which the second residual fraction ( 14 ) is removed. 
   
   
       8 . Apparatus for low-temperature air fractionation, comprising:
 a main heat exchanger ( 9 ) for cooling input air ( 8 ),   means ( 11 ,  43 ) for introducing the cooled input air into a single column ( 12 ) for obtaining nitrogen,   a nitrogen product line ( 15 ,  16 ,  17 ), which is connected to the upper region of the single column ( 12 ),   a first residual fraction line ( 18 ,  29 ,  31 ,  32 ) for the removal of a first residual fraction from the lower or central region of the single column ( 12 ), which is connected through a re-compressor ( 30 ) and subsequently to the single column ( 12 ) again,   means for the removal of an oxygen-containing stream ( 36 ,  39 ) from an intermediate point of the single column ( 12 ) and for its introduction into a pure oxygen column ( 38 ), and having   a pure oxygen product line ( 41 ,  56 ) for the removal of a pure oxygen product stream in the liquid state from the lower region of the pure oxygen column ( 38 ), characterized in that   the pure oxygen product line ( 41 ,  56 ) is connected to the main heat exchanger ( 9 ), and   the apparatus has a gas product line ( 57 ) for the removal of gaseous pure oxygen product from the main heat exchanger ( 9 ).   
   
   
       9 . Apparatus according to  claim 8 , characterized in that means ( 55 ) for increasing pressure in the liquid state are arranged in the pure oxygen product line ( 41 ,  56 ). 
   
   
       10 . Apparatus according to  claim 8 , characterized in that the re-compressor ( 30 ) is constructed as a cold compressor. 
   
   
       11 . A Process according to  claim 5 , characterized in that the first residual fraction ( 18 ) is drawn off from an intermediate point of the single column ( 12 ) which is arranged above the bottom, above the point at which the second residual fraction ( 14 ) is removed. 
   
   
       12 . A Process according to  claim 11 , characterized in that the second residual fraction ( 14 ) is drawn off at the bottom of the single column ( 12 ).