Method and device for obtaining pressurized nitrogen and pressurized oxygen by low-temperature separation of air

Abstract

The invention relates to a method and device for obtaining pressurized nitrogen and pressurized oxygen by low-temperature separation of air. Compressed and purified feed air is cooled down in a main heat exchanger and introduced into a distillation column system comprising at least one high-pressure column and one low-pressure column. The distillation column system for nitrogen-oxygen separation in addition contains a residual gas column operating at a pressure which is lower than the operating pressure of the low-pressure column. A liquid crude oxygen fraction from the high-pressure column ( 50 ) is expanded and passed to the residual gas column at a first intermediate point. A gaseous impure nitrogen stream from the low-pressure column is introduced into a bottoms evaporator of the residual gas column and there is at least partly liquefied. The at least partly liquefied impure nitrogen stream is expanded and introduced into the upper region of the residual gas column.

1 . A method for obtaining pressurized nitrogen and pressurized oxygen by low-temperature separation of air, comprising:
 cooling compressed and purified feed air ( 6 ,  10 ,  23 ,  33 ) in a main heat exchanger ( 8 ) and introducing the cooled, compressed and purified feed air into a distillation column system for nitrogen-oxygen separation that comprises at least a high-pressure column ( 50 ) and a low-pressure column ( 51 ), wherein the low-pressure column ( 51 ) is operated at a pressure which is at least 2 bar,   withdrawing at least one nitrogen stream ( 73 ,  74 ) from the upper region of said low-pressure column, warming said at least one nitrogen stream in said main heat exchanger ( 8 ), and removing the resultant warmed at least one nitrogen stream as pressurized nitrogen product ( 75 ),   withdrawing at least one oxygen stream ( 77 ) from the lower region of said low-pressure column ( 51 ), warming said at least one oxygen stream in said main heat exchanger ( 8 ) and removing the resultant warmed at least one oxygen stream as pressurized oxygen product ( 81 ,  84 ),   withdrawing an impure nitrogen stream ( 85 ) in the gaseous state from a first intermediate point of said low-pressure column ( 51 ), said first intermediate point being below the point at which said at least one nitrogen stream ( 73 ) is withdrawn,   wherein said distillation column system for nitrogen-oxygen separation further comprises a residual gas column ( 52 ), the operating pressure of said residual gas column is lower than the operating pressure of said low-pressure column ( 51 ), said residual gas column ( 52 ) comprising a bottoms evaporator ( 86 ) which is designed as a condenser-evaporator,   said method further comprising expanding a liquid crude oxygen fraction ( 89 ) expanded and passing the expanded liquid crude oxygen fraction into said residual gas column ( 52 ) at a first intermediate point,   introducing said gaseous impure nitrogen stream ( 85 ) into the liquefaction chamber of said bottoms evaporator ( 86 ) of said residual gas column ( 52 ) to at least partly liquefy said gaseous impure nitrogen stream,   expanding ( 88 ) the resultant at least partly liquefied impure nitrogen stream ( 87 ) and introducing the expanded at least partly liquefied impure nitrogen stream into the upper region of said residual gas column ( 52 ).   
     
     
         2 . The method according to  claim 1 , wherein said liquid crude oxygen fraction ( 89 ) is obtained from said high-pressure column ( 50 ). 
     
     
         3 . The method according to  claim 1 , further comprising withdrawing a liquid bottoms fraction ( 91 ,  93 ) from said residual gas column ( 52 ) and introducing said liquid bottoms fraction into said low-pressure column ( 51 ) at a second intermediate point which is situated below said first intermediate point of said low-pressure column ( 51 ). 
     
     
         4 . The method according to  claim 1 , further comprising withdrawing a gaseous residual stream from the top of said residual gas column ( 52 ), and warming said gaseous residual stream in said main heat exchanger ( 8 ). 
     
     
         5 . The method according to  claim 1 , wherein the pressure of said impure nitrogen stream ( 85 ) is not increased between said low-pressure column ( 51 ) and said bottoms evaporator ( 86 ). 
     
     
         6 . The method according to  claim 1 , wherein the liquefaction chamber of said bottoms evaporator ( 86 ) is operated substantially at the operating pressure of said low-pressure column ( 52 ). 
     
     
         7 . The method according to  claim 1 , further comprising withdrawing an oxygen stream ( 77 ) in the liquid state from the lower region of said low-pressure column ( 52 ), subjected said oxygen stream ( 77 ) in the liquid state to a pressure increase ( 78 ) and, in said main heat exchanger ( 8 ), vaporizing or pseudo-vaporizing said oxygen stream ( 77 ) in the liquid state by indirect heat exchange with feed air ( 10 ,  33 ), whereby a part ( 33 ) of the feed air is liquefied or pseudo-liquefied. 
     
     
         8 . The method according to  claim 7 , wherein at least a part ( 90 ) of the resultant (pseudo-)liquefied feed air ( 33 ,  35 ) is introduced into said residual gas column ( 52 ) at a second intermediate point) which is situated above said first intermediate point of said residual gas column ( 52 ). 
     
     
         9 . The method according to  claim 1 , wherein said residual gas column ( 52 ) does not have a top condenser. 
     
     
         10 . The method according to  claim 1 , wherein said low-pressure column ( 51 ) does not have a top condenser. 
     
     
         11 . An apparatus for obtaining pressurized nitrogen and pressurized oxygen by low-temperature separation of air, said apparatus comprising:
 a distillation column system for nitrogen-oxygen separation comprising at least one high-pressure column ( 50 ), at least one low-pressure column ( 51 ), and a residual gas column ( 52 ), the operating pressure being lower than the operating pressure of said at least one low-pressure column ( 51 ), said residual gas column ( 52 ) comprising a bottoms evaporator ( 86 ) which is designed as a condenser-evaporator,   a main heat exchanger ( 8 ) for cooling compressed and purified feed air ( 6 ,  10 ,  23 ,  33 ),   means for introducing cooled feed air ( 12 ,  35 ) into said distillation column system for nitrogen-oxygen separation,   a control appliance for open-loop control of the operating pressure of said at least one low-pressure column ( 51 ) to a value which is at least 2 bar,   means for withdrawing a nitrogen stream ( 73 ,  74 ) from the upper region of said low-pressure column,   means for introducing said nitrogen stream ( 74 ) into said main heat exchanger ( 8 ) to warm said nitrogen stream ( 74 ),   means removing warmed nitrogen stream as pressurized nitrogen product ( 75 ),   means for withdrawing an oxygen stream ( 77 ) from the lower region of said low-pressure column ( 51 ), warming the oxygen stream ( 77 ) in said main heat exchanger ( 8 ) and obtaining the warmed oxygen stream as pressurized oxygen product ( 81 ,  84 ),   means for withdrawing an impure nitrogen stream ( 85 ) in the gaseous state from a first intermediate point of said low-pressure column ( 51 ), said first intermediate point of said low-pressure column ( 51 ) being below the point at which the nitrogen stream ( 73 ) is withdrawn from said low-pressure column ( 51 ),   means for expanding a liquid crude oxygen fraction ( 89 ),   means for introducing the resultant expanded crude oxygen fraction ( 89 ) into said residual gas column ( 52 ) at a first intermediate point,   means for introducing the gaseous impure nitrogen stream ( 85 ) removed from said low-pressure column ( 51 ) into the liquefaction chamber of said bottoms evaporator ( 86 ) of said residual gas column ( 52 ) for the at least partial liquefaction the gaseous impure nitrogen stream ( 85 ),   means ( 88 ) for expanding the at least partially liquefied impure nitrogen stream ( 87 ), and   means for introducing the resultant expanded impure nitrogen stream into the upper region of said residual gas column ( 52 ).   
     
     
         12 . The apparatus according to  claim 11 , wherein said means for expanding a liquid crude oxygen fraction ( 89 ) is a means for expanding a liquid crude oxygen fraction from said high-pressure column ( 50 ).