Cryogenic Air Separation Method and Air Separation Unit

Abstract

According to the present invention, a method for cryogenic separation of air using an air separation unit comprising a rectification column is provided. Feed air is compressed, cooled and rectified in the rectification column obtaining an overhead gas, wherein a part of the overhead gas of the rectification column is condensed using fluid withdrawn from the rectification column, wherein the condensed overhead gas is used at least in part as a liquid reflux to the rectification column, wherein a first part of the fluid which is used for cooling the overhead gas of the rectification column is, after its use for cooling, compressed and reintroduced into the rectification column, and wherein a second part of the fluid which is used for cooling the overhead gas of the rectification column is, after its use for cooling, expanded and withdrawn from the air separation unit.

1 . A method for cryogenic separation of air, using an air separation unit comprising a rectification column, wherein feed air is compressed, cooled and rectified in the rectification column obtaining an overhead gas, wherein a part of the overhead gas of the rectification column is condensed using fluid withdrawn from the rectification column, wherein the condensed overhead gas is used at least in part as a liquid reflux to the rectification column, wherein a first part of the fluid which is used for cooling the overhead gas of the rectification column is, after its use for cooling, compressed and reintroduced into the rectification column, and wherein a second part of the fluid which is used for cooling the overhead gas of the rectification column is, after its use for cooling, expanded and withdrawn from the air separation unit, wherein compressing the first part of the fluid which is used for cooling the overhead gas of the rectification column a compressor which is coupled to an electric motor via a first gearbox is used, in that for expanding the second part of the fluid which is used for cooling the overhead gas of the rectification column an expansion turbine which is coupled to an electric generator via a second gearbox is used, and in that the first gearbox and the second gearbox are provided with an identical design including identical reduction or multiplication ratios in the first gearbox and the second gearbox. 
     
     
         2 . The method according to  claim 1 , the identical reduction or multiplication ratios in the first gearbox and the second gearbox being provided by using at least one of identical sprocket diameters, identical numbers of teeth of sprockets, and identical shaft diameters in the first gearbox and the second gearbox. 
     
     
         3 . The method according to  claim 1 , wherein the first gearbox and the second gearbox are operated, or designed to be operated, in identical directions of rotation. 
     
     
         4 . The method according to  claim 1 , wherein the first part of the fluid which is used for cooling the overhead gas of the rectification column is a cryogenic liquid withdrawn from the rectification column at a first position, and wherein the second part of the fluid which is used for cooling the overhead gas of the rectification column is cryogenic liquid withdrawn from the rectification column at a second position. 
     
     
         5 . The method according to  claim 4 , wherein the first position is above the second position and/or wherein the second position corresponds to a position at the bottom of the rectification column. 
     
     
         6 . The method according to  claim 1 , wherein the first part of the fluid which is used for cooling the overhead gas of the rectification column has a higher nitrogen content than the second part. 
     
     
         7 . The method according to  claim 1 , wherein electric energy generated in the generator is at least in part used to operate the motor. 
     
     
         8 . The method according to  claim 1 , wherein the compressor and the expansion turbine are operated at identical speed settings. 
     
     
         9 . An air separation unit comprising a rectification column, the air separation unit being adapted to compress, cool and rectify feed air in the rectification column obtaining an overhead gas, wherein means are provided which are adapted to condense a part of the overhead gas of the rectification column using fluid withdrawn from the rectification column, wherein means are provided which are adapted to use the condensed overhead gas at least in part as a liquid reflux to the rectification column, wherein means are provided which are adapted to compress and reintroduce into the rectification column a first part of the fluid which is used for cooling the overhead gas of the rectification column after its use for cooling, and wherein means are provided which are adapted to expand and withdraw from the air separation unit a second part of the fluid which is used for cooling the overhead gas of the rectification column after its use for cooling, wherein compressing the first part of the fluid which is used for cooling the overhead gas of the rectification column a compressor which is coupled to an electric motor via a first gearbox is provided, in that for expanding the second part of the fluid which is used for cooling the overhead gas of the rectification column an expansion turbine which is coupled to an electric generator via a second gearbox is provided, and in that the first gearbox and the second gearbox are provided with an identical design including identical reduction or multiplication ratios in the first gearbox and the second gearbox. 
     
     
         10 . The method according to  claim 9 , the identical reduction or multiplication ratios in the first gearbox and the second gearbox being provided by using at least one of identical sprocket diameters, identical numbers of teeth of sprockets, and identical shaft diameters in the first gearbox and the second gearbox. 
     
     
         11 . The method according to  claim 9 , wherein the first gearbox and the second gearbox are operated, or designed to be operated, in identical directions of rotation. 
     
     
         12 . The air separation unit according to  claim 9 , adapted to perform a method for cryogenic separation of air, using an air separation unit comprising a rectification column, wherein feed air is compressed, cooled and rectified in the rectification column obtaining an overhead gas, wherein a part of the overhead gas of the rectification column is condensed using fluid withdrawn from the rectification column, wherein the condensed overhead gas is used at least in part as a liquid reflux to the rectification column, wherein a first part of the fluid which is used for cooling the overhead gas of the rectification column is, after its use for cooling, compressed and reintroduced into the rectification column, and wherein a second part of the fluid which is used for cooling the overhead gas of the rectification column is, after its use for cooling, expanded and withdrawn from the air separation unit, wherein compressing the first part of the fluid which is used for cooling the overhead gas of the rectification column a compressor which is coupled to an electric motor via a first gearbox is used, in that for expanding the second part of the fluid which is used for cooling the overhead gas of the rectification column an expansion turbine which is coupled to an electric generator via a second gearbox is used, and in that the first gearbox and the second gearbox are provided with an identical design including identical reduction or multiplication ratios in the first gearbox and the second gearbox.