Method and system for low-temperature air separation

Abstract

A method for low-temperature air separation, in which an air-separation system having a column system is used that has a first column, a second column, a third column, and a fourth column, wherein fluid from the first column is fed at least into the second column, fluid from the second column is fed at least into the third column, fluid from the third column is fed at least into the fourth column, and fluid from the fourth column is fed at least into the third column, and wherein the fluid fed from the third column into the fourth column includes at least a portion of a side flow, which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid. The present invention also relates to a corresponding system.

1 - 15  (canceled) 
     
     
         16 . A method for low-temperature air separation, in which an air-separation system having a column system is used that has a first column, a second column, a third column, and a fourth column, wherein
 a) a first sump liquid is formed in the first column, a second sump liquid is formed in the second column, a third sump liquid is formed in the third column, and a fourth sump liquid is formed in the fourth column,   b) the first column is operated in a first pressure range, the second column is operated in a second pressure range below the first pressure range, and the third column is operated in a third pressure range below the second pressure range,   c) the second sump liquid is formed with a higher oxygen content and a higher argon content than the first sump liquid, and the third sump liquid is formed with a higher oxygen content and a lower argon content than the second sump liquid,   d) fluid from the first column is fed at least into the second column, fluid from the second column is fed at least into the third column, fluid from the third column is fed into the fourth column, and fluid from the fourth column is fed at least into the third column, and   e) the fluid fed from the third column into the fourth column comprises at least a portion of a side flow which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid, wherein   f) a reflux liquid is formed by condensing overhead gas of the first column, and the reflux liquid is fed back to the first column in liquid form,   g) in order to condense the overhead gas of the first column, a liquid cooling flow is evaporated or partially evaporated in indirect heat exchange with the overhead gas, and   h) gas formed during the evaporation or partial evaporation of the cooling flow is expanded, so as to perform work, to a pressure in the second pressure range and fed into the second column.   
     
     
         17 . The method according to  claim 16 , in which the cooling flow is formed using at least a fraction of the first sump liquid. 
     
     
         18 . The method according to  claim 17 , in which a further liquid cooling flow is evaporated or partially evaporated in indirect heat exchange with the overhead gas in order to condense the overhead gas of the first column, wherein the further cooling flow is withdrawn above the sump from the first column and at least partially compressed after evaporation or partial evaporation and fed back to the first column. 
     
     
         19 . The method according to  claim 16 , in which a forced-flow condenser evaporator is used for condensing the overhead gas of the first column and for evaporating the cooling flow. 
     
     
         20 . The method according to  claim 16 , in which the gas, which is formed during the evaporation or partial evaporation of the cooling flow and expanded and fed into the second column, is heated before the expansion. 
     
     
         21 . The method according to  claim 16 , in which the gas, which is formed during the evaporation or partial evaporation of the cooling flow and expanded to perform work and fed into the second column, is supplied to the expansion at a temperature at which it is present after evaporation or partial evaporation. 
     
     
         22 . The method according to  claim 16 , in which the gas, which is formed during the evaporation or partial evaporation of the cooling flow and expanded to perform work and fed into the second column, is fed into the second column at a temperature at which it is withdrawn from an expansion machine used for expansion. 
     
     
         23 . The method according to  claim 16 , in which overhead gas of the fourth column is at least partially condensed in a condensation chamber of a condenser evaporator, from the evaporation chamber of which a gas mixture is withdrawn, wherein at least a portion of the gas mixture withdrawn from the evaporation chamber of the condenser evaporator is used to form a reflux flow, which is heated, compressed, cooled, and fed into the second column and/or is used as regeneration gas for an adsorber in which feed air is prepared which is fed to the column system is prepared. 
     
     
         24 . The method according to  claim 16 , in which at least a portion of a gas mixture which is withdrawn from an upper region of the third column is used to form a reflux flow which is heated, compressed, cooled, and fed into the second column. 
     
     
         25 . The method according to  claim 23 , in which the adsorber, in which the feed air which is fed to the column system is prepared, is operated without the use of regeneration gas, which is withdrawn from the third column and fed to the adsorber in a materially-unchanged composition. 
     
     
         26 . The method according to  claim 23 , in which at least a portion of the gas mixture withdrawn from the evaporation chamber of the condenser evaporator is used as a first regeneration gas fraction, and in which at least a portion of the gas withdrawn from the third column is used as a second regeneration gas fraction, wherein the second regeneration gas fraction is provided at a lower pressure than the first one, compressed, and combined with the first regeneration gas fraction before it is fed to the adsorber. 
     
     
         27 . The method according to  claim 16 , in which power released during work-performing expansion of the evaporated or partially evaporated cooling flow, or at least its fraction which is expanded to perform work and fed into the second column, is used for operating an electric generator. 
     
     
         28 . The method according to  claim 16 , in which the second pressure range is 4 to 6.5 bar. 
     
     
         29 . The method according to  claim 16 , in which the side flow formed with a lower oxygen content and a higher argon content than the third sump liquid and withdrawn from the third column is subjected to preparation in a further column to obtain an oxygen-depleted gas mixture and a sump liquid, wherein the oxygen-depleted gas mixture is fed from the further column at least in part into the fourth column. 
     
     
         30 . An air-separation system which has a column system having a first column, a second column, a third column, and a fourth column and is configured
 a) to form a first sump liquid in the first column, to form a second sump liquid in the second column, to form a third sump liquid in the third column, and to form a fourth sump liquid in the fourth column,   b) to operate the first column in a first pressure range, to operate the second column in a second pressure range below the first pressure range, and to operate the third column in a third pressure range below the second pressure range,   c) to form the second sump liquid with a higher oxygen content and a higher argon content than the first sump liquid, and to form the third sump liquid with a higher oxygen content and a lower argon content than the second sump liquid,   d) to feed fluid from the first column at least into the second column, to feed fluid from the second column at least into the third column, to feed fluid from the third column at least into the fourth column, and to feed fluid from the fourth column at least into the third column, and   e) to use at least a portion of a side flow which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid as the fluid fed from the third column into the fourth column, wherein means are configured   f) to form a reflux liquid by condensing overhead gas of the first column, and to feed back the reflux liquid to the first column in liquid form,   g) to evaporate or partially evaporate a liquid cooling flow in indirect heat exchange with the overhead gas in order to condense the overhead gas of the first column, and,   h) to expand gas formed during the evaporation or partial evaporation of the cooling flow, so as to perform work, to a pressure in the second pressure range and to feed it into the second column.