Method And Device For Separating Air By Cryogenic Distillation

Abstract

A method and an apparatus for distilling air by cryogenic distillation is presented. The invention relates to an apparatus using a double air separation column comprising a medium pressure column and a low pressure column connected thermally together by a reboiler-condenser.

1 . An apparatus for separating air comprising a main exchange line, a first element with an elongated shape (A) comprising the medium pressure column ( 1 ) of a double column, surmounted by a reboiler-condenser ( 5 ) and an auxiliary column ( 2 ) containing at least one theoretical plate constituting the lower part of the low pressure column, a second element with an elongated shape (B) constituting the remainder of the low pressure column, means ( 11 ) for conveying air from the main exchange line to the medium pressure column, means for conveying a head gas from the medium pressure column to the reboiler-condenser, means for conveying the condensed head gas from the reboiler to the medium pressure column, means for conveying a head gas ( 15 ) from the auxiliary column to the vessel of the second element with an elongated shape, means for conveying a vessel liquid ( 13 ) from the second element with an elongated shape into the head of the auxiliary column, a sub-cooler ( 6 ) placed below the first or second element with an elongated shape, means for conveying a vessel liquid from the medium pressure column to the sub-cooler and then to the second element with an elongated shape and/or means for conveying a head liquid from the medium pressure column to the sub-cooler and then to the second element with an elongated shape, and means for conveying a head gas from the second element of elongated shape to the sub-cooler. 
   
   
       2 . The apparatus as claimed in  claim 1 , wherein the sub-cooler ( 6 ) is placed below the second element with an elongated shape (B). 
   
   
       3 . The apparatus as claimed in  claim 2 , wherein the sub-cooler ( 6 ) and the second element with an elongated shape (B) are placed in a pack of which the length does not exceed 35 meters, or even 30 meters.