Process and unit for the separation of air by cryogenic distillation

Abstract

An air separation unit having a medium-pressure column, a low-pressure column, a chamber, a heat exchanger, a bottom condenser of the low-pressure column and a condenser placed in the chamber is provided. The air separation unit also includes an expansion device configured to expand oxygen-rich liquid from the bottom of the low-pressure column before the oxygen-rich liquid is introduced to the chamber and a compressor configured to compress the gas from the chamber, wherein the compressor is downstream of the chamber and upstream of the low-pressure column.

1 - 10 . (canceled) 
     
     
         11 . A process for separating air by cryogenic distillation, the process comprising the steps of:
 i) introducing a cooled stream of compressed and purified air to a column operating at medium pressure;   ii) separating the cooled stream of compressed and purified air into a nitrogen-enriched stream and an oxygen-enriched stream;   iii) introducing a portion of the nitrogen-enriched stream to a low-pressure column;   iv) introducing at least one portion of the oxygen-enriched stream to the low-pressure column;   v) withdrawing a nitrogen-rich stream from the top of the low-pressure column;   vi) withdrawing an oxygen-rich stream from the bottom of the low-pressure column and sending the oxygen-rich stream to a chamber containing at least one condenser-reboiler;   vii) withdrawing a gaseous stream originating from the chamber and sending the gaseous stream originating from the chamber to the low-pressure column;   viii) at least partially condensing a portion of the nitrogen-enriched stream from step ii) in a condenser fed by liquid originating from the low-pressure column and sending the at least partially condensed portion to a column selected from the group consisting of the medium-pressure column, the low-pressure column, and combinations thereof;   ix) at least partially condensing a stream of warming gas in the condenser-reboiler of the chamber; and   x) withdrawing a fluid from the chamber, wherein the fluid is richer in oxygen than the stream withdrawn from the bottom of the low-pressure column,   wherein step vi) further comprises expanding the withdrawn oxygen-rich stream to a lower pressure upstream the chamber and downstream the low-pressure column, and   wherein step vii) further comprises compressing the gaseous stream originating from the chamber to a higher pressure upstream the low-pressure column and downstream the chamber.   
     
     
         12 . The process as claimed in  claim 11 , wherein the gaseous stream originating from the chamber is compressed in a compressor having an inlet temperature below −50° C. 
     
     
         13 . The process as claimed in  claim 11 , wherein the oxygen-rich stream withdrawn from the low-pressure column is expanded to a pressure at most 1 bar below the pressure at the bottom of the low-pressure column, and wherein the gaseous stream originating from the chamber is compressed in order to increase its pressure by at most 1 bar. 
     
     
         14 . The process as claimed in  claim 11 , wherein the oxygen-rich stream withdrawn from the low-pressure column is expanded to a pressure at most 0.5 bar below the pressure at the bottom of the low-pressure column, and wherein the gaseous stream originating from the chamber is compressed in order to increase its pressure by at most 0.5 bar. 
     
     
         15 . The process as claimed in  claim 11 , wherein the oxygen-rich stream withdrawn from the low-pressure column is expanded to a pressure at most 0.2 bar below the pressure at the bottom of the low-pressure column, and wherein the gaseous stream originating from the chamber is compressed in order to increase its pressure by at most 0.2 bar. 
     
     
         16 . The process as claimed in  claim 11 , wherein the chamber comprises an absence of mass-exchange means. 
     
     
         17 . The process as claimed in  claim 11 , wherein the chamber comprises an absence of packings. 
     
     
         18 . The process as claimed in  claim 11 , wherein the chamber comprises an absence of distillation plates. 
     
     
         19 . The process as claimed in  claim 11 , wherein the chamber comprises a second low-pressure column and mass-exchange means. 
     
     
         20 . The process as claimed in  claim 19 , wherein the mass-exchange means are selected from the group consisting of as packings, distillation plates, and combinations thereof, and wherein the mass-exchange means are disposed above the condenser. 
     
     
         21 . An air separation unit comprising:
 a medium-pressure column having a top and a bottom;   a low-pressure column in fluid communication with the medium-pressure column;   a chamber in fluid communication with the low-pressure column and the medium-pressure column;   a heat exchanger in fluid communication with the medium-pressure column, the low-pressure column, and the chamber;   a bottom condenser disposed in the low-pressure column;   a condenser disposed in the chamber;   a line configured to send compressed, purified air that is cooled in the heat exchanger to the medium-pressure column;   a line configured to transfer a warming gas to the condenser disposed in the chamber;   a line configured to transfer a nitrogen-enriched gas from the medium-pressure column to the condenser of the low-pressure column;   a line configured to transfer an oxygen-enriched stream from the bottom of the medium-pressure column to the low-pressure column;   a line configured to transfer oxygen-rich liquid from the bottom of the low-pressure column to the chamber;   a line configured to withdraw a fluid from the chamber that is richer in oxygen than that sent to the chamber;   a line configured to transfer a gas from the chamber back to the low-pressure column;   a line configured to withdraw an overhead gas from the low-pressure column, wherein the line configured to withdraw the overhead gas from the low-pressure column, comprises an expansion device that is operable to expand the oxygen-rich liquid downstream of the bottom of the low-pressure column and upstream of the chamber; and   a compressor operable to compress the gas from the chamber downstream of the chamber and upstream of the low-pressure column.   
     
     
         22 . The unit as claimed in  claim 21 , wherein the chamber further comprises mass-exchange means, wherein the mass-exchange means are disposed above the condenser. 
     
     
         23 . The process as claimed in  claim 22 , wherein the mass-exchange means are selected from the group consisting of as packings, distillation plates, and combinations thereof. 
     
     
         24 . The unit as claimed in  claim 21 , wherein the chamber comprises an absence of mass-exchange means. 
     
     
         25 . The unit as claimed in  claim 21  further comprising a turbine and a line configured to transfer a nitrogen-rich gas from the medium-pressure column to the turbine. 
     
     
         26 . The unit as claimed in  claim 21  further comprising a pump for pressurizing a stream of liquid oxygen originating from a device disposed upstream of the heat exchanger, wherein the device is selected from the group consisting of the low-pressure column the chamber, and combinations thereof.