Process and Apparatus for the Separation of Air by Cryogenic Distillation

Abstract

A process for separating air by cryogenic distillation in a column system comprising a high pressure column and a low pressure column comprises compressing all the feed air in a first compressor to a first outlet pressure, sending a first part of the air at the first outlet pressure to a second compressor and compressing the air to a second outlet pressure, cooling at least part of the air at the second outlet pressure in a heat exchanger liquefying at least part of the air at the second outlet pressure and sending the liquefied air to at least one column of the column system wherein at least 50% of the liquefied air sent to the column system has been compressed in the second compressor, cooling a second part of the air at the first outlet pressure in the heat exchanger and expanding at least part of the second part of the air in an expander from the first outlet pressure to the pressure of a column of column system and sending the expanded air to that column, at least partially vaporizing an auxiliary fluid, eventually further warming said auxiliary fluid in the heat exchanger, sending at least part of this auxiliary fluid to a third compressor to a third outlet pressure, introducing at least part of said auxiliary fluid at said third outlet pressure in the heat exchanger, cooling said auxiliary fluid and at least partially liquefying said auxiliary fluid, removing said auxiliary stream from the heat exchanger and expanding it to a fourth pressure level before reintroducing it in the heat exchanger where it will be partially vaporized as above-mentioned, removing liquid from a column of the column system and vaporizing the liquid by heat exchange in the heat exchanger.

1 - 8 . (canceled) 
     
     
         8 . A process for separating air by cryogenic distillation in a column system comprising a high pressure column and a low pressure column comprising the steps of:
 i) compressing all the feed air in a first compressor to a first outlet pressure;   ii) sending a first part of the air at the first outlet pressure to a second compressor and compressing the air to a second outlet pressure;   iii) cooling at least part of the air at the second outlet pressure in a heat exchanger;   iv) cooling a second part of the air at the first outlet pressure in the heat exchanger and expanding at least part of the second part of the air in an expander from the first outlet pressure to the pressure of a column of column system and sending the expanded air to that column;   v) removing liquid from a column of the column system, pressurizing the liquid and vaporizing the liquid by heat exchange in the heat exchanger; and   vi) at least partially vaporizing an auxiliary fluid in the heat exchanger, eventually further warming said auxiliary fluid in the heat exchanger, sending at least part of this auxiliary fluid to a third compressor to be compressed to a third outlet pressure, introducing at least part of said auxiliary fluid at said third outlet pressure in the heat exchanger, cooling said auxiliary fluid and at least partially liquefying said auxiliary fluid, removing said auxiliary stream from the heat exchanger and expanding it to a fourth pressure level before reintroducing it in the heat exchanger for the afore mentioned at least partial vaporization step.   
     
     
         9 . The process of  claim 8  wherein at least part of the first part of the air is cooled upstream of the second compressor. 
     
     
         10 . The process of  claim 9  wherein at least part of the first part of the air is cooled upstream of the second compressor in the heat exchanger. 
     
     
         11 . The process of  claim 9  wherein at least part of the first part of the air is cooled upstream of the second compressor in the heat exchanger using a refrigeration unit. 
     
     
         12 . The process of  claim 8  wherein additional air is liquefied in the heat exchanger at least one of the first and second pressures. 
     
     
         13 . The process of  claim 8  wherein the third compressor compresses an auxiliary fluid chosen from the group comprising containing at least one of the following gases: He, H 2 , Ne, N 2 , CO, Ar, O 2 , CH 4 , Kr, NO, Xe, CF 4 , HCF 3 , C 2 H 4 , C 2 H 6 , C 2 F 6 , C 3 F 8 , N 2 O, CO 2 . 
     
     
         14 . The process of  claim 13  wherein a principal component of the auxiliary fluid is at least one of: Ar, O 2 , CH 4  and Kr. 
     
     
         15 . An apparatus for the separation of air by cryogenic distillation comprising:
 a) a column system;   b) first, second and third compressors;   c) a first expander;   d) a conduit for sending air to the first compressor to form compressed air at a first outlet pressure;   e) a conduit for sending a first part of the air at the first outlet pressure to the second compressor to form air at a second outlet pressure;   f) a heat exchanger, a conduit for sending at least part of the air at the second outlet pressure to the heat exchanger to form cooled compressed air at the second outlet pressure;   g) a conduit for removing liquefied air at the second outlet pressure from the heat exchanger and for sending the liquefied air to at least one column of the column system;   h) a conduit for removing a second part of the air at the first outlet pressure from the heat exchanger and for sending at least part of the second part of the air to the expander conduit for sending air expanded in the expander to at least one column of column system;   i) a conduit for removing liquid from a column of the column system, means for pressurizing at least part of the liquid to form pressurized liquid and a conduit for sending at least part of the pressurized liquid to the heat exchanger; and   j) a refrigeration cycle comprising the third compressor and a second expander, a conduit for sending an auxiliary fluid from the third compressor to the heat exchanger, a conduit for sending the auxiliary fluid from the heat exchanger to the second expander, a conduit for sending the auxiliary fluid from the second expander to the heat exchanger and a conduit for sending the auxiliary fluid from the heat exchanger to the third compressor.