Method And Apparatus For Separating Air By Cryogenic Distillation

Abstract

A method and to an apparatus for producing oxygen by separating air using cryogenic distillation is presented.

1 - 15 . (canceled) 
     
     
         16 . A method for producing oxygen by separating air using cryogenic distillation in an installation comprising a double column comprising a medium-pressure column and a low-pressure column, the low-pressure column containing the bottom vaporizer, an intermediate vaporizer and an upper vaporizer, said method comprising:
 a) purifying compressed air in a purification unit, cooling said purified compressed air in an exchange line, and feeding the cooled compressed air to the medium-pressure column of the double column;   b) withdrawing an oxygen-rich fluid from the low-pressure column, heating the oxygen-rich fluid and sending the heated oxygen-rich fluid to a customer   c) withdrawing a nitrogen stream from the medium-pressure column, and splitting said nitrogen stream into at least three parts   d) expanding a first part of the nitrogen in a first turbine,   e) increasing the pressure of a second part of the nitrogen in a cold compressor and sending said pressurized nitrogen to the bottom vaporizer, sending the nitrogen thus condensed to at least one column of the double column;   f) condensing a third part of the nitrogen in the upper vaporizer, with no pressure-modifying step downstream of the column from which it is tapped off and upstream of the upper vaporizer, sending the nitrogen thus condensed to at least one column of the double column;   g) sending a gaseous flow to the intermediate vaporizer, this flow consisting of the nitrogen withdrawn from the medium-pressure column and compressed in a cold compressor.   
     
     
         17 . The method of  claim 16 , in which the first part of the nitrogen expanded in the first turbine is used for regenerating the purification unit. 
     
     
         18 . The method of  claim 16 , wherein the first turbine drives the cold compressor in which the pressure of the second part of the nitrogen is raised and provides substantially all cold energy required for the method. 
     
     
         19 . The method of  claim 16 , wherein the low-pressure column has no top condenser. 
     
     
         20 . The method of  claim 16 , wherein all the gaseous nitrogen from the top of the medium-pressure column is split into just the three parts. 
     
     
         21 . The method of  claim 16 , wherein all the gaseous nitrogen from the top of the medium-pressure column is split into just four parts, the fourth part being sent to the intermediate vaporizer. 
     
     
         22 . The method of  claim 16 , wherein substantially all cold energy required for the method is produced by expanding nitrogen from the medium-pressure column in at least one turbine. 
     
     
         23 . The method of  claim 16 , wherein a liquid oxygen flow from the low-pressure column is vaporized to produce the fluid sent to the customer. 
     
     
         24 . The method of  claim 23 , wherein said liquid oxygen is pressurized after removal from the low-pressure column and prior to vaporization. 
     
     
         25 . An apparatus for producing oxygen by separation of air using cryogenic distillation comprising a double column comprising;
 a) a medium-pressure column and a low-pressure column, the low-pressure column containing a bottom vaporizer, an intermediate vaporizer and an upper vaporizer,   b) a purification unit, a   c) n exchange line,   d) at least one first turbine,   e) at least one cold compressor,   f) means for sending compressed air, purified in the purification unit and cooled in the exchange line, to the medium-pressure column of the double column,   g) means for withdrawing an oxygen-rich fluid from the low-pressure column,   h) said means consisting at least in part of the exchange line means for sending the oxygen-rich fluid sent to the customer,   i) means for splitting the nitrogen withdrawn from the medium-pressure column into at least three parts,   j) means for sending a first part of the nitrogen to the first turbine,   k) means for sending a second part of the nitrogen to the cold compressor where its pressure is raised,   l) means for sending the raised-pressure second part to the bottom vaporizer,   m) means for sending the nitrogen thus condensed to at least one column of the double column,   n) means for sending a third part of the nitrogen to the upper vaporizer, without a pressure modifying means downstream of the column from which it was withdrawn from and upstream of the upper vaporizer,   o) means for sending the nitrogen thus condensed being sent to at least one column of the double column,   p) means for sending a gaseous flow to the intermediate vaporizer, this flow consisting of purified and cooled compressed air or of nitrogen   tapped off from the medium-pressure column and compressed in the second cold compressor,   
       also comprising means for connecting the intermediate vaporizer to the top of the medium-pressure column so that the nitrogen tapped off from the top of this column is sent to the intermediate vaporizer. 
     
     
         26 . The apparatus of  claim 25 , further comprising g′) means for heating said oxygen-rich fluid from step g). 
     
     
         27 . The apparatus of  claim 25 , further comprising means for connecting the outlet of the first turbine to the purification unit. 
     
     
         28 . The apparatus of  claim 25 , wherein the first turbine is coupled to the cold compressor in which the pressure of the second part of the fluid is raised and constitutes the only turbine in the apparatus. 
     
     
         29 . The apparatus of  claim 25 , wherein the low-pressure column has no top condenser.