Apparatus and method for separating air by cryogenic distillation

Abstract

An apparatus for separating air, comprising a double column, means for sending air to the purification unit at a pressure that is no more than 1 bar higher than atmospheric pressure, a pipe for sending a first air flow, the first air flow having been purified in the purification unit, to the heat exchanger at a fourth pressure that is no more than 1 bar higher than the second pressure, a pipe for sending the first purified air flow, which has been cooled in the heat exchanger, to the second column for separation, and a booster compressor, the apparatus not comprising any means for depressurizing the first flow.

1 - 15 . (canceled) 
     
     
         16 . An air separation apparatus comprising:
 a double column with a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure, the second column having a bottom reboiler;   means for sending nitrogen-enriched gas from the top of the first column to the bottom reboiler and means for sending at least a part of the condensed nitrogen-enriched gas from the bottom reboiler to the top of the first column;   a heat exchanger;   a purification unit;   means for sending air to the purification unit at a third pressure greater than atmospheric pressure by at most 1 bar;   a pipe for sending a first flow of air purified in the purification unit to the heat exchanger at a fourth pressure greater than the second pressure by at most 1 bar;   a pipe for introducing the first flow of purified air cooled in the heat exchanger into the second column in order to be separated therein, a booster;   a pipe for sending a second flow of air purified in the purification unit to the booster;   a pipe for sending at least a part of the second flow, compressed by the booster up to a fifth pressure between the first pressure and 1 bar above the first pressure, to the heat exchanger;   means for producing refrigeration;   a pipe for withdrawing at least one fluid enriched in oxygen or nitrogen from a column of the double column connected to the heat exchanger and a pipe for exiting at least one fluid enriched in oxygen or nitrogen from the heat exchanger as product; and   the apparatus not comprising any means of expansion of the first flow and comprising only a single purification unit;   wherein the second column comprises an absence of an intermediate condenser,   wherein the pipe for introducing the first flow of purified air is connected to the inside of the second column such that the first flow is included in the distillation.   
     
     
         17 . The apparatus as claimed in  claim 16 , in which the means for the production of refrigeration includes at least one of:
 a turbine for expansion of a part of the second flow,   a turbine for expansion of a nitrogen-rich gas originating from the first column, and   means for sending a cryogenic liquid from an external source to the double column.   
     
     
         18 . The apparatus as claimed in  claim 17 , in which the turbine for expansion of the part of the second flow is connected to the second column in order to send the expanded air to the second column. 
     
     
         19 . The apparatus as claimed in  claim 16 , in which the means for sending air to the purification unit at the third pressure comprises an absence of any compression means other than a single-stage compressor. 
     
     
         20 . The apparatus as claimed in  claim 16 , further comprising an absence of any means for compression of the first flow. 
     
     
         21 . A process for the separation of air by cryogenic distillation using a double column with a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure, the second column having a bottom reboiler, in which:
 a. sending air containing water and carbon dioxide to a single purification unit at a third pressure greater than atmospheric pressure by at most 1 bar;   b. separating the purified air into two;   c. sending a first flow of air purified in the purification unit to a heat exchanger at a fourth pressure greater than the second pressure by at most 1 bar;   d. sending the first flow of purified air cooled in the heat exchanger to the second column, without having expanded the first flow of purified air;   e. boosting a second flow of purified air to a fifth pressure between the first pressure and 1 bar above the first pressure, and then sending at least a part of the second flow at the fifth pressure to the heat exchanger and sending the at least a part of the second flow to the first column in gaseous form;   f. providing refrigeration;   g. at least partially condensing a nitrogen-rich gas from the first column in the reboiler and returning at least a part of the condensed nitrogen to the first column;   h. sending a nitrogen-enriched liquid and an oxygen-enriched liquid from the first column to the second column; and   i. withdrawing an oxygen-enriched gas or a nitrogen-enriched gas from the double column and reheating said oxygen-enriched gas or said nitrogen-enriched gas in the heat exchanger in order to form a product of the process,   wherein the first air flow is sent directly into the second column in order to be separated therein without having been condensed in a condenser.   
     
     
         22 . The process as claimed in  claim 21 , in which the first flow is sent to the second column at a level lower than or equal to the level of arrival of the oxygen-enriched liquid. 
     
     
         23 . The process as claimed in  claim 21 , kept cold by expansion of a part of the second flow in a turbine from the fifth pressure to the second pressure, the part of the air expanded in the turbine preferably representing between 6 vol % and 15 vol %, preferably between 6% and 8%, of the purified air. 
     
     
         24 . The process as claimed in  claim 23 , in which all the second flow is cooled in the heat exchanger down to an intermediate temperature of the heat exchanger, the inlet of the turbine is at the intermediate temperature of the heat exchanger and the part of the second flow sent to the first column is cooled in the heat exchanger down to the cold end of the latter. 
     
     
         25 . The process as claimed in  claim 21 , in which all the air is purified at a pressure which does not exceed 1.5 bara, indeed even does not exceed 1.3 bara. 
     
     
         26 . The process as claimed in  claim 21 , in which the oxygen-enriched gas contains at least 80 mol % oxygen, indeed even at least 90 mol % oxygen, but preferably less than 98 mol % oxygen. 
     
     
         27 . The process as claimed in  claim 21 , in which the first flow represents between 20 vol % and 30 vol % of the purified air flow. 
     
     
         28 . The process as claimed in  claim 21 , in which the second flow represents between 70 vol % and 80 vol % of the purified air flow. 
     
     
         29 . The process as claimed in  claim 21 , in which an oxygen-enriched gas and/or a nitrogen-enriched gas is withdrawn from the double column and it is reheated in the heat exchanger in order to form a product of the process by introducing it or by introducing them at the cold end of the heat exchanger. 
     
     
         30 . The process as claimed in  claim 21 , in which the first air flow and/or the part of the second flow intended for the first column is cooled in the heat exchanger down to a temperature at least 5° C. above its dew point.