Cryogenic Air Separation Process and Apparatus

Abstract

A cryogenic process for the production of oxygen by cryogenic distillation using an air separation unit comprising a double column, said double column comprising a high pressure column and a low pressure column comprising the steps of: sending compressed, cooled and purified air to the high pressure column in gaseous form, sending oxygen enriched fluid from the bottom of the high pressure column to the low pressure column, removing nitrogen enriched gas from the top of the high pressure column, sending a first portion of nitrogen enriched gas to a lower reboiler in the low pressure column following compression in a cold compressor having a cryogenic inlet temperature, sending a second portion of nitrogen enriched gas to an upper reboiler in the low pressure column, sending nitrogen enriched liquid from at least one of the first and second reboilers to at least one of the high pressure column and the low pressure column, expanding a stream of nitrogen enriched gas from the high pressure column in an expander following a warming step, driving the cold compressor using a motor and producing oxygen rich gas from the low pressure column by at least one of the steps of removing a gaseous stream and by vaporizing a liquid stream.

1 . A cryogenic process for the production of oxygen by cryogenic distillation using an air separation unit comprising a double column, said double column comprising a high pressure column and a low pressure column comprising the steps of:
 a) sending compressed, cooled and purified air to the high pressure column in gaseous form;   b) sending oxygen enriched fluid from the bottom of the high pressure column to the low pressure column;   c) removing nitrogen enriched gas from the top of the high pressure column;   d) sending a first portion of nitrogen enriched gas to a lower reboiler in the low pressure column following compression in a cold compressor having a cryogenic inlet temperature;   e) sending a second portion of nitrogen enriched gas to an upper reboiler in the low pressure column;   f) sending nitrogen enriched liquid from at least one of the first and second reboilers to at least one of the high pressure column and the low pressure column   g) expanding a stream of nitrogen enriched gas from the high pressure column in an expander following a warming step h) driving the cold compressor using a motor and   i) producing oxygen rich gas from the low pressure column by at least one of the steps of removing a gaseous stream and by vaporizing a liquid stream.   
     
     
         2 . Process according to  claim 1  wherein:
 a. During a first period;
 i) feeding a first air stream to the air separation unit at a first flow rate; 
 ii) feeding liquid oxygen from a liquid oxygen tank to at least one of a column and a heat exchanger of the air separation unit; 
 iii) recovering a gaseous oxygen stream with a higher flow than the liquid oxygen stream from the air separation unit; and 
 iv) sending at least one air derived component liquid to at least one air derived component liquid tank. 
   b. During a second period:
 i) feeding the at least one air derived component liquid stream from the at least one air component liquid tank to the air separation unit; 
 ii) extracting a liquid oxygen stream from a column of the air separation unit to the liquid oxygen tank; 
 iii) recovering a gaseous oxygen stream from the air separation unit; and 
 iv) increasing the flowrate of the first air stream to a value greater than the first flowrate. 
   
     
     
         3 . A process according to  claim 1 , in which at least one air derived component liquid is liquid nitrogen and wherein step iv) of period a) of  claim 1  comprises removing liquid nitrogen from a column of the air separation unit. 
     
     
         4 . A process according to  claim 1 , in which at least one air derived component liquid contains 80 mol % nitrogen or greater. 
     
     
         5 . A process according to  claim 1 , in which at least one air derived component liquid is liquid air. 
     
     
         6 . A process according to  claim 2 , in which at least one air derived component liquid contains 35 mol % oxygen or greater wherein step iv) of period a) of  claim 2  comprises removing liquid nitrogen from a column of the air separation unit. 
     
     
         7 . A process according to  claim 2  wherein the air flow to the air separation unit varies between the first and second period by at most 10%. 
     
     
         8 . A cryogenic apparatus for the production of oxygen by cryogenic distillation using an air separation unit comprising at least a double column, said double column comprising a high pressure column and a low pressure column, said low pressure column having a lower and an upper reboiler said apparatus comprising a cold compressor, a conduit for sending compressed, cooled and purified air to the high pressure column in gaseous form, a conduit for sending oxygen enriched fluid from the bottom of the high pressure column to the low pressure column, a conduit for removing nitrogen enriched gas from the top of the high pressure column, a conduit for sending a first portion of nitrogen enriched gas to the lower reboiler in the low pressure column following compression in the cold compressor having a cryogenic inlet temperature, a conduit for sending a second portion of nitrogen enriched gas to the upper reboiler in the low pressure column, a conduit for sending nitrogen enriched liquid from at least one of the upper and lower reboilers to at least one of the high pressure column and the low pressure column, an expander for expanding a stream of nitrogen enriched gas from the high pressure column following a warming step, said cold compressor being coupled to a motor, a conduit for removing at least one of a gaseous and a liquid stream from the low pressure column to produce an oxygen product. 
     
     
         9 . Apparatus of  claim 8  comprising a heat exchanger for vaporising liquid oxygen removed from the low pressure column. 
     
     
         10 . The apparatus of  claim 8  comprising a storage tank for liquid oxygen connected to the low pressure column and a storage tank for an air derived liquid connected to a column of the double column.