Process for the separation of air by cryogenic distillation

Abstract

A process for the separation of air by cryogenic distillation operates either with a product ratio greater than 2.5, in which case nitrogen enriched liquid is sent from a storage tank to the column system and nitrogen enriched gas from the column system is compressed in a first compressor having an inlet temperature of less than −50° C. and then warmed in the heat exchanger, or with a product ratio less than 2.5, in which case a second nitrogen rich gas removed from the column system is expanded in a turbine having an inlet temperature lower than the ambient temperature or liquefied in a liquefier and nitrogen enriched liquid is sent to the storage tank from the outlet of the turbine and/or from the column system and/or from the liquefier.

1 - 12 . (canceled) 
     
     
         13 . A process for the separation of air by cryogenic distillation in which air is purified, cooled in a heat exchanger and separated in a column system including at least a first column and a second column, the first column operating at a higher pressure than the second column and the top of the first column being thermally linked to the bottom of the second column via a first reboiler-condenser, oxygen enriched liquid is removed from the first column and sent to the second column or liquid derived from the oxygen enriched liquid is sent to the second column, nitrogen enriched liquid is removed from the first column and sent to the second column, oxygen rich liquid is removed from the second column, pressurized and vaporized in the heat exchanger to form an oxygen rich gas, nitrogen rich fluid is removed from the column system and warmed in the heat exchanger to form a first nitrogen rich gas, wherein
 i) during a first period, the product ratio, being the ratio between the amount of nitrogen rich gas produced and the amount of oxygen rich gas produced, is greater than 2.5, nitrogen enriched liquid is sent from a storage tank to the column system and a first nitrogen enriched gas from the column system is compressed in a first compressor having an inlet temperature of less than −50° C. and then sent to the heat exchanger, and   ii) during a second period, the product ratio is less than 2.5 and a second nitrogen rich gas removed from the column system is expanded in a turbine having an inlet temperature lower than the ambient temperature or liquefied in a liquefier and nitrogen enriched liquid is sent to the storage tank from the outlet of the turbine and/or from the column system and/or from the liquefier, wherein the first nitrogen enriched gas is removed from the second column before being compressed in the first compressor and after compression in the first compressor is warmed in the heat exchanger and removed as a product, wherein the second nitrogen rich gas expanded in the turbine is removed from the second column and wherein the second column operates at a pressure of at least 2 bars abs.   
     
     
         14 . The process according to  claim 13 , wherein during the first period, the product ratio is greater than 3. 
     
     
         15 . The process according to  claim 13 , wherein during the second period, the product ratio is less than 2. 
     
     
         16 . The process according to  claim 13 , wherein during the first period, nitrogen enriched gas is removed from the second column, compressed in the first compressor without having been warmed and sent to the heat exchanger. 
     
     
         17 . The process according to  claim 13 , wherein during the second period, the nitrogen rich gas removed from the column system is warmed in the heat exchanger expanded in the turbine and then warmed in the heat exchanger. 
     
     
         18 . The process according to  claim 13 , wherein the turbine has an inlet temperature of at most −50° C. 
     
     
         19 . The process according to  claim 13 , wherein the turbine has an inlet temperature of at most −100° C. 
     
     
         20 . The process according to  claim 13 , wherein during the second period, the outlet pressure of the turbine is substantially equal to the pressure of the second column. 
     
     
         21 . The process according to  claim 13 , wherein no nitrogen rich gas is sent to the turbine during the first period. 
     
     
         22 . The process according to  claim 13 , wherein no gas is sent to the first compressor during the second period. 
     
     
         23 . The process according to  claim 13 , where the price of electricity is less in the second period than in the first period. 
     
     
         24 . The process according to  claim 13 , wherein no nitrogen enriched liquid is sent to the storage tank during the first period. 
     
     
         25 . The process according to  claim 13 , wherein during the second period, at least one cryogenic liquid is withdrawn from the process as a final product. 
     
     
         26 . The process according to  claim 25 , wherein during the first period the same cryogenic liquid is not withdrawn from the process as a final product.