Method and apparatus for production of high-pressure nitrogen from air by cryogenic distillation

Abstract

Nitrogen gas at a single pressure is produced from a two-column cryogenic distillation of air. The bottoms liquid product from the high pressure column is divided into two portions, one of which is vaporized and then turboexpanded before its entry into the low pressure column as a feed stream. By these means, no stream bypasses the double distillation process, further enhancing nitrogen recovery and achieving low specific energy consumption for nitrogen product.

1 . A process for the production of nitrogen by distillation of air, consisting of two distillation columns, a high pressure column and a low pressure column, where:
 a. the bottoms liquid product of the high pressure column is divided into a first part which feeds the low pressure column; and a second part which serves as coolant for condensing at least one vapor stream from the high pressure column which is returned to the high pressure column as a reflux stream;   b. vaporization of said coolant against a condensing stream;   c. turboexpansion of all or substantially all of said vaporized coolant after optional further heating;   d. introduction of all or substantially all of said turboexpanded vaporized coolant into the low pressure column for effecting additional separation of its components by distillation.   
     
     
         2 . The process of  claim 1  where withdrawal of the total or major gaseous nitrogen product is from the high pressure distillation column. 
     
     
         3 . The process of  claim 1  where nitrogen drawn from the high pressure column is above 10.34 bar(a). 
     
     
         4 . The process of  claim 1  where the bottoms liquid product of the low pressure column is reduced in pressure and serves as coolant to the condenser of the low pressure column. 
     
     
         5 . The process of  claim 1  where gaseous nitrogen overhead from the low pressure column is condensed in the low pressure column condenser and divided into a first part which is returned as reflux to the low pressure column and a second part which is pumped to higher pressure and returned as reflux to the high pressure column. 
     
     
         6 . The process of  claim 1  where gaseous nitrogen overhead from the high pressure column, which is not condensed in the high pressure column condensers, is withdrawn as the gaseous nitrogen product. 
     
     
         7 . The process of  claim 1  where the vaporized coolant stream from the low pressure column condenser is warmed to ambient temperature in heat exchangers to recover its refrigeration. 
     
     
         8 . The process of  claim 1  where the gaseous nitrogen product is warmed to ambient temperature in heat exchangers to recover its refrigeration. 
     
     
         9 . The process of  claim 1  where streams which are warmed, in turn are used to cool incoming air. 
     
     
         10 . A process for the distillation of air consisting of two distillation columns, as described in  claim 1 , where refrigeration can be supplied by turboexpanding said vaporized coolant, by liquid-assisting with an external cryogenic refrigerant, or by a combination of both. 
     
     
         11 . An apparatus for the production of nitrogen from air comprising:
 a. equipment for compressing and purifying air;   b. heat exchange means for cooling air and warming products of air separation;   c. two distillation columns of higher and lower pressure for the separation of air by cryogenic distillation;   d. vapor generated by boiling a coolant for condensing the overhead product of the high pressure column is turboexpanded and introduced into the low pressure column;   e. means for returning condensed nitrogen vapor to higher pressure column as reflux;   f. means for withdrawing nitrogen vapor from the higher pressure column as nitrogen product of the plant;   g. means for transferring condensed additional streams, such as air, to higher pressure column, lower pressure column, or both;   h. means for transference of part of a bottom liquid product of the higher pressure column to the lower pressure column;   i. means for turboexpansion of vapor derived the condenser of the higher pressure column;   j. means of supplying supplementary or total refrigeration to the process by addition of a liquid cryogen, if desired;   k. means for transference of the liquid bottoms product of the lower pressure column to the condenser of the lower pressure column to effect condensation of the overhead nitrogen vapor of the lower pressure column;   l. means for pumping part of the condensed overhead vapor from the lower pressure column to sufficient pressure and then for injecting said part into the higher pressure column;   m. means for returning part of condensed overhead vapor from low pressure column back to the low pressure column as reflux.