Process for the cryogenic distillation of air

Abstract

Pressurized gaseous nitrogen (“GAN”) is produced in a process in which liquid nitrogen (“LIN”) is produced in a cryogenic air separation unit (“ASU”). The pressure of at least a portion of the LIN is increased to produce pressurized LIN. A fluid having an oxygen concentration at least equal to that of air is separated in an auxiliary cryogenic distillation column to produce nitrogen-rich overhead vapor and oxygen-enriched bottoms liquid. Heat and optionally mass is transferred between at least a portion of the nitrogen-rich overhead vapor and at least a portion of the pressurized LIN to produce nitrogen-rich liquid and pressurized GAN. At least a portion of said nitrogen-rich liquid is used as reflux to the ASU after suitable pressure adjustment. Such a process allows the production of high purity GAN without the loss of oxygen recovery typically observed in conventional pumped LIN cycles.

Description

TECHNICAL FIELD OF THE INVENTION [0001] The present invention relates to a process for the cryogenic distillation of air and, in particular, to the production of high purity, pressurized gaseous nitrogen (“GAN”). BACKGROUND OF THE INVENTION [0002] High purity GAN is typically prepared in a cryogenic air distillation process operating a pumped liquid nitrogen (“LIN”) cycle. In such a cycle, LIN taken from the distillation system is pumped to the required product pressure and vaporized in the main heat exchanger by indirect heat exchange against condensing high pressure air. The resulting liquid air (“LAIR”) is fed to the column system. However, the use of such a pumped LIN cycle usually leads to an unfavorable loss of oxygen recovery when compared to a high pressure (“HP”) GAN cycle in which the nitrogen is taken as vapor from the HP column of a dual column distillation system, warmed in the main heat exchanger and compressed to the desired pressure. This is because, in the pumped LI...

AI Technical Summary

Problems solved by technology

However, the use of such a pumped LIN cycle usually leads to an unfavorable loss of oxygen recovery when compared to a high pressure (“HP”) GAN cycle in which the nitrogen is taken as vapor from the HP column of a dual column distillation system, warmed in the main heat exchanger and compressed to the desired pressure.

As a result, the low pressure (“LP”) column of the dual column system has to do more of the separation, with the result that the overall oxygen recovery falls.

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