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.

Description

FIELD OF THE INVENTION[0001]The present invention is directed to the cryogenic separation of air by distillation for the production of primarily gaseous nitrogen.BACKGROUND ART[0002]Nitrogen is among the most heavily produced and used chemicals. It finds application in the petroleum, glass, foods, electronics, pharmaceutical, and metals industries. Cryogenic separation of air is a principal means of producing nitrogen.[0003]Cryogenic air separation plants, chiefly for the production of gaseous nitrogen, exist in a number of configurations. These, in turn, group around single distillation column and double distillation column designs. There are many variations of these designs in each category. In most cases the objective is to produce nitrogen at the lowest energy consumption for any given delivery pressure; but aspects such as capital cost and particular features of convenience are equally important.[0004]A simple single-column system has a relatively low nitrogen recovery, the bal...

AI Technical Summary

Benefits of technology

[0008]An object of the invention is to provide a process for a two-column cryogenic distillation of air which achieves high nitrogen recovery, low unit energy consumption, and, though nitrogen is produced by each distillation column operating at different pressures, the product gaseous nitrogen may be delivered at a single pressure, a desirable and convenient feature, while maintaining high nitrogen recovery and low unit energy consumption.SUMMARY OF THE INVENTION

[0013]It can be seen then that such a system described above becomes easier to effect as the pressure difference between the high pressure column and the reduced pressure derived from the bottoms product from the low pressure column becomes greater.

[0015]The current invention allows turboexpansion of a stream, which is a product of the high pressure column, to subsequently undergo another separation process in the low pressure column. This provides high recovery of the nitrogen product at relatively high pressure in an energy-efficient process.

Problems solved by technology

Nevertheless, simple two-column systems do not necessarily have lower unit energy requirements than improved single column systems.

It is usually expected that direct delivery of nitrogen from the distillation unit at higher pressures will result in lower nitrogen recovery.

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