Hybrid nitrogen generator with auxiliary column drive

Claim 1

A process for the production of nitrogen at relatively high yield and purity by cryogenic rectification of feed air comprising avoiding the need to employ a full scale double column by the steps of: (a) introducing the major portion of the feed air into a main rectification column which is operating at a pressure in the range of from 35 to 145 psia, and wherein feed is separated into nitrogen-rich vapor and oxygen-enriched liquid; (b) introducing a minor portion of the feed air into a prefractionation zone at a pressure greater than that at which the main column is operating, and wherein the minor portion is separated into a nitrogen-enriched vapor fraction and an oxygen-enriched liquid fraction; (c) condensing at least some of the nitrogen-enriched vapor fraction by indirect heat exchange with the oxygen-enriched liquid produced in the main column; (d) introducing at least some of the resulting condensed nitrogen-enriched fraction, as reflux liquid and additional feed, into the main column at a point at least one tray above the point where the major portion of the feed air is introduced into the main column; (e) condensing a first portion of the nitrogen-rich vapor by indirect heat exchange with vaporizing oxygen-enriched liquid; (f) passing at least some o the resulting condensed nitrogen-rich first portion to the main column at a point at least one tray above the point where the condensed nitrogen-enriched fraction is introduced into the main column; and (g) recovering a second portion of the nitrogen-rich vapor as product nitrogen.