Split shelf vapor air separation process

Claim 1

In a process for the separation of air by rectification wherein gaseous feed air at greater than atmospheric pressure and substantially free of water and carbon dioxide is introduced into a high pressure column operating at a pressure of from about 80 to 180 psia where said feed air is separated by rectification into a nitrogen-rich fraction and an oxygen-enriched fraction, and wherein a portion of said nitrogen-rich fraction is removed from said high pressure column and warmed by indirect heat exchange with said feed air by partial traverse of a reversing heat exchange zone, said portion being sufficient to maintain self-cleaning of the reversing heat exchange zone, the improvement comprising: (A) warming said portion comprising from about 10 to 18 percent of the feed air flow; (B) dividing the warmed portion into a first part comprising from about 50 to 90 percent of said warmed portion and a second part comprising from about 10 to 50 percent of said warmed portion; (C) expanding said first part to a pressure of from about 15 to 35 psia; (D) warming the expanded first part by passage through said reversing heat exchange zone; (E) removing from said process said first part as nitrogen-rich gas; and (F) directly recovering said second part as high pressure nitrogen-rich gas.