Patent ID: 7487648

Claim:
A method for carrying out cryogenic air separation employing a double column having a higher pressure column and a lower pressure column comprising: (A) condensing feed air to produce condensed feed air, passing a stream of the condensed feed air into the higher pressure column, and separating the feed air contained within the stream of the condensed feed air within the higher pressure column by cryogenic rectification to produce nitrogen-enriched vapor and oxygen-enriched liquid; (B) withdrawing nitrogen-enriched vapor from the higher pressure column, withdrawing oxygen-enriched liquid from the higher pressure column, and passing oxygen-enriched liquid withdrawn from the higher pressure column into the lower pressure column without undergoing subcooling; and (C) producing nitrogen-rich vapor and oxygen-rich liquid by cryogenic rectification within the lower pressure column, and withdrawing oxygen-rich liquid from the lower pressure column wherein the temperature of the condensed feed air exceeds the temperature of the oxygen-rich liquid withdrawn from the lower pressure column and the temperature of the nitrogen-enriched vapor withdrawn from the higher pressure column.