Cryogenic air separation method for the production of oxygen and medium pressure nitrogen

Claim 1

A cryogenic air separation method for the production of nitrogen at elevated pressure and oxygen comprising: (a) providing feed air into a primary column operating at a pressure within the range of from 40 to 95 psia and separating feed air in the primary column into nitrogen-rich vapor and oxygen-enriched liquid; (B) passing oxygen-enriched liquid into an auxiliary stripping column at the top of the stripping column which is operating at a pressure less than that of the primary column and which has one third or less equilibrium stages than the primary column; (C) passing oxygen-enriched liquid down the stripping column against upflowing vapor to produce oxygen-rich liquid; (D) recovering a first portion of the nitrogen-rich vapor as product elevated pressure nitrogen; (E) condensing a second portion of the nitrogen-rich vapor by indirect heat exchange with oxygen-rich liquid to produce oxygen-rich vapor; (F) passing oxygen-rich vapor up the stripping column as the upflowing vapor; and (G) recovering a portion of the oxygen-rich vapor as product oxygen, said oxygen-rich vapor portion taken from the stripping column at a point below the point where oxygen-enriched liquid is passed into the stripping column.