Abstract: A process is set forth for the cryogenic distillation of an air feed to produce a low to medium purity oxygen product using a single distillation column system. The air feed is partially condensed into a crude liquid oxygen stream and a remaining nitrogen-enriched vapor stream by boiling the liquid phase at the bottom of the distillation column. The pressure of the crude liquid oxygen stream is reduced and the nitrogen-enriched vapor stream is subsequently condensed against it to provide reflux to the top of the distillation column. The low to medium purity oxygen product (oxygen concentration between 65% and 99%) is withdrawn from the bottom of the distillation column as liquid, vapor or a combination of both.

Abstract: The present invention is an improvement to a process for the separation of air into its constituent components in a cryogenic distillation column system having a high pressure column and a low pressure column which are thermally integrated with each other. The improvement for producing both nitrogen and oxygen products at a medium pressure comprises the following steps: (a) operating the low pressure column at a pressure of between 10 to 75 psig and the high pressure column at a pressure which is about 60 to 160 psi higher than the low pressure column; (b) removing and subsequently warming at least a portion of the lower pressure nitrogen overhead from the top of the low pressure column and recovering the warmed, lower pressure nitrogen overhead portion as medium pressure gaseous nitrogen product; and (c) recovering medium pressure gaseous oxygen product from the low pressure column. There are two alternative ways to recover the medium pressure oxygen product of step (c).