Air Products and Chemicals, Inc.

Leigh A Stapf

Rakesh Agrawal

Donald W Woodward

William T Kleinberg

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 The low to medium purity oxygen product (oxygen concentration between 65% and 99%) is withdrawn from the bottom of the distillation column as liquid, vapor or a combination of both.

Process for the cryogenic distillation of an air feed to produce a low

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). In the first, a portion of the liquid oxygen bottoms can be removed from the low pressure column and boosted in pressure, and then subsequently vaporized. This vaporized, boosted pressure, liquid oxygen is recovered as medium pressure gaseous oxygen product. In the second, a portion of the vaporized liquid oxygen bottoms is removed from the low pressure column and warmed. This warmed, vaporized liquid oxygen bottoms would be recovered as the medium pressure gaseous oxygen product.

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Lansdale, PA, United States of America

Leigh A Stapf