A THREE COLUMN CRYOGENIC CYCLE FOR THE PRODUCTION OF IMPURE OXYGEN AND PURE NITROGEN

摘要

A cryogenic process for producing impure oxygen and/or substantially purenitrogen utilizes a classic double column arrangement and an additional third columnoperating at a medium pressure, i.e. between the pressure of the higher pressure stageand the lower pressure stage of the double column system. A portion of the feed air isseparated in the stages of the double column system, and another portion of the feed airis distilled in the medium pressure stage. Crude liquid oxygen from the higher pressurestage and/or the medium pressure stage is reduced in pressure and boiled in areboiler/condenser at the top of the medium pressure column. The vaporized crudeliquid oxygen from the top reboiler/condenser of the medium pressure column issubsequently introduced as a vapor feed to the lower pressure stage, which reducesirreversibilities of separation in the lower pressure stage.