Integrated adsorption/cryogenic distillation process for the separation of an air feed

摘要

An integrated adsorption/cryogenic distillation process is set forth for the separation of an air feed. The air feed is passed through a vacuum swing adsorption (VSA) unit to remove impurities comprising water and carbon dioxide which will freeze out at cryogenic temperatures. The VSA sequence includes an adsorbent regeneration step whereby the impurity-saturated adsorbent is purged under vacuum with a purge gas. The resulting impurity-depleted air feed is fed to a cryogenic distillation column for rectification into a gaseous nitrogen overhead and a liquid oxygen bottoms. A waste stream from the distillation column is expanded, warmed against the impurity-depleted air feed to recover its refrigeration and subsequently recycled as the purge gas to the VSA unit. A key to the present invention is that the waste stream is expanded to the required sub-ambient pressure level in the cryogenic portion of the process. This enables one to recover all of the available refrigeration from the cryogenic waste stream prior to using such waste stream as the purge gas for the adsorption portion of the process.