Patent ID: 7552599
Filing Date: 2009-06-30
Classification: F25J

Abstract:
1. In a process for the cryogenic separation of an air feed wherein: (a) the air feed is compressed, cleaned of impurities that will freeze out at cryogenic temperatures, and subsequently fed into an air separation unit comprising a main heat exchanger and a distillation column system; (b) the air feed is cooled in the main heat exchanger by indirectly heat exchanging the air feed against at least a portion of the effluent streams from the distillation column system; (c) the cooled air feed is separated in the distillation column system into effluent streams including a stream enriched in nitrogen and a stream enriched in oxygen; and (d) in order to provide the refrigeration necessary when at least a portion of the oxygen product is desired as liquid oxygen, refrigeration is extracted from LNG by indirectly heat exchanging the LNG in a heat exchanger against one or more nitrogen-enriched vapor streams withdrawn from the distillation column system in order to liquefy such nitrogen-enriched stream(s); the improvement comprising: (e) indirectly heat exchanging at least a portion of the nitrogen-enriched streams liquefied in part (d) against a portion of the air feed to the distillation column system in order to fully condense the portion of the air feed to the distillation column system.