Air separation process using warm and cold expanders

Details Air separation process using warm and cold expanders Air separation process using warm and cold expanders

1998-01-22

1999-06-01

Capossela, Ronald

Refrigeration

Cryogenic treatment of gas or gas mixture

Separation of gas mixture

62652, F25J 300

Patent

active

059079592

ABSTRACT:
The present invention relates to a process for the cryogenic distillation of air in a distillation column system having at least one distillation column operating at a higher pressure and one distillation column operating at a lower pressure, wherein feed air is cooled and fed to the higher pressure column, wherein the boil-up at the bottom of the lower pressure column producing the oxygen product is provided by condensing a stream having a nitrogen concentration equal to or greater than that of the feed air stream and wherein at least two expanders are employed to provide refrigeration to the distillation column system, wherein the first expander is operated at an inlet temperature near ambient or above ambient temperature and the second expander is operated at an inlet temperature colder than ambient, characterized in that at least one of the two expanders employs at least one of the following steps: (a) work expanding a portion of the feed air; (b) work expanding a process stream with a nitrogen content equal to or greater than that of the feed air, and, then, condensing at least a portion of the expanded stream by a latent heat exchange with at least one of the following two liquids: (i) a liquid at an intermediate height in the lower pressure column and (ii) one of the liquid feeds to low pressure column which has an oxygen concentration of at least the concentration of oxygen in the feed air; (c) condensing at least one process stream with nitrogen content equal to or greater than that in the feed air by latent heat exchange which vaporizes at least a portion of an oxygen-enriched liquid stream which has oxygen concentration of at least the concentration of oxygen in the feed air and which is at a pressure greater than the pressure of the lower pressure column, and work expanding at least a portion of the resulting vapor stream; and (d) work expanding a process stream from the higher pressure column with nitrogen content equal to or greater than that in the feed air and withdrawing the expanded stream as gaseous product stream.

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