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Air separation

  • US 5,287,704 A
  • Filed: 11/12/1992
  • Issued: 02/22/1994
  • Est. Priority Date: 11/14/1991
  • Status: Expired due to Fees
First Claim
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1. A method of separating air, comprising:

  • dividing a compressed air stream into first and second subsidiary streams;

    cooling the first subsidiary air stream by heat exchange to a temperature suitable for its separation by rectification;

    introducing the thus cooled air stream into the higher pressure stage of a double rectification column;

    further compressing the second subsidiary air stream;

    cooling at least part of it by heat exchange to a first intermediate temperature below ambient temperature but above those temperatures at which the double rectification column operates;

    expanding the thus cooled second subsidiary air stream in a first expansion turbine;

    withdrawing the thus expanded second subsidiary air stream from the first expansion turbine at a second intermediate temperature below the first intermediate temperature but above those temperatures at which the double rectification column operates and introducing it into a second expansion turbine;

    further expanding the second subsidiary air stream in the second expansion turbine and withdrawing the thus expanded second subsidiary air stream therefrom and introducing it into the lower pressure rectification stage of the double rectification column;

    separating the air in the double rectification column into oxygen and nitrogen, withdrawing oxygen and nitrogen streams from the said lower pressure stage, and producing a part of at least one of the oxygen and nitrogen as a liquid product.

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