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Cryogenic gas processing

  • US 4,444,577 A
  • Filed: 09/09/1982
  • Issued: 04/24/1984
  • Est. Priority Date: 09/09/1982
  • Status: Expired due to Term
First Claim
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1. A method for separating ethane and higher molecular weight hydrocarbons from a natural gas feed, predominating in methane and containing significant amounts of ethane and higher molecular weight hydrocarbons and carbon dioxide, having a first pressure substantially above atmospheric pressure and a first temperature substantially below atmospheric temperature and at which first pressure and first temperature said feed comprises both vapor and liquid phases, comprising:

  • (a) separating said feed, in a separation zone, to separate the vapor phase of said feed, as a first vapor phase, and the liquid phase of said feed, as a first liquid phase;

    (b) expanding at least a part of said first vapor phase to reduce the pressure thereof to a second lower pressure and reduce the temperature thereof to a second lower temperature and produce a first expanded fluid stream;

    (c) fractionally distilling said first expanded fluid stream, any unexpanded remaining portion of said first vapor phase and said first liquid phase, in a fractionation zone, to produce a second vapor phase, significantly enriched in methane and carbon dioxide, and a second liquid phase, predominating in ethane and higher molecular weight hydrocarbons and containing insignificant amounts of methane;

    (d) expanding at least a portion of said second vapor phase to reduce the pressure thereof to a third lower pressure and reduce the temperature thereof to a third lower temperature and produce a second expanded fluid stream, as a third vapor phase, predominating in methane, significantly enriched in carbon dioxide and containing insignificant amounts of ethane in higher molecular weight hydrocarbons, and a third liquid phase;

    (e) separating said second expanded fluid stream, in a separation zone, to separate said third vapor phase and said third liquid phase;

    (f) recycling said third liquid phase to said fractionation zone, as a reflux;

    (g) recovering said third vapor phase as a product; and

    (h) recovering said second liquid phase as a product;

    (i) maintaining the temperature and pressure at all times throughout the process substantially within the liquid range of carbon dioxide.

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