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Separation of low boiling constituents from a mixed gas

  • US 4,456,461 A
  • Filed: 09/09/1982
  • Issued: 06/26/1984
  • 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 said ethane and higher molecular weight hydrocarbons and having a first pressure substantially above atmospheric pressure and a first temperature substantially below atmospheric temperature, at which first pressure and first temperature, said feed comprises both a vapor phase, representing a first vapor phase, and a liquid phase, representing a first liquid phase, comprising:

  • (a) expanding at least a part of said vapor phase, in a first expansion step, to produce a first expanded fluid having a second pressure substantially lower than said first pressure and a second temperature substantially lower than said first temperature;

    (b) introducing all of said first expanded fluid and any unexpanded first vapor phase into a separation-contacting zone adjacent the top thereof and introducing all of said first liquid phase into said separation-contacting zone at a lower intermediate point thereof, under conditions and in proportions such that the pressure at the top of said separation-contacting zone is substantially lower than the pressure at the bottom of said separation-contacting zone and the temperature at said top of said separation-contacting zone is substantially lower than the temperature at said bottom of said separation-contacting zone;

    (c) separating said first expanded fluid, said unexpanded remaining portion of said first vapor phase and said first liquid phase, in said separation-contacting zone, to produce a second vapor phase and a second liquid phase;

    (d) introducing said second vapor phase into a fractional distillation zone adjacent the top thereof and introducing said second liquid phase into said fractional distillation zone at an intermediate point thereof below the point of introduction of said second vapor phase;

    (e) fractionally distilling said second vapor phase and said second liquid phase, in said frictional distillation zone, to produce a third vapor phase predominating in methane and containing insignificant amounts of ethane and higher molecular weight hydrocarbons and a third liquid phase predominating in ethane and higher molecular weight hydrocarbons and containing insignificant amounts of methane;

    p1 (f) recovering said third vapor phase as a product; and

    (g) recovering said third liquid phase as a product.

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