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Low pressure recovery of olefins from refinery offgases

  • US 5,502,971 A
  • Filed: 01/09/1995
  • Issued: 04/02/1996
  • Est. Priority Date: 01/09/1995
  • Status: Expired due to Term
First Claim
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1. A method of recovering olefins from refinery offgases containing hydrogen, methane, C2, C3, C4 and heavier components including paraffins, olefins and diolefins and nitrogen oxide, using a relatively low pressure comprising the steps of:

  • a) providing a feedstream of said refinery offgases at a pressure of 6.89 to 13.79 bars;

    b) cooling said feedstream to a temperature in the range of -20°

    to -60°

    C.;

    c) fractionating said cooled feedstream to produce an overhead containing at least essentially all of said hydrogen, methane and C2 components and a bottoms containing at least essentially all of said C4 and heavier components;

    d) cooling said overhead to a temperature in the range of -20°

    to -80°

    C. to produce a condensed fractionator recycle containing at least essentially all of said C4 and heavier components and a vapor stream containing at least essentially all of said hydrogen, methane and C2 components;

    e) further cooling said vapor stream to a temperature in the range of -75°

    to -100°

    C. and feeding said further cooled vapor stream into a demethanizer column containing a lower stripping zone, a central rectifying zone and an upper enriching zone at a location between said stripping and rectifying zones and at a pressure of 3.45 to 8.27 bars;

    f) feeding a stream of C2 or heavier paraffins at a temperature in the range of -80°

    to -100°

    C. into said demethanizer column between said rectifying and enriching zones to increase the paraffin content and reduce the olefin content of the demethanizer overhead;

    g) cooling said demethanizer overhead and separating a condensed demethanizer reflux and an overhead vapor product containing essentially only hydrogen and methane; and

    h) removing a demethanizer column bottoms containing essentially all of said C2 and heavier components.

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