PRECOOLING FOR ETHYLENE RECOVERY IN DUAL DEMETHANIZER FRACTIONATION SYSTEMS

A process for recovery of ethylene from a pressurised feed gas (I) containing ethylene, hydrogen and 1-3C hydrocarbons, includes (a) precooling and partially condensing (I); (b) fractionating the condensate (II) in a first demethaniser zone to yield an intermediate vapour (III) and a liquid (IV) enriched in C2+ hydrocarbons; (c) fractioning (III) in a second demethaniser zone to yield a light overhead product (V) and a second liquid (VI) enriched in C2 hydrocarbons; and (d) fractioning liquids (IV) and (VI) to recover an ethylene product and streams containing ethane and C3+ hydrocarbons. The improvement comprises (i) cooling and partially condensing (I) in a partial condenser in a first condensing zone operating at or above a characteristic temp. T; (ii) separating the product into a vapour stream (VII) and a condensed liquid (VIII); and (iii) cooling, partially condensing and rectifying (VIII) by dephlegmation in a second condensing zone operating below temp. T to yield a light gas product (IX) and a dephlegmator liquid (X). (VIII) provides the feed to the first demethaniser zone, and (X) provides the feed to the second demethaniser zone.