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METHOD FOR FRACTIONATING A STREAM OF CRACKED GAS, USING AN INTERMEDIATE RECIRCULATION CURRENT, AND RELATED PLANT

  • US 20160258676A1
  • Filed: 10/23/2014
  • Published: 09/08/2016
  • Est. Priority Date: 10/23/2013
  • Status: Active Grant
First Claim
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1. A method for fractionating a stream of cracked gas from a hydrocarbon pyrolysis plant to obtain an ethylene-rich cut and a C2+ hydrocarbon-lean fuel stream, the method comprising:

  • compressing the stream of raw cracked gas in at least one compressor a cooling and compression stage to form a compressed cracked gas stream;

    upstream cooling and partial condensing, in at least one upstream heat exchanger, of an upstream stream of cracked gas, obtained from the compressed cracked gas stream, and separation of an upstream liquid in at least one upstream balloon to form an intermediate stream of cracked gas pre-cooled at first temperature;

    intermediate cooling and partial condensing of the intermediate stream of cracked gas in an intermediate heat exchanger and separation of an intermediate liquid in an intermediate separating balloon to form a downstream stream of cracked gas cooled to a second temperature lower than the first temperature;

    downstream cooling and partial condensing of the downstream stream of cracked gas in at least one downstream heat exchanger to a third temperature lower than the second temperature;

    introducing of the downstream stream of partially condensed cracked gas from the downstream heat exchanger in a downstream separator;

    recovering, at the head of the downstream separator a gas stream of high-pressure fuel, lean in C2+ hydrocarbons, and recovering, at the bottom of the downstream separator, a downstream liquid, rich in C2+ hydrocarbons;

    passing of the stream of high-pressure fuel through the downstream exchanger and the intermediate exchanger to form a heated high-pressure fuel stream;

    expanding of the heated high-pressure fuel stream in at least one first dynamic expansion device to obtain a stream of partially expanded fuel;

    heating of the stream of partially expanded fuel through the downstream exchanger and the intermediate exchanger;

    treating of at least one liquid stream obtained during the upstream cooling, intermediate cooling and downstream cooling to form the ethylene-rich cut;

    forming an expanded intermediate recirculation stream (170) from a liquid obtained during the upstream cooling and/or intermediate cooling steps, upstream from the downstream cooling step;

    circulating the intermediate recirculation stream at east in the upstream heat exchanger to cool the upstream stream of cracked gas;

    reintroducing the reheated intermediate recirculation stream in the raw cracked gas upstream from at least one compressor of the cooling and compression stage,the upstream, intermediate and downstream steps being carried out without heat exchange respectively of the upstream stream of cracked gas, the intermediate stream of cracked gas and the downstream stream of cracked gas with an external refrigeration cycle.

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