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Process for cracking low-quality feed stock and system used for said process

  • US 5,580,443 A
  • Filed: 05/12/1994
  • Issued: 12/03/1996
  • Est. Priority Date: 09/05/1988
  • Status: Expired due to Term
First Claim
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1. A process for thermally cracking a heavy natural gas liquid containing heavy fractions in a cracking furnace having a convection zone containing a first preheater and a second preheater and a radiation zone containing a thermally cracking reactor comprising the steps of:

  • supplying said heavy natural gas liquid to the first preheater provided in a top portion of said convection zone of the cracking furnace;

    preheating the supplied heavy natural gas liquid to a temperature and pressure at which fractions unlikely to cause coking problems are fully evaporated and fractions likely to cause coking problems are maintained in a liquid phase, in the first preheater and maintaining an exit temperature thereof in the range of from 200°

    to less than 300°

    C. and a gas/liquid ratio of the preheated heavy natural gas liquid in the range of from 60/40 to 98/2;

    withdrawing the preheated heavy natural gas liquid from said first preheater;

    superheating a suitable amount of dilution steam at a temperature higher than that of the preheated heavy natural gas liquid;

    mixing a required amount of superheated dilution steam with the heavy natural gas liquid from said first preheater through a connection line between said first preheater and a gas-liquid separator to obtain an adjusted gas/liquid ratio of the heavy natural gas liquid, corresponding to the properties of differing heavy natural gas liquid feedstocks, to result in a predetermined gas/liquid separation in said gas-liquid separator;

    supplying said mixture of said superheated dilution steam and said heavy natural gas liquid, having an adjusted gas/liquid ratio, to said gas-liquid separator;

    separating and removing the heavy fractions from the withdrawn heavy natural gas liquid in said gas-liquid separator;

    mixing the heavy-fraction-removed heavy natural gas liquid from the separator with a remaining amount of the superheated dilution steam necessary for thermal cracking;

    passing said heavy-fraction-removed heavy natural gas liquid from the gas-liquid separator to said second preheater provided in said convection zone of the cracking furnace;

    preheating the passed heavy-fraction-removed heavy natural gas liquid to a temperature below the temperature at which cracking is promoted;

    introducing the preheated heavy-fraction-removed heavy natural gas liquid into the thermally cracking reactor; and

    thermally cracking the introduced heavy-fraction-removed heavy natural gas liquid in said thermally cracking reactor.

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