Process for cracking low-quality feed stock and system used for said process
AssigneeMitsui Petrochemical Industries, Ltd.
InventorsMasahiko Yoshida, Yutaka Kitayama, Tsukasa Iida
Life of this patent
Estimating the term…
Abstract
In a process for thermally cracking a low-quality feed stock containing a considerable proportion of heavy fractions such as high-boiling fractions, and evaporation residual oil, and a system used therefor, in which the low-quality feed stock is withdrawn from the preheater of the thermal cracking furnace to separate and remove a required proportion of said heavy fractions and thereafter returned to subject the feed stock to further preheating and thermal cracking. The low-quality feed stock thermally cracked has a predetermined proportion of the heavy fractions removed, and coking in the thermal cracking system at various lines is avoided from occurring.
Claims4
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.degree. to less than 300.degree. 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.
Dependencies are inferred from the claim text.