Patent ID: 7718839

Claim:
A process for vaporizing and pyrolyzing a portion of a hydrocarbon feedstock to olefins, and separating an unvaporized portion of said feedstock containing undesirable coke precursors and/or high boiling pitch fractions that cannot be completely vaporized under convection section conditions of a typical pyrolysis furnace, said process comprising: a) feeding the hydrocarbon feedstock to a first stage preheater provided in a convection zone of a pyrolysis furnace, and heating said feedstock to an outlet temperature of less than 405° C. within the first stage preheater to produce a heated gas-liquid mixture, b) withdrawing the heated gas-liquid mixture from the first stage preheater, combining it with high temperature steam and feeding the combined stream to a first vapor-liquid separator, c) separating and removing the gas from the liquid in the first vapor-liquid separator, heating the gas in a vapor phase superheater provided in said convection zone to a temperature of about 450 to 700° C., feeding 60 to 100 volume percent of the heated gas to a second vapor-liquid separator, and the remaining portion into a radiant zone of the pyrolysis furnace and pyrolyzing the gas to produce olefins and other pyrolysis products, d) withdrawing the liquid from the first vapor-liquid separator, and heating the removed liquid to a temperature of about 425 to about 510° C. by combining it with the majority portion of the vapor from the first vapor-liquid separator after it is further heated in said superheater in the convection zone and feeding the stream to a second vapor-liquid separator, e) separating and removing the gas from the liquid fraction in the second vapor-liquid separator, feeding the removed gas into a radiant zone of the pyrolysis furnace and pyrolyzing the gas to produce olefins and other pyrolysis products, and f) removing the remaining liquid fraction from the second vapor-liquid separator.