Method for processing hydrocarbon pyrolysis effluent

An apparatus for cooling and recovering energy from tar precursor-containing gaseous effluent from hydrocarbon pyrolysis, comprising:

• (a) at least one dry-wall quench exchanger through which said gaseous effluent passes to provide a cooled effluent above the temperature at which said tar precursor initially condenses;
• (b) at least one wet-wall quench exchanger comprising a tube having a process side and a shell side, said process side being covered with a substantially continuous liquid film, through which the cooled effluent from (a) can be passed through to provide a gaseous effluent stream of reduced tar content below 287° C. (550° F.), and below the temperature at which said tar precursor initially condenses;
• wherein said at least one wet-wall quench exchanger comprising an annular oil distributor at or near the exchanger inlet to distribute quench oil along the quench exchanger wall capable of condensing sufficient liquid from said effluent gas to provide a fluxing film;
• and
• wherein the inside diameter of said tube of said wet-wall transfer line exchanger is greater than or equal to the inside diameter of a tube of said dry-wall exchanger.