A method and apparatus are disclosed for treating the
effluent from a
hydrocarbon pyrolysis unit employing a small primary fractionator, i.e., a
rectifier. The method comprises cooling the gaseous
effluent, e.g., by direct quench and / or at least one primary
heat exchanger, and then cooling the gaseous
effluent to a temperature at which
tar, formed by reactions among constituents of the effluent, condenses, e.g., in a secondary exchanger. The resulting mixed gaseous and liquid effluent is passed through a
rectifier, to cleanly separate quench oil from the gaseous effluent comprising a
pyrolysis gasoline fraction, whose
boiling point can be lowered as a result of the
rectifier treatment. The effluent is then cooled to condense a liquid effluent comprising
pyrolysis gasoline and water condensed from steam, which fractions are separated in a distillate drum. The cooled gaseous effluent is directed to a
recovery train to recover light olefins. At least a portion of the
pyrolysis gasoline-containing fraction can be recycled to the rectifier to enhance separation of the quench oil from the
pyrolysis gasoline fraction.