PURPOSE: To remove impurities most efficiently from carbon black produced by thermal decomposition of liquid hydrocarbon in a high temp. gas stream, by passing it, carried by flowing gas, through a screen classifier.

CONSTITUTION: Raw material liquid hydrocarbon fed into a furnace 11 from an inlet 12 is thermally decomposed with high temp. gas introduced from an inlet 13. The produced carbon black is quenched with a cooling medium supplied from an inlet 14 and carried on a gas stream through a heat exchanger 15 to a bag filter 16. Then the carbon black in the filter is fed by means of a rotary feeder 17 into a screen classifier, carried by high temp. gas stream fed from the heat exchanger 15 and a combustion gas generator 30 and, after removal of impurities in small lumps such as refractory material in fragments, rust from equipment and coke, final product carbon black is taken out via a collector 22.