Abstract: A pyrolysis reactor is operated by passing the waste products into a reactor provided with a heating unit; after completion of the pyrolysis passing the gaseous and vaporous products including suspended solids resulting from said pyrolysis into a partial oxidation zone wherein preheated air is added in an amount insufficient for complete combustion but sufficient to cause the exiting gas to have a temperature of at least 1000.degree., thereby causing decomposition of substantially all hydrocarbons present; then passing the partially oxidized gas through separate heat exchange means in contact, successively, with (1) the purified gas, (2) the air to be fed into the heating unit of the reactor and (3) with the air for said partial oxidation; then subjecting the partial oxidation gas to a purification; introducing air separately to said oxidation zone and heating means of the reactor; and passing the purified gas together with part of said added air into the heating unit of the reactor.