The hot raw synthesis gas stream leaving the reaction zone of a free flow partial oxidation gas generator at a temperature in the range of about 1800.degree. to 3000.degree. F. is passed through a first gas diversion and residue separation zone where the velocity of the gas stream is reduced and its direction is diverted into a side transfer line. Solid material and molten slag separate by gravity from the gas stream. The hot gas stream is then introduced into a second gas diversion and residue separation zone where additional residue is separated. About 0.5 to 20 vol. % of the hot gas stream may be passed through bottom outlets in said first and second gas diversion zones in order to prevent bridging. The hot gas stream from the second gas diversion zone is passed upwardly through a radiant cooler where additional solid matter is removed by gravity and the gas temperature is reduced to a temperature in the range of about 900.degree. to 1800.degree. F. In one embodiment, the second diversion and residue separation zone is a thermally insulated cyclone. By the subject process, 70 to 95 wt. % of the combustion residue is removed from the raw stream of synthesis gas, and the temperature of the gas stream is reduced below the maximum safe operating temperature for downstream devices used to recover energy from the hot gas stream, such as a conventional convection type gas cooler.