Organic material, such as kraft black liquor, organic fuels, garbage and organic wastes, is destructively distilled and pyrolyzed at an elevated temperature and for a time sufficient to break down the material to noncombustible solids and to a stable gaseous clean burning fuel. The temperature is maintained to preclude recombination of intermediate products formed during the pyrolysis and which would otherwise pollute the atmosphere. A controlled amount of oxygen is continuously introduced during the cracking to provide energy by exothermic oxidative reactions but the oxygen is insufficient to effect stoichiometric or in other words complete combustion.