Processes for the thermal reduction of sulfur dioxide to elemental sulfur are described and disclosed. The processes described include three general reaction sections, including the reaction furnace portion where the SO.sub.2-containing stream is combusted, the hydrogenation portion wherein the effluent from the reaction furnace is hydrogenated over an appropriate catalyst, and a Claus conversion portion, wherein residual H.sub.2S and SO.sub.2 are further reacted to produce additional elemental sulfur.