Abstract: Processes for the thermal reduction of sulfur dioxide to elemental sulfur are disclosed. The processes described include three general reaction sections, including the reaction furnace portion where the SO2-containing stream is combusted, the second reaction zone where the temperature is moderated to encourage the reaction of sulfur with hydrogen to consume the hydrogen carbon monoxide and produce the H2S and CO. The temperature moderation is achieved by one or combinations of three different methods adding external waste heat boiler, followed by a vessel to provide adequate residence time for the reaction of producing H2S or to recycle the tail gas to a second zone of a 2-zone reaction furnace, using inter-stage internal cooling coil or adding a quench fluid in the second zone of a 2-zone reaction furnace. The third reaction zone is a Claus conversion portion, wherein residual H2S and SO2 are further reacted to produce additional elemental sulfur.

Abstract: The reduction of the gas stream containing sulfur dioxide to elemental sulfur is carried out by reacting a reducing gas, such as natural gas, methanol or a mixture of hydrogen and carbon monoxide, with recycled sulfur and recycled tail gas to produce a stream containing hydrogen sulfide that may be reacted with the gas stream that contains sulfur dioxide. Gas streams with a molar concentration of sulfur dioxide from 1 to 100% may be processed to achieve nearly 100% sulfur recovery efficiency.