Claus Sulfur Recovery Unit for sulfur recovery refers to the conversion of hydrogen sulfide (H2S) to elemental sulfur. Hydrogen sulfide, which is a byproduct of processing natural gas and refining high-sulfur crude oil is recovered and converted to elemental sulfur. The most common conversion method used for recovering sulfur is the Claus process. The process consists of multistage catalytic oxidation of hydrogen sulfide that involves burning one-third of the H2S with air in a reactor furnace to form sulfur dioxide (SO2). Emissions from the Claus process may be reduced by extending the Claus reaction into a lower temperature liquid phase, adding a scrubbing process to the Claus exhaust stream, or incinerating the hydrogen sulfide gases to form sulfur dioxide.