Recover sulphur from acid gas streams that contain hydrogen sulphide (H2S).
Acid gases from sweetening units and sour water strippers are sub-stoichiometrically burnt with ambient air (or air plus oxygen) in a refractory lined furnace in order to convert 1/3 of H2S to SO2. Subsequently, elemental sulphur is produced in accordance with the Claus reaction between 2/3 of the H2S and produced SO2. Conversion of ammonia to elemental nitrogen is also achieved together with complete combustion of hydrocarbons contained in the feed gas. High pressure steam is generated in a waste heat boiler which cools the acid gas from the high flame temperature to the lower catalytic reactor (converter) temperature. Hydrogen sulphide conversion to elemental sulphur is then enhanced by applying two or three stages of catalytic reaction in converters. Each converter is normally preceded by a reheater and followed by a sulfur condenser.
Several methods are available for reheating process gas depending on the heating medium.
Generally, the operating temperature ranges between 925°C and 1200°C but can be increased to 1450°C if NH3 is present in the feed gas. With a modified Claus unit the sulphur recovery efficiency ranges between 94.5% and 97.5% depending upon the number of catalytic converters installed and the feeds composition.