Recover sulfur from acid-gas streams that contain hydrogen sulfide (H2S) and ammonia (NH3).
Product: Bright yellow sulfur with 99.9 % purity and less than 10 ppmw of dissolved H2S after degassing. Front-end Claus tail gas is either processed in a tail gas clean-up (TGCU) unit for further sulfur recovery, or routed to the Claus incinerator where residual H2S is oxidized to SO2.
Acid gases from sweetening units and sour-water strippers are sub-stoichiometrically burnt with ambient air (or air plus oxygen) in a refractorylined furnace to convert 1⁄3 of H2S to SO2. Subsequently, elemental sulfur is produced in accordance with the Claus reaction between 2⁄3 of the H2S and produced SO2. Ammonia and hydrocarbons contained in the feed gas are also destroyed. High-pressure steam is generated in a waste-heat boiler (WHB), which cools the acid gas from the high-flame temperature to the lower catalytic reactor (converter) temperature. Further sulfur conversion is achieved in 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. Operating conditions: The temperature inside the combustion chamber depends upon the type and quantities of species accompanying the H2S and O2. Generally, the operating temperature ranges between 925°C–1,200°C, but can be increased to 1,450°C if NH3 is present in the feed gas. Total pressure drop of the process gas depends upon the numbers of converter stages. Typically, pressure drop can vary between
0.3 bar and 0.5 bar.
Sulfur recovery efficiency depends on the feedstream composition and the number of catalytic stages; typically, it ranges between 94.5% and 97.5 %.
Economics: Capital cost is approximately U.S.$10 million/100-tpd sulfur recovery unit designed to achieve 95% recovery efficiency from typical amine off gas. Operating costs can be considered negligible if credit for steam generation is taken into account.
Licensor: BP AMOCO through SIIRTEC NIGI