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Claus tail gas treating - SCOT process

Applications: The Shell Claus Off -gas Treating (SCOT) process has been developed to remove sulfur compounds from Claus tail gas to comply with stringent air emissions regulations. The standard SCOT process is able to easily meet less than 250 ppmv total sulfur in the SCOT off gas, which corresponds to an overall sulfur recovery efficiency of 99.9% on intake.

Description: The SCOT process essentially consists of a reduction and an ADIP absorption section of special design. The Claus tail gas feed to the SCOT process is heated to 300°C with an inline burner or heat exchanger. If reducing gas, H2 or CO, is unavailable, an inline burner is operated sub-stoichiometrically to produce reducing gas.

The heated gases then flow through a catalyst bed, where sulfur compounds,
including CS2 and COS, are reduced to H2S. The gas is cooled to about 165°C in a heat recovery boiler (generating steam) and, subsequently, by direct contact cooling with water to 40°C. Water vapor in the process gas is condensed, and the condensate is sent to a sour water stripper.

The cooled gas is counter-currently washed with an alkanolamine solvent in an absorber designed to absorb almost all H2S but relatively little CO2. The treated gas from the absorber contains only traces of H2S and is burned in a standard Claus incinerator. The concentrated H2S is recovered from the rich solvent in a conventional stripper and is recycled to the Claus unit.

The SCOT units are designed for minimum pressure drop so that they can be
easily added to existing Claus units.

If insufficient pressure is available, a gas booster can be installed, preferably between the cooling tower and the absorption tower.

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