To convert heavy distillates and residues into high-value products, including selective propylene production when required,…
SCOT Process by Shell Global Solutions International B.V.
A low-pressure drop, high-sulfur recovery efficiency process to recover sulfur components from tail gas of sulfur plants. The SCOT process is insensitive to variations in the upstream SRU, such as in the H2S/SO2 ratio, hydrocarbon or ammonia breakthrough. Products: Offgas from a SCOT unit contains a total sulfur content less than 120 ppmv; offgas from a Super SCOT unit contains maximum 50 ppmv total sulfur content and the offgas from Low Sulfur SCOT contains less than 10ppm.
The Claus tail gas feed to the SCOT unit is heated to 220°C to 280°C using an inline burner or heat exchanger (1) with optionally added H2 or a mixture of H2/CO. If reducing gas, H2 or CO is not available, an inline burner (1) is operated in an air-deficient mode to produce reducing gas. The heated gas then flows through a catalyst bed (2) where sulfur components, SO2, elemental sulfur (S), COS and CS2 are practically completely converted to H2S. The gas is cooled to 40°C in an optional heat-recovery system (3) and a water-quench tower (4), followed by selective H2S removal in an amine absorber (5) to typically 30 to 100 ppmv H2S. The semi-loaded amine is often further loaded in another absorber. The H2S absorbed in the SCOT, Super SCOT or Low Sulfur SCOT process is recycled to the Claus unit via the amine regenerator. The absorber offgas is incinerated.
The process is continuous, has a pressure drop of 4 psi or lower, provides excellent sulfur recovery and can
be operated at high reliability with less than 1% unscheduled downtime.
Economics: The total sulfur recovery efficiency of the SCOT process combined with the upstream Claus unit typically guarantees a sulfur recovery of at least 99.8%. In case of a Super SCOT unit, an overall sulfur recovery efficiency of 99.95% can be guaranteed. An integrated and cascaded SCOT unit has capital and operational expenditures comparable to other tail-gas treating technologies, but has higher total sulfur recovery efficiency.
Licensor: Shell Global Solutions International B.V.
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