Figure 10.6 illustrates how the SCOT Process is integrated with the Claus Unit to convert COS, CS2 and any remaining SO2 by reacting with H2 in the catalytic reactor back to H2S to be recycled to the Claus Unit to close the loop. The hydrogenating catalysts used in SCOT contain nickel or tungsten on alumina support, and the reaction takes place at 480-570°. By coupling Claus and SCOT processes, more than 99% of sulfur entering the Claus unit can be recovered as elemental sulfur to be sold as a refinery product.
Text description of Figure 10.6.
This diagram illustrates the Sulfur Recovery SCOT (Shell Claus Off-gas Treating) process, showing how Claus tail gas is treated in a reactor, followed by gas cleanup and recycling to improve sulfur recovery efficiency.
At a high level, the process shows Claus tail gas entering a hydrogenation reactor, where sulfur-containing compounds are converted to hydrogen sulfide (H₂S). The treated gas is then sent to an amine unit to remove H₂S, which is recycled back to a Claus unit for further sulfur recovery, achieving greater than 99% sulfur recovery.
Process flow (left to right):
A stream labeled “Claus tail gas” enters a vessel labeled “Reactor.” Hydrogen, labeled “H₂,” is injected into the reactor. Inside the reactor, compounds such as “COS,” “CS₂,” and “SO₂” react with hydrogen, as indicated by the reaction text “+ H₂ → H₂S + CO₂ + H₂O.” The reactor operates at a temperature labeled “480–570°F.” The outlet stream, labeled “H₂S + CO₂,” flows to a unit labeled “Amine Unit,” then to a unit labeled “Claus Unit,” with a return loop back to the front of the process.
Reactor section (left side):
- A line labeled “Claus tail gas” enters a vessel labeled “Reactor.”
- A separate inlet labeled “H₂” enters from above, indicating hydrogen addition.
- The reactor contains catalyst materials labeled “Al₂O₃ and Ni,” indicating alumina and nickel catalysts.
- Within the reactor, sulfur species labeled “COS,” “CS₂,” and “SO₂” are hydrogenated.
- A reaction note shows these compounds reacting with hydrogen to form “H₂S + CO₂ + H₂O.”
- The operating temperature range is labeled “480–570°F.”
Gas treatment and separation:
- The reactor effluent exits as a stream labeled “H₂S + CO₂.”
- This stream flows to a unit labeled “Amine Unit,” where hydrogen sulfide is selectively absorbed from the gas mixture.
Sulfur recovery and recycle loop:
- The recovered H₂S is sent from the amine unit to a unit labeled “Claus Unit.”
- The Claus unit converts H₂S into elemental sulfur.
- A process line loops from the Claus unit back to the inlet labeled “Claus tail gas,” indicating recycling of remaining gases for further treatment.