GPSA Ch. 22 / API Pub. 955
| Configuration | Recovery (%) |
|---|---|
| 2-stage Claus | 94–96 |
| 3-stage Claus | 96–98 |
| 2-stage + SCOT | 99.8–99.9 |
| 3-stage + SCOT | 99.9+ |
Overall Sulfur Recovery:
Where RClaus = Claus unit recovery (fraction), RSCOT = SCOT unit recovery (fraction)
Hydrogenation Reactions:
SCOT Process: All sulfur species in Claus tail gas are hydrogenated/hydrolyzed to H₂S over a CoMo or Titania catalyst, then absorbed in a selective amine unit for recycle to the Claus burner.
Understand SCOT tail gas treating, hydrogenation catalyst selection, amine absorber design, and emissions compliance
The SCOT (Shell Claus Off-gas Treating) process is a tail gas treating technology that increases overall sulfur recovery to meet SO₂ emissions compliance requirements.
It designs and rates SCOT tail gas treating units per GPSA Ch. 22 and API Pub. 955, calculating overall sulfur recovery, hydrogenation reactor sizing, amine absorber design, and SO₂ emissions.
The calculator follows GPSA Chapter 22 and API Publication 955 for tail gas treating unit design and rating.
The Shell Claus Off-gas Treating (SCOT) process converts all sulfur species in Claus tail gas to H2S over a CoMo or Titania catalyst through hydrogenation and hydrolysis. The H2S is then absorbed in a selective amine unit and recycled to the Claus burner to achieve overall sulfur recovery above 99.9%.
A two-stage Claus unit with SCOT tail gas treating typically achieves 99.8-99.9%+ overall sulfur recovery, meeting EPA 40 CFR 60 emissions requirements. SO2 emissions from SCOT units are typically 10-250 ppmv after incineration.
MDEA is preferred for selective H2S removal in SCOT absorbers because it leaves CO2 in the treated gas, reducing regeneration energy. DEA and DGA co-absorb CO2, which increases reboiler duty and amine circulation rate.
The reactor temperature must exceed 500°F for CoMo catalyst activation. Titania catalysts may operate at lower temperatures but have shorter service life. Proper reactor temperature ensures complete conversion of SO2, COS, and CS2 to H2S.