GPSA Ch. 22 / GPSA-style approximation
| 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 using GPSA Ch. 22 sulfur-recovery methods and GPSA-style engineering approximations, calculating overall sulfur recovery, hydrogenation reactor sizing, amine absorber design, and SO₂ emissions.
The calculator uses GPSA Chapter 22 sulfur-recovery methods plus GPSA-style engineering approximations for tail gas treating unit design and rating; the SO2 stack limit follows EPA 40 CFR 60 NSPS Subpart J/Ja.
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.