Objective There are two sets of sulfur recovery units in the Moxi Natural Gas Purification Plant of the Central Sichuan Oil and Gas District, PetroChina Southwest Oil & Gasfield Company, MCRC and CPS processes are used respectively, and the sulfur recovery rate is 99.0% and 99.2%, respectively. It is necessary to further improve the sulfur recovery rate of the units so that the mass concentration of SO₂ in the discharged flue gas can meet the requirements of the GB 39728—2020 Emission standard of air pollutants for onshore oil and gas exploitation and production industry.

Method Based on the existing sulfur recovery units, a new set of SCOT tail gas treatment unit was built. Combined with the trial operation of the unit, the key problems affecting the operation stability of the unit, the total sulfur recovery rate and the full-time compliance of pollutants discharge were analyzed. The modification and optimization measures were summarized for the problems of leakage between the tube side and the shell side of the hydrogenation reactor waste heat boiler and the frequent blocking of the regeneration tower.

Result The performance evaluation results of the newly built SCOT tail gas treatment unit showed that the total sulfur recovery rate of the unit reached 99.96%, the SO₂ conversion rate of the hydrogenation catalyst was not less than 99.9%, the organic sulfur hydrolysis rate of the hydrogenation catalyst was about 93.4%, the average mass concentration of SO₂ in the discharged flue gas was 164.2 mg/m³, and the average mass concentration of H₂S in the lean liquid was 0.14 g/L. The evaluation results were better than the design values.

Conclusion The new tail gas treatment unit runs smoothly and can provide a reference for similar units.