Function of Sulfur Recovery Unit in refineries

Sulfur Recovery Unit

The sulfur recovery process used in most refineries is a "Claus Unit". In general, the Claus Unit involves combusting one-third of the hydrogen sulfide (H2S) into SO2 and then reacting the SO2 with the remaining H2S in the presence of cobalt-molybdenum catalyst to form elemental sulfur.

The conversion chemistry is:
2H2H2S + 3 O2 → 2 SO2 + 2 H2O (Combustion)
2 H2S + SO2→ 3 S + 2 H2O (Conversion)

Generally, multiple conversion reactors are required. Conversion of 96-97% of the H2 to elemental sulfur is achievable in a Claus Unit. If required for air quality, a Tail Gas Treater may be used to remove remaining H2S in the tail gas from the Sulfur Recovery process.

Tail Gas Treater:- tail gas treating unit converts the small amount of sulfur compounds (< 5%), which were not converted in the sulfur recovery unit , into hydrogen sulfide (H2S) and recycles it back to the the sulfur recovery unit for additional processing. The the sulfur recovery unit tail gas is heated and sent to the catalytic reactor where essentially all of the sulfur compounds are converted into H2S. The gas from the catalytic reactor is cooled in the waste heat exchanger and the quench tower. Excess water is removed in the cooling process and is sent to the sour water stripper.

The cooled gas is the sent to the absorber column, where amine removes the H2S and some of the CO2 in the gas stream. The remaining gas (vent gas) is sent to the thermal oxidizing unit. The rich amine from the absorber is heated in the lean/rich exchanger and fed to the regenerator column. Steam, generated in the reboiler, heats the amine and removes the hydrogen sulfide (H2S) and carbon dioxide (CO2) from the amine. The lean amine from the stripper is cooled, in the lean/rich exchanger and the lean solvent cooler and returned to the absorber. The H2S and CO2 removed from the amine is cooled (and water removed) in the overhead condenser and recycled to the sulfur recovery unit for additional processing into sulfur.

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