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Sulfur Recovery Unit

Sulfur Recovery Unit

Recovering sulfur from acid gases

Sulfur Recovery Units (SRU) from Air Liquide Engineering & Construction use a combustion and catalytic process to recover a pure form of sulfur from acid gas streams containing hydrogen sulfide. If credit is given for steam produced in the SRU, operating costs can be negligible.

Technical Solutions for increasing sulfur recovery and purity

Sulfur Recovery Units, also known as Claus Units, use a feedstock of acid gases from sweetening units and sour-water strippers. The feedstock is sent into a proprietary burner system, where it is burnt sub-stoichiometrically with air. The resulting mixture of hydrogen sulfide and sulfur dioxide reacts to form elemental sulfur (“Claus reaction”) , which is then removed through condensation. This initial combustion section  is followed by two or three catalytic sections to increase sulfur recovery rates to 94.5% – 97.5%.

Customers can choose from two tail gas treatment options to further increase sulfur recovery. With SulfreenTM, the Claus tail gas is catalytically purified, resulting in an overall sulfur recovery rate of up to 99.5%. Here the Claus reaction takes place below the sulfur dew-point so that the sulfur is adsorbed on the SulfreenTM catalyst. The LTGTTM process, meanwhile, purifies the Claus tail gas through wet-scrubbing. By recycling the hydrogen sulfide rich stream to the unit, this method can raise sulfur recovery to 99.9%.

Finally, the degassing section decreases the hydrogen sulfide content in the liquid sulfur product to less than 10 parts per million by weight (ppm wt.) using the AquisulfTM  (Catalyst based) technology.

Offgas from tail gas treatment and degassing is then incinerated.


  • Standard sulfur recovery rates of 94.5%-97.5%
  • Tail gas treatment can boost sulfur recovery to 99.9%
  • Negligible operational expenditure (OPEX) if credit is given for steam produced in SRU
  • Proven Technology with more than 150 references

Key figures

  • Capacity: up to 1 000 tons per day per train
  • Sulfur recovery: >95%