SRU (sulphur recovery unit)

SRU stands for Sulphur Recovery Unit, a process plant that converts the toxic hydrogen sulphide (H₂S) removed from sour crude oil and natural gas into solid, saleable elemental sulphur. It almost universally uses the Claus process: a portion of the H₂S is burned to SO₂, which then reacts catalytically with the remaining H₂S to yield sulphur and water. Modern SRUs with tail-gas treatment recover 95-99.9% of the sulphur in the feed.

The SRU exists to keep sulphur out of the atmosphere. Burning or flaring sulphur-bearing gas would release SO₂ — the major acid-rain pollutant — while venting raw H₂S would be lethally toxic. By turning it into solid sulphur (a feedstock for sulphuric acid and fertiliser), the SRU is the main reason refineries can meet their SO₂ emission limits. Its recovery efficiency directly determines refinery air compliance.

For recyclers, the SRU acronym is worth knowing because the same H₂S problem recurs in their world. In biogas and CBG production, raw biogas contains H₂S that corrodes engines and pipelines and must be removed before upgrading; large plants may recover sulphur from it. In tyre pyrolysis, the sulphur in vulcanised rubber carries into the oil and gas and must be managed so it is not emitted as SO₂.

The takeaway is the principle behind the acronym: sulphur should be captured as a product, not released as SO₂. CBG operators apply it through H₂S scrubbing before upgrading; tyre pyrolysis operators through oil desulphurisation and char management. The SRU is simply the refinery-scale industrial embodiment of that goal.