Sulphur Recovery Unit Design and Operation

The Claus process is the standard industrial process for converting hydrogen sulphide (H₂S) in acid gas streams to elemental sulphur. It consists of a thermal stage — a reaction furnace where a portion of the H₂S is combusted with air to form SO₂ — followed by a series of catalytic conversion stages where the remaining H₂S reacts with SO₂ to form sulphur and water.

Elemental sulphur produced in the catalytic stages is condensed and removed as a liquid. The Claus process is thermodynamically limited, meaning that conversion to sulphur does not reach 100% and the tail gas from the final Claus condenser still contains sulphur compounds.

SRUs process acid gas streams from amine treating units in refineries and gas processing plants. Amine treating removes H₂S (and CO₂) from refinery gas streams and natural gas to meet product specifications and protect processing equipment. The rich amine is regenerated in a stripper to release the acid gas, which is fed to the SRU.

The composition of the acid gas feed — particularly the H₂S concentration and the presence of hydrocarbons and CO₂ — affects the reaction furnace design and the overall SRU performance.

The tail gas from the Claus unit contains residual sulphur compounds including unreacted H₂S, SO₂, carbonyl sulphide (COS) and carbon disulphide (CS₂). Environmental regulations in many regions require tail gas treating to achieve higher overall sulphur recovery than is achievable with the Claus process alone.

Various tail gas treating processes are available, including reducing-gas processes that convert residual sulphur compounds to H₂S, which is then absorbed by an amine solvent and recycled to the Claus unit front end. The choice of tail gas treating technology depends on the required recovery efficiency and the specific regulatory requirements.

SRU design must account for the acid gas feed composition, the required sulphur recovery efficiency, the product sulphur specification, and the applicable environmental regulations. The thermal stage design — particularly the reaction furnace temperature and the air/acid gas ratio — is critical to achieving good conversion and managing contaminants such as ammonia in the feed.

Catalyst selection in the catalytic stages, and the number of catalytic stages, affects the overall sulphur recovery. Operating temperature control between stages is important for catalyst performance and avoiding sulphur condensation on the catalyst.

Howe Baker provides engineering and EPC services for Sulphur Recovery Units including Claus SRU design, tail gas treating integration and revamp of existing SRU facilities. Engineering scope covers process design, equipment specification, detailed engineering and EPC delivery.