Claus unit and sulphur recovery unit

A Claus unit - also called a sulphur recovery unit (SRU) - recovers elemental sulphur from H2S-bearing acid gas in a refinery or gas-processing plant. The Claus process partially combusts H2S to SO2, then catalytically reacts the remainder of the H2S with SO2 to form liquid sulphur in two or three downstream converter stages.

Cleaning targets

• Waste-heat boiler (WHB) downstream of the Claus reaction furnace - high-temperature economiser surfaces foul with ammonium-salt and sulphur deposits
• Sulphur condenser tubes - periodic external cleaning during outages
• Acid-gas line dust traps - particulate from upstream

Sonic-horn duty

Sonic horns on the SRU waste-heat boiler economiser keep ammonium-salt and sulphur deposits from consolidating between scheduled maintenance windows. The high-value, continuous-operation nature of SRUs makes the avoidance of unplanned shutdowns particularly valuable.

Process layout

A Claus unit converts hydrogen sulphide in acid gas to elemental sulphur. In the thermal stage, part of the hydrogen sulphide is burned to sulphur dioxide in a reaction furnace. The hot gas then passes through a waste-heat boiler where heat is recovered and sulphur begins to condense downstream. Catalytic stages complete the conversion over alumina or titanium catalyst with reheating and sulphur condensation between stages.

The unit is tightly linked to refinery, gas-processing or coke-oven gas operations because it handles toxic hydrogen sulphide and controls sulphur emissions. Tail-gas treatment may be added when higher recovery is required by permit.

Fouling and reliability issues

Cleaning challenges concentrate around the waste-heat boiler, sulphur condensers, reheaters and tail-gas path. Deposits can include ammonium salts, sulphur mist, catalyst dust, refractory debris and corrosion products. If surfaces foul, pressure drop rises, heat recovery changes and sulphur condensation can occur in the wrong place.

The safety context is severe. Hydrogen sulphide toxicity, sulphur fires, oxygen control, acid-gas pressure stability and hot sulphur handling all make access and maintenance more constrained than in ordinary dust collection service. Any online cleaning equipment must be compatible with hazardous-area requirements and plant isolation procedures.

Acoustic-cleaning context

Sonic horns can be relevant where dry deposits form on waste-heat boiler or downstream gas-side surfaces and where non-contact cleaning avoids opening toxic or hot equipment. They are not a cure for liquid sulphur pooling, catalyst deactivation or process chemistry imbalance. The value is keeping heat-transfer and gas passages stable so the SRU can stay inside its recovery and emission limits between planned outages.

Field checks

Claus-unit reliability is followed through acid-gas feed composition, combustion-air control, reaction-furnace temperature, condenser outlet temperature, sulphur drain performance, catalyst bed temperature and tail-gas analyser data. Small errors in air demand can push the unit away from the required hydrogen sulphide to sulphur dioxide balance and reduce sulphur recovery. Fouling is often linked to sulphur mist, ammonium salts, soot, refractory dust or catalyst fines.

Maintenance checks focus on burner condition, waste-heat boiler tubes, condenser tubes, demisters, sulphur seals and reheater performance. Sulphur can freeze in drains or low-temperature pockets, while hot reducing gas can damage refractory and tube surfaces. Safety implications are high because acid gas, hydrogen sulphide and sulphur dioxide are toxic, and pyrophoric iron sulphide can ignite during opening. Acoustic cleaning is relevant only where dry or weakly bonded deposits restrict heat transfer or gas passages. It does not replace temperature control, sulphur draining or gas testing.

Related terms

• Reformer furnace
• Waste-heat boiler
• Sonic horn