Wet electrostatic precipitator

A wet electrostatic precipitator (WESP) is an electrostatic precipitator whose collecting surfaces are washed with water or kept wet by condensation instead of being rapped dry. It is used where the target material is fine, sticky, acidic, saturated or difficult to collect in a dry ESP.

Typical applications include acid mist, sulphuric acid aerosol, wet FGD outlet gas, biomass and waste-to-energy polishing, coke-oven and metallurgical off-gas, and process streams where condensable material would blind a dry collector.

Tube-type and plate-type designs

Tube-type WESPs use vertical tubes as collecting electrodes with discharge electrodes suspended down the centre. The collected liquid film drains downward into a sump. Plate-type WESPs use flat plates and are often selected where a retrofit must fit an existing rectangular casing. Both designs need stable water distribution, reliable high-voltage insulation and careful materials selection for corrosive service.

Unlike a dry ESP, a WESP does not rely on rapper energy to shed dust from plates. The wash film or flush cycle removes collected material.

Operating risks

Common problems include poor wash distribution, dry streaks, scaling, plugged spray nozzles, high-voltage tracking across wet insulators, sump sludge build-up, mist carryover, corrosion under deposits and freezing risk on outdoor equipment. Conductivity, pH and solids loading of the washwater can affect both collection and wastewater treatment.

Maintenance should focus on water quality, drain reliability, electrode alignment, insulator purge air, access to spray headers and sludge removal. A WESP can perform well electrically while still losing availability because the downstream sump or recirculation loop plugs.

Where sonic horns help

Sonic horns are not normally used to clean the wet collecting tubes or plates because water is already doing that job. They can help in dry or semi-dry areas around the WESP: inlet ducts, upstream hoppers, solids handling below the sump, mist-eliminator approach sections and ash transfer points. Where deposits are wet sludge rather than friable solids, flushing, drainage and mechanical access are more important than acoustic energy.

Design and operating variables

A wet ESP collects fine particulate, acid mist or aerosol on wetted collecting surfaces. It is used downstream of wet scrubbers, sulphuric-acid mist sources, biomass or waste systems, metallurgical processes and other duties where dry collection is difficult. Because the collecting surface is washed, the unit can handle sticky or submicron material that would blind a dry ESP or fabric filter.

Key variables include gas saturation, temperature, mist loading, particle resistivity, collection tube or plate geometry, electrical field strength, wash water distribution, purge rate, materials, pH and chloride content. Uniform wetting is critical. Dry patches can accumulate solids, spark or corrode, while excess water can create carry-over and overload downstream mist control.

Maintenance and acoustic-cleaning relevance

Common failure modes include plugged spray nozzles, scaling, corrosion, broken or misaligned electrodes, dirty insulators, poor drainage, high-voltage trips, mist carry-over and sludge accumulation in sumps. Inspections focus on wash coverage, internal deposits, electrode alignment, casing leaks, transformer rectifier behaviour and wastewater quality. Safety issues include high voltage, confined space, acidic liquid, slippery surfaces and possible toxic or odorous gas residues.

Acoustic cleaning is usually not applied inside a wet ESP because the deposits are wet and the internals are designed for washing. It may be useful upstream in dry ducts, reactors or hoppers to reduce particulate load before the gas becomes saturated. If a wet ESP is fouling, the first checks are water distribution, chemistry, drainage and electrical condition, not horn output.

Related terms

• Electrostatic precipitator
• Plate-type ESP / tube-type ESP
• Corona discharge
• Sonic horn