What is a Wet Electrostatic Precipitator?
A Wet Electrostatic Precipitator (WESP) is a high-efficiency final-stage air pollution control system designed to remove the finest particulate matter, aerosols, acid mists and condensable emissions from industrial exhaust gases.
Installed as the final polishing stage of an emission control system, a WESP captures contaminants that conventional scrubbers, cyclones and bag filters struggle to remove, including sub-micron particles smaller than PM2.5.
Inside the vessel, high-voltage electrostatic fields place a strong negative charge on every particle in the gas stream. The charged particles migrate to grounded, continuously-irrigated collecting tubes, where a water film washes them down into the sump. No build-up on the collecting surface, no manual cleaning, no clogging.
Typical performance:
Outlet concentration of <5 mg/Nm³ dust
Stack opacity below 5%
Why Choose a Wet Electrostatic Precipitator?
Wet Electrostatic Precipitators (WESPs) are the proven technology for capturing sticky, wet, condensable or sub-micron pollutants. Frequently, these are loads that pass straight through bag filters, dry ESPs and exit a wet scrubber as a residual blue haze.
They are commonly specified for glass-wool insulation, fertilizer production, lime kilns, pulp & paper recovery boilers, sulfuric-acid plants and metallurgical off-gases, for example when producing steel.
Sub-micron capture: >99% efficiency on PM2.5, mists and aerosols down to 0.1 µm.
Self-cleaning: A continuous water film keeps collecting tubes clear, with no scheduled cleaning and no derate over time.
Low pressure drop: Typically <25 mm w.g., a fraction of a bag filter. Fan-power savings recover a meaningful share of the CAPEX over the life of the unit.
Handles condensables: Wet operation captures phenols, formaldehyde, tar and acid mists that degrade dry collection systems.
Corrosion-resistant build: AISI 304L / 316L vessel, tubes and ionizing rods, specified for decades of saturated service.
Why Wet ESP Instead of Wet scrubbing or Dry ESP?
While wet scrubbers and Dry ESPs are effective for many applications, they can struggle with ultra-fine particulate matter, condensable aerosols, and acid mist. Wet Electrostatic Precipitators (Wet ESPs) are specifically designed to capture these challenging sub-micron emissions, making them a preferred solution for processes requiring the highest particulate removal efficiencies and the elimination of visible plumes.
Advantages:
Captures sub-micron Particles: >99% removal on PM2.5 acid mists and aerosols down to 0.1 μm: the size range where bag filters and cyclones lose efficiency.
Continuously self-cleaning: A continuous or pulsing water film washes collected particles away automatically. No scheduled tube cleaning or manual intervention.
Handles condensable & Sticky aerosols: Phenols, formaldehyde, tar mist, ammonium-nitrate aerosols and sulfuric-acid mists are collected wet, with no build-up or explosion risk.
Eliminate visible plume: Drops stack opacity below 5%. Often the fastest path to closing a community-permit gap
Disandvantages:
Higher CAPEX than a wet scrubber: High-voltage power supply, ionizing rods and AISI 316L tube bundles cost more upfront. Best justified when sub-micron capture is genuinely required.
Wastewater handling required: Collected pollutants leave the system as a liquid effluent that must be treated, neutralised or recirculated. Plan the wastewater loop alongside the WESP, not after.
High-voltage hazard: Voltages of 60 to 80 kV require strict interlocks, isolation procedures and competent maintenance staff. Not a “set-and-forget” install, but well-understood and routinely managed.
Not a gas absorber: WESPs do not remove gas-phase SO₂, NH₃ or HCl by themselves. Pair them with an upstream wet scrubber when soluble gases are present.
Sub-micron Challenges Across Industries
Every industrial process generates particulate emissions differently. Particle size distribution, condensable aerosols, acid mist formation, moisture levels, and process conditions all influence emission control performance. Wet Electrostatic Precipitator (Wet ESP) is designed for industries where conventional filtration technologies struggle to capture fine particulate matter, acid mists, and sub-micron aerosols.
Food & Ingredients
Thermal processes can generate fine particulate matter, oil aerosols, and condensable organic compounds. Many of these particles are smaller than one micron and can pass through separation equipment. Wet ESP captures sub-micron particles and visible plume-forming aerosols while maintaining stable performance in high-moisture exhaust streams.
Fertilizer Industry
Fertilizer manufacturing generate sulfuric acid mist, phosphoric acid aerosols, and other fine liquid droplets. These emissions are typically too small for conventional particulate collectors to remove effectively. Wet ESP is specifically suited for acid mist control, providing exceptional removal efficiency for sub-micron liquid aerosols while preventing visible emissions.
Chemicals & Plastics
Chemical production frequently generates acid mists, condensable vapors, polymer fumes, and fine particulate matter that are difficult to capture using dry collection technologies. These emissions often contain particles well below one micron in size. Wet ESP provides highly efficient removal of sub-micron aerosols and acid droplets, making it particularly suitable for processes involving corrosive compounds and demanding emission limits.
Metal Processing & Smelting
Metal production processes such as sintering, smelting, and metal refining can generate metal oxide fumes and fine particulate emissions in the sub-micron range. These particles are often difficult to capture with conventional dust collectors. JOA’s Wet ESP delivers high collection efficiencies for fine particulate matter and metal fumes, helping facilities comply with strict environmental regulations.
Why JOA for Wet ESP
Pre-Engineering Study
Nobody dives as deep as we do. Before any design begins, we map your process conditions, emission profile, operational variability, and site constraints. This study determines whether wet scrubbing with ozone is the right approach, and exactly how to configure it for your specific exhaust emissions.
Air Technical Modelling
We identify, validate, and predict outcomes through proprietary air technical modelling. Your Wet ESP system is proven before it is built. No tinkering on site. No trial and error. First time right implementation.
Process Guarantees
JOA provides written performance guarantees on emission levels. Our validated designs give you the certainty that your system will meet its targets from day one. That is peace of mind you will not get from a catalogue system supplier.
How JOA delivers your Wet Electrostatic Precipitator
Every JOA project, WESP or otherwise, follows the same four-phase method. The goal is a clear plan: known CAPEX, known OPEX, known outlet concentration, signed off on a process guarantee.
Pre-Engineering Study
Design & Engineering
System Realization
Clients That Trust JOA
Leading manufacturers rely on tailored solutions to achieve environmental compliance while maximizing operational efficiency. We are proud to support some of the world’s largest industrial manufacturers, helping them address complex production challenges with innovative and reliable solutions.
Wet Electrostatic Precipitator FAQ
A Wet ESP is an air-pollution control device that uses high-voltage electric fields to remove sub-micron particles, mists and condensable aerosols from a saturated gas stream. Inside the vessel, ionizing rods charge every particle in the gas. The charged particles migrate to grounded collecting tubes that are continuously washed with a water film. Pollutants leave the unit as liquid effluent rather than as deposits on the equipment.
Both technologies share the same physics: corona discharge, particle charging and electrostatic migration. The difference is in collection.
Dry ESP: Collected dust builds up on the plates and is removed by mechanical rapping. This is suited to hot, dry gas streams with non-sticky dust.
Wet ESP: A continuous water film washes particles off the tubes in real time. This is suited to saturated gases, sticky condensables, sub-micron aerosols and acid mists.
Yes. WESPs are the technology of choice in this size range. Removal efficiency is typically above 99% on particles between 0.1 and 1 µm, where cyclones, scrubbers and even bag filters lose effectiveness. WESPs are routinely specified to capture PM2.5, sulfuric-acid mists and ammonium-nitrate aerosols.
A wet scrubber uses mass transfer through gas-liquid contact to absorb soluble gases such as SO₂, NH₃ and HCl, and to capture coarse particles. A WESP uses electrostatic forces to capture the fine particles, mists and aerosols a scrubber misses. The two are complementary. The scrubber absorbs gases and saturates the stream, while the WESP polishes the sub-micron load and reduces stack opacity. Many JOA installations include both in series.
A Wet Electrostatic Precipitator is designed to remove fine particulate matter, aerosols and condensable emissions that are often too small or too sticky for conventional air pollution control technologies.
- Sub-micron particulate matter, including PM2.5 and smaller
- Sulfuric acid mist
- Ammonium sulfate and ammonium nitrate aerosols
- Condensable VOCs
- Oil mist and hydrocarbon aerosols
- Metal fumes and metal oxide particles
- Tar, resin and sticky organic condensates
- Visible stack plumes and blue haze
Unlike bag filters, cyclones and many wet scrubbers, a WESP uses electrostatic forces rather than mechanical filtration. This allows it to achieve removal efficiencies above 99% in many aerosol and mist applications while maintaining a very low pressure drop.
Wet Electrostatic Precipitators are commonly applied in fertilizer production, pulp and paper, sulfuric acid manufacturing, steel and non-ferrous metal production, glass fiber manufacturing, waste-to-energy facilities and chemical processing plants.
In many installations, a WESP is installed downstream of a wet scrubber to capture remaining fine particulate matter and aerosols before the cleaned gas is discharged to the atmosphere.
In many applications, yes. Visible stack emissions are often caused by fine aerosol droplets, sulfuric acid mist or condensable particulate matter that remain in the gas stream after a wet scrubber. Because these particles are often smaller than one micron, they scatter light and create a visible blue or white plume.
A WESP can remove more than 99% of these fine aerosols and mists, significantly reducing stack opacity and, in many cases, eliminating visible blue haze or plume formation.
Wet scrubbers are highly effective at removing soluble gases such as SO₂, HCl and ammonia, as well as larger particulate matter. However, they are less effective at capturing sub-micron particles, condensable emissions and fine aerosol droplets.
By installing a WESP downstream of the scrubber, these remaining contaminants can be removed before the cleaned gas reaches the stack. This helps facilities achieve ultra-low particulate emissions, reduce visible plume formation and comply with strict environmental regulations.
A bag filter captures particles by forcing gas through fabric media. It is highly effective for dry dust but can struggle with sticky, wet or condensable pollutants that blind the filter media and increase pressure drop.
A Wet ESP uses electrostatic forces rather than filtration. Because there is no filter media, WESPs can efficiently collect acid mist, aerosols, oil mist, condensable VOCs and sub-micron particulate matter while maintaining a very low pressure drop.
Condensable particulate matter consists of pollutants that leave a process as gases but condense into fine liquid droplets or solid particles as the exhaust gas cools. Examples include sulfuric acid mist, condensable VOCs, organic aerosols and ammonium salts. WESPs are particularly effective at capturing these aerosols and droplets smaller than one micron.
A Wet ESP continuously washes pollutants from the collecting surfaces using a water film. The captured particulate matter, aerosols and condensates are transferred into a liquid stream that can be treated, recycled or discharged according to site requirements.
Yes. WESPs are frequently selected when the exhaust stream contains sticky, condensable or combustible particulate that may create operational challenges for dry collection systems. Because the collection surfaces remain continuously wet, there is no dust build-up that can blind filters or create layers of combustible material.
In some applications, yes. A WESP can capture valuable aerosols or condensable compounds before they leave the stack, reducing product losses and improving process efficiency. Examples include sulfuric acid mist, metal compounds, oils, tars and other condensable process materials.
Yes. WESPs are highly effective at removing oil mist, tar aerosols and other sticky condensable pollutants that are difficult to capture with conventional filtration technologies. These pollutants often exist as extremely fine droplets that can pass through cyclones, scrubbers and some filter systems.
Wet ESPs are commonly applied in biomass gasification, charcoal production, chemical processing and other processes where oil or tar aerosols are present.
