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Wet ElectroStatic Precipitator

Wet Electrostatic Precipitators

Dr. Frederick Cottrell developed the first wet electrostatic precipitator (WESP) in 1907 to control sulfuric acid mist from a copper smelting process in Pinole, California.

Since that time WESP technology has become well-established in both industrial and utility applications around the world to remove sub-micron particulate, condensables, and acid mist as a final polishing device in an air pollution control system where an upstream dry ESP, fabric filter or wet scrubber cannot capture the sub-micron particulate due to its small size.

Wet Electrostatic Precipitators



A WESP can be configured with flat plate collecting electrodes handling a horizontal gas flow similar to a dry ESP. Alternatively, a WESP can be configured in an up-flow tubular configuration on top of the wet scrubber to minimize foot-print.


WESP Configuration


The collecting tubes can be either round, square, rectangular or hexagonal. Hamon Research-Cottrell offers both plate and tubular WESP designs.



Hamon Research-Cottrell can supply WESPs in modules fully assembled in the shop and trucked to site ready for installation. For larger installations either multiple modules or field erection can be offered depending upon scheduled and field costs



WESP removal efficiency is dependent upon several parameters – gas velocity, collection surface area, corona power, and electrical sectionalization. The Hamon Research-Cottrell WESP can achieve very high removal efficiencies, in excess of 90% on sub-micron particulate and acid mist. Increasing treatment time while minimizing size is critical to designing a cost-effective wet ESP that can meet required emission guarantees.



A WESP is typically installed after a wet flue gas desulfurization (WFGD) system in the utility industry or after a wet scrubber in an industrial application where the flue/process gas has been cooled to moisture saturation. Once cooled, gaseous pollutants condense to form sub-micron aerosols that can be captured within the WESP. The WESP can be integrated into the scrubber unit (left), or it can be located after the scrubber unit (right).


WESP Location



A Wet Electrostatic Precipitator (WESP) operates in the same three-step process as a dry ESP;

  1. Charging of incoming particulate with negative ions from corona generation through the use of a high voltage system
  2. Collection of the negatively charged particulate on a positively charged collection electrode surface
  3. Cleaning of the captured particulate on the collecting electrode surface via use of water sprays, irrigation or condensation versus rapping or sonic horns. This is the primary difference between a dry and wet ESP.

WESP Operation

Technology Features

  • Performance – over 90% typical and up to 99% possible
  • Compact Size – minimizes space and cost
  • Opacity – less than 10% possible
  • Reliability – well-established technology in hundreds of applications
  • Fuel Flexibility – allows for use of various fuels to reduce fuel cost
  • Multi-Pollutant Control – sub-micron solid particulate, condensables, and sulfuric acid mist
  • Modular Design – allows for scale up to any size air-flow
  • Maintenance – no moving mechanical parts; continuous self-cleaning
  • Pressure Drop – typically less than 1” w.c. through the WESP


Materials of Construction

Due to the saturated conditions of the process gas WESPs are susceptible to corrosion. Proper selection of the materials of construction depends upon analysis of the process gas, expected pH and chloride levels in the water. Material of construction can range from carbon steel, stainless steel, FRP to high end alloys such as Hastelloy®. Each industry and plant site is unique. Hamon Research-Cottrell will select an appropriate material of construction that provides long life, resistance to corrosion and reliability.

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