---
title: "Wet ESP (WESP)"
description: "A wet electrostatic precipitator (WESP) is an ESP in which the collecting surfaces are continuously washed with water rather than rapped dry. WESPs are specified where the particulate is sub-micron, sticky, hygroscopic or acidic — typically downstream of FGD scrubbers, on biomass and waste-to-energy plants, in coke-oven flue paths and on certain refinery and metals off-gas streams."
canonical_url: "https://sylio.co/glossary/wet-esp"
last_updated: "2026-06-28T02:29:31.615Z"
---

A **wet electrostatic precipitator (WESP)** is an [ESP](/glossary/electrostatic-precipitator) in which the collecting surfaces are continuously washed with water rather than rapped dry. WESPs are specified where the particulate is sub-micron, sticky, hygroscopic or acidic — typically downstream of [FGD scrubbers](/glossary/electrostatic-precipitator), on [biomass](/glossary/waste-to-energy) and waste-to-energy plants, in coke-oven flue paths and on certain refinery and metals off-gas streams.

## Tube-type vs plate-type WESPs

Most WESPs are tube-type, with vertical cylindrical collectors and a coaxial discharge electrode in each tube. Plate-type WESPs also exist for retrofit duty into existing dry-ESP shells. Water sluicing is either continuous, intermittent flushing, or condensate-driven.

## Where sonic horns help

The wash-water film usually keeps the collecting surfaces clean, but solids accumulate in the **sumps and dust-handling hoppers below the WESP**. [Sonic horns](/glossary/sonic-horn) prevent sludge bridging and pluggage in these low-level hoppers and pipework, where conventional rapping is impractical and manual cleaning is hazardous.

## Related terms

- [Electrostatic precipitator](/glossary/electrostatic-precipitator)
- [Plate-type ESP / tube-type ESP](/glossary/plate-type-esp-tube-type-esp)
- [Corona discharge](/glossary/corona-discharge)
- [Sonic horn](/glossary/sonic-horn)