---
title: "Electrostatic precipitator (ESP)"
description: "An electrostatic precipitator (ESP) is an air-pollution-control device that removes particulate matter from a flue-gas stream by electrostatically charging dust particles and collecting them on grounded plate electrodes. ESPs are the dominant particulate-control technology on coal-fired boilers, cement kilns, waste-to-energy plants, biomass plants, sinter strands and many other heavy-industry off-gas streams."
canonical_url: "https://sylio.co/glossary/electrostatic-precipitator"
last_updated: "2026-06-28T02:29:30.581Z"
---

An **electrostatic precipitator (ESP)** is an air-pollution-control device that removes particulate matter from a flue-gas stream by electrostatically charging dust particles and collecting them on grounded plate electrodes. ESPs are the dominant particulate-control technology on coal-fired boilers, cement kilns, [waste-to-energy](/glossary/waste-to-energy) plants, [biomass](/glossary/waste-to-energy) plants, sinter strands and many other heavy-industry off-gas streams.

## How an ESP works

Flue gas flows horizontally between a parallel array of vertical [collecting electrodes](/glossary/collecting-electrode) (plates) and [discharge electrodes](/glossary/discharge-electrode) (high-voltage wires or rigid spikes). A negative DC potential of 40–80 kV applied to the discharge electrodes generates a [corona discharge](/glossary/corona-discharge) that ionises the gas. Charged dust particles drift to the collecting plates, accumulate as a dust layer, are rapped down into hoppers below and removed by ash-handling equipment.

## Where sonic horns fit

ESPs accumulate dust faster than mechanical rapping can release it, and hoppers below ESP fields routinely [bridge](/glossary/bridging) and choke. [Sonic horns](/glossary/sonic-horn) installed on the ESP [penthouse](/glossary/esp-penthouse) and on hopper walls keep dust dislodged, supplement [rappers](/glossary/esp-rapper), prevent [back-corona](/glossary/back-corona) by limiting plate dust thickness, and eliminate hopper [rat-holing](/glossary/rat-holing) without the structural fatigue of [tumbling-hammer rappers](/glossary/tumbling-hammer-rapper).

## Common failure modes

- **High opacity / particulate emissions** from thick dust layers reducing collection efficiency
- **Back-corona** in high-resistivity ash that reverses ionisation and collapses collection
- **Re-entrainment** as rapper puffs return dust to the gas stream
- **Hopper bridging** that stops ash extraction and triggers field shutdowns
- **Discharge-electrode breakage** from rapper fatigue or sparking

## Related terms

- [Collecting electrode](/glossary/collecting-electrode)
- [Discharge electrode](/glossary/discharge-electrode)
- [Back-corona](/glossary/back-corona)
- [ESP hopper](/glossary/esp-hopper)
- [Sonic horn](/glossary/sonic-horn)