Glossary
Electrostatic precipitators
Hot-side and cold-side ESPs
Also known as hot side ESP, cold side ESP, hot precipitator, cold precipitator.
Hot-side and cold-side describe where an electrostatic precipitator sits in the flue-gas path relative to the boiler air heater.
| Type | Position | Gas temperature | Why used |
|---|---|---|---|
| Hot-side ESP | Upstream of air heater | 300–400 °C | Avoids high ash resistivity that causes back-corona on low-sulphur coals |
| Cold-side ESP | Downstream of air heater | 130–180 °C | Lower capital cost; standard for medium- and high-sulphur fuels |
Trade-offs
Hot-side ESPs handle larger gas volumes (lower density at high temperature) and need bigger shells. They were popular in the 1970s–80s for Western US sub-bituminous and lignite coals. Most new installations are cold-side, often combined with flue-gas conditioning to manage resistivity.
Cleaning implications
Both designs benefit from acoustic cleaning. Hot-side ESPs need high-temperature horn materials such as Inconel 625 or 718; cold-side ESPs can use 316 stainless but face cold-end corrosion risks if dew-point excursions occur.
Related terms
Related terms
- Electrostatic precipitatorAn ESP removes particulate from flue gas by charging dust and collecting it on plate electrodes. Sonic horns are widely used to dislodge ash from plates and to keep hoppers from bridging.
- Fly-ash resistivityFly-ash resistivity is the electrical resistance of a deposited dust layer. Resistivity above ~10¹¹ Ω·cm triggers back-corona and degrades ESP performance.
- Back-coronaBack-corona is reverse ionisation through a high-resistivity dust layer on ESP collecting plates. It collapses collection efficiency and is mitigated by keeping plates clean.
- Air heaterAn air heater (also air preheater, APH) recovers low-grade heat from flue gas to preheat combustion air. Cold-end fouling and corrosion are the dominant operational challenges.