Electrostatic precipitators
Corona discharge
Also known as corona (electrical), negative corona.
A corona discharge is a self-sustaining electrical discharge that occurs when the field gradient around a sharp electrode exceeds the breakdown threshold of the surrounding gas. In an ESP the corona forms around the discharge electrode, ionises flue-gas molecules, and the resulting ions attach to dust particles. The charged particles then drift to the collecting electrodes under the electric field.
Negative corona dominates
Industrial ESPs almost always run on negative corona because it sustains a higher voltage before sparking — but it also produces some ozone, which is one of the reasons WESPs in confined ventilation paths sometimes use positive corona instead.
What disrupts the corona
- Excessive dust on the collecting plate — raises plate-face voltage, narrows the working gap
- High ash resistivity — traps charge in the dust layer, leading to back-corona
- Bent or broken discharge electrodes — local field collapse, sparking, eventual short
- Fouled discharge electrode tips — suppressed corona, reduced ion current
Acoustic cleaning addresses two of these (plate dust thickness and discharge-electrode fouling) without the broken-electrode risk of aggressive mechanical rapping.
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.
- Discharge electrodeThe discharge electrode is the high-voltage electrode that generates the corona discharge inside an ESP. Charged dust drifts from it to the collecting plates.
- 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.
- 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.