Electrostatic precipitators
Collecting electrode
Also known as collecting plate, collection plate, ESP plate.
The collecting electrode — usually called the "collecting plate" in plate-type ESPs — is the grounded surface on which charged particulate accumulates inside an electrostatic precipitator. Collecting plates are typically 9–15 m tall, rolled or profiled steel sections with stiffening pockets, hung in parallel rows 250–400 mm apart.
How dust accumulates and releases
Charged particles migrate from the discharge electrode towards the grounded plate, transfer their charge and adhere as a dust layer. The layer must be released regularly: too thick and it raises plate-face voltage, reducing the field, eventually triggering back-corona. Release is achieved by rapping (mechanical impact) or sonic horns (acoustic vibration), with the released dust sheet falling into the hopper below.
The re-entrainment problem
Aggressive rapping releases dust faster than the hopper can swallow it, and some of the falling sheet is caught back up by the gas stream — this is re-entrainment, and it shows up as periodic opacity spikes on stack CEMS traces. Sonic horns produce gentler, more continuous release that reduces re-entrainment compared to mechanical rapping alone.
Profile types
Collecting plates come in many profiled forms (CW, ZT, ECO, Opzel, baffle, etc.), each chosen to balance electrical performance against dust-release behaviour. Specialist ESP vendors (B&W, FLSmidth, Hamon, Mitsubishi) supply matched plate-and-rapping packages.
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.
- ESP rapperAn ESP rapper is the mechanical hammer or magnetic impulse device used to dislodge accumulated dust from ESP plates and discharge electrodes. Sonic horns complement and partly replace this duty.
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.
- Re-entrainmentRe-entrainment is the recapture of just-rapped dust by the flue-gas stream before it falls into the hopper. It causes opacity spikes and is the main reason continuous sonic cleaning is preferred.