Discharge electrode

The discharge electrode (also called the emitting electrode) is the high-voltage element inside an electrostatic precipitator that generates the corona discharge. It is energised at 40-80 kV DC negative relative to the grounded collecting electrodes.

Geometry

Two families dominate:

Wire electrodes - fine spiral or barbed wires, typically weighted at the bottom and suspended from a top frame. Lightweight; easy to retrofit; prone to fatigue and breakage under rapping impacts.
Rigid discharge electrodes (RDE) - pipe or mast sections with formed spikes or points. Used in modern American-style and rigid-frame ESPs. More robust against rapper breakage but heavier.

Fouling on discharge electrodes

Just like the collecting plates, discharge electrodes accumulate dust. A thick coating on a wire or RDE reduces the local field gradient, suppresses corona, and lowers collection efficiency. The cleaning challenge is geometrically harder than for plates - discharge electrodes are point or line sources surrounded by gas. Sonic horns addressing the whole field volume help dislodge dust from discharge electrodes as well as from plates.

Electrical performance

The discharge electrode creates the intense local electric field required for corona. Sharp points, wires or spikes concentrate voltage so gas ionisation starts there rather than randomly across the field. The electrode must be centred between collecting plates to maintain clearance and avoid local sparking.

Electrode geometry affects corona current, spark rate, collection efficiency and mechanical reliability. Wires are simple and effective but can break from fatigue, corrosion or rapper shock. Rigid electrodes tolerate mechanical duty better but need stronger support frames and careful alignment.

Failure modes

Dust coating rounds off sharp points and suppresses corona. Broken wires can short to plates or fall into hoppers. Misalignment creates uneven fields and repeated sparking. Insulator leakage or tracking can trip fields even when the electrode itself is intact. High-resistivity ash can make the electrical symptoms look like an electrode problem while the root cause is dust-layer behaviour on the collecting plate.

Maintenance includes de-energising and grounding, inspecting clearances, replacing broken wires, cleaning insulators, checking rapper systems and verifying transformer-rectifier response. ESP work is high-voltage work, so grounding discipline is central.

Acoustic-cleaning context

Sonic horns help by reducing dust accumulation on discharge electrodes and support frames. Cleaner electrodes maintain stronger corona at lower spark rates and reduce opacity instability caused by weak or intermittent fields. Acoustic cleaning cannot fix broken electrodes or failed insulators, but it can reduce the fouling load that makes electrical faults more frequent.

Field checks

Discharge electrodes are checked for alignment, tension, broken points, ash build-up, corrosion and clearance to collecting plates. Even small misalignment can concentrate the electric field and cause sparking before the ESP reaches useful voltage. In wire designs, a broken wire can short the field or whip into plates. In rigid-frame designs, distorted masts or dirty points reduce charging consistency across the gas lane.

Electrical trends help locate the problem. A field with low current, early sparking or unstable voltage may have fouled discharge electrodes, dirty insulators, warped plates or high-resistivity dust. Outage inspection confirms whether the issue is electrical, mechanical or deposit-related. Acoustic cleaning can support electrode performance when dry ash builds up on frames, points or surrounding gas-distribution equipment. It is not a substitute for rapper maintenance, correct clearances or transformer-rectifier repair, but it can reduce the deposit load that weakens corona formation between outages.

Clearance checks are especially important after thermal cycling or internal maintenance. A bent frame, loose weight or mispositioned electrode can create a local high-field point that limits energisation for the entire electrical section. Reliable ESP performance depends on keeping every lane mechanically boring enough for the controls to apply power.