Electrostatic precipitators
Electrostatic precipitator
Also known as ESP, electrostatic precipitators, dry ESP.
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.
How an ESP works
Flue gas flows horizontally between a parallel array of vertical collecting electrodes (plates) and discharge electrodes (high-voltage wires or rigid spikes). A negative DC potential of 40–80 kV applied to the discharge electrodes generates a 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 and choke. Sonic horns installed on the ESP penthouse and on hopper walls keep dust dislodged, supplement rappers, prevent back-corona by limiting plate dust thickness, and eliminate hopper rat-holing without the structural fatigue of tumbling-hammer rappers.
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
Related terms
- Wet electrostatic precipitatorA wet electrostatic precipitator continuously washes its collecting surfaces with water, used for sub-micron particulate, acid mist and sticky aerosols downstream of FGD or biomass scrubbers.
- Collecting electrodeThe collecting electrode is the grounded plate or tube on which charged particulate accumulates inside an ESP. Dust must be released to hoppers without re-entraining into the gas stream.
- 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.
- Corona dischargeCorona discharge is the electrical breakdown around an ESP's discharge electrode that ionises gas molecules and charges dust particles for collection.
- ESP hopperAn ESP hopper is the inverted-pyramid vessel below each ESP field that collects rapped-down fly ash. Bridging and rat-holing are common failures; sonic horns are the standard mitigation.
- 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.
- 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.
- 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.