Electrostatic precipitators
ESP hopper
Also known as ESP ash hopper, precipitator hopper, dust hopper.
An ESP hopper is the inverted-pyramid (or trough) vessel below each ESP field that collects ash dislodged from the collecting electrodes. Ash falls into the hopper and is extracted by pneumatic, drag-chain or hydraulic conveyors. ESP hoppers are one of the most chronic failure points in a coal, biomass, WtE or cement-plant flue-gas train.
Why ESP hoppers fail
- Bridging — the ash forms a stable arch across the narrowing hopper, stopping discharge.
- Rat-holing — a narrow channel forms above the outlet and the surrounding mass packs and hardens.
- Sneakage — gas short-circuits through hopper voids when extraction stops.
- Pluggage — full hoppers back ash up into the field, raising plate-face voltage and triggering back-corona.
- Failed level switches that mask developing pluggage from operators.
Once an ESP hopper plugs, the affected field must be taken offline; full-load operation may not be possible while the hopper is cleaned by vacuum truck or manual lancing. A single hopper-cleaning outage can cost hundreds of MWh in lost generation.
Sonic horns on ESP hoppers
A 60–125 Hz sonic horn mounted at the hopper wall is the standard mitigation. The horn fires every few minutes during normal operation, keeping the ash mobile and preventing the cohesive structures that lead to bridging and rat-holing. Acoustic horns are particularly favoured over air cannons here because they cause no impact stress on the hopper structure, no fatigue on weld joints, and can be installed during a routine outage rather than a major shutdown.
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.
- HopperA hopper is an inverted-pyramid or conical vessel for storing and discharging bulk solids. Bridging and rat-holing are the universal failure modes; sonic horns are a clean, low-maintenance remedy.
- Bridging (bulk-solids)Bridging (also arching) is the formation of a stable arch of bulk solids above the discharge outlet of a hopper or silo, stopping material flow. The universal failure mode of bulk-solids storage.
- Rat-holingRat-holing is a flow pattern in which material discharges through a narrow vertical channel above the outlet, while the surrounding material remains stagnant and consolidates.
- Fly-ash hopperA fly-ash hopper collects particulate ash from ESP, baghouse, economiser and air-heater equipment. Bridging and rat-holing of fly ash are persistent operational problems.
- 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.