Coal bunker - intermediate coal-storage vessel above the pulveriser

A bunker, or coal bunker, is an intermediate storage vessel that feeds coal to mills, feeders or boilers. In power stations it normally sits between the conveying system and the pulveriser or stoker feed system, providing short-term inventory so upstream handling can vary without immediately starving the boiler.

Coal bunkers handle a difficult material: coal can be wet, segregating, abrasive, dusty, prone to freezing, capable of self-heating and variable in particle size. Fine coal and surface moisture increase cohesion, while long residence time can compact material against the walls.

Failure modes

The classic failure is bridging above the outlet, followed by ratholing, feeder starvation and mill trips. Other problems include liner wear, fires or smouldering, dust explosions, inaccurate level indication, blocked gates and tramp material. Operators may see erratic feeder demand before the bunker fully blocks.

Design and maintenance

Reliable bunkers need suitable outlet size, wall angles, liners, fire detection, inerting or suppression where required, level measurement, access controls and safe discharge procedures. Flow aids must be installed so they do not damage liners or create ignition risks in coal dust areas.

Acoustic-cleaning relevance

Sonic horns are widely relevant to coal bunkers because they provide non-contact flow promotion through the gas space and can fire frequently without hammering the vessel wall. Sylio-style use focuses on preventing weak arches from forming near the outlet and shoulders. Wet, frozen or heavily compacted coal may still need mechanical clearing or upstream fuel-handling changes.

Operating variables

A coal bunker must store fuel while feeding mills or conveyors at a controlled rate. Flow depends on coal size, moisture, fines content, clay content, weather exposure, storage time, wall liner, outlet geometry and the condition of feeders below the bunker. Wet fine coal can bridge or rat-hole, while dry coal can create dust and explosion hazards.

Operators track bunker level, feeder demand, feeder current, mill starvation, bunker temperature, dust, odour and the frequency of manual intervention. Long storage can lead to self-heating, especially with reactive coals. Water ingress can turn fines into a cohesive mass and accelerate corrosion of liners, gates and feeders.

Maintenance and safety

Inspection focuses on liners, outlet transitions, gates, feeders, level instruments, dust seals, fire detection, explosion relief or suppression where fitted, and safe access for clearing blockages. Personnel should not enter or stand below bridged coal without a formal isolation and rescue plan because sudden collapse is a serious engulfment hazard.

Acoustic horns can help keep dry coal or fines from forming weak arches near outlets, and they may reduce manual poking. They are not suitable for extinguishing fires, breaking hard wet masses or compensating for an outlet that is too small for the coal being handled. Combustible-dust and methane risks must be considered when adding any pneumatic or electrical device.

Operating evidence

Bunker problems should be recorded by coal source, moisture, fines content, bunker level and feeder operating mode. If flow failures occur after rain or after a long weekend hold, moisture and consolidation are likely causes. If failures occur at the same level every time, the cause may be a ledge, liner joint or geometry change.

Acoustic cleaning is easiest to justify where it reduces manual poking and feeder starvation events. Its settings should avoid unnecessary firing into an empty bunker, where sound energy does little useful work and can add noise without improving flow.

Operating checks

Coal-bunker troubleshooting is strongest when level, feeder demand and coal condition are reviewed together. A high level with low feeder output points to outlet bridging or a blocked gate. A normal indicated level with feeder starvation may indicate a rathole around the instrument, a failed level device or segregation that has left coarse material above the outlet. Wet coal, frozen coal, fine coal, long residence time and worn liners all increase the risk. Acoustic or vibration devices should be assessed against the flow pattern they create: the goal is stable mass discharge into the feeder, not merely movement near the wall. Any intervention also needs dust, fire and confined-entry controls.

Bunker (coal bunker)