---
title: "Bunker / coal bunker"
description: "A bunker (in industrial usage almost always a coal bunker) is an intermediate coal-storage vessel located above each pulveriser mill on a PC boiler. Coal arrives from the main coal-handling system, is held in the bunker for short-term buffering, and is metered by gravimetric feeders into the mill below. A typical utility unit has 4–8 bunkers, one per pulveriser."
canonical_url: "https://sylio.co/glossary/bunker-coal-bunker"
last_updated: "2026-06-28T02:29:33.044Z"
---

A **bunker** (in industrial usage almost always a **coal bunker**) is an intermediate coal-storage vessel located above each [pulveriser mill](/glossary/raw-mill-cement-mill-coal-mill) on a [PC boiler](/glossary/pc-boiler). Coal arrives from the main coal-handling system, is held in the bunker for short-term buffering, and is metered by gravimetric feeders into the mill below. A typical utility unit has 4–8 bunkers, one per pulveriser.

## Why coal bunkers bridge

- Sub-bituminous and lignite coals are particularly prone to cohesion under self-weight
- Wet coal from rain-exposed yards consolidates rapidly
- Long residence times in lightly-loaded bunkers harden surface material
- Vibration from operation gradually compacts the mass

A bridged bunker interrupts mill feed; the mill trips on low coal flow, the burner loses fuel, and the unit derates or trips. On a 600 MW utility unit, a single bunker pluggage can mean an hour or more of lost generation.

## Mitigation

[Sonic horns](/glossary/sonic-horn) installed at the discharge cone keep the coal mobile. They are usually rated for [ATEX](/glossary/atex-directive) Zone 22 dust-area service and feature stainless-steel construction to handle the abrasive-and-corrosive environment of coal storage.

## Related terms

- [Silo](/glossary/silo)
- [Hopper](/glossary/hopper)
- [Bridging](/glossary/bridging)
- [Sonic horn](/glossary/sonic-horn)