What Are Coal Bunkers?

Coal bunkers, installed as part of the plant structure, not only store a given capacity of coal, but function as part of the system in maintaining a continuing supply to the boiler furnaces. Normally the bunker may hold a 24 to 48 hour supply of coal, may take various shapes generally funnel-like with one or more openings at the bottom.

They may be built of tile, reinforced concrete, steel plate, with or with- out acid resisting linings.

The coal bunker should be located so that the fl ow to the fuel consuming equipment is as nearly vertical as possible. It should also be as far away as possible from fl ues, hot air ducts, steam pipes or other external sources of heat which might aid in starting bunker fires.

Bunker fires may be started from coal already overheated or burning in storage, or from spontaneous combustion from long storage in the bunker itself. Dead pockets within a bunker should be eliminated.

High moisture, or wet, coal may encounter difficulties in passing through the bunkers. The most frequently encountered difficulties are termed “rat holes” and “coal arches.”

Wet coal packs and adheres to the sides of the bunkers to an extent that only the coal directly above the outlet flows out. Often this will progress until a hole slightly larger than the outlet is opened from the top of the pile to the outlet, and the flow of coal may be stopped entirely.

This is called “rat holing.” When this condition occurs, it is necessary that the hole be filled by mechanical means so that the flow of coal from the bunker be resumed. This is usually accomplished by manually ramming the coal with a long bar or air-lance.

The air-lance employs a strong blast of compressed air. If the wet coal packs solidly over the bunker outlet, a strong arch may be formed that is capable of withstanding the weight of the coal above it.

When the coal under the arch is used up, the fl ow will stop. Air-lances are usually employed to break this arch and allow the flow to resume. Sometimes ports are provided in the base of the bunkers and equipped with compressed air piping that is used to break up such arches.

Coal from the coal pile is brought to the bunkers by lorry, drag line, conveyor, or other handling equipment.

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