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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