1. Coal stored in silos can spontaneously combust over time due to oxidation processes, generating heat. If not properly managed, this can lead to coal fires in the silo. 2. There are three stages of oxidation - intrinsic, surface, and general oxidation - which cause coal to heat up over time when exposed to oxygen. As temperature increases, the rate of oxidation accelerates. 3. To control fires, inerting the coal with carbon dioxide vapors is widely used. The CO2 displaces oxygen and cools the coal by filling void spaces between particles. This reduces oxygen levels and heat generation to extinguish the fire over time.

1. Fire Protection.!!
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Fire in Coal bunker ,Silo & DE HOPPER
SANTOSH PARDHI

2. Causes:-The spontaneous combustion of stored coal has been a recognized problem
as long as coal has been used Studies of the phenomenon have shown that there are
three overlapping oxidation processes taking place below 120 ̊ C ,each with its own
fundamental characteristics.
1.The first stage, Intrinsic Oxidation, starts at temperatures about 15 ̊C.A very low
order of oxidation starts that is almost independent of the partial pressure of oxygen
in the ambient air but is determined almost solely by the oxygen content of the coal
substance itself. This stage occurs mainly with low rank, high oxygen coal. It
appears likely that the oxidation is in habited by absorbed methane and can be
accelerated by bacteria and the presence of pyrites. Iron pyrites and iron sulfides in
the coal combine with water and oxygen to for miron sulfate and sulfuric acid.
These reactions are exothermic and can provide the triggering temperature to start
the hydrocarbon and carbon reactions with entrained oxygen in the coal. If the heat
generated from this intrinsic oxidation and/or pyrites reaction is removed as It is
generated, spontaneous combustion will not occur and the aged coal will be
generally stable. How-ever, retaining the heat at its source of generation can lead
into the second stage of oxidation.
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3. 2. Surface Oxidation starts at about 30 ̊ C .It is conditioned by active centers
on the macro surface of the coal which increases with rise in temperature
and so becomes self-accelerating. This process could be in habited by water
or wetting agents if they are applied in such away as to block the coal
surface from contact with air(02).If sufficient oxygen is available and heat
dissipation is poor or nonexistent, the oxidation will proceed into the third
stage.
3.General Oxidation starts at temperatures about 70 ̊ C. Above that
temperature some fundamental changes take place in the coal substance, the
effect of which see ms to be an increase in the available surface area and,
consequently , a marked acceleration in the rate of oxidation. Provided with
sufficient oxygen, the positive feedback action in the process can push their
action temperature to about 250 ̊C where the oxidation becomes spontaneous
Ignition to vigorous burning is achieved at 350 ̊C.
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4. Coal stored in silos before it is fed into the coal mills of a steam
electric generating station (or other similar short term storage
application) continually oxidizes and generates heat. In the event of
an unscheduled shutdown, coal trapped in the silo will oxidize
enough to eventually start to burn. The length of time that it takes to
heat the coal to burning is a function of the reactivity of the coal.
Some of the imported coal will reach this point in just a few days .
Fires will be more frequent if the silo/bunker is not cleaned
periodically and/or proper filling procedures are not followed. In the
event of a fire, it is usually not practical to run the coal from the silo
out onto the ground; therefore, fire control in the silo/bunker is
necessary. Inerting and fire control with CO2 vapor is widely used.
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The principle of this protection is to push CO2 vapor through the
coal, reach the level of adsorption, and fill all the void spaces
between the coal particle store duce the oxygen available to the
fire to near zero. At some point, the generation of heat by
oxidation will become less than the heat loss by conduction, and
the burning mass will cool. Holding this condition long enough
will effect fire extinguishment. To inert the coal, CO2 vapors
used. If liquid CO2 is discharged to atmospheric pressure dry
ice particles are formed, which could block the gas flow.
C02 injected in to the bottom of the bunker has been reported
effective in smothering fires.

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7. 1.Water spray on feeder belt as it passes under the down spout.
2. Diversion pipe adapters to enable them to dump burning
coal out of the feed bunkers without damaging the feeders.
3. Installation of thermocouples above the coal shutoff valves
to warn the operators of the presence of hot coal.
Study Report:
No fool proof way of eliminating fires in some bunkers.
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