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4 Spontaneous Combustion of Coal
4.2 Naturally Occurring Spontaneous Combustion
(a) Below ground
Coal burning below ground has been detected for a long time and some had been
burning for hundreds and thousands of years emitting smoke, detected above ground.
Examples have been described from many parts of the world; such as the Burning
Mountain (Mt Win-Jen) in New South Wales, Australia where a coal seam has been
burning for thousands of years. It was part of a territory owned by the indigenous
Wanaruah people and is tied up in their ancient past legends. The coal seam is 2 m
thick and 30 m below ground and is detected by smoke coming out of the ground in
the area, moving southward at a rate of about 1 m every year. The coal seam is part
of Permian coals of the Sydney Basin. Many such occurrences have been reported
from around the world.
The largest concentration of coal fires caused by spontaneous combustion, both in
coal seams as well as coal piles occur in the Permian coals of India, first documented
from the Raniganj coal Basin in 1865.
(b) Above ground coal fires caused by spontaneous combustion
Spontaneous combustion in stock-piles of coals is a constant hazard that can be and
is controlled in well managed mines. There are special ways of building coal stock
piles that prevents spontaneous combustion.
Spontaneous combustion is a chemical oxidation reaction whereby heat generated
from the oxidation reaction is unable to dissipate by convection or conduction. The
temperature rises and the oxidation reaction speeds up increasing the heat until the
coal ignites. In most coal mines methane gas is present in varying quantities. Drainage
of coal mines of methane and other gases is a specialised engineering feat well
documented and usually planned and constructed with the mine going ahead. The
methane already present in coal seams may have been sourced from the coal that is
mined at some stage in its maturation history: As organic matter is buried deeper and
is subjected to increase in temperature it matures. The temperature with depth varies
in places, depending on the geothermal gradient of the depositional basin. The coal
undergoes physical and chemical changes with depth and increase in temperature.
These changes have been documented in many books on coal (e.g. Taylor et al. 1998).
At a certain stage of the coal maturation process methane is released. The methane
flows upwards through cleats and fractures and may end up in a coal mine where coal
has not reached methane generation stage yet. An example is a mine in Huaibei Basin
in Anhui province, China (Glikson et al. 2001) where methane is present in small
amounts even though the coal that is being mined has not reached methane generation
stage. Vitrinite reflectance of 0.8%Rm (Glikson et al. 2001) places the coal in the
lower part (A) of the volatile bituminous rank. Both reflectance and fluorescence
place the coal within the oil window, with very little potential of any thermogenic
methane generation in the seams of the Huaibei mine. The low bitumen content,
4 Spontaneous Combustion of Coal
4.2 Naturally Occurring Spontaneous Combustion
(a) Below ground
Coal burning below ground has been detected for a long time and some had been
burning for hundreds and thousands of years emitting smoke, detected above ground.
Examples have been described from many parts of the world; such as the Burning
Mountain (Mt Win-Jen) in New South Wales, Australia where a coal seam has been
burning for thousands of years. It was part of a territory owned by the indigenous
Wanaruah people and is tied up in their ancient past legends. The coal seam is 2 m
thick and 30 m below ground and is detected by smoke coming out of the ground in
the area, moving southward at a rate of about 1 m every year. The coal seam is part
of Permian coals of the Sydney Basin. Many such occurrences have been reported
from around the world.
The largest concentration of coal fires caused by spontaneous combustion, both in
coal seams as well as coal piles occur in the Permian coals of India, first documented
from the Raniganj coal Basin in 1865.
(b) Above ground coal fires caused by spontaneous combustion
Spontaneous combustion in stock-piles of coals is a constant hazard that can be and
is controlled in well managed mines. There are special ways of building coal stock
piles that prevents spontaneous combustion.
Spontaneous combustion is a chemical oxidation reaction whereby heat generated
from the oxidation reaction is unable to dissipate by convection or conduction. The
temperature rises and the oxidation reaction speeds up increasing the heat until the
coal ignites. In most coal mines methane gas is present in varying quantities. Drainage
of coal mines of methane and other gases is a specialised engineering feat well
documented and usually planned and constructed with the mine going ahead. The
methane already present in coal seams may have been sourced from the coal that is
mined at some stage in its maturation history: As organic matter is buried deeper and
is subjected to increase in temperature it matures. The temperature with depth varies
in places, depending on the geothermal gradient of the depositional basin. The coal
undergoes physical and chemical changes with depth and increase in temperature.
These changes have been documented in many books on coal (e.g. Taylor et al. 1998).
At a certain stage of the coal maturation process methane is released. The methane
flows upwards through cleats and fractures and may end up in a coal mine where coal
has not reached methane generation stage yet. An example is a mine in Huaibei Basin
in Anhui province, China (Glikson et al. 2001) where methane is present in small
amounts even though the coal that is being mined has not reached methane generation
stage. Vitrinite reflectance of 0.8%Rm (Glikson et al. 2001) places the coal in the
lower part (A) of the volatile bituminous rank. Both reflectance and fluorescence
place the coal within the oil window, with very little potential of any thermogenic
methane generation in the seams of the Huaibei mine. The low bitumen content,