prevention and control of spontaneous combustion - Mining and

Liquid phase: Cools by conduction and increases the humidity of coal and rocks; restricts the
access of oxygen during the period of foam existence; inerts regions of porous media when
reaching high-temperature zones. A significant compacting effect is observed when this phase is
injected into rocks with high clay content.
Solid phase: Creates a wet solid layer on the surface of coal pieces and fills filtration channels,
which inhibits convective and diffusive oxygen transfer.
Gas phase: Ensures treatment of coal masses located in high zones of gob by increasing slurry
viscosity. Inert gas dilution during foam destruction makes this zone inert. There are
mathematical solutions as well as laboratory test results for optimisation, which are discussed in
detail in the paper.
6.1.2 Extinguishing
6.1.2.1 Inert gas injection
The tube bundle system has been used to assess the use of inert gas injection as means of
controlling spontaneous combustion. Nitrogen or carbon dioxide is injected into goaf areas
affected by a spontaneous heating to help control the heating by excluding oxygen and to give a
cooling effect. The favoured gas is nitrogen as it is cheaper and more easily expelled from the
mine after the heating has been controlled than is carbon dioxide.
Three nitrogen inerting experiments were done at Bowen No. 2 Colliery at Collinsville. The
experiments were conducted to find the optimum nitrogen flow rate and configuration of the
injection points. At the end of the experiments, they were not able to draw a conclusion about
the effectiveness of inert gas injection as a means of controlling spontaneous combustion.
Major advances have been made using inert gases to control spontaneous combustion. The
objective of inerting is to reduce the concentration of oxygen in the atmosphere. To ensure the
prevention of spontaneous combustion, it is necessary to reduce the oxygen content below 3%
by volume.
One essential condition is that nitrogen should be applied quickly. It is common in Germany to
have inertisation plants at the mine site. This enables them to apply nitrogen to a fire area at
very short notice, often within four to 12 hours after detection. Many fires have been controlled in
German mines using the technique of inertising with nitrogen (Kock and Linberg (1985)).
Carbon dioxide may be used for inertisation instead of nitrogen, and is sometimes preferable to
nitrogen. Because its density is higher than that of air, carbon dioxide is particularly suitable in
situations where the heating is taking place at the bottom of a steeply sloping area or at the
bottom of a shaft.
Generating an inert gas at the mine site is usually cheaper than obtaining a supply of carbon
dioxide or nitrogen. In this way, it is also possible to produce gases at a greater flow rate.
However, some disadvantages are mentioned:
• The need for a large volume of cooling water
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