JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MINE ENVIRONMENTAL ENGINEERING - II Previous Question Paper (August - 2022 - R18)

Spontaneous combustion in coal mines is the process of self-heating of coal due to the oxidation of coal at ambient temperatures, which can lead to ignition without any external heat source. It occurs when the rate of heat generation from oxidation exceeds the rate of heat dissipation to the surroundings, causing the coal temperature to rise until it reaches its ignition point.

The adverse effects include the loss of valuable coal resources, the risk of underground fires which are difficult to extinguish, the production of toxic gases such as carbon monoxide, the potential for methane explosions, and the significant economic burden of sealing off affected mine areas or abandoning entire districts.

Prevention and control measures for spontaneous combustion are categorized into preventive strategies and reactive control techniques:

1. Mining Method Selection: Employing methods that minimize coal left in the goaf, such as longwall mining with high recovery rates, and avoiding the formation of pillars that are prone to crushing.
2. Ventilation Control: Reducing air leakage into abandoned areas (goaf) by maintaining pressure balance, using pressure-balancing chambers, or applying sealants like foam or specialized chemicals to stop air ingress.
3. Inertization: Injecting inert gases like nitrogen or carbon dioxide into the goaf to displace oxygen and suppress oxidation reactions.
4. Monitoring: Utilizing gas chromatography to detect early indicators of heating, such as increased ratios of carbon monoxide to oxygen deficiency (Graham's Ratio), and monitoring temperature changes using infrared sensors.
5. Surface Sealing: Applying fire-resistant coatings or spray-on sealants to coal ribs and roof surfaces to prevent oxygen contact with exposed coal faces.
6. Emergency Response: In the event of confirmed heating, control measures include isolating the affected zone with explosion-proof seals, pressure equalization, or, in extreme cases, flooding the area with water or inert slurries.