Bulletin of the Geological Society of Malaysia, Volume 19, April 1986, pp. 393 – 404
Dept. of Geological Sciences Faculty of Sciences, Chiang Mai University Thailand
Abstract: Coal deposits in northern Thailand are mainly of low quality, ranking from lignite to high volatile bituminous coal according to American Standards. Spontaneous fires in these coals are common and have caused many problems in mining practices and loss during storage.
Observations of spontaneous fires of stockpile show that the reaction starts from accumulation of heat, the direct result of absorbing energy from the sun. The dehydration reaction that first occurs is represented by disintegration of coal lumps on the surface of the stockpiles, followed by release of steam from inside of the stockpiles. The passage of steam and air flow causes oxidation, hydrolysis and hydration reactions inside the stockpiles and this gives rise to an increase in temperature from the heat of reactions, leading to partial distillation of low-temperature combustible gases such as methane and ethane. Spontaneous fires occur within 28 to 40 days for Mae Moh lignites and within 45-60 days for the coals from other places.
The prime factor causing spontaneous fires in the mining areas is the geological structures especially those related to mass movement such as faulting and slumping. These movements produce void spaces and passageways for combustile gases that originate from coalification processes and for oxygen from the outside. The low rank coals which produce low-temperature combustile gases either by coalification processes or by partial distillation as a result of increasing temperature are the major source. The spontaneous ignition could originate from a ‘flash‘ rise in temperature which could be due to the reaction between water and sulphide minerals present in the coal. The loss can be minimized by preventing the air-oxidation through compaction both at mine fronts and stockpiles.