Low-temperature oxidation of single and blended coals

The oxidation of different types of coal under self-heating conditions is considered using the crossing point method performed in a cubical wire-mesh basket. This study investigates the effect of particle size and the physical structure of coals (including pore size and surface area) on the self-heating character of high and low rank Indonesian coals and their blends. The results confirm that both particle size and surface area give considerably different effects on critical ambient temperature, the activation energy and the product of exothermicity and the pre-exponential factor of low and high rank coals. It was found that the self-heating characteristics of high rank coals were strongly dependent upon the particle size of the coals. For low rank coals, the dependence was weaker. A coal bed with mixed sizes is thus more vulnerable than one with segregated sizes. This means that one must carefully consider the particle size distribution to judge the spontaneous ignition behaviour of coal. It is suggested that the potential for spontaneous combustion of blended coal is greater following the increased percentage of more reactive coal.