A Parametric Study of Spontaneous Ignition in Large Coal Stockpiles

Self-heating of coal during its storage and transportation has been a serious problem for decades. Coal stored in large piles for long duration is subjected to weathering by atmospheric air that prevails with different temperatures and moisture content. Chemisorption of atmospheric oxygen results in low-temperature oxidation of pile, which generates heat due to exothermic reactions. If the local heat release rate is higher as compared to the heat dissipated, a significant increase in temperature is possible and this results in spontaneous ignition of the pile. The presence of moisture in coal delays the occurrence of self-heating. This motivates to analyze a scenario of using moist coal to delay or even prevent the self-ignition in dry coal until a given time period of its storage. The main objective of this work is to investigate the critical conditions, which may lead to spontaneous ignition in large coal stockpiles containing dry and moist coal layers. A one-dimensional numerical model is used for this purpose. A parametric study is carried out considering different porosity, superficial air velocity and reactivity values. The time period of coal pile storage is fixed as 360 days. The location and time taken for self-ignition in the pile within this period is reported for each case. In summary, considering several cases, the simulations systematically reveal that highly reactive coal with high pile porosity and higher superficial gas velocity takes the least time to reach the self-ignition temperature.