Ash, Volatile Matter and Carbon Content Influence on Spontaneous Combustion Liability of Coal-Shales

Self-heating of coal-shales has been reported in some South African coal mines to be one of the causes of spontaneous combustion but not the coal alone. Spontaneous combustion tests were conducted on a series of coal-shale samples collected from affected coal mines using a newly developed liability index referred to as the Wits-CT index. The ash content, volatile matter and the carbon content of the samples were investigated, and their effects towards spontaneous combustion liability were established. The study indicated that as ash content increases, the liability towards spontaneous combustion decreased, while as the volatile matter and carbon content increases, the liability towards spontaneous combustion increased. It was further found that the ash content showed a negative effect on the liability index, while volatile matter and carbon content showed positive effect on the liability index. Coal-shales with low ash content and high volatile matter and carbon content are more likely to be prone to spontaneous combustion.