Alternative spontaneous combustion testing methods

The spontaneous combustion of coal is a persistent ongoing risk within the coal mining industry. To assess this risk, coal samples are regularly screened for their propensity to spontaneously combust. Within Australia, the predominant method adopted by the Australian mining industry for assessment is the Adiabatic Self-Heating (R70) test. However, limitations related to the difficulty of inducing the initial stage of self-healing process for low reactive coals, significant testing times, and lack of standardisation of instrumentation have remained present to this day. Alternative testing methodologies have emerged in the last few years, including: an alternative adiabatic self-heating test using humidified oxygen showing promise for low-reactive coals and the use of simultaneous thermal analysis (STA) to provide thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) within one test. The modification of the adiabatic self-heating test with sample moisture and gas humidification allows insight into the reaction kinetics under different self-heating environments. A novel adiabatic test with moist sample and humidified oxygen was compared against alternating testing conditions of sample drying/moisture and gas humidification. All testing except one showed a heightened rate of reaction when extrinsic humidity was introduced. Additionally, combined thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) is able to provide rapid testing results and their proposed spontaneous combustion indicators are shown to provide agreed metrics for a sample’s propensity to spontaneously combust when compared with adiabatic self-heating testing. The Burnout Index and Self-Heating Temperature derived from the first-order differential thermogravimetric (DTG) analysis aligned closely with the tested R70 values, with a R2 of 0.851 and 0.953, respectively.