Self-ignition risk classification for coal dust layers of three coal types on a hot surface

H I G H L I G H T S• Thermal combustibility and susceptibility for coal dust were investigated. • Chemical reaction mode regulated the temperature after thermal runaway. • Thermokinetic parameters were measured and calculated by TGA and hot surface test. • Self-ignition risk of samples was determined using modified risk matrix method. Pulverised coal in industrial sites and their dust can experience spontaneous combustion and self-heating, increasing the risk of fire and dust explosion. The main objective of the present study was to resolve thermal combustibility (as reflected by comprehensive combustibility index [S_n] and kinetic properties) for three types of coal (S1-BN, S2-CY, and S3-JM) through thermal analysis. The S_n values of the samples indicated a degradation in the quality of comprehensive combustibility. Apparent activation energies (E_a) at the initial stage of spontaneous coal combustion (130–300 °C) were decided through Achar and Coats–Redfern methods. Moreover, thermal susceptibility (minimum auto-ignition temperature [MAIT] and thermodynamic parameters) was evaluated using the hot plate method. The MAIT values for the three coal dust layers were 210, 220, and 300 °C. The results exhibited that heat conduction was the dominant heat transfer mode that originated the temperature distribution within the coal dust layer under the subcritical conditions for ignition; while it converted chemical reaction controlled-mode after thermal runaway. Furthermore, the results based on an improved risk matrix approach showed the S1-BN and S2-CY samples had a high self-ignition risk, whereas the S3-JM sample had a moderate ignition risk.