Thermokinetics behaviour and parameters for spontaneous combustion of carbonised powders and oxidised powders from preparation of coal-based activated carbon

Abstract

The spontaneous combustion of carbonised and oxidised powders has been long considered an intricate physicochemical process, and their combustion is often concealed and difficult to detect. The self-ignition characteristics and parameters of carbonised and oxidised powders were thus explored. The thermokinetic behaviours of carbonised and oxidised powders (303–1073 K) were assessed at four different heating rates (5.0, 10.0, 15.0, and 20.0 K min−1) through thermogravimetry–differential scanning calorimetry (TG–DSC). The variation of the thermogravimetric curve was obtained, and the apparent activation energy (Ea) of the carbonised and oxidised powders was calculated using the Kissinger–Akah–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods. The LFA457 laser-flash apparatus was employed to measure thermophysical parameters of experimental samples. The results revealed that the TG–derivative thermogravimetry curve shifted towards high temperatures, and overall, the characteristic temperature increased as the heating rate increased (e.g. at heating rates of 5.0–20.0 K min−1, the critical temperatures were 329–349 and 332–356 K for carbonised and oxidised powders, respectively). The Ea values in the combustion stage obtained using the two calculation methods were similar. The Ea values of the carbonised powders were 148.64 (KAS) and 153.58 (FWO). The Ea values of the oxidised powders were 171.23 (KAS) and 175.68 kJ mol−1 (FWO). The specific heat capacity of carbonised powders was higher than that of oxidised powders, whereas the thermal diffusivity and thermal conductivity were lower than those of oxidised powders.