Assessing the effectiveness of a high-temperature-programmed experimental system for simulating the spontaneous combustion properties of bituminous coal through thermokinetic analysis of four oxidation stages

Highlights: • A self-designed high-temperature-programmed experimental system was adopted. • Four stages were divided to probe the dangerous stages in high-temperature oxidation. • Kinetic characters were reckoned by two methods based on oxygen concentration. • The crack-active-speedup temperature stage is the critical stage. -- Abstract: The spontaneous combustion of coal is characterized by high-temperature oxidation. This study used a self-made programmed experimental system to maintain temperature parameters at specified levels to simulate the combustion properties of coal. The oxygen concentration was determined to be inversely proportional to indicator gas concentrations. Five characteristic temperatures were achieved: critical temperature (97.45 ± 7.15 °C), crack temperature (149.28 ± 8.32 °C), active temperature (206.95 ± 15.05 °C), speedup temperature (263.45 ± 6.35 °C), and ignition temperature (390.85 ± 27.05 °C). Thermal characteristics were analyzed by dividing the oxidation into the following temperature stages: the critical temperature stage, crack–active–speedup temperature stage, speedup-ignition temperature stage, and combustion stage. Furthermore, the differential and integral kinetic methods were used to compute the apparent activation energy in the four aforementioned stages. The results indicated that the apparent activation energies decreased through the first three stages and then increased in the fourth stage. Therefore, the crack–active–speedup temperature stage was determined to be potentially dangerous during oxidation because gases increased rapidly at this stage; such gases included CO, which is particularly harmful to human health. The thermal energy release also increased gradually at this stage.