Experimental Study on the Variation of Characteristic Temperatures and Activation Energy of Coal Oxidation under Thermal Airflow Erosion

Abstract

Coal spontaneous combustion (CSC) poses severe threats in deep mining environments with high ground temperature and thermal airflow. This study investigates thermogravimetric characteristics and activation energy variations of lignite subjected to thermal airflow erosion. Coal samples were pretreated at 35 and 65 °C with airflow rates of 0–200 mL/min for 30 days, followed by TG-DSC analysis. Eight characteristic temperatures and activation energies were determined using the Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW) methods. Results show that elevated temperature (65 °C) pretreatment universally reduced critical temperature (T1), dry-cracking temperature (T2), and activation temperature (T3), significantly increasing CSC propensity. Temperature was the primary influencing factor, while the airflow rate was secondary. Notably, thermally airflow-eroded samples exhibited monotonically decreasing activation energy with conversion rate, indicating pronounced self-accelerating oxidation. The most significant “activation” effect occurred under 35 °C with a low airflow rate (100 mL/min), substantially lowering the activation energy barrier. These findings reveal that residual coal exposed to “low temperature with restricted ventilation” undergoes the most detrimental transformations, becoming extremely susceptible to spontaneous combustion.