A Parametric Study on the Inception and Evolution of Underground Coal Fires Based on a Lab-Scale Experimental Setup

The tendency of self-ignition of coal is the root cause of underground coal fires (UCFs). A parametric study is carried out on a lab-scale experimental setup developed based on the essential heat and mass transfer characteristics of actual UCFs to understand the factors influencing the inception and evolution of coal fires. Effects of heat accumulation, moisture content and coal layer height are systematically examined by varying the relevant parameters on the experimental setup. Temporal evolution of coal temperature and volumetric fractions of CO and CO2 are measured and analyzed. The results indicate that heat accumulation, moisture content and coal layer height mainly influence the time needed to reach the ignition state. Without sufficient heat accumulation, coal-oxygen reactions are not self-sustainable even after they enter the rapid reaction stage. The reaction regimes inside the coal tank are mainly determined by the local oxygen concentration, while the temperature changing rate depends on the relative magnitudes of heat generation and heat transfer (gain/loss). The ratio of CO2/CO is more informative in the detection of high-temperature stage of UCFs.