Experimental study on CO and CO₂ emissions from spontaneous heating of coals at varying temperatures and O₂...

Laboratory experiments were conducted to investigate carbon monoxide (CO) and carbon dioxide (CO₂) emissions from spontaneous heating of three U.S. coal samples in an isothermal oven at temperatures between 50 and 110 °C. The oxygen (O₂) concentration of an oxygen/nitrogen (N₂) mixture flowing through the coal sample was 3, 5, 10, 15, and 21%, respectively. The temperature at the center of the coal sample was continuously monitored, while the CO, CO₂, and O₂ concentrations of the exit gas were continuously measured. The results indicate that the CO and CO₂ concentrations and the CO/CO₂ ratio increased when the initial temperature was increased. As the inlet O₂ concentration increased, the CO and CO₂ concentrations increased, while the CO/CO₂ ratios tended to converge to the same value. The ratio of CO/CO₂ was found to be independent of coal properties, approaching a constant value of 0.2. The maximum CO production rate correlated well with the maximum coal temperature rise. The apparent order of reaction for coal oxidation was estimated to be between 0.52 and 0.72. The experimental results in this study could be used for early detection and evaluation of a spontaneous heating in underground coal mines.