An experimental investigation of early warning index for coal spontaneous combustion with consideration of particle size: a case study

Accurate prediction and forecasting are the important prerequisites for preventing and controlling the spontaneous combustion of coal. In this study, the production of CO, C2H4, C2H6, and other gases during the oxidation processes was studied by the temperature-programmed method with different particle sizes at a heating rate of 0.3 degrees C/min and a dry airflow rate of 120 mL/min. Based on the quantitative relationship between the temperature and gaseous products, the index gases and their critical values at different oxidation stages were identified. By the gas growth rate method, the critical temperatures for the spontaneous combustion of the coal samples were determined to be in the range of 70 degrees C similar to 80 degrees C, and dry cracking temperatures were 130 degrees C similar to 140 degrees C. By the critical and dry cracking temperatures, the coal oxidation process was classified into three stages, the slow oxidation stage, rapid oxidation stage, and accelerated oxidation stage. A three-level early warning index for predicting coal spontaneous combustion quantificationally was proposed, including CO/CO2, CO2/O-2, Delta O-2, and C2H4.