Study on the formation law of free radicals and main combustion products in non-caking coal combustion process based on ReaxFF

To explore the formation mechanisms of free radicals and major combustion products during the combustion of non-caking coal, this study conducts a comprehensive characterization analysis of non-caking coal using X-ray photoelectron spectroscopy (XPS) and ¹³C NMR nuclear magnetic resonance spectroscopy. A molecular model of non-caking coal (C₂₀₈H₁₉₉O₂₃N₃S) is developed. Utilizing the reaction molecular dynamics (ReaxFF MD) method, molecular dynamics simulations of coal combustion are performed under varying O₂ molecule numbers and temperatures to explore the generation and consumption patterns of free radicals and main products. The results indicate that the OH free radical was consumed 1 906 times in total, while the H and O free radicals were consumed 3 733 times and 2 033 times respectively. Increasing temperature and the number of O₂ molecules resulted in a more significant increase in the peak yield of relatively stable OH free radicals, with smaller increases in the peak yields of H and O free radicals. The total number of primary reactions consuming CO₂ was 1 781, which was lower than the total number of primary reactions consuming CO and H₂O. Increasing temperature and the number of O₂ molecules caused a greater increase in the peak yield of relatively stable CO₂. The peak yield of H₂O initially increased and then decreased with the increase in the number of O₂ molecules. H, O, and OH free radicals were primarily generated through the decomposition of small molecule compounds or other radicals. The main pathways for the formation of CO, CO₂, and H₂O were the polymerization of free radicals or the decomposition of small molecule compounds.