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 (C ₂₀₈H ₁₉₉O ₂₃N ₃S) is developed. Utilizing the reaction molecular dynamics (ReaxFF MD) method, molecular dynamics simulations of coal combustion are performed under varying O ₂ 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 O ₂ 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 CO ₂ was 1 781, which was lower than the total number of primary reactions consuming CO and H ₂O. Increasing temperature and the number of O ₂ molecules caused a greater increase in the peak yield of relatively stable CO ₂. The peak yield of H ₂O initially increased and then decreased with the increase in the number of O ₂ 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, CO ₂, and H ₂O were the polymerization of free radicals or the decomposition of small molecule compounds.