Molecular Dynamics Investigation on Combustion Mechanism and Nitrogen Migration Pathways of Low-Rank Coal Blended with Ammonia

To clarify the combustion mechanism and nitrogen (N) migration pathways of low-rank coal blended with ammonia (NH3) under multi-factor conditions, the combustion processes were systematically explored using ReaxFF molecular dynamics simulations, combined with Python self-programming and reaction network extraction tools. Multi-factor analysis was conducted to investigate the effects of temperature, chemical equivalence ratio, and NH3 blending ratio on reactant consumption, product distribution, and N transformation. The results of NH3/low-rank coal co-combustion conditions showed that increasing temperature and chemical equivalence ratio significantly accelerated oxygen (O2) consumption, while temperature and NH3 blending ratio dominated NH3 consumption due to the O2-independent dehydrogenation of NH3 at high temperatures. Elevated chemical equivalence ratio promoted volatile oxidation, advancing the peak time of light tar and organic gases by 50–100 ps and increasing the inorganic gas proportion to over 99% under O2-rich conditions. NH3 blending delayed coal pyrolysis, reducing the peak proportion of heavy tar and organic gases by 20–30% but increasing inorganic gas yield. For N migration, O2-rich and high-temperature conditions increased NOx emissions, while low-O2 and medium-temperature conditions favored N2 formation, reducing NOx by 30–40%. This work offers a theoretical basis for optimizing low-carbon power generation technologies using low-rank coal blended with NH3.