Application of experiments and density function theory on the formation mechanism of NH₃ during O₂/Ar and O₂/H₂O combustion process of demineralized coals

Understanding the formation mechanism of NH₃ during the pulverized coal combustion process is a feasible approach to reducing NOx emissions. In this study, the emission characteristics of NH₃ during the O₂/Ar and O₂/H₂O combustion processes were investigated by the isothermal combustion experiments and the Density Functional Theory (DFT) method. The experimental results demonstrated that H₂O accelerated the conversion of HCN to NH₃, and the positive effects of H₂O were applied to all kinds of coal-based fuels. The DFT calculations deeply revealed the formation mechanism of NH₃ through the homogeneous conversion of HCN and the heterogeneous hydrogenation of coal-N. The hydrogenation of coal-N is the primary source of NH₃ emissions during O₂/Ar combustion. During O₂/H₂O combustion process, the heterogeneous generation of NH₃ was modified by the synergetic effects of O₂ and H₂O, and the additional H₂O strengthened the proportion of the homogeneous reaction. The homogeneous conversion of HCN was the main NH₃ formation pathway. This study is prone to coupling the experiments and quantum chemistry to deeply reveal the formation mechanisms of NH₃ during O₂/Ar and O₂/H₂O combustion processes, providing a relatively complete pathway for the emissions of NH₃.