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.