A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study

The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog, which would seriously affect the quality of atmospheric environment. Therefore, the decrease of NOx is of great importance for improving the efficient utilization of coal. The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation. Firstly, in the process of pyrolysis: the occurrence state and transformation of nitrogen were concluded. The influence of temperature, atmosphere, heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized; Secondly, during the process of combustion: the influence of temperature, ambient oxygen concentration, physical structure of coal char, catalyst on heterogeneous oxidation of char (N) were summarized; The effects of char surface properties, catalyst and ambient atmosphere on heterogeneous reduction of NOx were also concluded. Based on the quantum chemical calculation, the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail. Current studies focus more on the generation of HCN and NH3, but in order to reduce the pollution of NOx from the source, it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrolysis, as well as clarify the path of the generation of N2. Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.