Molecular Dynamics Simulation Of The Formation And Reduction Of Nitrogen Oxides In Coal Combustion

China is a coal-based energy production and consumption country,but in the process of coal power generation,a lot of nitrogen oxides and other pollutants emit into the atmosphere,causing serious environmental problems.Under the background of carbon peak in 2030 and carbon neutralization in 2060,it is very important to strengthen the research on NOx generation and reduction in coal combustion process and further control NOx emission to control environmental pollution.In this paper,lignite model and three typical coal char models of Zigzag,Armchair and Bay were constructed by MS 7.0 software,and their molecular mechanics and molecular dynamics were optimized.Then,Amsterdam Density Function（ADF）is applied to simulate the formation and reduction of nitrogen compounds in lignite combustion under different oxygen conditions,the reaction processes of three typical coal char models under different NO molecular numbers and different temperatures.Coal char macromolecules with carbon atom number greater than 14 generated during lignite combustion were selected to simulate the reduction of NO by real coal char under different oxygen numbers.Through the analysis of the simulation results,the reaction process of NOx generation and reduction in coal combustion is deeply understood.When the excess air coefficients are 0.45,0.6 and 0.8,with the increase of the excess air coefficients,the ability of O₂to attack nitrogen-containing groups in coal is enhanced,dehydrogenation or carboxyl oxidation reactions are strengthened,HCN or its precursors are oxidized,and HNO and NCO are directly converted to NO.NO can be directly reduced to N₂or NCO by NCO or CO at high concentrations of NCO and CO.A large amount of NCO is adsorbed and reduced,and becomes tar nitrogen,soot nitrogen and coke nitrogen,which is an important reason for the reduction of NO.The Armchair structure in the three typical coal coke models is easy to be destroyed by oxidation,and have more defects in the process of reaction.More CO and N₂is generated.In the Zigzag-rich coal char macromolecule model,there are three binding modes of NO in the reduction process:O-down,N-down and parallel adsorption.N-down mode is slightly more than O-down mode,and parallel adsorption is observed only once.NO molecules and oxygen atoms together induce nitrogen transfer,ring formation,ring opening,oxygen insertion and other reactions to break the edge surface.C atoms are consumed and N₂,NCO,CO₂and other products are generated.When the oxygen number is 10,NO is more reduced.When the number of oxygen molecules,that is,the oxygen concentration increases to a certain content,the oxidizing atmosphere is strong,which is not conducive to the generation of reducing gas.Oxygen-containing functional groups or oxygen atoms on macromolecules directly participate in the reduction process of NO,that is,oxygen-containing functional groups or surface oxygen atoms play a catalytic role in the reduction process of NO.