Numerical Simulation Of Char-N Conversion And NO_x In Situ Reduction In A Single Particle Coke Combustion In Oxy-fuel Atmosphere

Oxy-fuel combustion technology has significant advantages in promoting efficient fuel combustion and reducing nitrogen oxides generated during coke combustion,and has therefore received high attention from researchers in recent years.Although a large number of scholars have studied the formation and reduction of nitrogen oxides during oxy-fuel combustion,the mechanism is not completely clear.This work uses Fortran language programming to simulate the combustion process of a coke particle.The conversion of coke nitrogen and the reduction mechanism of nitrogen oxides and the transport characteristics of various gases in the interior of the particles were studied by changing the operating conditions such as combustion atmosphere and combustion temperature.The best combustion atmosphere is obtained which is beneficial to the efficient combustion of coke particles and is beneficial to in situ reduction.Coke particles are formed by high-temperature coking of pulverized coal particlesand have developed pore structure.Char-N is basically organic nitrogen,carbon atoms combine with atoms such as nitrogen and hydrogen to form cyclic or chain compounds.These structures are aggregated into graphite microcrystalline structures to form carbon-based,the reaction of coke nitrogen is similar to the nucleation reaction due to the structural characteristics.Molecular reaction kinetics model?heat transfer model?mass transfer model and conversion model of coke nitrogen were established based on the structural characteristics of the particles and the reaction characteristics of coke nitrogen.Comparison with experimental data shows that the model can better characterize the combustion characteristics of a coke particle,the conversion of coke nitrogen and insitu reduction.In the early stages of combustion,a short accumulation of NO occurs inside the particles.The main factors affecting the concentration of NO inside the particles are the formation,consumption and diffusion of NO.The increase in NO concentration shows that the amount of NO produced in the early stage of combustion is greater than the sum of the amount of consumption and the amount of diffusion.This is because in the initial stage of combustion,the combustion inside the particles is slow,the pores are not developed,the gas is transported slowly,the reducing ability of the particles is weak,the consumption of nitrogen oxides is less,resulting in an increase in the concentration of NO inside the particles.In the combustion process of coke particles,there are two kinds of reduction reactions of homogeneous reduction and heterogeneous reduction of nitrogen oxides.CO gas is generated inside the particles due to lack of oxygen.CO will be homogeneously reduced with nitrogen oxides,nitrogen oxides will also adsorb to the carbon-based surface to undergo heterogeneous reduction.The calculation results show that the formation of nitrogen mainly comes from the homogeneous reduction reaction.That is the homogeneous reduction reaction plays a major role and the heterogeneous reduction reaction plays a secondary role.The coke particles have a change in the ability to reduce nitrogen oxides throughout the combustion process.In the early stage of combustion,coke particles have weaker ability to reduce nitrogen oxides due to the inhibition of carbon dioxide and the slower rate of reduction.As the combustion progresses,the pore structure becomes more developed,which is conducive to gas transport.CO₂ is easily desorbed from the carbon-based surface,while the carbon-based surface continuously generates a large number of carbon active sites,nitrogen oxides adsorb to the carbon-based surface and the possibility of a reduction reaction increases.The increasing temperature also promotes the increase of the reduction reaction rate,therefore,in the middle and late stages of combustion,the reduction ability of the particles to nitrogen oxide is enhanced and the amount of nitrogen is increased.Further study on the conversion characteristics and insitu reduction mechanism of coke nitrogen by changing the working condictions such as combustion temperature and combustion atmosphere.The calculation results show that coke particles can be burned efficiently and facilitate the reduction of nitrogen oxides when the oxygen concentration is25%,which is an ideal combustion atmosphere.In a certain temperature range,the increase of the ambient temperature is beneficial to the reduction of nitrogen oxides,nitrogen oxides can be reduced by appropriately increasing the combustion temperature.