Study On Reaction Characteristics And Kinetic Model Of Selective Non-Catalytic Reduction Denitration Of Fluidized-Bed Flue Gas

With the increasingly tense situation of air pollution and the increasingly stringent regulations on the emission of nitrogen oxides,the realization of ultra-low emission of nitrogen oxides has become an important goal of coal-fired circulating fluidized bed boilers.Due to the large variation of operating load and temperature fluctuation of fluidized bed boiler,the selective non-catalytic reduction denitrification technology?SNCR?faces the problems of low reaction rate and high ammonia escape rate due to the limitation of reaction temperature window.It is necessary to study the mechanism and dynamics of selective non-catalytic reduction reaction in order to provide a basis for the technology to adapt to the complex operation conditions of fluidized bed.Firstly,the characteristics of SNCR denitrification of fluidized bed flue gas were studied in depth.Based on the experiments and the detailed reaction mechanism model of SNCR,the effects of key operating parameters on the denitrification reaction were systematically studied.The results show that both O₂ and the additives?CH₄,CO,H₂?can reduce the reaction temperature required by SNCR.Increasing the ammonia-nitrogen ratio can significantly reduce the corresponding temperature of the optimal denitrification efficiency.Prolonging the residence time can improve the denitrification efficiency to a certain extent,in the meantime,it will lower slightly the temperature window.The effect of steam concentration and initial NO concentration on the denitrification efficiency is opposite at low temperature and high temperature.The increase of reaction pressure can reduce the reaction temperature required for SNCR,but at the same time it can increase the NO₂ content at the outlet.Then,the SNCR denitrification reaction with gasification syngas was studied in detail.Through experiments and simulation calculation of SNCR elementary reactions with syngas,the variation of SNCR denitrification reaction characteristics was studied with varying the influencing factors such as ammonia-nitrogen ratio,reaction residence time,type and concentration of additives.The results show that there is a weak synergistic effect between the concentration of syngas and the reaction residence time.At low temperature,with the increase of syngas concentration,the removal efficiency of NO and the optimum reaction temperature are less affected by residence time,while at high temperature,the effect of residence time is less affected by additive concentration.But the synergistic effect of syngas additive and ammonia-nitrogen ratio is strong.With the increase of syngas concentration,the effect of ammonia-nitrogen ratio on SNCR reaction is gradually strengthened,and the ammonia needed to achieve the same denitrification efficiency can be reduced.Therefore,although syngas cannot completely replace ammonia reductant in the removal rate of NOx,the presence of syngas can accelerate the reaction rate and shorten the reaction residence time in a certain range,while allowing appropriate reduction of ammonia-nitrogen ratio and reduction of ammonia escape.Finally,in order to describe the SNCR reaction process conveniently in the comprehensive numerical simulation of fluidized bed combustion,based on the previous work,the Arrhenius coefficients of the overall reaction of SNCR was optimized by genetic algorithm,where the solution value was analyzed and verified.The overall reaction model of SNCR in two temperature ranges was established,and the temperature correction was determined for different additives.The results show that the overall reaction model can predict the change of SNCR reaction temperature window in the presence of additives,and can also predict the SNCR reaction results accurately.