Numerical Study And Structural Optimization Of SCR Denitration Reaction System Of Sintering Flue Gas

Selective catalytic reduction（SCR）is the critical technology of sintering flue gas denitration.At present,the numerical simulation and optimization of SCR reactor has seldom considered chemical reaction,and most of them judge the denitration effect by the relative standard deviation coefficient of flow rate and ammonia nitrogen molar ratio,rather than by denitration efficiency.Even considering chemical reaction,the non-uniformity parameters of SCR reactor inlet is rarely considered in combination with the actual situation,so there is a deviation from the actual situation.The research on denitration efficiency is generally based on experiments,and there are few numerical simulation studies to establish an accurate chemical reaction model,so as to serve the numerical simulation of SCR denitration;The denitration efficiency of SCR denitration reactor has reached a high level,and excessive denitration will inevitably lead to ammonia escape,resulting in many problems.In view of the shortcomings in the research of sintering flue gas SCR denitration reaction system,this paper focuses on the numerical simulation of denitration efficiency of SCR reactor based on response surface method（RSM）and the confidence of outlet no measurement results and the influence of denitration efficiency based on Monte Carlo method,so as to provide theoretical guidance for the optimization of SCR denitration reaction system.Firstly,the feasibility of catalyst macro numerical simulation of SCR denitration reaction system was determined through the comparison and analysis of catalyst macro numerical simulation,meso numerical simulation and experimental data;Then,the accuracy of the numerical simulation of overall SCR reactor was verified by experiments,and the quadratic multinomial regression model model of three factors affecting the denitration efficiency was established based on response surface method.Then,the effects of velocity relative standard deviation and temperature relative standard deviation on the confidence of NO concentration measurement results at a single measuring point and denitration efficiency were studied,so as to provide a basis for optimizing the structure of SCR reactor and reducing ammonia slip.The conclusions are as follows:（1）The CFD numerical simulation results showed that the denitration efficiency under macro scale simulation and meso scale simulation were both in good agreement with the experimental data,the deviation between denitration efficiency and experimental results was within the acceptable range,and the distribution trend of NO concentration in the catalyst was consistent under macro scale and meso scale,which confirmed the accuracy and rationality of macro simulation of catalyst.On this basis,the numerical simulation of SCR overall reaction system was carried out,and the denitration efficiency and outlet temperature of SCR denitration reactor are experimentally tested.The results obtained from the experiment and simulation were compared and analyzed,which proved that the realizable k-εmodel,component transport model and chemical reaction model are completely feasible to simulate the flow field and concentration field of SCR reactor.（2）Based on response surface methodology,the effects of catalyst inlet wind velocity,reaction temperature and ammonia nitrogen molar ratio on denitration efficiency were studied,and a quadratic multinomial regression model of three factors affecting the denitration efficiency was established.The three factors all had significant effects on denitration efficiency,and the interactive influence of catalyst inlet wind velocity and reaction temperature was significant.When the NH₃/NO molar ratio is constant,the denitration efficiency mainly decreases with the catalyst inlet gas velocity and increases with the reaction temperature;When the reaction temperature is constant,the denitration efficiency increases with the increase of NH₃/NO molar ratio,and when the NH₃/NO molar ratio exceeds 1,the increasing rate of denitration efficiency becomes smaller and smaller;when the catalyst inlet gas velocity is constant,the denitration efficiency increases with the NH₃/NO molar ratio and the reaction temperature.（3）The Normrnd Function in MATLAB was used to generate the catalyst inlet boundary conditions under different relative standard deviations of velocity and temperature.The effects of different working conditions on the denitration efficiency and the confidence of the measurement results of outlet NO concentration were statistically obtained by Monte Carlo simulation.The catalyst inlet wind velocity had a great impact on the central concentration deviation and the confidence of measurement results under different temperature relative standard deviations.When the temperature relative standard deviation was constant,with the increase of catalyst inlet wind velocity,the mean value of central concentration deviation first increased and then decreased,and the confidence of measurement results showed the opposite trend.Within the air volume range studied in this paper,in order to ensure the confidence of the measurement results,the relative standard deviation of temperature must be within 0.005 and the relative standard deviation of speed must be within 0.1.When the wind speed at the catalyst inlet was greater than 4m/s,it can be relaxed to the relative standard deviation of temperature within 0.01 and the relative standard deviation of speed within 0.1.（4）With the increase of the relative standard deviation of temperature,the denitration efficiency decreased slightly,and the variation range of denitration efficiency with the relative standard deviation of temperature was similar when the mean value of temperature was different.When the mean velocity is different,the corresponding denitration efficiency decreases with the increase of temperature relative standard deviation.With the increase of the relative standard deviation of speed,the denitration efficiency decreased slightly.The greater the velocity was,the greater the decreasing amplitude of the corresponding denitration efficiency with the increase of the relative standard deviation of velocity was.（5）In order to verify the correctness of the conclusion on the confidence of the measurement results,based on the non-uniform inlet temperature,the hot air duct structure and guiding plate were optimized with the relative standard deviation of catalyst inlet temperature less than or equal to 0.01 and the relative standard deviation of temperature less than or equal to 0.1 as the optimization objectives.The optimization can improve the denitration efficiency and the relative standard deviation of NO concentration at the outlet.After optimization,the NO concentration measured at the central measuring point was closer to the average NO concentration at the outlet section,which can better represent the overall concentration level,so as to ensure that ammonia injection is more reasonable,which also confirmed the correctness of the conclusion.