Simulation And Optimization Of Cooperative Reaction For N₂O Decomposition And NO Reduction

At present,N2O catalytic decomposition technology and NO reduction technology are mainly used in the removal of nitrogen oxides in chemical production process.The cost of the treatment is too high for the long process.In this thesis,a Fe-Beta zeolite catalyst with a loading capacity of 1.5%was prepared by liquid phase ion exchange method.Through the activity evaluation experiment,it was found that the conversions of N2O decomposition can reach more than 90%and the conversions of NO reduction is above 85%at temperatures between 490? and 500?.Based on the 3D fluid dynamics software(CFD),the reactor model was established,and then the grid-independent verification was performed to obtain an optimum grid number of 900,000.The established model was evaluated by the model reliability verification,proving that the model was reliable.Based on this model,the N2O decomposition and the NO reduction were separately and cooperatively simulated on the particulate catalyst and the monolith catalyst.For the granular catalyst reactor,the reaction conditions under different conditions were investigated by changing parameters such as inlet temperature,velocity,ration of length to diameter and porosity.The simulation results show that the axial temperature in the reactor gradually increases with the progress of the reaction.The higher the inlet temperature and the lower the velocity are,the higher the reaction conversion is.The larger the ratio of length to diameter and the porosity are,the higher the reaction conversion is.The optimum parameters on the granular catalyst are:inlet temperature 500?,inlet gas velocity 0.6 m/s,length to diameter ratio 2,porosity 0.4.The two reactions were simulated separately by using a square single channel instead of a porous channel to study.the reaction characteristics of the two reactions on the monolith catalyst.The simulation results show that the temperature and concentration in the channel are symmetrical,the temperature is highest near the solid phase or porous medium,and is lowest at the center of the channel.The temperature gradient is mainly distributed in the main gas phase,and the temperature change is small in the porous medium;the optimum parameters on the monolith catalyst are:inlet temperature 505?,inlet gas velocity 1.0 m/s,length to diameter ratio 6.In this thesis,the simulations of the reaction characteristics of N2O decomposition and NO reduction on granular catalysts reactor and monolithic catalysts reactor were also carried out.It was found that,the NO reduction reaction in the cooperative reaction was greatly affected by the N2O decomposition reaction,while the N2O decomposition reaction was basically not affected by the NO reduction;the optimum parameters for the cooperative reaction on thegranular catalysts reactor were:inlet temperature 495?,inlet gas velocity 0.5m/s,length to diameter ratio 2,porosity 0.4;the optimum parameters on the monolithic catalyst reactor are:inlet temperature 500?,inlet gas velocity 0.95 m/s,length to diameter ratio of 6.In this thesis,the simulations of the monolithic catalysts with different pore opening shapes were also studied.It was found that under the same operating conditions,the reaction conversions decrease according to the order of circular,square,triangle,regular hexagon and rectangle;The pressure drops decrease with the sequence of triangular,rectangular,square,hexagona and circular.According to the simulation results of the cooperative reaction,the reactor model was established,and the flow field distribution of the reactor was analyzed and compared for the case of with or without the sieve plate distributor.It was found that the flow field distribution is improved with the distributor.Furthermore,the influence of the thickness,aperture and free space length of the sieve plate distributor on the flow field were studied.The results show that the gas distributor can effectively improve the gas distribution.In case of the thickness of the distributor is 10 mm,the pore diameter is 5 mm,and the free space length is 80 mm,the gas is distributed well.