Simulation Study On The Structure Optimization Of Toluene Catalytic Oxidation System

China is in a period of rapid economic development,facing the dual problems of high energy consumption and environmental pollution.Among them,the impact of air pollution on the economic development and the public people’s health has increasingly been widely concerned by the public and governments at all levels.The research on air pollutants in China mostly focuses on SO₂,NOx and other pollutants.In recent years,more and more attention has been paid to the control of pollutants such as fine particles(PM_2.5),ozone and volatile organic pollutants（VOCs）.The 14th Five Year Plan for the development of national environmental science and technology puts forward the control requirements for energy conservation and emission reduction.By 2025,the total emission of volatile organic compounds will be reduced by more than 10%compared with 2020.The primary aspect of VOCs control is the industrial field.A large number of VOCs is produced in the production process of various chemical industries,which has a wide range of sources and diverse components,and need to be treated urgently.At present,the VOCs control technology widely used in industry is catalytic oxidation technology,in which catalyst is the core of this technology.To ensure the catalytic effect and service life of the catalyst,it is necessary to avoid the problem of catalyst sintering caused by bed flying temperature.Through the optimization of the flow field in the reactor,the uniform distribution of the flow field can be realized,so as to realize the homogenization of the temperature field in the system,which can better avoid the problem of system flying temperature.In this study,the existing toluene catalytic combustion reactor was redesigned and optimized on the basis of early research.After comprehensively evaluating the advantages and disadvantages of cross plate,strip plate,grille plate and porous plate,a new deflector called Asterisk plate was designed.The new deflector effectively increased the guiding capacity of the air flow,reduced the interference to the air flow,and improved the limitation of the air flow field in the central area of the perforated plate.In the study,the Asterisk plate was arranged at the inlet section of the main area of the reactor.CFD software was used to simulate and test the effect of the Asterisk plate with different model parameters（10 types of 2.5-2.5,5-5,10-5,5-2.5,6-2,9-3,5-1.25,10-2.5,5-1 and 10-2mm）,different plate thickness（5,10,15,20,25,30mm）and different placement positions（moving distance to the right from the inlet section is 5,10,15,20,25,30,35,40mm）on flow field optimization with or without heat storage.The results showed that when no regenerator was added,the 15mm thick Asterisk plate should be placed 33.5mm behind the inlet of the main pipe section to ensure the highest uniformity when entering the catalytic section,that is,the area weighted uniformity index was greater than 0.95;When adding the heat storage body,10mm thick 5-2.5mm Asterisk plate could achieve uniformity at the earliest,so that the heat storage body can obtain an effective heat storage distance.Selected the combination of cross plate and porous plate,explored the optimal placement distance between them,and calculated the air distribution under this optimal condition,so as to compare the performance of Asterisk plate and existing composite plate.The results showed that when the distance between the cross plate and the porous plate was 7mm,the flow field optimization effect was the best.But there was still a large gap between the combined plates and the Asterisk plate,with a difference of about 5cm to achieve a similar uniformity.Similar results also appeared in the flow reversal system.Moreover,the impact of air flow opposition caused by commutation increases the optimal length of both by 1～2cm.Based on the above digital simulation optimization results,in order to effectively test the air flow movement and flow rate in the system and verify the reliability of the digital simulation results,a physical simulation device is built in the research,and the test of practical application effect is carried out.The inlet and outlet conditions consistent with the mathematical model was maintained in the physical model research.The air velocity distribution at each point in the main pipe section was measured every 5cm by anemometer and compared with the numerical simulation results.The results showed that the data fluctuation of physical model was stronger than that of digital model,but their laws and trends were consistent.It could be seen that the results of digital model are credible.To sum up,the optimization of Asterisk plate had application value for practical industrial production.Based on the simulation results of cold flow field,this topic explores the distribution of temperature field of the system under heating conditions.On the premise that the flow in the main pipe section has been optimized to be uniform,the gradually expanding and shrinking pipe sections on both sides are removed,and only the main pipe section is modeled 1:1.The temperature field distribution in the system furnace and the factors affecting the furnace temperature were analyzed by simulating the system under the condition of hot heating.The temperature field distribution under the conditions of pipe wall insulation,natural heat dissipation and wrapped with insulating cotton were calculated,and heat accumulators were added on both sides of the catalytic area in the pipe to calculate the heat storage effect.Considering the application of flow reversal technology,the effects of unilateral heat source and bilateral heat source on the temperature rise were calculated for the above models under different conditions.The experimental results showed that the temperature difference in the furnace was about 50℃under heat dissipation conditions and adiabatic conditions.It could be seen that the wall heat dissipation could not be ignored in the process of numerical simulation calculation.The thermal insulation effect of thermal insulation cotton was very significant.The temperature in the pipe increased by about 20～25℃.The regenerator also had a certain effect.The furnace temperature increased by 5～15℃under different wall conditions.Considering heat dissipation,the primary heating could not reach the complete combustion temperature of toluene catalytic combustion.After secondary heating,it exceeded the burnout temperature of catalytic combustion,but did not reach the temperature required for thermal combustion.In the flow reversal system,the heat could be effectively accumulated in the catalytic area and achieve the desired heating effect.It had the significance of energy conservation and emission reduction and had high industrial application value.