Analysis And Health Risk Assessment Of Typical Halogenated Organics Treated By Regenerative Thermal Oxidizer(RTO)

With the continuous strengthening of ecological civilization construction,the treatment of volatile organic compounds in China is becoming more and more strict.Halogenated organic compounds are a kind of difficult to deal with organic pollutants.Halogenated polycyclic aromatic hydrocarbons and dioxins are harmful and have a long half-life.Long term exposure to halogenated organic compounds will pose a serious threat to human health.As one of the efficient treatment equipment of organic waste gas,regenerative oxidation furnace(RTO)shows outstanding advantages,but there are also some problems in the treatment of halogenated organic waste gas,such as defective component design and unreasonable valve switching frequency,which not only affect the treatment effect,but also may cause serious damage to the environment.Therefore,it is of great practical significance to study the simulation of RTO equipment and treated waste gas emission.In this paper,the three chamber RTO is selected as the research object.Through the experiment with CFD simulation software,the internal structure of RTO and different operating conditions are compared and analyzed.It is found that some structures will lead to turbulence,uneven local heating and insufficient gas combustion,resulting in serious secondary pollution.In this study,the structure of RTO is optimized and improved,and the optimal working conditions of RTO are determined by comparing different purging cycles and operating conditions of RTO.In order to explore the impact of the application of RTO in the actual industry on the emission of pollutants in the environment,eight enterprises in the coating industry were selected to analyze the actual emission data,carry out AERMOD diffusion simulation and health risk assessment,and deeply understand the factors affecting the emission in the actual emission process and the actual impact of the pollutants discharged by RTO on the environment.The innovation of this subject is mainly reflected in the multi-faceted analysis of pollutants from treatment process to emission diffusion with the simulation software help of CFD and software of AERMOD.The exploration and optimization of key parts of RTO equipment,and the improvement of equipment with the help of theoretical analysis;We carry out human health risk assessment on the waste gas treated by RTO,and provide relevant suggestions for the environmental protection management department in the layout and application of RTO.After careful and careful exploration,the following conclusions are obtained:1.During the simulation test of RTO,the simulation test of flow rate,pressure and other parameters of waste gas entering RTO equipment shall be carried out.It is found that the upper cavity of the air inlet is too narrow and the bending angle of the combustion chamber wall is unreasonable,resulting in obvious vortex and prolongation of the residence time of the exhaust gas.After the improvement of the equipment structure,the vortex phenomenon and prolongation of the residence time of the exhaust gas are improved.At the same time,it is found that the three cycles of RTO operation have different effects on waste gas treatment.It is further found that the different proportion of intake air at the purge side to intake air at the intake side also has an impact on the waste gas treatment capacity of RTO.Through the comparison of different schemes,the scheme C of increasing the cavity above the inlet and the scheme of cutting corners at both ends of the combustion chamber are determined α for the optimal combination,it can effectively reduce the generation of turbulence and greatly reduce the time of dioxin generation environment in theory.The three different operating cycles of RTO have different effects on waste gas treatment.The third cycle is the best,and the second cycle is better than the first cycle.There will be a sudden temperature drop area in the second cycle and the first cycle,which may lead to the production of dioxins.It is necessary to adjust the working hours of three different cycles in terms of valve switching frequency,and explore the impact of different air intake at different purge sides.It is found that when the air intake at purge side accounts for 10% of the air intake at inlet side,the low-temperature area and vortex area are the least.2.The AERMOD atmospheric diffusion model is used to analyze and simulate the measured values of RTO waste gas emission from 8 factories involved in the coating industry.It is found that some factories produce new halogenated organics in RTO operation.In the AERMOD simulation process,we founded that the diffusion direction of the dye agrees well with the opposite direction of the wind frequency,indicating that the simulation value is effective.Among the 8 plants selected in this study,5 plants include A,B,C,E and H have detected the emission of dioxins at the RTO outlet,and other halogenated organic pollutants other than dioxins have been generated in the process of waste gas treatment,such as carbon tetrachloride,dichloroethylene,etc.It shows that there are some problems in RTO operation in actual production,which should be further explored on the spot.Based on the analysis of meteorological data,it is determined that the dominant wind direction in Shanghai is northeast wind and southeast wind.Further analysis of the diffusion of air pollutants shows that the diffusion direction of pollutants agrees well with the opposite direction of wind frequency,indicating that the simulation value is effective.3.According to the data analyzed by AERMOD diffusion model,the health risk of residents in the study area is calculated and evaluated.The health risk characterization ratios with threshold health hazard effects of RTO pollutants are less than 1,and no unreasonable health risks are found.It is found that dichloromethane and tetrachloroethylene have possible cancer risk,and carbon tetrachloride has very possible cancer risk.The noncarcinogenic risk of dichloromethane,carbon tetrachloride,tetrachloroethylene and dioxin pollutants are less than 1,so it is considered that there is no non carcinogenic risk to human body.It is suggested that the monitoring and control of dichloromethane,carbon tetrachloride and tetrachloroethylene should be strengthened in the future.Through RTO simulation experiment and optimization,diffusion simulation and health risk assessment of RTO waste gas,it is considered that RTO treatment of halogenated organic waste gas is technically feasible,but there are still some risks due to design and working conditions.Put forward suggestions to the environmental protection management department and the industrial park on the use and management of RTO.