Studies On SF₆ Degradation By Atmospheric Dielectric Barrier Discharge Plasma And Its Combination With Catalysts

SF6 is a synthetic gas.Due to its excellent electrical properties,arc extinguishing performance and unique physical and chemical properties,it has been widely used in electrical power,metal smelting and semiconductor manufacturing industries.Accordingly,the huge use of SF6 leads to the increase in the SF6 exhaust gas emission,which makes the concentration of SF6 in the atmosphere increase sharply.However,SF6 is an extremely strong greenhouse gas.Its global warming potential value is 23900 times that of CO2 in a horizon of 100 years,and it is very stable and has a long atmospheric life span of about 3200 years.In order to mitigate threats of the greenhouse effect to global climate,it is very necessary to control the emission of SF6.The removal of SF6 is an effective means to reduce SF6 emissions.Dielectric barrier discharge(DBD)plasma technology can produce a large number of high-energy electrons and various active particles to achieve the degradation of SF6 at room temperature.However,the destruction and removal efficiency and energy yield for SF6DBD degradation need to be improved,and toxic and harmful products may be produced in the degradation process.Therefore,this paper focuses on the degradation characteristics of SF6,the influence rule and the influence mechanism of experimental parameters,the formation path of SF6 products,the synergistic effect of dielectric barrier discharge and catalysts in SF6 removal process.The main research work and the results are shown as follows:(1)Many SF6 degradation experiments were conducted on the dielectric barrier discharge experimental platform.The SF6 destruction and removal efficiency under different reduced electric field,background gas,gas flow rate,additional gas and ambient medium was obtained.Based on the discharge characteristics and related electronic parameters,the influence mechanism of the above experimental parameters on the SF6 degradation was analyzed.Research shows that:the increase of the reduced electric field in the discharge area promotes SF6 removal,and the reduced electric field of the reactor should be improved as much as possible on the premise of meeting the manufacturing process;compared with He,N2 and air,Ar is superior as the background gas;under the same specific energy density,increasing gas flow rate in a certain range can improve the SF6 destruction and removal efficiency;among different additional gas,0.5%of the water is the most effective when removing SF6,followed by a low concentration of oxygen;the reactor immersed in oil has a better degradation effect of SF6 than the reactor placed in the air.(2)The energy yield for SF6 degradation by DBD under different experimental parameters was calculated and analyzed.Results show that:the reduced electric field has little effect on energy yield;among different background gases,the energy yield is the highest when Ar is used as the background gas;the energy yield can reach more than13g/kWh with flowing feed gas,which is much larger than that with stationary feed gas,and lower gas flow rate leads to lower energy yield;among different additional gas,energy yield is the highest when moisture is added,followed by a low concentration of oxygen;the energy yield of the reactor immersed in oil is higher than that of a reactor placed in the air.The energy yield of DBD degradation of SF6 is between9.56×10~4~3.11×10~5gCO2e/kWh,which is much greater than the CO2 emission intensity of power generation and consumption(950gCO2e/kWh).It shows that the degradation of SF6 by DBD can effectively reduce the emission of greenhouse gases.(3)In order to figure out the SF6 degradation mechanism and the pathways of products under DBD,the dissociation of SF6 was calculated by molecular dynamics simulation,the emission optical spectroscopy was used to detect active particles in plasma discharge,and the Fourier transform infrared spectroscopy and gas chromatography mass spectroscopy were used to detect degradation products of SF6.Based on detection results,the generation pathways of SF6 products were analyzed.The results show that:the products include SOF2,SOF4,SO2F2,SO2,SiF4,SF4 and S2F10when water or oxygen is added,and SiH4 is formed only when water is added;the dissociation of SF6 molecules is a key step in the degradation process,and the generated SFx is easy to react with OH or O radicals;the additional gas and the reaction path and its energy determine the proportion of degradation products;when water vapor is added,the selectivity of SOF4 and SO2 is high while the selectivity of SOF4 and SO2F2 is high when oxygen is added.These degradation products of SF6 can be absorbed by alkali solution.In order to achieve the harmless abatement of SF6 more conveniently,the SF6degradation products can be regulated by the selection of the additional gases and catalysts or the two-stage plasma system.(4)The dielectric barrier discharge plasma combined with?-Al2O3 catalyst was used to remove SF6.The discharge characteristics of the plasma catalysis system was analyzed,and the catalysts were characterized before and after use.By comparing the destruction and removal efficiency of SF6 and energy yield,the effects of different additional gas and catalyst mass on SF6 degradation were studied.The results show that:the DBD with catalytic technology for SF6 abatement shows obvious synergistic effect both under water vapor and oxygen conditions,and the combined degradation technology improves the degradation efficiency of SF6 and energy yield;but when the catalyst mass is too large,it weakens the micro discharge in plasma,affecting the dissociation of SF6 and decreasing degradation efficiency and energy yield.When the DBD plasma is combined with catalyst,the amount of catalyst should be selected properly.In SF6 degradation process,?-Al2O3 directly participates in the degradation reaction.