Study On NO Conversion In Industrial Silicon Furnace By Non-thermal Plasma

With the rapid development of Chinese economy,the energy consumption is increasing,the coal demand,as the main energy consumption in China,is also increasing.The combustion of coal produces a large number of atmospheric pollutants such as particulate matter,sulfur oxides,nitrogen oxides and heavy metals,which lead to the problem of haze.In 2019,China published the"Comprehensive treatment plan for air pollution of industrial furnaces".Attention has been paid to the problem of excessive emission of pollutants from industrial coal-fired furnaces.Among them,industrial silicon smelting is an important part of the industrial field.In recent years,its scale has expanded significantly,but its pollution treatment progress is slow,and the emission of dioxin,polycyclic aromatic hydrocarbons,particulate matter and other pollutants has been gradually controlled.However,the pollution of nitrogen oxides is becoming serious.Due to the high adhesion of particles,the traditional SCR technologies are difficult to be applied to the treatmet of industrial silicon flue gas.Non-thermal plasma technology can generate high-energy electrons and OH,O,N and other high active substances at room temperature.These substances have strong chemical reaction activity and can react with nitric oxides to convert them.Dielectric barrier discharge（DBD）technology is an excellent non-thermal plasma reactor with stable discharge and high concentration of radicals.Due to the complex reaction in the process of nitrogen oxide removal by DBD,the current investigation on DBD is basically in the semi quantitative research.The gas composition and oxygen content play a key role in NO oxidation,and the flue gas composition of industrial silicon submerged arc furnace is complex,and the working conditions are changeable,so the existing research results are not enough to support the application of DBD in industrial silicon smelting flue gas denitration.In this paper,the reaction path of NO conversion by non-thermal plasma was studied through experiments and theoretical analysis.In this paper,the reaction path of conversion of nitric oxide by dielectric barrier discharge was studied.The effects of SED（specific energy density）on the concentrations of NO,NO₂,N₂O and NO_x in different reaction systems were investigated.The results showed that for N₂/O₂ system,the high-energy electrons in the dielectric barrier discharge reaction region can dissociate N₂ and O₂ in the gas,generating active free radicals and react to produce NO,and part of NO was transformed into NO₂ and by-product N₂O.For Ar/O₂/NO and N₂/O₂/NO systems,the increase of SED will increase the temperature of dielectric barrier discharge reactor and inhibit the oxidation of NO,meanwhile,part of NO₂ will generate NO through backward reaction,so that the NO₂ concentration reached the highest value with the increase of SED and then decreases with the increase of SED.The variation of flue gas parameters will affect the utilization of radicals and the conversion of nitric oxide.In this paper,the effects of flue gas components such as flue gas temperature,gas residence time,initial concentration of NO,SO₂,water vapor and oxygen content on the conversion of nitric oxide by non-thermal plasma were investigated experimentally.The results showed that when SED is low,the generated NO₂concentration in the reaction system decreased with the increase of flue gas temperature.When SED was high,gas temperature had little effect on NO₂concentration in the reaction system.With the increase of gas residence time and SED,NO removal by dielectric barrier discharge can be divided into incomplete NO conversion zone,complete NO conversion zone and excessive NO generation zone.The changes of NO,NO₂,N₂O and NO_x concentrations under different initial NO concentrations showed that dielectric barrier discharge technology is suitable for flue gas with low NO concentration.SO₂ contained in flue gas will react with O radical to inhibit N₂ oxidation and backward reaction.When the flue gas contains water vapor,H₂O can react with high-energy electrons to generate OH and other highly oxidizing radicals to promote the oxidation of NO.The deposition of particles in industrial silicon furnace flue gas in dielectric barrier discharge reactor will affect the formation of radicals and the conversion of nitric oxide.In this paper,the effects of SED and oxygen content on the concentration of NO,NO₂,N₂O and NO_x in the conversion of nitric oxide by dielectric barrier discharge under particle deposition were investigated by experiments and characterization.The results showed that the deposition of particles in the discharge area of dielectric barrier discharge reactor will strengthen the generation of high-energy electrons and active substances,which is unfavorable for the conversion of NO.Based on experimental research and theoretical analysis,an artificial neural network model simulating the conversion of nitric oxide by dielectric barrier discharge was established and optimized.The relative weights of discharge power,flue gas residence time,oxygen content and initial concentration of NO on the concentrations of NO,NO₂,N₂O and NO_x were obtained.The results of NO conversion by dielectric barrier discharge under experimental conditions were predicted.The simulation results fit well with the experimental data,and the effects of multiple reaction parameters on the concentrations of NO,NO₂,N₂O and NO_x were predicted.