Study Of Muti-Needle-to-Plate Corona Discharge And DeNO_x Using Plasma And Photocatalysis Coupling

In this thesis, the distance of the discharge electrode for multi-needle-to-plate dc corona discharge has been optimized. The voltage-current relationship has been been modified and re-deduced. The microscopic characteristics of corona discharge are studied using optical emission spectrometry. Corona discharge is used to remove NO_x coupling with TiO₂ photocatalyzer and a kind of MnO_x photocatalyzer, and the removal mechanism is analysised preliminarily.Firstly, the definition and classification of corona discharge is given in introduction. The application status of various corona discharges in environmental pollutuion control is overviewed, and their advantages and disadvantages are pointed out. Then the research progress of plasma diagnostics using optical emission spectrophy (OES) is overviewed and it is safely to say that the study of needle-to-point dc corona discharge using OES has not yet been developed, the microscopic characteristics of needle-to-point dc corona discharge need to be further studied. The pollution status of low concentration NO_x is emphatically overviewed. The harm of low concentration NO_x is thought to be concealed and persistent. Furthermore, since the wide existence of low concentration NO_x cause great difficulty in its preventing, it is imperative to develop the removal research. Finally, the denitration status using plasma and catalytic methods are overviewed respectively and it is found out that these two methods are characterized by various defects when singly applied. Based on the above investigation, it is believed that making them coupling is the development direction of denitration in future. Thus a method using muti-needle-to-plate corona discharge, TiO₂ and MnO_x coupling to remove low concentration NO_x is proposed accordingly.The effects of the distances of needle-to-plate d_NP and those of needle-to-needle d_NN on point-to-plate dc corona discharge are investigated to achieve the greatest discharge power density and also the best discharge stability. The optimal distances of d_NP and d_NN are determined as 20-30mm and 20mm respectively. Then the optimal structure of discharge reactor is designed accordingly. The voltage-current relationship is deduced as c=I/U(U-U_s) approximately, and the voltage-current characteristics in optimal discharge reactor structure are detected. c-U curves are obtained according to U and I, and the discharge stages are distinguished from the shape of c-U curve. The effect of needlepoint radiusαon voltage-current characteristics is investigated, and find out that only whenαis let to be 1mm, the calculateion value of c is in agreement with the value in c-U curve smooth stage. Using U_c to replace U_s, the voltage-current relationship of point-to-plate corona discharge ismodified to be I≈(?). In respect of both discharge power densityand the discharge stability comprehensively, the optimal value ofαis decided to be less than 1mm. At last, the effects of RH on voltage-current characteristics and discharge stability are investigated.The emission of N₂ in discharge gap is detected using optical emission spectrophy. The discharge reactor was put in lightproof box to avoid the disturbance from outside lights. A small hole was drilled in one sidewall of the box, and the fibre was mounted coupling to the inlet (1mm) into the hole. A tube with the inner diameter of 1.1mm was set in the front of the hole. In this way, only the light from a certain direction emitted from the discharge reactor could transfer into the inlet through the tube. The reactor could be moved in the vertical direction of the fibre, and the spectrometry can collect the total emission along the fibre inlet in single-shot measurement. The spectral intensity at every point around needlepoint is obtained by subtracting the sum of emission at outer layer from the sum at inner layer, and the morphology of ionization region is determined. The analysis result shows that the number of energetic electron n_e is near liner to spectral intensity, so the distribution of energetic electron is determined.The sum intensity (?) of N₂ second positive band peak I_SPB in ionization region is found to be liner to I approximately, and the numerical relations between (?) and n_e is determined through calculating. Then a method for measuring n_e through detectingI_SPB in ionization region is presented.Use micro-arc discharge to prepare TiO₂ photocatalyzer. By this method, TiO₂ preparation and laden are fulfilled in one step, and TiO₂ are of nano particle size and fine mechanical strength. Using this TiO₂ plate as ground electrode to obtain one kind method for corona discharge and photocatalysis coupling (PPC), and PPC is applied to remove low concentration NO_x. The removal effect of NO_x by PPC is compared with that by corona discharge alone, and the influences of discharge polarity and discharge power to the plasma-photocatalysis synergistic effect are also investigated. The result shows that PPC still has relative higher energy efficiency when discharge power is high, which resolves the problem of lower energy efficiency in DeNO_x using plasma method. The production principle and mechanism of NO_x by positive corona discharge is analyzed, and it is found that positive corona discharge can produce NO₂, so PPC cannot remove NO₂ completely.MnO_x catalytic gauze is installed behind the PPC device, which hopes to remove NO₂ completely. MnO_x is supported by silicon-aluminium molecular sieve and doped with transition metals such as Fe. Removal effect and service life of MnO_x on NO₂ is detected. MnO_x catalytic gauzes are analyzed using BET,SEM and IR before and after treatment. The result shows that the specific surface area, total pore volume and average pore size of MnO_x reduce dramatically, and the infrared absorption band of N-O enhances. The removal mechanism of NO₂ using MnO_x catalyzer is preliminarily believed as absorption-catalysis process.