【作者】 宿鹏浩；

【导师】 朱益民；

【作者基本信息】 大连海事大学 ， 环境科学， 2008， 博士

【摘要】 本论文对针-板式直流电晕放电电极间距进行优化，修正推导伏安关系式，并使用光学发射光谱进行电晕放电微观特性研究；将电晕放电与TiO₂光催化剂以及一种MnO_x催化剂耦合协同作用去除NO_x，并初步分析了去除机理。绪论中首先给出了电晕放电定义、分类，综述了各类电晕放电在环境污染治理中的应用现状，并指出它们的优点和缺点。然后对光学发射光谱法OES诊断等离子体研究进展进行了综述，认为目前国内外用OES法对针板式直流电晕放电的研究尚未开展，针板式直流电晕放电的微观特性需深入研究。接着着重对低浓度NO_x的危害和污染现状进行了综述，得出低浓度NO_x危害隐蔽而持久，更为广泛且难以防范，开展对低浓度NO_x去除的研究工作势在必行。最后对等离子体法和催化法脱硝现状进行了综述，认为两种方法在脱硝过程中存在诸多缺陷，指出将二者结合共同作用是脱硝的未来发展方向，提出用针阵列对板电晕放电、纳米TiO₂和MnO_x三者协同作用去除低浓度NO_x。以放电功率密度大小为判据，兼顾放电稳定性，分别考察针板间距d_NP和相邻针尖间距d_NN对针-板式直流电晕放电的影响，确定最佳相邻针尖间距约为20mm，最佳针板间距为20-30mm，以此为根据设计出优化的放电反应器结构。近似推出针对板直流电晕放电伏安关系式为c=I/U（U-U_s），测量最优电极结构下电晕放电的伏安特性，根据测得的U、I值作出c-U曲线，以c-U曲线形状为判据区分放电阶段。考察针尖半径α对伏安特性的影响，发现只有当α约为1mm时实验曲线c-U中平滑段c值与计算结果相吻合，用U_c代替伏安关系式中的U_s，修正推导得到针-板式电晕放电伏安关系式为，I≈（?）。综合考虑放电区能量密度和放电稳定性，得到最佳针尖半径为小于等于lmm。最后考察了相对湿度对伏安特性和放电稳定性的影响。利用光学发射光谱仪对多针对板电晕放电中放电间隙内的N₂发射光谱进行测量，放电反应器置于暗箱中以避免外界对光谱测量的影响，将光谱仪的光纤耦合入口固定在暗箱侧壁的小孔内，小孔孔径为光纤耦合入口直径（为lmm），在小孔前方安装孔径为1．1mm的细直管，只采集与光纤耦合入口在同一直线上的发光，避免放电区其它区域的发光被同时接收。反应器可上下和左右移动，发射光谱单次测量可得到光纤耦合入口所在直线上的光强之和。用内层光强之和减去外层光强之和，得到针尖周围各点处光谱强度，由此确定了电离区形貌。分析得到高能电子数n_e与光谱强度成正比，故电离区内高能电子分布被确定。N₂的第二正带跃迁发射光谱强度I_SPB在电离区内的总和（?）与放电电流近似成正比，计算确定了（?）与n_e之间的数值关系，提出一种通过测量电晕放电电离区内I_SPB的大小粗略测定n_e的方法。用微弧放电法制备和固定TiO₂，达到TiO₂制备和固定一次完成，得到的TiO₂粒径为纳米级，同时机械强度高。将制得的TiO₂作为地电极，实现电晕放电与光催化剂耦合PPC，共同作用去除较低浓度NO_x。将PPC对NO_x的去除效果与单纯使用电晕放电的去除效果进行比较，并考察了放电极性、放电功率对PPC去除NO_x效果的影响。PPC法脱硝在放电功率较高时仍具有较高的能量效率，解决了等离子体放电脱硝中放电功率高则能量效率低的问题。对正电晕放电产生NO_x的规律和机理进行了初步研究，认为电晕放电自身产生NO₂，故PPC无法完全脱除NO₂。将以硅铝分子筛为载体、掺杂Fe等过渡金属的MnO_X催化网安装在PPC装置后以完全去除NO₂，对MnO_x催化网对NO₂的去除效果和使用寿命进行了考察。对使用前后的MnO_x催化网进行线性扫描和红外光谱分析，得到使用后催化剂比表面积、总孔容和总孔面积明显减小，N-O键增多，初步分析认为NO₂被MnO_x催化网去除的机理为先吸附后发生催化反应为酸。更多还原

【Abstract】 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.更多还原