Collection Mechanism And Application Technology Of Electrostatic Preciptitation With Bipolar Barb Electrodes

The technical problem of the high-efficient collection for high resistivity fine dust (p> 1011Ω·m) has not been well solved in electrostatic precipitation till now. In order to solve this problem, a bipolar ESP is developed. In this bipolar ESP, barbs are fixed on the high voltage plate and ground plate respectively. The high voltage barbs and the ground barbs are arranged alternatively to prevent short-circuit. Most of the charges emitted by high voltage barbs and a part of charges deposited on the dust layer will go to through the ground plate electrode directly. In this case, few charges would be accumulated in the dust layer on the ground plate electrode. The back corona of the high resistivity dust layer can then be avoided. Furthermore, bipolar charges can be produced just by one high voltage supplier. The charged particles agglomeration will be enhanced due to these bipolar charges in ESP. Therefore, the collection efficiency for high resistivity fine particles is increased.Collection mechanism and application technology of electrostatic precipitation with bipolar barb electrodes is investigated by theoretical analysis, bench scale experiment and industrial pilot experiment.The more uniform the current density is, the more efficient the dust collection and back corona restriction. The experimental results show that the current density distribution on the plane of single barb to plate electrode is t-distribution with 4 degree of freedom. The t-distribution law is not influenced by the variation of applied voltage and the distance between the barb and plate electrode. In the ESP proposed in this thesis, multi-barbs are fixed on both the high voltage plane and the ground plane uniformly. In this case, both the influence of the interaction between two adjacent barbs on the current density distribution and the influence of the interaction between the back plate and the barb fixed on it on the current density distribution must be condsiderd. The current distribution of single barb to plate electrode, single barb plate to plate, two barbs to plate and two barbs plate to plate electrode is measured respectively. The results indicate that the corona current is restricted simultaneously by both the barb nearby and back plate for two barbs plate to plate electrode which is used in the bipolar ESP proposed by this thesis. The results indicate that either the metal back plate or the adjacent barb can limit the current. The corona current is restricted simulataneously by both the barb nearby and the back plate for two barbs plate to plate electrode. Based on the experimental data, the most optimized range of the distance between adjacent barb row is 4cm-6cm. In this range, current density distribution is more uniform and the max total current can be obetained.According to Gaussian theorem, the normal distribution theory of electric field strength distribution of wire-plate electrode is extended to barb to plate electrode. The theoretial of normal distribution of single barb to plate electrode is derived by using the characteristic of current density distribution between electrodes when the surface of the collecting electrode is taken as the boundary condition. The regularity of electric field distribution of the ESP with bipolar barbs is found by the superposition of the expression of single barb at different position.The results of the discharge experiment show when the applied voltage is above 30kV, the bipolar ESP has 2 times greater corona current than other ESPs. The highest ionic wind velocity measured by Particle Image Velocimetry (PIV) can reach above 2m/s when the electric field strength is about 3.5kV. Both Particle agglomeration and deposition are all enhanced due to the intense ionic wind.In industrial application, ESP is commonly composed of multiple electric fields. Therefore, industrial ESP should be considered as dust collectors in series. The relation between overall efficiency and fractional efficiency of dust collectors in series is discussed. A calculation model for overall efficiency is established by using fractional efficiencies. For a system with two collectors in series, based on the exponential distribution of fractional efficiency, a method is presented to calculate the fractional efficiency of one collector when the fractional efficiency of another collector is given. The problem of efficiency distribution between pre-collecting zone and agglomeration collecting zone is solved. Based on the theoretical investigation and the bench scale experimental study, a plan of the two-electric-field, three-zone ESP to collect industrial high resitivity fine dust is finally suggested. Furthermore, the feasibility for industrial application of the ESP with bipolar barbs is confirmed by the pilot experiment.