Theoretical And Experimental Investigation Of Electrostatic Precipitator With Stagger Plate-electrodes For High Resistivity Dust Collection

Electrostatic precipitation (ESP) is an air cleaning equipment widely used in collecting dust contamination. ESP collection performance, closely relates to its operating condition. Especially, resistivity of dust is one of important causes affecting ESP collection efficiency. If resistivity of dust is too high or too low, ESP collection efficiency will be able to reduce. Nowadays, the methods and techniques to increase ESP collecting efficiency of high resistivity dust includes ①ameliorating ESP structures and electrode configuration, ②wetting or dropping temperature to reduce resistivity of dust in ESP, ③developing new power supply to provide steady electric field. Based on ameliorating structures and electrode configuration to increase ESP collecting efficiency of high resistivity dust, the paper studied collection performance of ESP―new type high efficiency high resistivity dust ESP with one pair of auxiliary electrodes and alternate collecting plates. The study includes: deducing electric field intensity of the new type ESP between corona electrode and collection electrode, studying dust charging and movement of charged dust in collecting, measuring the new type ESP collection efficiency, analyzing V-I characteristic, determining the relation of the dust layer thickness at the back corona spark point, the rapping periodicity and the working current and so on. To premise electric intensity is normal distribution, electric field distribution of wire-plate ESP is deduced. Electric field intensity of the new type ESP considered as the superposition of electric intensity with wire-plate electrode ESP and plate-plate electrode ESP. To compare with regular wire-plate ESP, the new type ESP enhances the electric field intensity and makes it more uniform. Based on simulating and analyzing gas-solid two phase flow in experimental set-up, the flow field of the new type ESP is uniform. Before setting up the experiment, we analyzed the collection mechanism of the new type ESP and deduced efficiency formula based on turbulent diffusion model. Then V-I characteristics and dust removal efficiency were studied in laboratory research. and boiler dust ( ρ≈0.5×1012??cm at ordinary temperatures) is used in the experiment. The study obtained different V-I characteristics and efficiencies through altering the corona wires quantity and adjusting the interval between corona wires and auxiliary electrode plates. The results of study show, dust removal efficiency of the new type ESP is higher than regular ESP, especially prominent when the interval between auxiliary electrode plates is wider. So, in actual application,choosing proper interval between corona wires and auxiliary electrode plates founding on V-I characteristics make the new type ESP not only better restrain back corona but obtain higher collection efficiency. The charges in the high resistivity dust layer on the collection electrode in the electrostatic precipitator can be accumulated due to the poor dust conductivity when the corona current flows through this layer. In this case, an additional electric field in the dust layer can be built up by these accumulated charges. The mathematical models of the charges and the additional electric field in the changed dust layer are developed by the electrostatics. The change distribution and the additional electric field strength distribution are both proportional to the square of the dust layer thickness. A formula for calculating the charged dust layer thickness at the back corona spark point is then obtained in accordance with the condition equation of the back corona breakdown field strength. The theoretical result indicates that the dust layer thickness at the back corona spark point is the function of the corona current density and the dust resistivity, and as well as the structure dimensions of the electrodes of ESP. A principle that the connection line of the back corona spark points is perpendicular to the curves of the voltage-current characteristics is discovered. From this feature, a new and simple graphical method is proposed to determine the dust layer thickness at the back corona spark point. Therefore, the rapping periodicity and the working current could be selected reasonably by the theoretical and experimental methods in this paper.