Mechanism Of Back Corona And Anticoagulation In Electrostatic Precipitator

The gas produced by industry production is contained any dust which can cause harm for both human and environment, Therefore it's very necessary to purify the gas. The electrostatic precipitator is far-ranging used to purify the gas because of high efficiency,strong adjustability and so on. But, so far the problem that the gas is contained high resistivity dust has not been solved commendably. The purpose of this paper is to make an investigation on the mechanism of back corona to effectively collect high resistivity dust. Firstly the electric field distribution between the wire-plate electrode,the wire-cylinder electrode ,the barbed nail corona electrode and the collection electrode is discussed in the paper. Then the physical characteristic of dust layer on the collection electrode is investigated, including the factor affected the resistivity of dust layer and the form,distribution of the surface voltage. The result shows that the resistivity of dust layer take on definite rule when the composition of the dust layer,the chemic component of dust,the thickness and the morphology of the dust layer alter ,and the curve of the distribution of the surface voltage looks like the shape of hump. All this is necessarily ready for farther investigating the mechanism of back corona. When the additional electric field intensity caused by the high resistivity dust layer on the collection electrode is stronger than the electric field intensity of the aerial gap sparked in dust layer, back corona is broken. 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. Used the mathematical models of the charges and the additional electric field in the changed dust layer, and ignored the re-entrainment caused by air flow, Based on the analysis of the coagulation and anticoagulation forces we yield that the critical dust layer thickness thereafter the particle re-entrainment could occur is inverse proportional to the square root of the corona current density and the dust resistivity. Our theoretical results have also shown that the critical dust layer thickness is about 10²0mm when the dust resistivity is in the range of 5×10¹¹ï½ž1×10¹³Î©Â·cm if the particle re-entrainment caused by the aerodynamic effect is neglected in the wire-plate electrostatic precipitators. Finally, The differential equation is can be established to obtain the adhesive force on the collection electrode. Therefore, a theoretical formula used to calculate the rapping acceleration is derived in accordance with the Newton's second law. This result shows that the rapping acceleration is the function of the product of the dust resistivity ρ and the corona current density J, and is inverse proportional to the particle diameter. If the voltage is keeping unchangeable, however, the product of the dust resistivity and the current density, ρ×J, is constant according to the published experimental data and the theoretical values. In this case, the rapping acceleration is independent of ρ×J. From this new point of view, a critical rapping acceleration equation can be given based on the correlation curve of ρ and J presented by Oglesby. According to this equation a simple graphical method is also proposed to determine the critical rapping acceleration.