Effect Of Charge Accumulation Restraining In Electrostatic Enhanced Fabric Filtration Based On Bipolar Charging Method

Electrostatic enhancement fabric filters,which can be operated with low emission,reliable operation and energy saving,are widely used in the purification of dust pollutants in industrial flue gas.However,the dust discharging methods are unipolar in most of the conventional electrostatic enhancement fabric filters.It has been found in practice that unipolar charged particles in electrostatic enhancement fabric filters may cause the problem of the dust cleaning difficulty and the bag burning risk due to the charge accumulation on the fabrics.Therefore,the bipolar charged particles are introduced into the electrostatic enhancement fabric filter in this study.In order to improve the performance of the electrostatic enhancement fabric filter,it is necessary to discuss the electric field distribution,electrode optimization,electro-hydro dynamics(EHD)simulation of the precharger,the charge accumulation reduction effect,and the agglomeration phenomenon of the bipolar charged particles deposited on the filter material.The main contents are as follows:(1)Firstly,the electrode configuration and the bipolar charging principle of the wire-tube bipolar precharger are analyzed.According to Gauss flux theorem and superposition law,the theoretical normal expressions of electric field strength distribution of the wire-tube electrodes are derived.The wire-tube bipolar precharger can realize bipolar discharging with only one power supply.And the tube electrode which is light in weight,and easy to be manufactured is conducive to the mixing of positive and negative charged particles,and not easy to be deformed.(2)The corona discharging characteristics are significant to the performance of the precharger.Therefore,the electrodes of the wire-tube bipolar precharger are optimized experimentally based on corona current maximization.When the RS barbed wire and the stainless steel tube are used as precharger electrodes,the optimal electrode configuration of the bipolar precharger is that the tube electrode diameter,the span of the tubes,and the distance between wire electrodes and tube electrodes are 25 mm,120 mm,and 80 mm respectively.(3)In order to clarify the interaction among potential distribution,space current density and velocity field distribution in the precharger,electro-hydro dynamics(EHD)simulation of the precharger is carried out.The results show that space charge density plays a dominant role in the distribution of electric potential and electric field.Especially near the corona wire,the electric potential changes rapidly,which is conducive to the generation of non-uniform electric field.Compared with the unipolar precharger,the gas velocity of the bipolar precharger fluctuates greatly in the airflow direction.Strong turbulent disturbance promotes the transport of electric ions to improve the effect of electrostatic enhanced dust removal.(4)In order to verify the effects of charge accumulation restraining and agglomeration of bipolar charged particles on the filter material,the comparative experimental study on unipolar charging method and bipolar charging method is carried out based on the optimized precharger.The results show that the current produced by charge accumulation of bipolar charged particles on the filter material is about 25% lower than that of unipolar charged particles on the filter material under the same conditions.With the increase of gas velocity,the cumulative charge on the filter material under bipolar charging increases,while the cumulative charge on the filter material under unipolar charging change little.This means that the charge accumulation on the filter material can be restrained when the bipolar discharging method is used.Finally,based on SEM analysis,it is shown that the agglomeration of the fine particles is significant when the bipolar charging method is used in the electrostatic enhancement fabric filter.