Characteristics Of Corona Discharge In Electrostatic Precipitator And Optimal Design

With the continuous improvement of industry,air pollution which is getting worse has become a social problem which can not be ignored.Electrostatic precipitator(ESP)is one of the most effective equipments based on high-voltage corona discharge for removing dust.With its unique advantages,ESP occupies the market share of the main application of dust removal equipments.The process of charging,transport and settlement dust particles inside is the core process,and the gas ionization based on corona discharge is the basis,and the power source is the only energy source for ESP.Therefore,the research on the problems above has important guiding significance for improving the efficiency of ESP equipments.In this paper,focusing on the basic physical problems of high-voltage corona discharge in electrostatic precipitator,all the research is carried out,including the following parts:Firstly,from the view of microscopic particles movement,the state and kinetic equation of dust particles are established and the state of charging,transport and settlement of dust particles is analyzed.The results show that according to the difference of dust particle radius,there are electrical field charging mechanism and diffusion charging mechanism.No matter what kind of charging mechanism takes effect,there is a saturation value for the charge of a dust particle.Under the electrical charging mechanism,the charge of a dust particle is proportional to electric field and radius of the dust particle.Under the diffusion charging mechanism,the charge of a dust particle is proportional to temperature and radius of the dust particle.It is given theoretically that the transport equation of a charged dust particle in the electric field and the reasonable boundary conditions.The force condition of charged particles is analyzed from the view of mechanics,and the relationship between the thickness of dust and the voltage drop and the expression of strength of superimposed electric field in the discharge area are given,which provides some theoretical guidance for improving the efficiency of electrostatic precipitator.Secondly,focusing on the typical discharge structure in Electrostatic precipitator,the characteristics of needle-plate and line-plate negative corona discharge are studied experimentally.Using the Trichel pulse as the basic element,the probability distribution of pulse parameters is analyzed with statistical method.It is found out that there is a mode transition of Trichel pulse during the period of voltage rising,which is from large-amplitude-pulse discharge to small-amplitude-pulse discharge.Based on the the basic principle of gas discharge,the reason is that with voltage increasing,the main factor for the discharge process changes.During the period of large-amplitude-pulse discharge,the main factor for Trichel pulse discharge is the establishment of the discharge channels.During the period of small-amplitude-pulse discharge,the main factor for Trichel pulse discharge is the accumulation and dissipation of anion clouds in discharge area.As the expansion of needle-plate negative corona discharge,the characteristics of line-plate negative corona discharge are studied.By comparing the probability distribution of current pulses of the two discharge structures,it is inferred that line-plate negative corona discharge can be equivalent to the superposition of needle-plate negative corona discharge in different modes,which can explained theoretically the features of randomness and probability distribution of line-plate negative corona discharge.It is of great significance to study line-plate negative corona discharge in the future.Thirdly,considering the diversity of working environment of ESP,the influence of environmental on the parameters of pulses is studied,including temperature,humidity,airflow direction and velocity,dust particles.With the simulation of negative ion distribution in discharge zone by COMSOL,the physical mechanism of the experimental results is given.The experimental results show that with temperature rising,the inception voltage of negative corona discharge reduces,and the average current is bigger under the same voltage,meanwhile the amplitudes and frequency of pulses becomes larger.With the humidity rising,the inception voltage of negative corona discharge becomes lower,and the average current and the frequency of pulses is lower under the same voltage,meanwhile the amplitudes of pulses become larger.Different airflow directions have different effects on the negative corona discharge intensity.When the direction of airflow is perpendicular to the direction of electric field,the discharge intensity is almost unaffected.However,as the velocity of airflow rising,the amplitudes of pulses and the time between pulses becomes larger.When the direction of airflow is as the same as the direction of electric field,the discharge intensity is weakened,and as the velocity of airflow rising,the amplitudes of pulses and the time between pulses becomes larger.When the direction of airflow is opposite to the direction of the electric field,the discharge intensity is enhanced,and as the velocity of airflow rising,the amplitudes of pulses and frequency of pulses becomes larger.With the densities of dust particles increasing,the inception voltage of negative corona discharge reduces,and the average current is lower under the same voltage,meanwhile the amplitudes and frequency of pulses becomes lower.With the analysis of the distribution of negative ions in the discharge area under the different condition using COMSOL,it is found out that negative ions play an important role in Trichel pulse discharge.Temperature,humidity and dust particles affect the negative ion density and velocity of negative ion cloud,and the airflow affects the trajectory and the distribution of negative ion cloud in the discharge area.Fourthly,based on the analysis of the coupling relationship of all the influencing factors of ESP,the method of optimizing the efficiency and stability of electrostatic precipitator by optimizing high-frequency high-voltage power supply control system is put forward.Based on characteristics of the needle-plate and line-plate discharge,electrostatic precipitator high-frequency high-voltage power supply main circuit topology is designed with the design method of resonant circuit to solve the problem of complication of the distribution parameters of high-frequency high-voltage transformer and the optimization design method of high-frequency high-voltage transformer to solve heat and insulation problems.Based on the analysis of the working process of electrostatic precipitator,a control method of rising voltage based on the numbers of spark discharge per unit time is proposed.Finally,High-frequency high-voltage power supply prototype is designed with the rated power of 30 k W,the maximum output voltage of-75 k V and the maximum output current of 400 m A.By comparing the other types of power supply,the results show that the power supply designed in this paper can improve the electrostatic dust removal efficiency and provide some references for the future electrostatic precipitator optimization.