Study On The Effect Of Flue Gas Composition On The Discharge And Removal Efficiency Of Electrostatic Precipitator

With the rapid development of Chinese economy,the demand for energy is increasing.Because of the energy distribution pattern in China,coal has been dominant in China's energy structure for a long time.However,lots of PM produced by coal combustion caused serious pollution of Chinese air environment.Therefore,as one of the largest coal consumption industries in China,thermal power industry has always been an important target of energy conservation and emission reduction.Increasingly strict environmental protection standards put forward higher requirements for the emission of PM in thermal power generation.Exploring the influence of different flue gas components on the discharge and removal characteristics of electrostatic precipitator has great significance to further improve the efficiency of PM removal.In this paper,the influence of gas composition on the discharge volt-ammetric characteristics and discharge reaction of electrostatic precipitator was studied by methods of experiment and numerical simulation,and the influence of gas composition on the charge and removal efficiency of particles is discussed.First of all,The corona discharge model of simulated flue gas was established by COMSOL software,and the influence mechanism of the concentration changes of O₂,H₂O and CO₂ in flue gas on the negative corona discharge characteristics was analyzed.Results show that in the N₂/O₂discharge system,with the increasing of O₂ concentration,the electron number density decreases,and the O₂⁺ion number density is the highest among the positive ions,while the negative ion number density increases with the increasing of O₂,and the O₂^-ion number density is the highest.In the N₂/O₂/CO₂ system,with the increasing of CO₂ concentration,the electron density decreases,and the number density of CO₃^-and CO₄^-ions increases.In the system of N₂/O₂/CO₂/H₂O,when the concentration of CO₂ increases and the concentration of O₂ decreases,the number of electrons increases.When the relative humidity increases,the number of negative ion clusters in the space increases and the mobility of ions decreases.Temperature rise increases discharge current and space charge density.Then,the experimental system for volt ampere characteristics of electrostatic precipitator under simulated flue gas was set up.The volt ampere characteristics of electrostatic precipitator under different flue gas components were studied and compared with the numerical simulation results.Results show that when the concentration of CO₂increases and the concentration of O₂ decreases,the corona onset voltage increases,the current is negatively correlated with the concentration of CO₂ at low voltage,and positively at high voltage.When the relative humidity increases,the corona onset voltage decreases.The current is positively correlated with the relative humidity at low voltage and negatively at high voltage.Secondly,the influence of flue gas composition on the charge and motion characteristics of particles were studied by numerical simulation.The results show that the field charge,diffusion charge and total charge increase with the increase of particle size.However,when the particle size is small,the particle charge is mainly caused by diffusion charge,and when the particle size is large,the particle charge is mainly caused by field charge.The decreasing of O₂ concentration,the increasing of CO₂ concentration and relative humidity will increase the charge of particles,and the increase of charge will decrease with the increase of particle size,and the removal efficiency of particles will also be improved.With the increase of particle size,the particle removal efficiency decreases first and then increases.At the particle size of 0.4?m,it reaches the minimum value of removal efficiency,and the driving speed of particles to the dust collection plate also reaches the minimum value at 0.4?m.To some extent,thermophoresis improves the efficiency of particle removal.The greater the temperature difference between flue gas and wall,the greater the efficiency of particle removal;the effect of thermophoresis decreases with the increasing of particle size.Thirdly,an experimental system for simulating removal of particulate matter under flue gas was built,and the effects of gas composition and spray on particle removal efficiency were measured and compared with the numerical simulation results.The results show that with the increasing of CO₂ concentration and the decreasing of O₂ concentration,the removal efficiency of particles under 1?m is higher than that of particles above 1?m.The particle removal efficiency increases with the increasing of relative humidity.The addition of spray can increase the average particle size,significantly improving the removal efficiency,but will reduce the breakdown voltage.Finally,according to the research results of this paper,a particulate removal system with spray system was designed.On the basis of the traditional electrostatic precipitator,the system adds spray system to increase the humidity of the flue gas and enhance the agglomeration effect of the particles,so as to enhance the removal efficiency.A baffle is set at the entrance of the electrostatic precipitator to make the flue gas close to the dust collecting plate and enter the precipitator to further increase the removal efficiency.The spray device is opened based on the environment and the maximum removal efficiency is expected to reach over 99%.