Numerical Research On Simultaneous Removal Of Mercury And Particulate Matter Within An E Electrostatic Precipitator

Mercury and ultra-fine particulate matter are the main pollution emissions from coal-fired power plants,which may cause great damage to human health and the environment.As one of the most mature pollutant control devices,the electrostatic precipitator(ESP)inevitably undertake the task of simultaneously removing mercury and ultra-fine particulate matter.However,there is still room for further study on the mechanism of simultaneous capture of mercury and ultra-fine particulate pollutants within electrostatic precipitators,and reliable models to describe this process qualitatively and quantitatively are scarce.Therefore,a fully verified multi-physical field numerical model coupled with electric field,flow field,particle movement,particle charging and mercury adsorption is established in this paper.Based on this model,the mechanism of simultaneous removal of mercury and particulate matter in the electrostatic precipitator is preliminarily revealed,providing deep insights for theoretical research and industrial production.Firstly,the interaction between electric field,turbulence,particle movement and mercury adsorption of activated carbon and their effects on mercury removal efficiency are investigated.It is found that there were two different mercury adsorption mechanisms in the ESP,namely suspended particle adsorption and wall-bounded adsorption.Reducing the size of activated carbon can improve the efficiency of mercury ejection,but may produce additional particulate pollutants such as PM2.5.The initial concentration of mercury and activated carbon particles are proportional to the removal rate of mercury,while the effect of the mercury concentration in flue gas on the mercury removal rate is relatively weaker.Ionic wind forms vortices in the ESP which increase the turbulence intensity,improving the adsorption of mercury by suspended activated carbon as well as the particle layer on the collection plate.However,enhancing the ionic wind intensity by raising the voltage may reduce the efficiency of mercury removal.Secondly,the motion and charge characteristics of ultrafine particles in electrostatic precipitator are discussed.The charge of ultrafine particles mainly comes from the diffusion charge and decreases with the reducing of particle size.At the same time,particle charge density increases with the decrease of particle size.Small size and high concentration of nanoparticles will reduce the current density of corona discharge,raise the initial corona voltage,reduce the velocity of ion wind and the maximum deposition efficiency of particles.The drag force and Coulomb force of the ultra-fine particles in the electrostatic precipitator decrease with the reducing of particle size,while the Brownian force increases with the decrease of particle size.The decrease of drag force caused by Cunningham correction is the main reason for the increase of deposition efficiency of nanoparticles in the 30-60 nm range.When the particle size is less than 50 nm,the Brownian force on the particle increases,and Brownian diffusion will reduce the deposition efficiency of nanoparticles,but it is not primarily responsible for the decrease of deposition efficiency when the particle size is less than 20 nm.Finally,the simultaneous removal characteristics of mercury and ultrafine particles within an electrostatic precipitator are studied.The simultaneous removal efficiency factor of mercury and ultrafine particles in the electrostatic precipitator is proposed.Within the range of typical flue gas velocity at the ESP inlet in coal-fired power plants,the lower the flue gas velocity,the higher the removal efficiency.When the operating voltage increases,the simultaneous removal efficiency firstly increases rapidly and then decreases slowly.When the operating voltage is about 50 kV,the simultaneous removal efficiency reaches its maximum value.When the particle size decreases from 20 ?m to 0.1 ?m,the simultaneous removal efficiency firstly increases rapidly,then decreases slowly,and finally increases within a small range.The simultaneous removal efficiency reaches its maximum value when the particle diameter is about 1.5 ?m.Lower flue gas velocity,moderate operating voltage and moderate activated carbon particle size should be choosed at the electrostatic precipitator of coal-fired power plants to ensure higher simultaneous removal efficiency of mercury and particulate pollutants.