Numerical Study On The Secondary EHD Flow And Collection Efficiency In Electrostatic Precipitator

In recent years,with the rapid development of the national economy,coal energy consumption in the process of industrialization is still as high as 60%.Environmental problems caused by burning coal have increasingly become the focus of attention.For this reason,it has become particularly important to find a suitable device and method to reduce the emission of fine particles.Electrostatic precipitators?ESPs?have been widely in industrial applications used to remove dust particles from untreated flue gas,in which the overall mass collection efficiency of conventional ESPs can easily exceed 99%.However,the collection efficiency of sub-micron dust particles is relatively lower?sometimes less than 50%?Therefore,increasing the collection efficiency of submicron particles is still necessary and a challenging problem.Based on Fluent software,this paper conducts numerical study on the secondary flow and particle transport behaviour in electrostatic precipitator.Firstly,the electric field,flow field,particle dynamics and particle charging model involved in the electrostatic precipitator were established and verified.At the same time,the effects of particle charge and Brownian diffusion on the particle transport behaviour were studied in detail.The results show that when the particles move to the first discharge electrode,the diffusion charges of the0.2?m and 0.6?m particles increased linearly between the wire electrodes spacing,and then the change was small.With the same voltage increase,the higher the voltage,the greater the increase in the corresponding particle exit height.Brownian diffusion causes the trajectory of the particles to fluctuate up and down,but does not change the main direction of motion of the particles,only affecting the deposition and escape time of the particles.Secondly,the effects of the discharge electrode structure,inlet flow velocity and applied voltage on the secondary electrohydrodynamic?EHD?flow and particle collection efficiency in a spiked electrode are studied in detail.The simulation results show that when the direction of the secondary EHD flow is opposite the primary of main airflow,a pair of vortices can be formed near the spiked electrode.The strength of two vortices close the spikes electrode are affected by inlet of flow velocity,negative applied voltage and the position of spike tip,the size of vortices increases with decreasing the velocity of the inlet flow and increasing applied voltage.The higher of dimensionless parametersEhd/Re² ratio,the larger of the vortices size and the stronger of the intensity.In addition,the distribution of deposited particles with spikes on two sides and one side directed either upstream or downstream indicates that the particles are mainly deposited near at the directly opposite the spiked electrode position.Among them,the particle collecting efficiency of spiked electrode with one side directed upstream is higher than that of one side directed downstream,and the larger of the particle size,the larger of the difference,especially the 1?m particle has a difference of 10%.Finally,numerical studies on the secondary EHD flow and particle deposition in spiked multi-electrode were carried out.The effects of inlet flow velocity and applied voltage on secondary EHD flow and particle deposition were studied.The results show that as the inlet flow velocity increases,the vortices near the inlet position changes the most,followed by the vortices in the middle position,and finally the vortices near the exit position.The lower the inlet flow velocity and the higher the applied voltage,the stronger of vortices occurs at the higher of the dimensionless parameterN_EHD.In addition,a large number of particles are deposited on the surface of the collecting plates at the directly opposite the first spiked electrode position.The lower of the inlet flow velocity and the higher of the voltage,the more the number of particles deposited,the higher of the collecting efficiency.The multi-electrode can increase the particle collecting efficiency by about 20%compared to a single spike electrode at the same inlet flow velocity and voltage.