| Industrial combustion emits a large amount of particulate matter,causing serious air pollution,which is considered as one of the most important causes of atmospheric haze.Under China’s national strategic demand for continuous improvement of air quality,achieving the efficient removal of particulate matter of industrial sources,such as coal-fired power plants,non-ferrous metals,and cement,is an inevitable requirement in order to defend the blue sky.Electrostatic precipitators（ESP）,as an important method to reduce the particle emission,has been widely used in various industries,such as coal-fired power plants,steel,cement,non-ferrous metals.However,the dust layer inside the ESP will decrease the discharge stability and decline the particle collection efficiency,which will significantly affect the efficiency of the ESP.Therefore,it is necessary to carry out studies to explore how to reduce the adverse effects of dust layer on the particle removal.This thesis will focus on the influence of the dust layer on the electrostatic removal process of particle,and through a combination of theory and experiment,explore methods of achieving high-efficiency particle removal by dust layer adjustment.Firstly,in view of the adhesion force and electric field distribution between the deposited particles,a model of the force between the deposited particles and the electric field distribution around the particles surface was established.And the adhesion force characteristics and electric field distribution between the deposited particles under the influence of various factors such as resistivity,voltage,temperature,layer thickness were studied.It was found that as the resistivity and voltage increased,the adhesion force between the deposited particles and the contribution of the electrostatic effect to the adhesion force would significantly increase.Specifically,when resistivity increased from 1×109Ω·cm to 1×1010Ω·cm,the contribution of electrostatic effect to adhesion force increases from 22%to 78%,and when the voltage increased from 40 k V to 60 k V,the proportion of electrostatic effect increased from 56%rose to 78%.It was also found that increasing the particle resistivity and surface energy would help prevent particle re-entrainment.In addition,it revealed the electric field distribution characteristics between the deposited particles,and found that there would be extremely high field strength at the particle contact point,which would easily cause breakdown between deposited particles.Besides,a theoretical method was established to predict the critical voltage of breakdown between deposited particles,which is useful for the stable operation of ESP.Secondly,a model was established to investigate the impact of the dust layer on the particle migration process.It was found that when the temperature and resistivity increased,the space electric field strength would significantly decrease;it was also found that when there was a dust layer with high resistivity inside the ESP,the temperature had different influences on the charge of the particles with different size.In other words,it would increase the charge of small particles and reduce the charge of large particles,leading to different particle migration velocity at different temperatures.At the same time,it clarified variation of the particle migration velocity under the influence of high resistivity and high temperature,and further obtained the criterion of the deterioration of the migration velocity of particles with different particle sizes in a wide temperature range.Meanwhile,it gives some suggestions on how to prevent dust layer from reducing the efficiency.After these adjustments,the particle migration velocity can be increased by 3.67 times.Thirdly,in view of the differences in the particle removal characteristics in different industries,a comparative study of electrostatic removal characteristics in the temperature range of 373 K-773 K of five typical industries of coal-fired power plants,copper smelting,nickel smelting,cement kilns,and steel under the influence of different parameters was carried out.It was found that high gas velocity and high temperature would reduce the particle removal efficiency.Bases on further study of dynamic removal characteristics of particles,it was found that appropriately increasing the voltage or reducing the gas velocity would reduce the ultimate particle emission concentration.Meanwhile,the difference in the removal efficiency and ultimate emission concentration of particle from copper smelting,nickel smelting,cement kilns,steel and coal-fired plant at different temperature was studied,and the wide-temperature particle removal characteristics in different industries were clarified,which can guide the design and operation of ESP in different industries.Finally,based on the theoretical and experimental results,an efficient particle removal method based on a new type collection plate was proposed,and the enhanced particle removal effect of the new type collection plate under the influence of different parameters was studied.Through simulation studies,it was found that there were low gas velocity areas and low electric field strength areas in the particle trap structure of the new type collection plate,which would effectively prevent the deposited particles re-entrainment and breakdown between particles.In addition,it was found that the new type collection plate improved the removal efficiency of particle with diameter of 0.1-3μm,which increased the mass median diameter of outlet particle.In addition,the study found that compared with the that of traditional BE plate,because of the particle trap structure,the highest value of the particle outlet relative mass concentration of the new plate after rapping was only 1.43,which was much lower than the 2.10 of the traditional BE plate.At the same time,it was found that compared with the traditional BE plate,new plate can help increase the particle removal efficiency of coal-fired power plants,copper smelting,nickel smelting,cement kilns,and iron and steel.What’s more,as the applied voltage was 20 k V,the particle would be effectively removed,which the particle emission concentration was reduced to 2.01 mg/m3.Besides,when the particle inlet concentration increased to 203 mg/m3,the particle removal efficiency could reach98.5%if the new type collection plate was used in the ESP.And when the relative humidity was increased to 30%,if the new type collection plate was used in ESP,the particle removal efficiency could reach 99%,indicating the new type collection plate could significantly enhance particle removal. |
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