【作者】 张昊；

【导师】 高翔； 郑成航；

【作者基本信息】 浙江大学 ， 能源环境工程， 2021， 硕士

【摘要】 工业燃烧源排放了大量的颗粒物,造成了严重的大气污染,被认为是导致大气灰霾的重要原因之一。在我国持续改善空气质量的需求下,进一步实现燃煤电厂、有色、水泥等工业源烟气中颗粒物的高效脱除是打赢蓝天保卫战的必然要求。静电除尘技术是实现工业源烟气颗粒物高效脱除的重要手段,在燃煤电厂、钢铁、水泥、有色等行业有着广阔的应用前景,但从目前研究现状及工业需求来看,除尘器内部形成的堆积粉尘将会造成放电稳定性及脱除能力下降,影响了除尘器的高效稳定运行,因此亟需研究如何减少粉尘层对颗粒物高效脱除的影响。本文将聚焦于粉尘层对颗粒物静电脱除过程的影响,通过理论和实验相结合的方法,探究基于粉尘层调控进而实现颗粒物高效脱除的方法。首先,研究了堆积颗粒间的受力规律和堆积颗粒诱导气隙击穿的发生机制,建立了堆积粉尘颗粒间受力及颗粒周围电场分布模型,在明晰了颗粒堆积特性的基础上,研究了比电阻、电压、温度、粉尘层厚度等参数影响下堆积颗粒间受力规律及颗粒周围的电场分布,发现随着比电阻、电压的提高,静电吸引力在颗粒间粘附力的占比将会显著增加,当比电阻从1×10⁹Ω·cm增加到1×10¹⁰Ω·cm时,静电吸引力对粘附力的贡献从22%增长到78%,当电压从40 k V增加到60 k V时,静电吸引力的占比从56%上升到78%,同时还发现提高堆积颗粒比电阻和表面能将会有利于防止堆积粉尘在气流的影响下重新返回收尘空间;揭示了堆积颗粒诱导气隙击穿的发生机制,发现当粉尘层厚度和比电阻增加时,堆积颗粒表面的电场强度将会迅速增加,同时发现在颗粒接触点将会产生极高的场强,容易造成颗粒间气隙的击穿,并建立理论方法预测了堆积颗粒诱导气隙击穿的临界电压,为除尘器的稳定运行提供了支撑。其次,研究了粉尘层对空间颗粒荷电迁移过程的影响,建立了粉尘层影响下的颗粒荷电迁移模型,发现当温度和比电阻提高时,空间电场强度将会显著下降,同时当除尘器内部存在高比电阻粉尘层时,增加温度将会提升小颗粒荷电量,减少大颗粒的荷电量,进而导致不同粒径段颗粒的驱进速度随温度增加的变化趋势不同,同时阐明了高比电阻和高温影响下颗粒驱进速度的衰减规律,并进一步获得不同粒径段颗粒在宽温度范围内的驱进速度衰减曲线,提出了颗粒物强化迁移的方法,调控后驱进速度最大可提高3.67倍。再次,针对于典型行业粉尘静电脱除特性的差异,对比研究了不同参数影响下燃煤电厂、铜冶炼、镍冶炼、水泥窑、钢铁五种典型行业粉尘在373 K-773 K温度范围内的静电脱除特性,发现了当流速和温度增加时,颗粒的脱除效率将会明显下降,并进一步分析了颗粒的动态脱除特性,发现适当提高工作电压或者降低流速将会降低颗粒的极限排放浓度,同时对比研究了铜冶炼、镍冶炼、水泥窑、钢铁四种典型行业粉尘和燃煤电厂粉尘在不同温度下脱除效率和极限排放浓度的差异,明确了不同行业粉尘的宽温脱除特性,指导除尘器在不同行业的设计和应用。最后,开发了新型的阳极板结构,提出了基于新型极板的颗粒物高效捕集方法,研究了不同参数影响时新型极板的颗粒物强化脱除效果。通过模拟研究发现,新型极板的颗粒陷阱结构内存在低流速区和低电场强度区,将有效避免堆积颗粒被气流夹带或者堆积颗粒诱导气隙击穿。另外发现新型极板提升了0.1-3μm粒径段颗粒的脱除效率,使出口烟气颗粒物的质量中值粒径明显提升。进一步研究了新型极板在不同工况下的脱除性能,同传统BE板对比,振打后新型极板条件下颗粒物的出口相对质量浓度有了明显下降,最高值为1.43,优于传统BE板的2.10;同时发现相较于传统BE板,新型极板下燃煤电厂、铜冶炼、镍冶炼、水泥窑、钢铁五种典型行业粉尘的脱除效率均明显提高,并且当电压为20 k V时,新型极板时颗粒物的排放浓度将降低至2.01 mg/m³,当颗粒入口浓度增加至203mg/m³时,颗粒物的脱除效果高达98.5%,当相对湿度增加到30%时,颗粒物的脱除效率达99%,具有优异的脱除效果。更多还原

【Abstract】 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.更多还原