静电除尘器内微细颗粒的多场协同作用研究

发布时间：2018-02-11 04:17

  本文关键词： 静电除尘 微细颗粒 受力 水膜 换热 多场协同 运动特性　出处：《山东大学》2017年博士论文　论文类型：学位论文

【摘要】：微细颗粒质量轻、颗粒小、跟随性好、吸附性强且较难脱除,是造成大气能见度降低、灰霾天气等问题的重要因素,由其引发的污染已成为我国突出的大气环境问题。现有燃煤电厂大多采用静电除尘器进行除尘处理,其对粒径10μm以上的颗粒除尘效率高达99%以上,但对微细颗粒(粒径小于10μm)的脱除效率并不理想。研究表明,将电场、温度场和湿/浓度场的综合作用应用于静电除尘器中可以有效提高微细颗粒的脱除效率,但是在流场、电场、温度场、湿度场及浓度场各自及协同作用下,静电场中微细颗粒的浓度分布状况及运动特性的相关研究较少,本文通过ELPI在线测试与数值模拟方法,考察了场协同作用下颗粒在静电除尘器内部的颗粒总浓度分布、沿程颗粒分级浓度分布、沿程分级浓度减少率、颗粒运动轨迹、沉积效率等,深入研究静电除尘器内部颗粒分布与运动特性等内在物理过程,为提高微细颗粒脱除效率提供理论基础。对静电除尘器内颗粒受力类型、大小和方向进行总结分析,并将这些力在静电除尘器内部的不同区域(极线区、主流区、近壁区和壁面上)、不同的工况(原始状态、干式状态、湿式状态、换热状态和协同状态)下进行分类,通过已知的参数对这些力进行量级分析,基于受力类型、大小、方向和量级分析对静电除尘器内部颗粒的力学行为进行建模,分别建立了微细颗粒趋于壁面运动的运动模型和微细颗粒与收尘极板之间的粘结模型。搭建了基于静电除尘的多场协同脱除微细颗粒试验台,通过测试不同状态下除尘器内部温湿度场的分布,进一步分析微细颗粒在除尘器内部多场协同作用下的分布与运动特性。基于ELPI在线测试分析的方法,对微细颗粒的分布状态及运动特性进行试验研究,分别对比研究了不同状态下横截面上的颗粒总浓度分布规律,沿程颗粒分级浓度变化规律以及沿程分级浓度减少率,得到以下结论:(1)干式状态下,截面中与极线平行的位置处颗粒的汇集程度最高;壁面换热后,高浓度区随着气流的发展向壁面方向移动,且返混现象减缓;壁面布水后,近壁区出现低浓度区,且随着气流的发展面积增大,返混现象消失;协同状态下,场协同效果均优于以上场叠加效果,近壁区浓度梯度较湿式状态下更高,近壁区低浓度区更明显。(2)干式状态下,粒径0.04～0.6μm范围内的颗粒的收尘效果不佳,出现返混现象。壁面换热后,0.4～0.6μm范围内的颗粒返混现象消失,近壁区颗粒浓度大幅度增加。壁面布水后,0.1～1μm范围内的颗粒浓度大幅度的降低,近壁区最多降低30%左右。协同状态,与湿式状态下颗粒的沿程数浓度变化曲线相似,但整个粒径范围内颗粒的浓度均有所下降,0.1～1μm范围内的颗粒沿程最多降低了 50%左右。(3)干式状态,电压升高对粒径大于或者小于0.3μm颗粒有明显的脱除效果,沿程分级浓度减少率升高了 20%～50%左右。壁面换热后,粒径0.01μμm的颗粒的减少率有30%的提高,而其他粒径范围内的颗粒的减少率提高幅度相对略低,10%左右。壁面布水后,液桥力造成小颗粒团聚后数目减少,同时较大粒径的颗粒的数目增多,在近壁区更明显,变化幅度更大。协同状态下,多场协同使整个粒径范围内的颗粒的浓度减少率均有所提高。与湿式状态相比,粒径大于1μm的颗粒的浓度减少率的提高更明显,10%左右,近壁区0.1～1μm范围内的颗粒的效果最明显,沿程最多降低了 15%左右。综合考虑流场模型、电晕电场模型、颗粒运动模型、颗粒荷电模型、壁面换热模型和水膜蒸发扩散模型,采用COMSOL对不同状态下微细颗粒的分布状况及运动特性进行数值模拟研究,对电场分布状况、温湿度变化,颗粒轨迹、沿程浓度分布状况以及沿程效率分布状况做详细的分析,建立多场协同下微细颗粒分布与运动特性数值模型,得到以下结论:电场强度和颗粒饱和荷电量的分布均以芒刺线为对称轴呈现轴对称形式,极线区的电场强度和颗粒饱和荷电量最强,随着电压的升高,芒刺尖端的电场强度增大,颗粒的饱和荷电量也逐渐增大;不同状态下,数值模拟计算得到的温湿度变化趋势、沿程浓度分布状况及沿程沉积效率分布与试验结果符合良好,模型可以准确描述温度、湿度、浓度分布;微细颗粒在电场中运动时有向收尘极板偏移的趋势,随着电压的升高,颗粒的偏移程度加强,颗粒的沉积位置逐渐前移且沉积量逐渐增加,在换热/换热/协同状态下,与干式状态相比,颗粒的沉积位置逐渐前移且沉积量逐渐增加。综合以上理论分析、试验和模拟结果,对不同状态下微细颗粒的受力变化及力学行为进行总结,揭示了微细颗粒物在流场、颗粒场、电场、温度场、湿度场、浓度场及其耦合作用下的力学行为和受力模型,分析了电场/壁面换热/壁面水膜/协同作用引起的静电除尘器内部颗粒的受力类型及其变化,建立不同状态下微细颗粒的受力模型并确定微细颗粒的量级大小,绘制了在电场/换热/水膜/协同作用下静电除尘器内部的颗粒的基本运动情况图。
[Abstract]:Fine particles of light weight, small particles, with good adsorption ability and is difficult to be removed, is caused by the atmospheric visibility, the important factors of haze weather problems, caused by air pollution has become a prominent environmental problem in China. Most of the existing coal-fired power plants by electrostatic precipitator dust treatment, the grain the size of more than 10 m particle removal efficiency reaches more than 99%, but the fine particles (particle size less than 10 mu m) the removal efficiency is not ideal. The results show that the electric field, temperature field and concentration field of wet / comprehensive effect used in electrostatic precipitator can effectively improve the removal efficiency of fine particles, but in the flow field, electric field, temperature field, humidity field and concentration field and their synergistic effect, research concentration distribution and movement characteristics of fine particles in electrostatic field less, through the test and the number of online ELPI value simulation method, investigation The field synergy particles under the action of particles in the interior of the electrostatic precipitator concentration distribution along the particle concentration distribution along the hierarchical classification, concentration reduction rate, particle trajectory, deposition efficiency, particle size distribution of electrostatic precipitator and the internal movement characteristic of the inner physical process of in-depth, in order to improve the removal efficiency of fine particles and provide a theoretical basis for the force on the particle. The type of electrostatic precipitator, summarized and analyzed the size and direction, and the force of different regions in the internal electrostatic precipitator (polar region, the main region, the area near the wall and the wall surface), different conditions (original state, dry state, wet state, heat transfer and the state under the collaborative state) classification, magnitude analysis to these forces by the known parameters, the size of the force type, based on the direction and magnitude of the mechanical behavior analysis of particles inside the electrostatic precipitator for modeling, are established. The bonding model between fine particles tend to fine particle motion model and wall motion and collecting plate. To build a multi field collaborative electrostatic dust removal of fine particles by test bench based on distribution test under different conditions of temperature and humidity inside the collector field, further analysis of the distribution in the ESP internal field under the synergistic action and the motion characteristics of micro fine particles. Analysis method of ELPI online test based on the experimental study of distribution and movement characteristics of fine particles, were studied the total particle concentration distribution law of cross section under different conditions on the particle concentration variation along the classification and grading along the concentration reduction rate, obtained the following conclusions: (1) dry state, aggregation degree of position in parallel grain section and pole top; wall heat transfer, the high concentration area with the development of the wall surface to air movement, and 杩旀贩鐜拌薄鍑忕紦;澹侀潰甯冩按鍚，

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