高温微细粉尘的强化异性荷电及其在颗粒层内的聚并与沉积特性

High-temperature flue gas dust collection is an important issue in energy and environment fields, of which fine dust removal is the most difficult. This project aims at developing an innovative technique: the ternary rare-earth tungsten is used as thermionic emission cathode; The high temperature flue gas diffusion discharge will be intensified by the coupling effect of thermionic emission and external pulsed electric field, which promotes the oppositely charging of fine dusts, and thus strengthens the electrostatic precipitation and coagulation through the microporous channel of granular-bed filter. At first, the cathode V–I characteristics will be investigated experimentally in high-temperature flue gas ambience and various operating conditions. Secondly, through numerical simulations, the kinetic regularity of cathode thermionic field emission and high-temperature flue gas ionization will be obtained, and then the high-temperature flue gas diffuse discharging mechanism under the cooperative action of thermionic emission and pulsed electric field be revealed. Thirdly, the high-temperature dust removing experiments will be made, and the influence of temperature, pressure drop, pulse power parameters, dust collecting voltage, velocity, dust concentration and its size distribution on the grade filtration efficiency and the change regularity also be investigated. Additionally, the mathematical models which describe the driving, migration, aggregation and deposition of fine dusts with high quantity of opposite electric charge by the multi-field coupling also be established. Through combining numerical simulation results with experimental findings, the main influencing factors of grade collection efficiency and its variation laws will be obtained, then the aggregation and deposition mechanism of high-temperature fine dusts with high quantity of opposite electric charge in granular-bed filter be studied. Finally, the technical way and the related technical parameters, with which the removal efficiency of PM2.5 in high temperature flue gas is more than 95%, will be determined.

高温除尘是能源与环境领域面临的重要课题，其中微细颗粒物的脱除是难点。本课题以三元稀土钨功能复合材料为阴极，通过热电子发射与外加脉冲电场的耦合效应，强化高温烟气弥散放电，从而促进微细粉尘的异性荷电，增强其穿越颗粒层微孔通道过程的静电沉降与聚并效果。实验研究高温烟气、不同工况条件下阴极伏-安特性；通过数值模拟，获得阴极场助热电子发射与高温烟气电离动力学规律，探索热电子发射与外加脉冲电场耦合作用下高温烟气弥散放电机理；进行高温除尘实验，探讨温度、压力降、脉冲电源参数、收尘电压、流速、粉尘浓度及其粒径分布等对分级过滤效率的影响及其变化规律。建立颗粒层内强异荷电微细粉尘在多场耦合作用下的受力、迁移、聚并和沉积数学模型，通过实验与数值模拟，揭示影响分级过滤效率的主要因素及变化规律，探讨强异性荷电高温微细粉尘在颗粒层内的聚并与沉积机理，获得对高温烟气中PM2.5的除尘效率达95%以上的技术途径和参数。

作为能源、冶金、化工等领域的一个难题，高温除尘问题正愈来愈受到人们的高度关注。迄今为止，人们已经进行了大量的高温除尘技术研究，并取得了重要进展。现有技术已经能够很好地脱除5μm以上的较大粉尘，但对微细颗粒的高效捕集仍然是难点，尚没有明显的突破。为此，本项目通过三元稀土钨阴极热电子发射与外加纳秒脉冲电场的耦合效应，强化高温烟气弥散放电，从而促进微细粉尘的异极性荷电，实现颗粒层微孔对其高效过滤。. 项目开展了三元稀土钨（W-La2O3-CeO2-Y2O3）阴极放电实验和数值模拟研究，探究热电子发射与脉冲电场耦合作用下气体弥散放电特性与微观作用机制。发现以圆锥状三元稀土钨作为电子发射体，通过外加纳秒高压脉冲电场的协同效应，可使烟气形成类似“弥散放电”现象；提高温度或电源峰值电压，均可使阴极内部更多的电子获得足够的能量而逸出表面，从而提高烟气的放电强度；阴极热电子发射对气体放电有一定的促进作用，与中低温环境相比，高温环境下热电子发射对烟气放电的强化效果更为明显。开展了荷电高温微细粉尘在颗粒层内分级过滤特性的实验研究，获得了不同工况参数对高温烟气分级过滤效率的影响。发现与传统的颗粒层过滤器（CGBF）相比，静电增强式颗粒层过滤器（EGBF）的除尘效率显著提高，提高烟气温度和预荷电电压，对强化细粉尘的捕集起着非常重要的作用。开展了荷电高温微细尘粒穿越静电场增强式颗粒层过程的数值模拟与动态仿真，探究其在多场耦合作用下的过滤机制。发现施加静电力能显著提升颗粒层对微细粉尘的捕集效率，粉尘粒径越大，荷电量越高，所受的静电力越大，彼此碰撞聚并以及被颗粒层捕集的概率也越高；通过湍流边界层、库伦力以及交变电场的综合作用，能促进超细异极性荷电粉尘的凝并，再结合多孔颗粒层过滤，可实现其深度净化。. 研究工作获得了高温烟气中微细粉尘的强化异极性荷电及其高效脱除的技术途径和相关技术参数，可望为高温除尘新技术的研究与发展提供理论基础。