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当前，我国颗粒物污染形势依然严峻，特别是亚微米颗粒物（又称PM1.0，指空气动力学直径小于1 μm的颗粒物）问题尤为突出。传统除尘设备对亚微米颗粒物存在穿透窗口，去除效率较低。因此，面对燃煤及钢铁等行业颗粒物超低排放标准，亟需开发出高效脱除亚微米颗粒物的技术。学者们提出的通过外加物理或化学的作用使亚微米颗粒物团聚长大的凝并技术成为国内外研究的热点。交变电凝并技术被认为是最有效的凝并技术之一，但已有交变电凝并的研究主要是用空气或氮气模拟烟气，少见烟气组分对PM1.0电凝并的影响规律的报道，而实际烟气十分复杂，多种气体组分会影响电晕放电特性，进而影响颗粒的凝并。因此本文基于双区式交变电凝并实验平台探索不同条件下颗粒的电晕特性及颗粒凝并规律。旨在为电凝并技术的应用提供一些参考。第一，探索了预荷电电压、凝并电压及停留时间对亚微米颗粒物交变电凝并效率的影响规律，实验结果表明：（1）升高预荷电电压有利于增加颗粒的带电量，但过高的电压会具有明显的收尘效应，改变颗粒浓度的分布，影响后续凝并效果的检测。（2）当交流凝并电压从0升高到25 kV时，颗粒在凝并电场中的运动增强，碰撞几率增大，凝并效果增强。相比入口，颗粒的质量平均粒径增大了1.57倍；粒径小于1 μm及粒径处于1~2.5 μm的颗粒质量分别下降了16.3%、22.8%。针对粒径小于1 μm的颗粒，粒径处于0.5~1 μm的颗粒质量下降了29.2%；粒径处于0.15~0.5 μm的颗粒由于荷电穿透窗口呈现无序的波动；凝并电压的增加几乎无法提高粒径小于0.15 μm的颗粒去除效率。（3）当颗粒在凝并区的停留时间从0.5 s增加到1.5 s，颗粒总去除效率最大可提升11.0%。停留时间为1.5 s时，相比入口，粒径低于1 μm及粒径处于1~2.5 μm的颗粒质量分别下降了33.7%、40.6%。粒径处于0.5~1 μm、0.15~0.5 μm、小于0.15 μm的颗粒质量分别下降了43.9%、18.2%、35.7%。 第二，考虑到实际烟气中的SO3和H2O会吸附、冷凝在颗粒表面，改变颗粒的理化特性及电晕放电特性，影响颗粒物的凝并效果。因此探索烟气湿度、SO3对亚微米颗粒物交变电凝并效率的影响规律十分重要。实验结果表明：（1）随着烟气的相对湿度从20%提高至80%，单个颗粒的带电量增加了20%~120%不等。相比入口，颗粒的质量平均粒径最大可增大1.93倍。粒径小于1 μm及粒径处于1~2.5 μm的颗粒质量分别下降了80.1%、54.5%。粒径处于为0.5~1 μm、0.15~0.5 μm、低于0.15 μm的颗粒质量分别下降了83.2%、64.5%、66.6%。（2）当烟气中SO3浓度从0 ppm增至30.8 ppm时，单个颗粒的带电量增加了20%-270%不等。颗粒总去除效率最大可提升39.1%。粒径小于1 μm及粒径处于1~2.5 μm的颗粒质量分别下降了91.3%、67.7%。粒径处于0.5~1 μm、0.15~0.5 μm、小于0.15 μm的颗粒质量分别下降了92.7%、67.9%、61.5%。对比粒径小于1 μm和粒径处于1 ~2.5 μm的颗粒质量的变化，发现增加烟气中的湿度和SO3的量更有利于将粒径小于1 μm的的亚微米颗粒凝聚成更大的颗粒。相同冷凝液相体积下，SO3气氛中的电凝并效果优于单独H2O的气氛下。;Nowadays, the pollution of particulate matter is still severe in China, especially in submicron particles (PM1.0). Besides that, submicron particles are difficult to be removed by conventional electrostatic precipitators (ESPs) due to the extremely low charge. Therefore, in the face of ultra-low emission standards for particulate matter in coal burning, steel and other industries, it is urgent to develop some technologies to improve the collection efficiency of submicron particles. Particle agglomeration, a most simple and effective way to increase mean particle size through physical and chemical methods, is drawing interest in increasing the collection efficiency of submicron particles in ESPs. Alternating electric coagulation, considered to be one of the most effective coagulation techniques, is widely studied at home and abroad. However, the researchs about Alternating Electric Coagulation have been carried out not in actual and complex smoke, strongly affect the electric field and coagulation, but mainly in air or nitrogen.Therefore, in this paper, based on the two-zone alternating electro-coagulation platform, the corona characteristics and particle condensation law of particles under different conditions were explored.Firstly, exploreing the effect of pre-charge voltage, condensation voltage and residence time on condensation law of particles. The results of the experiments are as follows. With the increasing of pre-charge voltage, charge amount of particles is improved, but too high voltage will change the distribution of particle concentration due to part of the particles are trapped by grounded platem, which has a centrian degree of interference to the detection of coagulation efficiency. With the AC voltages going up from 0 to 25 kV, the collision between particles intensified, the mass average particle diameter of the particles is increased by 1.57 times, and the mass of the particles with particle size below 1 μm and from 1 μm to 2.5 μm decreased by 16.3% and 22.8%, respectively, Besides that, For particles with diameters less than 1μm, the particle mass change rate of 0.5 μm~1 μm was -29.2%, the tendency on particle mass change of 0.15 μm~0.5 μm was disordered, and the mass of the particles below 0.15 μm hardly varies with the voltages. With the residence time growing up from 0.5 s to 1.5 s, the total removal efficiency maximum increased by 11% and the mass of the particles with particle size below 1 μm and from 1 μm to 2.5 μm decreased by 33.7% and 40.6%, respectively. In addition, the particle mass variation rates of 0.5 μm-1 μm, 0.15μm-0.5 μm, and less than 0.15 μm were -43.9%, -18.2%, and -35.7%, respectively.Secondly, exploreing the effect of air humidity and SO3 concentration on condensation law of particles. The results of the experiments are as follows With the air relative humidity increasing from 20% to 80%, the average charge of per particle increases by 20%~120%, and the mass average particle diameter of the particles is increased by 1.93 times. Besides that, the mass of the particles with particle size below 1 μm and from 1 μm to 2.5 μm decreased by 80.1% and 54.5%, respectively. The particle mass variation rates of 0.5 μm-1 μm, 0.15 μm-0.5 μm, and less than 0.15 μm were -83.2%, -64.5%, and -66.6%, respectively.With the SO3 concentration going up from 0 ppm to 30.8 ppm, the average charge of per particle increases by 20%~270%, and the total removal efficiency maximum increased by 39.1%. Besides that, the mass of the particles with particle size below 1 μm and from 1 μm to 2.5 μm decreased by 91.3% and 67.7%, respectively. The particle mass variation rates of 0.5 μm -1 μm, 0.15 μm -0.5 μm, and less than 0.15 μm were -92.7%, -67.9%, and -61.5%, respectively.In addition to that all, compared with the particle with a aerodynamic diameter from 1 μm to 2.5 μm, the increase of air humidity and SO3 concentration is more conducive to the coagulation of particles below 1 μm.
|吴湾. 复杂气氛下PM1.0交变电凝并机理研究[D]. 中国科学院大学,2019.|
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