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电除尘器作为工业烟气净化的主要设备之一,由于其总除尘效率高、本体阻力低、处理烟气量大、耐高温强腐蚀性气体以及运行维护费用低等优点,广泛应用在电力、冶金、建材等工业领域[1]。理论上,电除尘器可以高效捕集任何粒径的气溶胶粒子,但在实际工业应用中,对亚微米粒子和超细粒子(粒径小于0.1 μm)的捕集效率并不理想[2-5]。为了提高电除尘器对细颗粒物的捕集效率,开发新型电极电除尘器是采取的主要措施之一[6]。基于电风效应对细颗粒物运动状态的影响,减缓收尘电极附近的湍流现象,提出的多孔收尘电极电除尘器是其中之一,其电极结构特征是多孔板型式的收尘极板,在较低的比集尘面积条件下,对细颗粒物有较高的捕集效率。为引导该新型电除尘器设计选型,研究微细颗粒物在其电场内部沉降过程与除尘性能尤为重要。
由于对电除尘通道内各种电气、流动和粒子参数进行实测存在困难,数值模拟方法广泛应用在电除尘器通道内电气特性、流场特性和粒子运动特性的研究。GAO等[7]利用数值模拟方法描述双区电除尘器的物理过程,通过实验验证了该数值模型的准确性,并建立了双区电除尘器除尘性能与影响因素之间的定量关系。DONG等[8]对尖端放电极形式的电除尘器进行了气固两相流的数值研究,详细分析了进口气流速度、负电晕电压、放电极上的尖端位置对气流流线分布的影响。ZHU等[9]利用数值模拟方法研究了波型板电除尘器和平行板电除尘器中微粒的捕集过程,研究发现波型板电除尘器比平行板电除尘器具有更强的电场特性,并且对离子风流动具有更强的抵抗能力。目前,采用数值模拟方法对该新型电极电除尘器的研究内容鲜见报道,而且对其除尘性能及颗粒沉降规律尚不清晰。
多项研究表明,新型电极可从多方面提高电除尘器除尘性能。本研究采用数值模拟方法研究荷电粒子在多孔收尘电极电除尘器内迁移与沉降规律,并以平板电极为基础,结合多孔板电极利用数值模拟软件Comsol Multiphysics探究2种不同收尘极结构下电除尘器通道内的电气特性、流场特性和粒子运动特性,以揭示多孔收尘电极电除尘器的提效机理,并为该新型电极电除尘器的选型设计提供参考。
多孔收尘电极电场中荷电粒子的沉降规律及其除尘性能预测
Sedimentation law of charged particles in electric field of porous dust collecting electrode and prediction of dust removal performance
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摘要: 为了探究多孔收尘电极电除尘器的除尘性能,采用COMSOL Multiphysics建立电除尘器气固两相流数值模型,对多孔收尘电极电除尘器中的颗粒荷电沉降过程进行数值模拟,研究其电场、流场分布及粒子荷电、运动和沉降过程。结果表明,电除尘器气固两相流模型计算值与实验值符合良好。多孔收尘电极电除尘器能够有效提高微细粒子有效驱进速度约30%。极板开孔后显著提高了电场通道中距板表面25 mm内电场强度,开孔不会对空间电荷密度与颗粒荷电过程产生影响;多孔板结构表面5 mm处电场风速水平分量相较于平板结构降低了12.5%,消弱了气流对收尘区域的冲刷作用,进入多孔板空腔内的粒子最终沉降在多孔板壁面上。本研究结果可为多孔收尘电极电除尘器对微细粒子提效捕集的机理探究及新型电除尘器的选型设计提供参考。
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关键词:
- 多孔收尘电极电除尘器 /
- 数值模拟 /
- 气固两相流 /
- 微细粒子 /
- 有效驱进速度
Abstract: In order to explore the dust removal performance of the Porous-dust-collecting-electrode electrostatic precipitators(PDCE-ESPs), COMSOL Multiphysics was used to establish a numerical model of the gas-solid two-phase flow of the electrostatic precipitators, and the particle charge sedimentation process in the PDCE-ESPs was numerically simulated in this study. The distributions of electric and flow fields and the charging, motion, and precipitation of particles in this specific structure were studied. The results showed that the calculated value of the gas-solid two-phase flow model of the electrostatic precipitators was in good agreement with the experimental value. The PDCE-ESPs can effectively increase the effective driving speed of fine particles by about 30%. After opening the plate, the electric field intensity within 25 mm from the plate surface in the electric field channel was significantly increased, and the opening had no effect on the space charge density and particle charge process. The horizontal component of electric field wind speed at 5 mm on the surface of porous plate structure decreased by 12.5% compared with that of flat plate structure, which weakened the scouring effect of air flow on dust collecting area, and the particles entering the cavity of porous plate eventually settle on the wall of porous plate. The results can explain the mechanism of the PDCE-ESPs for improving the trapping of fine particles, and provide a reference for the selection and design of the new type of electrostatic precipitators. -
表 1 2种板型几何参数
Table 1. Geometric parameters of two plate types
板型 线间距A/mm 板间距B/mm 通道长度C/mm 极板长度D/mm 空腔厚度E/mm 线径r/mm 孔径H/mm 孔间距P/mm 平板 240 400 2 000 1 440 50 1 — — 多孔板 240 400 2 000 1 440 50 1 30 50 表 2 边界条件设置
Table 2. Boundary condition setting
位置 流场 颗粒 电场 空间电荷 入口 $ {U}_{x}={U}_{0} $ $ {U}_{x}={U}_{0} $ $\dfrac{\text{∂}\text{ϕ} }{\text{∂}{n} }\text{=0}$ $\dfrac{\text{∂}{\text{ρ} }_{\text{ion} } }{\text{∂}{n} }\text{=0}$ 出口 压力出口 冻结 $\dfrac{\text{∂}\text{ϕ} }{\text{∂}{n} }\text{=0}$ $\dfrac{\text{∂}{\text{ρ} }_{\text{ion} } }{\text{∂}{n} }\text{=0}$ 收尘极 无滑移 冻结 φ=0 $\dfrac{\text{∂}{\text{ρ} }_{\text{ion} } }{\text{∂}{n} }\text{=0}$ 放电极 无滑移 反弹 φ= $ {\text{φ}}_{0} $ Peek law 圆孔边界 无滑移 冻结 φ=0 $\dfrac{\text{∂}{\text{ρ} }_{\text{ion} } }{\text{∂}{n} }\text{=0}$ -
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