高温静电除尘过程的数值模拟研究

发布时间：2018-04-03 05:08

本文选题：电流体动力　切入点：静电除尘　出处：《浙江大学》2015年硕士论文

【摘要】：高温下除尘过程普遍存在于工业生产中,例如整体煤气化联合循环(IGCC)和增压流化床燃烧联合循环(PFBC)过程。高温静电除尘器是满足上述气体净化要求的重要设备。对高温静电除尘过程的研究有助于揭示除尘机理,也能为工程实际中除尘设备的设计和优化提供指导。本文应用计算流体力学(CFD)对高温下的线板式静电除尘器进行了数值模拟研究。建立了综合考虑温度场、电场、流场和颗粒动力场的多场耦合模型,采用有限体积法对计算域进行离散进而求解电场,采用欧拉一拉格朗日方法求解气固两相流动。主要研究内容包含以下三部分：第一部分是对静电除尘器内电场、流场和颗粒动力场之间相互作用的研究。结果表明,电场对流场的影响表现为离子风效应,离子风的主要形态结构是漩涡,它会在每个电晕极两端形成一对反向的涡结构。静电场施加于颗粒的电场力对实现颗粒与气体的分离起着重要作用。荷电颗粒形成的空间电荷使电势和离子电荷密度稍有减小,颗粒在电场中形成的较大偏移会增强气体的湍流。湍流脉动使部分颗粒沉淀的时间变短,部分颗粒的沉积时间变长,部分颗粒甚至未能淀积。第二部分是温度对静电除尘器内流场特性、电场特性以及离子风效应影响的研究。模拟结果表明,气体密度随着温度的升高而减小,气体粘度随着温度的升高而增大。高温会增厚收尘板处的边界层,增强了全场的平均湍流强度。静电除尘器的工作电压范围随着温度的升高而变窄。电晕极表面场强和整个电除尘器内的平均场强均减小,离子电荷密度也减小。随着温度的升高,离子风的影响强度减弱,范围拓宽。第三部分是温度对静电除尘器内颗粒荷电、受力和轨迹的影响以及对整个除尘效率的影响的研究。首先研究了颗粒在运动过程中的荷电历程,接着对颗粒所受曳力和电场力进行了研究,最后总结高温对除尘效率的影响并给出提高除尘效率的建议。模拟结果表明,对于10岬的颗粒,随着温度的升高,颗粒的荷电量减小,静电力减小而Saffman升力、布朗力以及曳力均增大。颗粒的受到的力主要是静电力和曳力。高温增强了颗粒与流体的相互作用。温度升高可能会使颗粒捕集变得困难,其原因可能有以下几方面：运行电压的降低、烟气量的增大、颗粒荷电减少导致的电场力减小、气体粘度增大引起的曳力增加、高温造成的颗粒与流体间相互作用的增强。
[Abstract]:The process of dust removal at high temperature generally exists in industrial production, such as integrated coal gasification combined cycle (IGCC) and pressurized fluidized bed combustion combined cycle (PFBC) process.High temperature electrostatic precipitator is an important equipment to meet the above gas purification requirements.The study of electrostatic dust removal process at high temperature is helpful to reveal the mechanism of dust collection and to provide guidance for the design and optimization of dust removal equipment in engineering practice.In this paper, computational fluid dynamics (CFD) is used to simulate the linear plate electrostatic precipitator at high temperature.A multi-field coupling model considering the temperature field, electric field, flow field and particle dynamic field is established. The finite volume method is used to discretize the computational domain and the electric field is solved. The Euler-Lagrangian method is used to solve the gas-solid two-phase flow.The main research contents include the following three parts:In the first part, the interaction among electric field, flow field and particle dynamic field in electrostatic precipitator is studied.The results show that the effect of electric field convection field is ionic wind effect, and the main form of ion wind is vortex, which forms a pair of opposite vortex structures at both ends of each corona pole.Electrostatic field applied to particles plays an important role in the separation of particles and gases.The space charge formed by charged particles decreases the potential and ion charge density slightly, and the larger migration of particles in the electric field will enhance the turbulence of the gas.Turbulence pulsation shortens the precipitation time of some particles, prolongs the deposition time of some particles, and even fails to deposit some particles.In the second part, the effect of temperature on flow field, electric field and ion wind effect in electrostatic precipitator is studied.The simulation results show that the gas density decreases with the increase of temperature, and the gas viscosity increases with the increase of temperature.The high temperature will thicken the boundary layer at the dust collecting plate and increase the average turbulence intensity of the whole field.The working voltage range of electrostatic precipitator becomes narrow with the increase of temperature.The electric field intensity on the corona electrode surface and the average field intensity in the whole electrostatic precipitator are both decreased, and the ion charge density is also decreased.With the increase of temperature, the influence of ion wind is weakened and the range is widened.In the third part, the influence of temperature on the charge, load and trajectory of particles in electrostatic precipitator and the effect of temperature on the dust removal efficiency are studied.Firstly, the charge history of particles in motion is studied, then the drag force and electric field force of particles are studied. Finally, the influence of high temperature on the dust removal efficiency is summarized and some suggestions to improve the dust removal efficiency are given.The simulation results show that the charge of particles decreases and the Saffman lift, Brownian force and drag force increase with the increase of temperature.The force of particles is mainly hydrostatic force and drag force.The interaction between particles and fluids is enhanced by high temperature.The increase of temperature may make it difficult to trap particles, which may be caused by the decrease of operating voltage, the increase of flue gas, the decrease of electric field force caused by the decrease of particle charge, and the increase of drag force caused by the increase of gas viscosity.The enhancement of particle-fluid interaction caused by high temperature.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X701.2

【参考文献】