基于颗粒运动行为调控的旋流器分离过程研究及结构设计

发布时间：2018-01-01 15:23

本文关键词：基于颗粒运动行为调控的旋流器分离过程研究及结构设计　出处：《华东理工大学》2016年博士论文　论文类型：学位论文

【摘要】：水力旋流器是利用离心力场实现多相体系高效分离的单元设备,结构非常简单,但内部多相流场却十分复杂。旋流器分离机制与多相流体运动行为密切相关,深入研究两者之间的影响规律有利于调控分离过程和优化结构设计。本文以数值模拟和实验测试为研究方法,全面探索了旋流器内部气液固多相运动规律、颗粒相分离特性与运动行为和高精度颗粒分级影响机制。通过计算流体力学(CFD)方法建立了准确描述旋流器内多相流动的数学模型。在时均纳维斯托克斯(N-S)方程之上,采用雷诺应力模型(RSM)预测各向异性的液相湍流流场；采用流体体积分率模型(VOF)捕捉气相瞬时变化特性；采用拉格朗日颗粒追踪模型(DPM)描述颗粒相的运动行为。将计算得到的液相速度分布、空气柱半径和颗粒相分离效率与实验数据比较,证明了数学模型的准确性和可靠性。利用所建立的数学模型,以分离效率、受力状态和运动轨迹为研究内容全面探讨了颗粒相的分离机制。结果发现：流体曳力、压力梯度力和离心力的共同作用控制颗粒的运动。对于不同粒径颗粒的分离机制,单位质量颗粒所受径向流体曳力起决定性作用,而离心力和径向压力梯度力基本保持不变。随着颗粒粒径的增大,流体曳力呈指数降低,离心力和压力梯度力的控制作用增强,表现为分离效率的提高。在溢流离开的颗粒中,较大比例的颗粒运动时间较短,会快速运动至溢流管下端即进入内旋流。对于底流离开的颗粒,随着粒径的增加,颗粒会以更快的旋转速度,较为清晰的轨迹进入外旋流。研究还考察了颗粒密度、料液粘度、进料流量、进料方式和分流比对颗粒相分离特性与运动行为的影响。采用系统的分级精度评价指标,以粗细颗粒精确分级为分离目标进行了旋流器结构优化。研究表明：无量纲进口直径(Di/Dc)、无量纲溢流管直径(Do/Dc)、无量纲锥段长度(Lz/Dc)和无量纲底流管直径(Du/Dc)对于分级精度的影响最为显著。分级精度随着无量纲进口直径的增加逐渐提高,但是无量纲进口直径超过临界值(Di/Dc=0.35)后,由于短路流现象的加剧,粗颗粒底流回收效率的急剧降低会引起分级精度的下降。分级精度随着无量纲溢流管直径的增加先增大后减小,分流比的降低引起细颗粒溢流分离效率的提高,切向速度的减小则导致粗颗粒底流回收效率的降低。随着无量纲锥段长度的增加,分级精度呈现先增大后减小的趋势,分流比的增大造成细颗粒溢流分离效率的降低,而停留时间的延长引起粗颗粒底流回收效率的提高。分级精度随着无量纲底流管直径的增加逐渐减小,由于分流比的大幅提高引起细颗粒溢流分离效率的显著减小,导致分级精度的降低。最终,颗粒精确分级的旋流器结构优化范围为：Di/Dc=0.20～030、 Do/Dc=0.35～0.60、Lz/Dc=1.25～2.00和Du/Dc=0.05～0.15。通过响应曲面方法进行高精度旋流器设计,结果发现：无量纲溢流管直径是影响分级精度的关键结构参数,其次为无量纲锥段长度,无量纲进口直径和无量纲底流管直径的影响最弱。并且,无量纲溢流管直径与无量纲锥段长度之间相互作用的影响最为显著。优化旋流器几何结构为Di/Dc=0.20、Do/Dc=0.35、L2/Dc=1.67和Du/Dc=0.10,模拟所得的细颗粒溢流分离效率和粗颗粒底流回收效率分别为89.9%和96.7%。高精度旋流器分级性能测试数据表明：对于酸解尾渣体系,细颗粒溢流分离效率可达96.0%,粗颗粒底流回收效率为69.7%。通过工艺运行发现,底流回收颗粒中含有较少的细颗粒泥渣,无需二次溢流漂洗；减缓了“溢流跑粗”导致的过多钛矿损失,二氧化钛回收率可达51.0%。
[Abstract]:Hydrocyclone is the use of centrifugal force field to achieve multi phase system of efficient separation unit, the structure is very simple, but the internal multiphase flow is very complex. The cyclone separation mechanism and multiphase fluid motion behavior is closely related to an in-depth study of the law between the beneficial to control the separation process and optimize the structure design method in this paper. By numerical simulation and experimental test, a comprehensive exploration of the internal gas-liquid cyclone solid multiphase motion, particle phase separation characteristics and influence mechanism of motor behavior and high precision particles. Using computational fluid dynamics (CFD) method to establish an accurate mathematical model to describe the hydrocyclone of multiphase flow in the time averaged Navier Stokes (. N-S) equation, the Reynolds stress model (RSM) to predict the anisotropy of liquid phase turbulent flow; rate model using volume of fluid (VOF) characteristics of gas phase transient capture Lagrange; using particle tracking model (DPM) to describe the motion of particles. The calculated velocity distribution of liquid phase, air cylinder radius and particle separation efficiency is compared with experimental data, proved the accuracy and reliability of the mathematical model. Using the model, the separation efficiency, stress state and motion track as the research content comprehensively discusses the separation mechanism of particles. The results showed that the fluid drag force, interaction control particle pressure gradient force and the centrifugal force of the movement. The separation mechanism of different size particles, per unit mass of particles by radial fluid drag force plays a decisive role, and the centrifugal force and radial pressure gradient force remained the same. With the increase of particle size, fluid drag force decrease exponentially, enhance the control effect of centrifugal force and pressure gradient force, the performance for the separation efficiency. In the overflow left The particles in the particle movement, a large proportion of the time is short, quick movement to the bottom of the overflow pipe into the inner vortex. For bottom left particles, with increasing particle size, particle will spin faster, more clear trajectory to the outer vortex. The study also investigated the particle density, liquid viscosity. The feeding flow characteristics and movement behavior of feeding mode and diversion ratio on the particle phase separation. The classification accuracy evaluation index system, to the precise classification particle structure of hydrocyclone is optimized for separation of the target. The study shows that the dimensionless inlet diameter (Di/Dc), dimensionless overflow pipe diameter (Do/Dc). The dimensionless cone length (Lz/Dc) and the dimensionless underflow pipe diameter (Du/Dc) influence on the classification accuracy is the most significant. The classification accuracy increased with the dimensionless inlet diameter, but the dimensionless inlet diameter exceeds the critical Value (Di/Dc=0.35), because of the short circuit flow phenomenon intensified dramatically reduces the recovery efficiency of coarse particles underflow can decrease the classification accuracy. The classification accuracy with increasing dimensionless overflow pipe diameter increases first and then decreases, the decrease of the diversion ratio of fine particle overflow separation efficiency, the tangential velocity decreases, which leads to the decrease of coarse underflow recovery efficiency. With the increase of dimensionless cone length, the accuracy of classification was first increased and then decreased, the increasing of split ratio caused the reduction of fine particle overflow separation efficiency, and prolong the residence time caused by coarse underflow recovery efficiency increased. The classification accuracy decreases with the increase of dimensionless bottom flow pipe diameter because of the greatly increased, the split ratio caused by fine particles significantly reduced the overflow separation efficiency, reduce the accuracy of classification. Finally, the structure of swirler and particle accurate classification Range: Di/Dc=0.20 ~ 030, Do/Dc=0.35 ~ 0.60, Lz/Dc=1.25 ~ 2 and Du/Dc=0.05 ~ 0.15. by response surface method, high precision cyclone results showed that the dimensionless diameter of the overflow pipe is the key structural parameters of the classification accuracy, followed by the dimensionless cone length. The influence of dimensionless inlet diameter and dimensionless bottom the diameter of the tube. The weakest and the dimensionless overflow pipe interaction between the diameter and the dimensionless cone length is the most significant. The geometric structure of hydrocyclone optimization for Di/Dc=0.20, Do/Dc=0.35, L2/Dc=1.67 and Du/Dc=0.10, the simulation results of fine particles and coarse particle separation efficiency overflow underflow recovery rate was 89.9% and the high precision 96.7%. cyclone classification performance test data show that for the solution of acid slag system, overflow fine particle separation efficiency can reach to 96%, coarse underflow recovery efficiency is 69.7%. through. The art of operation found that fine particle sludge contains less particles in underflow recovery, without two overflow rinsing; slow down the "overflow coarse" caused by excessive loss of titanium, titanium dioxide recovery rate can reach 51.0%.

【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH122

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