【作者】 张建；

【导师】 金有海；

【作者基本信息】 中国石油大学 ， 化工过程机械， 2009， 博士

【摘要】 旋风分离器是利用含尘气体旋转时所产生的离心力将粉尘从气流中分离出一种干式气固分离设备。由于其具有结构简单、高效、能承受高温高压等优点,已经广泛应用于能源、化工、冶金、环保等众多领域。立置多管式三旋的核心部件是轴流导叶式旋风管,针对导叶式旋风管对于5 m的颗粒除尘效率较低的缺点,利用数值计算和实验为手段,结合理论解析方法,用发展中的现代多相流理论、湍流原理、计算流体动力学理论为指导,对其内部气固两相流动、分离机理和压力损失等性能特性进行深入分析。首先,为更好了解导叶式旋风管内部气相流动机理,利用理论解析方法和数值模拟方法对旋风管内部气相流场及压力场进行分析。其中,从柱坐标系下的Navier-Stokes方程和连续性方程出发,建立导叶式旋风管分离柱内旋风流场涡旋流动的精确解,采用无粘性流体假设,对于流场内部进行较为全面的求解。给出了径向速度、切向速度和轴向速度的表达式,以及压力梯度与静压的解析解。利用先进计算流体动力学(Computtational Fluid Dynamic, CFD)技术对于导叶式旋风管内部气相流动规律进行数值预测,采用雷诺应力模型(Reynold Stress Model, RSM)模拟气相流场,运用有限体积法和SIMPLEC(压力速度耦合算法)分析了旋风管内部流场和压力场分布。重点针对导向叶片内部流动进行分析,提出合理叶型准线设计方法。同时分析不同排气和排尘结构对于气相流场的影响,得到结构参数影响内部流动的一般规律。在流场分析基础上,从导叶式旋风管阻力沿程损失方式及组成出发,认为旋风管阻力可以分为进口阻力,本体内部损失,出口损失三部分,而旋风管本体阻力损失包括摩擦损失和涡流损失。在旋风管流场分析的基础上,构建了基于阻力复合原理的旋风管阻力模型,计算表明,进口损失约占15.7%,在分离空间旋转流场中阻力损失最大约为64.15%,而出口损失基本上属于纯能耗,占能量损失的19.79%,涡流损失为最主要的阻力损失,约为整体损失的40.88%。与试验结果相比,基本符合导叶式旋风管的阻力分布情况。其次,在气相流场模拟基础上,应用Euler-Lagrange气固两相流理论,气相流场采用雷诺应力模型,固相模型采用双相耦合的颗粒离散相模型计算颗粒轨迹,并采用单元内颗粒源法计算颗粒的浓度分布。得到不同入口位置对于颗粒运动轨迹的影响规律,以及旋风管内部不同粒径颗粒浓度分布特点,同时总结出计算导叶式旋风管分离效率和压力损失的数值计算方法,数值预测结果与实验结果较为吻合。然后,在流场分析基础上,通过引进旋风管颗粒浓度分布修正因子,充分考虑旋风管内部颗粒浓度分布呈现中间浓度较低,边壁浓度较高的特点,突破了传统意义上固相颗粒浓度径向混合均一的假设,提出转圈理论和边界层理论相结合的新型混合的旋风管性能理论计算方法。第三,利用数值模拟技术,研究不同操作参数下(诸如入口流量、温度、压力和底部灰斗抽气等)的导叶式旋风管内部气固两相流动特点,有利于进一步开发设计出高效低阻型导叶式旋风管,以及进一步发展全面的旋风管气固分离的机理模型。最后,对于多管组合旋风管进行全模型数值分析,研究不同进口结构参数对进气室内部气流均匀性的影响,提出在进口处设置多层扩散锥以提高气流分布均匀性的方法,并进行数值模拟验证。对于三旋装置不同流动空间来说,在进气室内单管入口流量不同,进气室内部压力分布并不均匀,其中各个入口附近出压力变化比较明显,且存在一定影响区域,一般小于进气室内部的平均压强,靠近入口区域的单管入口压降较大。而在公共灰斗内的窜流返混比较严重,可通过灰斗泄气有效抑制。更多还原

【Abstract】 Cyclone separators are by far the mostly used type of particulate control equipment using centrifugal force to remove particles. Their simple construction, no moving parts involved, low maintenance costs and adaptability to a widely range of operating conditions make them one of the most widely used particle removal devices in energy resources, chemical engineering, metallurgy industry and environment protection. Swirl tube is the core part of the vertical Third Stage Separators (TSS) for Fluidized Catalytic Cracking (FCC). Due to low efficiency for particles less than 5 microns in size, the gas-solid flow detail and performance characteristics including collection efficiency and pressure drop for swirl tubes are investigated by using the experimental, theoretical and numerical methods in this study. Firstly, based on the method of theoretical derivation and numerical simulation, the flow details and pressure distribution inside swirl tube are analyzed. Starting from Navier-Stokes equations and continuity equation in cylindrical coordinates, the exact solution of flow in the separation space of swirl tube is presented assumed on the condition of inviscid. And the CFD methods is used to investigate the gas flow characteristics. The governing gas flow equations, along with the three-dimensional Reynolds Stress Model (RSM), are solved using the finite volume method and the SIMPLEC pressure-velocity coupling algorithm. So the detail of gas-solid flow behavior in swirl tube is full displayed. For being the shortcoming flow characteristics, such short circuit flow under vortex finder and solid entrainment and back-mixing phenomenon near dust outlets. To be specific, the flow characteristics inside guide vane are addressed, and thus the suitable design of blade directrix is presented. Based on the flow characteristics, a new theoretical pressure drop model was developed based on the consist of pressure drop. This model includes the effect of the geometrical dimension and flow parameters, and pointed out that total pressure drop consists of three main partial pressure drop: the entrance loss, separation space loss and gas outlet loss. The separation loss included the loss of swirling motion of gas flow and friction loss. This model predicted that pressure drop above three parts come up to 15.7%, 64.15% and 19.79% of the total.Secondly, based on the gas flow field, a stochastic tracking two-phase coupling model is used to calculate the particle trajectories, and Particle-Source-in-Cell (PSIC) method is used to calculate particle concentrations. During the simulations, the interaction between continuous gas-phase and discrete particles is taken into account. The rules of solid motion trajectory at different inlet positions and solid concentrations at different sections in swirl tube are also presented. Based on that, a new collection efficiency model of swirl tube is developed with the investigation of flow pattern, spiral theory and boundary theory. Considering characteristic of solid concentration in swirl tube, that is lower in the middle zone and higher in the near tube wall region, the new revised solid concentration factor is put forward. So the assumed uniform radial particle concentration within swirl tube is broken. The availability of the efficiency model is verified by comparisons of the calculated grade efficiency with experimental data.Thirdly, the different operating condition parameters, such as flowrate, temperature, operating pressure and blowdown on the hopper, are also investigated by CFD method, and some useful conclusions were obtained. The research on gas-solid flow behavior helps to develop the new high-efficiency-low-resistance type swirl tube, and further explore the separation mechanism in swirl tube.Finally, the numerical simulation of TSS with three swirl tubes are carried out for investigating the flow characteristics in TSS. The effect of construct parameters in inlet room of TSS on flow uniform distrbution is presented with k-εturbulence model. Based on the above analysis, the new multi-layer diffuse cone is presented for better gas uniform distribution. The TSS can be divided into four parts, the inlet room, the separation room, common hopper space and gas outlet space. Due to the different flowrate at the every single swirl tube, the working condition of each TSS space is also different. The pressure distribution in inlet room is non-uniform, and existed for some certain region. The different pressures on dust outlet of each single tube lead to solid entrainment, and the flow pattern in common hopper is more complicated, and blowdown in the bottom of common hopper can reduce this negative phenomenon.更多还原