流化床内固液两相流特性及底板布孔优化的模拟研究

发布时间：2018-08-05 18:27

【摘要】：随着经济社会的发展,环境问题已成为制约我国社会发展的重要问题之一,而在诸多的环境问题中水污染问题又最为突出和严重,尤其是城市的快速发展产生了大量的生活污水,而这些生活污水大多都不经处理直接排放到自然界的水体中,对河流、湖泊、海洋等的环境造成了严重的污染,要想恢复到自然状态是十分困难的。水资源在我国并不丰富,而各种水体的污染,将使可利用的水资源进一步减少,影响人民的正常生活及工农业的生产。要想实现水资源的可持续利用,就必须对工业和生活污水进行净化处理,发展建立一整套经济实用的污水处理设备和方法,而在众多的污水处理方法中生物膜污水处理技术由于其操作方便,运行成本较低,而使其成为最重要的污水处理方法之一。本文采用RNG k-ε湍流模型结合欧拉-欧拉多相流模型对一典型的液流动力流化床进行数值模拟研究,比较了不同分布板开孔形式下的多种物理量,从而确定出合理的流化床进口分布板的布孔形式,分析了不同载体属性及操作条件下流化床内的固体体积分数、流场流态、湍动能及其湍动能耗散率等物理参量,从而确定了流化床的最优操作参数,发现不同运行工况的优缺点,从而使读者可以根据需要选择适合自己工况的分布板布孔方式、载体属性及操作参数。通过分析比较,得出如下结论:(1)通过对模型验证一的比较分析,发现采用欧拉-欧拉多相流模型辅以RNGk-ε湍流模型可以很好的模拟流化床内的固液两相流。通过模型验证二对所选用的多相流模型、湍流模型及其边界条件和数值求解方法进行了验证,模拟值与试验数据吻合较好,得出:所选数学模型、数值求解方法及边界条件可较好地模拟出流化床内固液二相流的流动特性。(2)通过与布设其他形式的载体分布板相比,布设分布板A时载体颗粒在流化床内处于完全流化状态,形成均一流动层,无局部高浓度区域,轴向浓度有波动但是不明显,流化床内浓度分布最为均匀。载体在流化床内轴向速度分布较均匀,无过大的速度产生,沿轴向和径向轴向速度梯度变化较小。布设分布板A时,载体径向速度分布范围明显大于布设其他分布板的情况,最大径向速度为0.17m/s,在径向上载体颗粒之间的碰撞与摩擦程度更为激烈。(3)在其他初始条件不变的情况下,随载体粒径的增大,流化床内载体体积分数和轴向速度均减小,床层的膨胀高度也明显减小,流速均匀性和流态都变差。随载体密度的增大,流化床内载体体积分数相应变大,床层膨胀率和轴向速度均减小,流速均匀性变差,流态也变得不稳定。随载体初始填充高度的增大,流化床内载体体积分数相应变大,轴向速度减小,床层膨胀率有小幅波动,流速均匀性和流态都变差。。随流化床入口处液体速度的增大,流化床内载体体积分数减小,床层膨胀率和轴向速度均有明显增大,流速均匀性变差。(4)通过对流化床内的载体体积分数、载体轴向速度分布及流速不均匀系数等的分析比较后得出:载体颗粒的密度为1500kg/m3,载体粒径为1mm,载体初始填充高度为0.3m,流化床入口处液体速度为0.15m/S时为所给定生物流化床的最优载体属性和运行参数。对提高流化床的污水处理效率最为有利。
[Abstract]:With the development of economy and society, environmental problems have become one of the most important problems that restrict the development of our society. In many environmental problems, water pollution is the most prominent and serious problem. In particular, the rapid development of the city has produced a large number of domestic sewage, and most of these domestic sewage are not treated directly to the water in the natural world. In the body, it has caused serious pollution to the environment of rivers, lakes and oceans. It is very difficult to restore to the natural state. Water resources in our country are not rich, and the pollution of various water bodies will make the available water resources further reduced, affecting the people's normal life and the production of industry and agriculture. To realize the sustainable benefit of water resources. It is necessary to purify industrial and domestic sewage and develop a complete set of economical and practical sewage treatment equipment and methods. In many sewage treatment methods, the biofilm sewage treatment technology is one of the most important sewage treatment methods because of its convenient operation and low operating cost. This paper uses RNG k- e turbulence. The flow model is combined with the Euler Orla multiphase flow model to simulate a typical fluid flow dynamic fluidized bed. A variety of physical quantities are compared in the opening form of different distributed plates, thus the pore form of a reasonable fluidized bed inlet distribution plate is determined, and the solid volume in the fluidized bed is analyzed under the different carrier properties and operating conditions. The physical parameters such as fraction, flow flow, turbulent kinetic energy and turbulent energy dissipation rate have been determined, and the optimal operating parameters of the fluidized bed are determined. The advantages and disadvantages of different operating conditions are found, so that readers can choose the distribution pattern of distribution plates suitable for their own working conditions according to their needs, the carrier and the operating parameters. Through analysis and comparison, the following conclusions are drawn. (1) through the comparison and analysis of the model verification one, it is found that the Euler Euler multiphase flow model can be used to simulate the solid and liquid two phase flow in the fluidized bed with the RNGk- epsilon turbulence model. Through the model verification, two models of the selected multiphase flow, the turbulence model and its boundary conditions and numerical solution methods are verified, the simulation values and the experiments are carried out. The data are in good agreement, and the mathematical model, numerical solution and boundary condition can be used to simulate the flow characteristics of solid-liquid two-phase flow in the fluidized bed. (2) the carrier particles in the fluidized bed are completely fluidizing in the fluidized bed, forming a homogeneous flow layer, and there is no local flow layer. (2) compared with other forms of carrier distribution plate, the carrier particles are in the fluidized bed. In the high concentration region, the axial concentration fluctuates but is not obvious, the concentration distribution in the fluidized bed is the most uniform. The axial velocity distribution of the carrier is more uniform in the fluidized bed, and the velocity gradient along the axial and radial direction changes little. When the distribution plate A is set up, the distribution of the radial velocity of the carrier is obviously larger than that of the other distribution plates. The maximum radial velocity is 0.17m/s, and the collision and friction between the carrier particles in the radial direction is more intense. (3) in the case of the other initial conditions, the volume fraction and axial velocity of the carrier in the fluidized bed decrease with the increase of the carrier particle size, and the expansion height of the bed layer decreases obviously, the velocity uniformity and the flow state of the fluidized bed are all worse. With the increase of carrier density, the volume fraction of carrier in the fluidized bed becomes larger, the expansion rate and axial velocity of bed layer decrease, the velocity uniformity becomes worse and the flow state becomes unstable. With the increase of the initial filling height of the carrier, the volume fraction of carrier in the fluidized bed is correspondingly larger, the axial velocity decreases, the bed expansion rate has small amplitude fluctuation and the flow velocity is uniform. With the increase of the liquid velocity at the entrance of the fluidized bed, the volume fraction of the carrier in the fluidized bed decreases, the bed expansion rate and the axial velocity are obviously increased and the velocity uniformity becomes worse. (4) the analysis and comparison of the carrier volume fraction in the fluidized bed, the axial velocity distribution of the carrier and the non uniform velocity coefficient of the flow velocity are compared. The density of the body particles is 1500kg/m3, the carrier particle size is 1mm, the initial filling height is 0.3m, and the liquid velocity at the inlet of the fluidized bed is 0.15m/S, which is the best carrier property and operating parameter for the given biological fluidized bed. It is the most favorable for improving the efficiency of the sewage treatment in the fluidized bed.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703

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