死端过滤中空纤维膜系统过滤模型研究

发布时间：2018-04-19 23:12

本文选题：中空纤维膜 + 死端过滤　；参考：《山东大学》2017年硕士论文

【摘要】：中空纤维膜具有结构简单、分离效率高、装填密度小、成本和操作费用低以及应用灵活等优势,在污水和饮用水处理领域受到越来越多的关注。然而膜污染的存在使得中空纤维膜系统过滤性能受到严重影响,膜污染已成为制约中空纤维膜分离技术发展的关键因素。数学模型是研究中空纤维膜污染、优化中空纤维膜系统过滤性能的重要手段。现有的死端过滤中空纤维膜过滤模型多以Hagen-Poiseuill方程为基础,尚未考虑到中空纤维膜腔内流体加速造成的动压损失对流体流动阻力的影响,削弱了模型模拟结果的准确度。另外,模型均是基于商业或开源计算流体力学(CFD)软件进行求解,CFD过程复杂,需要输入多个边界条件才能运行,而这些边界条件一般情况下是未知的,因此使用起来并不方便或误差较大。本研究以流体力学和膜过滤理论为基础,构建了一个描述死端过滤中空纤维膜过滤过程的数学模型,在模型构建时同时考虑了膜腔内摩擦造成的压力损失和流体加速造成的动压损失在膜长度方向上的累积,并以此模型为基础解析死端过滤中空纤维膜系统过滤特征参数及膜污染的时空分布规律,确定影响系统过滤性能的关键因子,为中空纤维膜系统的优化提供了科学依据。研究发现,模型模拟结果很好地吻合了实验结果,通过增加膜腔内动压损失对流体流动阻力的影响,模型模拟结果与实验结果吻合度明显提高。在进行模型求解时,死端处跨膜压差的确定是模型得以求解的关键。本研究提出了一种以二分法为基础的死端处跨膜压差的反向迭代计算法,该解法效率高,适用范围广,对恒流和恒压运行模式、不同膜污染机理作用下死端过滤中空纤维膜过滤模型均适用。基于上述死端过滤中空纤维膜过滤模型和数值解计算方法,研究模拟了中空纤维膜污染及系统各过滤特征参数的时空分布规律。研究发现,随着过滤时间的增加,膜长度方向上各点处膜污染均逐渐加剧;而任意时间时,膜长度方向上从死端到出水端,膜污染程度均逐渐增加。另外,各过滤参数跨膜压差、点通量及轴向流速在膜长度方向上的分布均呈现出从死端到出水端逐渐升高的规律。随着过滤时间的增加,近出水端部分点通量逐渐降低,近死端部分点通量逐渐升高,同时膜长度方向上存在部分区域,点通量呈现先升高到达峰值后再逐渐下降的趋势。膜长度方向上不同位置处跨膜压差均随过滤时间的增加而逐渐升高。对于轴向流速,死端和出水端处在整个过滤过程保持不变,而其他位置处则随着过滤时间的增加逐渐升高。死端过滤中空纤维膜系统运行压力随过滤时间的增加而逐渐增加。膜长度越小、膜内径越大、膜固有阻力越低、运行通量越低、污染物质浓度越低时,系统运行压力越低,能耗越小。另外,随着过滤时间的增加,膜内径、运行通量及污染物质浓度对运行压力的影响逐渐增大,而膜长度及膜固有阻力对运行压力的影响程度基本不发生变化。另外,死端过滤中空纤维膜系统点通量在膜长度方向上的分布均匀度随过滤时间的增加而逐渐增加。膜长度越小、膜内径越大、运行通量越高、污染物质浓度越高,则点通量分布均匀度越高,系统膜污染趋势越低。另外,随着过滤时间的增加,膜内径、运行通量及污染物质浓度对点通量分布均匀度的影响均呈现先增加后减小的趋势,而膜长度对点通量分布均匀度的影响逐渐减小。膜固有阻力对点通量分布均匀度的影响包括两个阶段,过滤前期膜固有阻力越大,点通量分布均匀度越高,而过滤后期点通量分布均匀度随膜固有阻力的增加而降低。特别注意的是,膜内径对死端过滤中空纤维膜系统过滤性能有重要影响,当膜内径过低时,系统运行压力显著升高,点通量在膜长度方向上的分布均匀度大幅降低,系统过滤性能迅速恶化。因此在中空纤维膜系统的实际应用中,应注意膜内径的优化。
[Abstract]:Hollow fiber membrane has the advantages of simple structure, high separation efficiency, small filling density, low cost, low operating cost and flexible application, and has attracted more and more attention in the field of sewage and drinking water treatment. However, the existence of membrane fouling has made the filtration performance of hollow fiber membrane seriously affected, and membrane pollution has become a restriction of hollow fiber. The key factor in the development of membrane separation technology is that the mathematical model is an important means to study the pollution of hollow fiber membrane and optimize the filtration performance of the hollow fiber membrane system. The existing dead end filter hollow fiber membrane filtration model is based on the Hagen-Poiseuill equation, and the fluid pressure loss caused by the fluid acceleration in the hollow fiber membrane cavity has not been taken into account. The effect of flow resistance weakens the accuracy of model simulation results. In addition, the model is based on commercial or open source computational fluid dynamics (CFD) software to solve the problem. The CFD process is complex and needs to enter multiple boundary conditions to operate, and these boundary conditions are generally unknown, so it is not convenient to use or have large error. Based on the theory of fluid mechanics and membrane filtration, a mathematical model describing the filtration process of hollow fiber membrane in dead end filtration is constructed. In the model construction, the pressure loss caused by the friction in the cavity and the accumulation of dynamic pressure loss caused by fluid acceleration in the direction of the membrane are also taken into account. The filtration characteristic parameters of the end filter hollow fiber membrane system and the temporal and spatial distribution of membrane fouling are used to determine the key factors affecting the filtration performance of the system. It provides a scientific basis for the optimization of the hollow fiber membrane system. The results of the model simulation are well consistent with the experimental results, and the flow resistance of the fluid is increased by increasing the dynamic pressure loss in the cavity. The simulation results of the model and the experimental results are obviously improved. When the model is solved, the key of the model is to determine the transmembrane pressure difference at the dead end. A reverse iteration calculation method based on the dichotomy method is proposed. This method has high efficiency, wide application range, and constant current and constant pressure. The hollow fiber membrane filtration model of dead end filtration under the action of different membrane fouling mechanism is all suitable. Based on the above dead end filter hollow fiber membrane filtration model and numerical solution calculation method, the spatial and temporal distribution of the hollow fiber membrane pollution and the characteristic parameters of the system are simulated. The membrane fouling at each point in the length direction of the membrane increased gradually, and the membrane fouling degree increased gradually from the dead end to the effluent end at any time. In addition, the distribution of the filtration parameters across the membrane and the axial flow velocity in the film length showed a gradual increase from the dead end to the effluent end. With the increase of time, the passage amount in the near end of the water end gradually decreases, the passage amount in the near dead end increases gradually, and there is a partial region in the direction of the membrane. At the flow rate, the dead end and the outlet end are kept unchanged throughout the filtration process, while the other positions increase gradually with the increase of the filtration time. The operating pressure of the dead end filter hollow fiber membrane system increases gradually with the increase of the filtration time. The smaller the length of the membrane, the larger the inner diameter of the membrane, the lower the inherent resistance of the membrane, the lower the flux, the thicker the contaminant material. At the lower degree, the lower the system operating pressure and the smaller the energy consumption. In addition, with the increasing of the filtration time, the influence of the inner diameter of the membrane, the flux and the concentration of the contaminant on the operating pressure gradually increases, and the influence degree of the membrane length and the inherent resistance of the membrane to the operating pressure is basically not changed. The uniformity of distribution in the length of the membrane increases with the increase of the filtration time. The smaller the membrane length, the larger the inner diameter of the membrane, the higher the flux, the higher the concentration of the pollutants, the higher the uniformity of the distribution of the dots, the lower the pollution trend of the system membrane. In addition, the inner diameter, the flux and the concentration of the contaminant material are increased with the increasing of the filtration time. The influence of the uniformity of the distribution uniformity is increased first and then decreased, while the influence of the film length on the uniformity of the point distribution is gradually reduced. The influence of the inherent resistance of the membrane on the uniformity of the point distribution is two stages. The greater the inherent resistance of the membrane, the higher the uniformity of the point distribution is, and the distribution of the late point distribution of the filtration is all The uniformity of the film decreases with the increase of the intrinsic resistance of the membrane. Especially, the inner diameter of the membrane has an important effect on the filtration performance of the hollow fiber membrane system. When the inner diameter of the membrane is too low, the system operating pressure rises significantly, the distribution uniformity of the flow rate in the film length is greatly reduced and the system filtration performance deteriorates rapidly. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. Therefore, the filtration performance of the system is rapidly deteriorated. In the practical application of the membrane system, we should pay attention to the optimization of the inner diameter of the membrane.

【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.893;X505

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