Analysis of Local Liquid Distribution in a Pilot-scale Packed Bed with Gas-Liquid Cocurrent Flow

本论文进行了四个方面的研究，为工业规模的气液并流填料床（所谓的“滴流床”）的合理设计和操作提供了基础和有用的知识。1）液体流量径向分布的测定：在直径为0.38 m、高度为3.0 m的中试床中，填充了横截面为三叶草叶形状的三角形催化剂颗粒。填料床底部液体流量沿径向分布基本均匀。2）持液率径向分布的测量：采用10对铂电极测量了电阻随局部持液率的变化。在小颗粒填充床中，床层中心区域的持液率基本相同，而壁面区域的持液率略高。3）液体流动的X射线CT可视化观察：应用X射线CT技术对催化滴流床反应器内的液体流动进行可视化观察。4）用Ergun方程对填料床内的流动进行数值模拟：将常用的计算床层压降的Ergun方程推广到整个床层内，并考虑了局部空隙率的分布。当对流动的粘性阻力占主导地位时，流动偏向具有较高空隙率的区域。当惯性阻力控制床内流动时，沟流不严重。

Four studies were carried out to provide the fundamental and useful knowledges for the rational designing and operation of the gas-liquid cocurrent packed bed, so-called 'trickle bed', of the commercial scale.1) Measurement of the radial distribution of liquid flowrate :A pilot-scale bed of 0.38 m in diameter and 3.0 m in height was packed with the trigonal catalyst particles of which cross section is the shape of clover leaf. The distribution of liquid flowrate at the bottom of the packed bed was almost uniform in the radial direction. The 'wall flow' which means the liquid flow in the region close to the wall was not observed.2) Measurement of the radial distribution of liquid holdup :Ten pairs of platinum electrode were used to detect the electric resistance varying with the local liquid holdup. In the packed bed with small particles the liquid holdup was almost same in the center of the bed and slightly higher than that in the wall region. It is suposed that the 'wall flow' does not exist in the catalitic trickle bed reactor.3) Visual observation of the liquid flow with X-ray CT technique :The X-ray computed tomography (CT) technique was applied to visualization of the liquid flow pattern inside the bed. A contrast medium injected into liquid showed the liquid flow pattern and the 'wall flow' was not observed.4) Numerical simulation of flow pattern in the packed bed with vectorial Ergun equation :Ergun equation which is commonly used to estimate the pressure drop across the packed bed was extended to simulate the flow pattern in the whole bed with the distribution of local voidage. When the viscous resistance against the flow is dominant, the flow deviates toward the region with higher voidage. On the other hand, the channelling flow is not severe when the inertia resistance controls the flow in the bed.