随机固定填充床内孔道结构及其内气液两相流动的多态现象及统计分析

A much higher performance of packed-bed reactor used for clean fuel production is required to meet the requirements of more and more rigorous environmental protection and improving of quality of the fuel product. Such higher reactor performance is mainly determined by the gas-liquid distribution inside the packed beds. There are many factors that affect the gas-liquid distributions inside the packed bed, and there exists a macro-(whole bed), meso- (channels) and micro- (particles) multi-scale relationships in that. However, most researches are mainly focused on the whole reactor, i.e., the macro scale, and less was concerned about the meso- (channels) and micro- (particles) scales..The void inside trickling beds can be regarded as parallel channels with different shape and size, some inter-connect with each other. Under trickling operation conditions, flow hysteresis is in-evitable thus plays an important role in gas-liquid mal-distribution. Since most previous studies were conducted for parallel channels with regular shape and uniform size, the hysteresis for parallel channels with non-regular shape and non-uniform size is one of important object in this study which can deeply unveil the mechanism of flow mal-distribution. Also a random packing bed domain is established with particles dropping under the effect of gravity. The void size and its distribution then can be analyzed statistically. The random packing bed is numerically studied, and then the local distribution of liquid and gas are further statistically analyzed. The fully unveiled mechanism of local liquid holdup distribution could significantly benefit the understanding of gas-liquid flow hysteresis inside packed beds thus to improve the reactor performance.

生产高标准清洁油品主要采用加氢滴流床反应器，但在工业操作中沟流短路等液相分布不均现象普遍存在，最终影响反应器的效率使得产品不合格。滴流床内部存在一个整床－空隙－颗粒多尺度的相互关联，其中空隙尺度起承上启下的作用，非常重要。空隙可视为并联的不规则通道，而在滴流区流体分布的多态现象会不可避免的出现。对这些微孔道内的气液分布尚无基于微观机制上的分析。.因此拟深入研究滴流床床层微孔道内气液分配规律及其影响因素，首先基于颗粒在重力场自由下落机制，建立随机填充床模型，对床内空隙率的分布规律进行统计分析。对不同级别的空隙或空隙群内可出现的气液流动多态现象进行研究，从微观层面揭示其产生机制，探讨其控制方法。对随机填充床进行CFD模拟，在局部流动分布的研究基础上进行统计，还可直接得到滴流床整床关键流体力学性质，实现从微观到宏观尺度的直接关联。课题最终目的是通过改善反应器效率，提高油品精制深度，满足市场需求。

滴流床反应器是一种重要的气液固三相催化反应器，广泛应用于石油炼制、石油化工等各个行业。目前对滴流床内气液两相局部流动行为以及孔隙尺度上研究单相和多相流体绕过和穿过多孔颗粒的流动特性的研究报道较少。本文深入研究滴流床床层微孔道内气液分配规律及其影响因素，从微观层面揭示流动机制，.1.使用VOF模型来模拟并考察位于滴流床床层中间位置和近壁位置的颗粒滴流过程中液体在颗粒表面的流动现象。分别考察了各影响因素对位于不同颗粒表面液膜分布和颗粒下端气相漩涡大小的影响。.2.采用VOF模型研究了气液两相流体通过滴流床反应器内单颗粒、两颗粒和三颗粒时的流体流动特性。催化剂颗粒表面和周围的流体流动特性受相邻的其他颗粒影响较大。.3.采用四参数随机生成法对颗粒内的多孔结构进行了重构。随后采用格子Boltzmann方法，对单个多孔球形颗粒、及由其堆积的面心及体心立方单元的单相绕流进行了模拟。.4.采用四参数随机结构生成法QSGS对多孔介质进行重构，在此基础上采用格子Boltzmann方法在孔隙尺度下对多孔介质内的流动和传热特性进行模拟研究。.5.使用离散元法建立了固定床的填充模型，并进行平均空隙率和径向空隙分布分析。研究了颗粒摩擦系数、壁面和填充方式对空隙分布的影响。采用路径追踪法得到固定床内可能的流体路径。.6.利用刚体动力学RBD法模拟三叶草颗粒的填充过程。从总空隙率、径向空隙分布和颗粒朝向分布三个方面对空隙结构进行分析，通过CFD模拟三叶草颗粒填充床内压力和速度分布规律。

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