喷射型内环流反应器流体力学的实验和模拟研究

发布时间：2018-05-07 11:08

本文选题：喷射型内环流反应器 + 气液鼓泡流　；参考：《浙江大学》2017年硕士论文

【摘要】：内环流反应器广泛的应用于重质油加氢、生物发酵、污水处理等化工过程。工业上普遍使用带均匀分布器的内环流反应器,反应器内部气泡尺寸均匀,气含率差异不大,循环速度有限。使用气液喷射器可产生不同尺寸的大小气泡,大气泡加强流体的湍动,有效地克服传统内环流反应器循环速度不足的缺陷,小气泡同时可以促进气液传质。将喷射型分布器和内环流反应器结合应该是一种是理想的气液两相反应器构型。目前针对均匀分布型内环流反应器的研究较多,而对喷射型内环流反应器的实验与模拟研究均较少。喷射型内环流反应器涉及高速射流、较宽的气泡尺寸分布、大尺度的全塔液相循环等过程,流动状况复杂,对该类反应器的流体力学状况还不甚清楚。本文对喷射型内环流反应器的流体力学行为进行了系统研究,在安装有喷嘴和锥形底的内置(?)100× 1400mm导流筒的(?)200×2500mm装置内开展冷模研究,测量了气含率和液速的空间分布,考察了反应器的多相流动规律,并建立相关的CFD模型。实验结果表明,喷射型内环流反应器中喷嘴的射流会在底部产生较大尺寸的气泡,气泡在提升管中随浮升而破碎,气含率沿高度而增加,分布器影响区贯穿全塔;降液管中,由于液相对不同尺寸的气泡携带能力不同,气含率沿轴向递增。喷嘴产生的大气泡促进了液相的循环流动,使循环速度成倍增大,有利于液相混合与固体悬浮。在实验的基础上修正了曳力系数模型,并通过对比模拟结果和实验数据,认为大涡模拟要优于可实现的k-ε模型。曳力修正因子的引入,使该模型能够较好的模拟平均气含率等宏观量的变化,但由于单气泡模型的缺陷,对于局部流动特征的描述不尽如人意,仅在降液管内得到了和实验吻合的气含率和液速分布,在提升管内的数值结果和实验差异较大,无法表现出喷射影响区贯穿全塔的特点。液相的进料会显著的促进气泡的破碎,使全塔的气含率明显增高。为了契合喷射型内环流反应器中气泡分布较宽的特征,使用CFD-PBM耦合模型来对体系进行模拟。该模型表现出了反应器中由射流产生的大气泡随浮升而破碎,气含率沿轴向高度增加,分布器影响区显著延长的特征;大气泡对液相循环流动的促进作用也得到了良好的展现。通过分析反应器内的速度矢量图以及气泡尺寸分布云图,发现在液相流动方向发生剧烈变化的区域,湍流耗散率较高,气泡破碎更加显著。实验和模拟研究表明,喷射型内环流反应器是一种能够有效强化液相混合、气液传质、固体悬浮的理想反应器构型。
[Abstract]:Internal annular flow reactor is widely used in heavy oil hydrogenation, biological fermentation, sewage treatment and other chemical processes. The inner ring flow reactor with uniform distributor is widely used in industry. The internal bubble size in the reactor is uniform, the gas holdup has little difference and the circulation speed is limited. The turbulence of strong fluid can effectively overcome the defect of insufficient circulation speed in traditional inner loop reactor. Small bubbles can promote gas-liquid mass transfer at the same time. The combination of jet distributor and inner ring flow reactor should be an ideal gas-liquid two phase reactor configuration. The experimental and Simulation Research of the internal annular flow reactor is less. The jet type inner ring flow reactor involves the high speed jet, the wider bubble size distribution, the large scale whole tower liquid cycle and so on, the flow condition is complex, and the hydrodynamics of the type reactor is not clear. The behavior was systematically studied. Cold model study was carried out in the (?) 100 x 1400mm guide tube (?) 200 x 2500mm installation with a nozzle and a conical bottom. The spatial distribution of gas holdup and liquid velocity was measured, the multiphase flow law of the reactor was investigated, and the related CFD model was established. The experimental results showed that the spray type inner ring flow reactor was sprayed. The jet of the nozzle produces a larger size bubble in the bottom, and the bubble is broken in the riser with the rise in the riser. The gas holdup increases along the height and the distributor affects the whole tower. In the drop pipe, the gas holdup increases along the axial direction because of the different carrying capacity of the liquid relative to different sizes. The large bubbles produced by the nozzle promote the circulation of liquid phase. On the basis of the experiment, the drag force coefficient model is modified. By comparing the simulation results and the experimental data, the large eddy simulation is considered to be better than the k- epsilon model. The introduction of the drag force correction factor makes the model better simulate the macroscopic gas holdup, such as the mean gas content. However, due to the defects of the single bubble model, the description of the local flow characteristics is not satisfactory. The gas holdup and the liquid velocity distribution that coincide with the experiment are only obtained in the downfall tube. The numerical results and the experimental differences in the riser can not show the characteristics of the penetration of the whole tower in the ejection area. The feed of the liquid phase will be significantly promoted. The gas holdup of the whole tower is obviously increased. In order to fit the wide distribution of the bubble in the jet type inner ring flow reactor, the CFD-PBM coupling model is used to simulate the system. The model shows that the large bubbles produced by the jet in the reactor are broken with the floating rise, the gas holdup increases along the axial height and the distributor affects the area. The effect of large bubbles on the liquid circulation flow is well demonstrated. Through the analysis of the velocity vector map and the bubble size distribution cloud in the reactor, it is found that the region where the liquid phase flow is changing sharply is higher and the bubble fragmentation is more significant. Experimental and simulation studies show that The jet type internal loop reactor is an ideal reactor configuration which can effectively enhance liquid phase mixing, gas-liquid mass transfer and solid suspension.

【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ021.1

【参考文献】