规整填料塔中精馏过程的三维模拟(Ⅱ)模型的验证及液相分布和混合行为对精馏过程的影响

用简化三维混合池模型对Gorak所做精馏实验作了实例计算。模型的计算结果与Gorak实验数据符合良好,以简化三维混合池模型为工具,用数值计算的方法研究了规整填料塔中液体流动分布和混合对精馏过程的影响。结果表明：液相轴向返混对精馏有着显著的不利影响;当液体流动分布为严重壁流分布（严重沟流分布）时,必须用三维模型描述才不会产生较大偏差;横向混合系数的增大有利于填料塔分离效率的提高,但不能完全抵消液相严重不均匀分布对精馏过程的不利影响。     

A new multi‐scale model based on CFD and macroscopic calculation for corrugated structured packing column

A multi‐scale approach with the combination of computational fluid dynamic (CFD) and macroscopic calculation methods has been proposed to predict the hydrodynamics behavior in the corrugated structured packing column. On the basis of the concept of the representative unit, the three‐dimensional (3‐D) volume of fluid (VOF) model of the structured packing is applied in the small scale simulation, and the stream split fraction coefficients and effective wetted area ratio are calculated. The unit network model, which is a mechanistic model, is applied in large scale calculation basing on the small scale results. The liquid holdup distribution in the entire column can be available by this multi‐scale method. A comparison between the simulation results and the experimental data of our previous work is given to validate the present model. The multi‐scale model is proved to be prospective to assist the analysis and design of structure packing columns in chemical engineering. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3119–3130, 2013     

Gas–liquid flow modeling in columns equipped with structured packing

The modeling of gas–liquid flow in distillation columns equipped with structured packing has been dealt. The devices are seen as bistructured porous media, and a macroscale model is proposed taking into account this specific geometry. In this model, the two liquid films, one‐per‐sheet, are treated separately and are allowed to exchange matter at the vicinity of the contact points between corrugated sheets. The model emphasizes mechanisms that lead to the liquid radial dispersion effects: a main part comes from the geometry itself, another part is due to the capillary effects. A particular attention is paid to model these phenomena from a macroscale point of view. Finally, the simulation results are confronted to tomography imaging within a lab‐scale column and show a qualitative good agreement of the liquid distribution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3665–3674, 2014     

规整填料塔精馏的Marangoni效应

选用 6种代表性物系对陶瓷板波纹和不锈钢丝网规整填料进行全回流精馏实验 ,考察Marangoni效应对规整填料液体流动分布及传质的影响 .结果表明 :对纯有机体系 ,Marangoni效应影响较小 ;而对有机物的水溶液 ,Marangoni效应严重影响着填料的润湿和传质效率     

Interfacial area measurement in a catalytic distillation packing using high energy X-ray CT

In this paper, we report on the use of X-ray tomography to visualize and quantify the gas–liquid interfacial area in modular catalytic distillation packing elements.The calculation method is based on processing of tomographic images. It is validated by comparing specific surface area determined on dry packings (Mellapak? 752Y and Katapak? SP12) tomographic binary images (gas and solid) to values announced by manufacturers, based on geometrical considerations. These data agree fairly well. However, tomographic images show that the specific area is not distributed uniformly over the height of a packing element due to the presence of perforations in corrugated sheets and of wall wipers between the packing and the column wall. X-ray tomography is a unique technique to access to the spatial distribution of these geometrical details in a non-intrusive way.The method used to determine the specific surface area of dry packing is then applied to irrigated packing in order to determine the gas–liquid interfacial area. The axial distribution of the interfacial area is non-uniform and is correlated to the packing specific area. The maxima of the specific surface area correspond to the presence of wall wipers.The gas–liquid interfacial area averaged over the column length is determined. It increases logically with the liquid superficial velocity and slightly with the gas velocity. The effect of the gas velocity is however more pronounced when reaching loading point.     

规整填料表面液体分布的计算流体力学

采用计算流体力学(computational fluid dynamics,CFD)中的VOF方法对规整填料表面液相分布进行了三维建模和仿真,实现规整填料内液相分布的可视化并得到了液膜厚度和有效相界面积比等相关定量信息。通过分析比较不同物系的数值模拟结果,发现液体的表面张力和黏度都对填料表面上液体分布有影响。表面张力越小,液相在填料片上分布越均匀,有效相界面积比越大,液膜厚度越小;黏度增加,有效相界面积比和液膜厚度也随之增加。较之于黏度对液相分布的影响程度,表面张力的影响程度更大,为主要影响因素。本文还提出一个预测有效相界面积比的新公式,并将数值模拟结果与已有文献进行对比,吻合性较好。     

CFD Studies of Pressure Drop and Increasing Capacity in MellapakPlus 752.Y Structured Packing

Packed columns equipped with structured packings are widely used in separation processes. In this study, the hydrodynamics of MellapakPlus 752.Y was investigated using a computational fluid dynamics (CFD) approach. This packing includes short smooth bends at both ends of each corrugated sheet. Two adjacent sheets of a whole packing module were considered as computational domain. The CFD results indicated that the gas phase should be simulated using a turbulent model for F factors higher than 0.8. Thus, various two‐equation turbulence models were evaluated for the gas phase in the CFD model. It was shown that the baseline k‐ω (BSL) model leads to a slightly improved prediction of the pressure drops compared with the experimental data. The effects of the bends on the structured packing were studied by the model. It was found that using bends in the packings is useful for increasing the capacity and decreasing the pressure drop of the systems.     

激光诱导荧光技术测量规整填料内的液体分布

介绍了利用激光诱导荧光技术（LIF）测量规整填料内的液体分布的实验方法,实现了液体分布的可视化,得到了液膜厚度和持液量等定量信息。利用LIF技术分别测量了3种物系在750Y型规整填料的实验装置内的液体分布。结果表明,表面张力和黏度都对填料表面上的液体分布有影响,但表面张力对液膜厚度和持液量的影响较大,是主要影响因素。     

Investigation of flow parameters and efficiency of mixture separation on a structured packing

Results of experimental study of the effect of initial maldistribution of structured packing irrigation on efficiency of binary mixture separation are presented in this article. The studies were carried out in the experimental distillation column with the diameter of 0.9 m using the R114 and R21 freon mixture. Experiments were performed on the structured Mellapak 350.Y packing of stainless steel 316L, containing 19 layers with the total height of 4.016 m at the ratio of mole liquid and vapor flow rates L/V = 1 and 1.7, respectively, and the pressure in the upper part of the column p_top = 3 bars. Nonuniformity at the packing inlet was generated via the blocking of some holes in the liquid distributor. Here, we present some results on efficiency of mixture separation, pressure drop on the packing, distribution of local liquid flow rate under the packing over the cross‐section and on the column wall within the range of vapor loading factor (0.69 < F_v < 1.61 Pa^0.5), as well as experimental data on distribution of local concentration of the low‐boiling component over the cross‐section and along the height of the structured packing. It is found out that significant maldistribution of mixture concentration and liquid flow rate over the cross‐section slightly changes along the height in the lower part of the column at a change in the degree of packing irrigation nonuniformity at the inlet. It is shown that efficiency of mixture separation depends considerably on the value of parameter L/V, vapor flow factor F_v, and size of the zone underirrigated by liquid at the inlet. In the studied range of liquid and vapor flow rates, the relative pressure drop on the packing does not depend on the ratio of liquid and vapor flow rates L/V and degree of irrigation maldistribution. © 2013 American Institute of Chemical Engineers AIChE J 60: 690–705, 2014     

A Study on Modern High Effective Random Packings for Ethanol‐Water Rectification

Raschig Super‐Ring is a modern and high‐efficient packing used for intensification of absorption and distillation processes. The aim of this work is to characterize the efficiency of this packing applied to rectification of an important industrial system, ethanol‐water, and to compare its efficiency to that of some random packings of the third generation as well as to the structured packing, HOLPACK, which is used in the ethanol production industry. The experiments were carried out in a column installation, 0.213 m in diameter with a packing height of 2.8 m. The column is heated by a number of electrical heaters (total power 45 kW), which can be switched gradually. Operation at total and partial reflux is possible. Eight types of random packings were studied: five types of Raschig Super‐Ring, four metallic (with characteristic dimensions 0.5, 0.6, 0.7, and 1”) and one of plastic material 0.6”; two types of packing IMTP and one plastic Ralu Flow. Some experiments were conducted at total reflux operation at vapor velocity, 0.253–0.936 m/s, and liquid superficial velocity, 4.44 · 10^–4–1.63 · 10^–3 m³/(m²s). Experiments at partial reflux were carried out at constant liquid superficial velocity and changeable vapor velocity as well as at constant vapor velocity and changeable liquid velocity. The results are presented as height of transfer unit, HTU, and height equivalent to a theoretical plate, HETP, as a function of the velocity of phases.     

泡沫碳化硅波纹规整填料内的液体流动特性

通过采用配备微距镜头的高速摄像仪记录单波纹片上的液体流动行为,发现了泡沫碳化硅波纹规整填料内同时存在液膜流动和准壁流两种液体流动模式。同时测定了组合波纹片之间的液体传递量,并将泡沫碳化硅波纹规整填料与金属丝网波纹填料和金属板波纹规整填料的测试结果进行比较,结果表明泡沫碳化硅波纹规整填料的单波纹片上的液体扩散程度较大,组合波纹片之间的液体传递量高于金属丝网波纹填料和金属板波纹规整填料。研究结果揭示了泡沫碳化硅波纹规整填料具有高效传质特性的根本原因在于其独特的三维空间网孔结构增强了液体在单波纹片上的横向扩散能力和在组合波纹片之间的径向传递能力,为新型高效规整填料的机理研究和进一步开发开拓了思路。     

波纹板规整填料塔液体分布

将填料单元处理成立体节点网,根据节点网内网线液流和节点液流各自的运动方式建立了填料单元的液体分布模型.通过将填料与塔壁间的液体交换规范成填料节点网与塔壁节点网间的液量传递建立了填料单元对应塔壁区的流体分布模型.提出了规整填料塔液体分布问题的边界条件.2个描述填料单元及其对应塔壁区液体分布的数学模型与2类边界条件共同构成了波纹板规整填料塔的液体分布模型.采用单纯形法对3个模型参数进行了估计.模型计算结果与实验数据一致,表明模型能合理地描述波纹板规整填料塔的液体分布性能.     

波纹板填料表面液体降膜流动的特性分析

基于降膜流动实验台,结合计算流体力学方法(Computational Fluid Dynamics, CFD)研究了波纹板表面液体的平均液膜厚度和有效润湿面积等定量信息,并通过三维模拟进一步分析了喷淋密度和波纹倾斜角度β对降膜流动特性的影响。结果表明,液体在波纹板表面的流动并非均匀,分为沟流和溪流两种形式;当喷淋密度较小时,液体在波谷内形成沟流,当喷淋密度达到400 m3/(m2?h),液体跨越相邻波纹进行溪流流动;两种形式波纹板整体的润湿性能均较差,且液膜厚度分布不均;波纹倾斜角度对降膜流动特性影响较大,90°时更有利于提高有效润湿面积。     

Separation of isotope C using high-performance structured packing

A special high-performance structured packing, PACK-¹³C, with the surface area high as 1135 m² m⁻³ was developed, and the first stable isotope ¹³C pilot-scale plant using structured packing was designed and constructed by carbon monoxide cryogenic distillation, which has run smoothly over 6 months. The height and inner diameter of the distillation column were respectively, 20 m and 45 mm and the height of packing bed was 18 m. The column was well insulated by vacuum multilayer insulation and the total heat leakage of the column was less than 30 W. When the F-factor changes from 0.18 to 0.90 ms⁻¹ (kg m⁻³)^1/2, the numbers of theoretical plates per meter decreases from 30 to 20, the pressure drop is less than 25 Pa for each theoretical plate, the dynamic liquid holdup is between 11% and 21%, and the pilot-scale plant produces 2.1 g 15% isotope ¹³C each day. The fluid mechanical and mass transfer empirical equations were developed according to the experimental data of PACK-¹³C. The PACK-¹³C structured packing exhibits very high performances in isotope separation efficiency and operational flexibility, which is far superior to the traditional random packing. PACK-¹³C is a perfect packing to serve in ¹³C separation to increase productivity and reduce consumption.     

金属板波填料液流分布的研究

根据金属板波填料的结构,建立其液流分布模型.在φ500mm和φ200mm塔内,实测了6.3型和4.5型不锈钢板波填料的液流分布.结果表明:模型值与实测值基本相符.对不同填料在相同条件下的实测证明:金属板波填料的液流分布性能,优于拉西环、鲍尔环和阶梯环.文中就气液负荷和喷淋装置等因素的影响作了讨论,并提出了分布器喷淋点密度的推荐范围.     

Mass transfer in structured corrugated packing

The performance of structured corrugated packing has been simulated by establishing mechanistic models for liquid distribution, liquid flow on the packing surface and mass transfer. The models were used to investigate the effect of packing height, liquid load, initial maldistribution as well as differing initial distribution and solid-liquid contact angle on the packed column performance. Wetted surface area is the primary value of interest and the simulated results compare very well with those predicted by Onda (1968). The results clearly demonstrate that the wetted surface area is a strong function of the solid-liquid contact angle. Other predicted values such as mass transfer coefficients and overall height of a transfer unit show reasonable agreement with published data.     

Experimental and CFD Simulation Study for the Wetting of a Structured Packing Element with Liquids

The hydrodynamics of liquid flow in packed columns affects the column performance from the point of view of heat and mass transfer. The interfacial and the specific wetted areas are decisive in this case. The complex three‐dimensional liquid flow on a single structured and flat packing element of Rombopak 4M was investigated. It consists of four connected wavy inclined plates in an X‐shape configuration. The geometric characteristics of the packing were related to the fluid mechanics of the liquid distribution. CFD simulation results for different cell sizes and flow rates, obtained using the VOF (volume of fluid) model, are presented as being capable of describing this complex geometry. With the help of the CFD simulation and the experimental results from Rombopak 4M, correlations from the literature describing the interfacial and wetted area and liquid holdup in packed columns were adjusted to describe the hydrodynamic performance of Rombopak 4M.     

Liquid film flow on structured wires: Fluid dynamics and gas‐side mass transfer

The liquid film flow on different structured wires and chains is observed experimentally to assess the suitability of a structured packing consisting of vertical wires. The results show that liquid beads as they appear on cylindrical wires are inhibited by certain chain geometries. This increases the flooding gas load up to F = 12 Pa^0.5. As the stabilized film shows no liquid bead motion, the liquid velocity at the interface is less which results in lower gas‐side mass‐transfer coefficients. An estimation of the packing characteristics for different chain geometries with an assumed wire packing density of 40,000 wires/m² is made. The interfacial area, mass‐transfer coefficients, and consequently the separation efficiency strongly depend on the liquid load. However, the proposed gas‐side separation efficiencies are slightly lower compared to common structured packings but the advantages are higher load limits, a better liquid distribution, and lower pressure drop. © 2012 American Institute of Chemical Engineers AIChE J, 59: 295–302, 2013     

Liquid distribution and liquid hold-up in modern high capacity packings

In order to model and optimise industrial gas/liquid contactors such as those used for distillation or for post-combustion capture of CO₂, liquid hold-up and liquid distribution have been measured for two modern high capacity packings, a structured packing and a random packing. A gamma-ray tomographic system has been used to obtain liquid flow maps over a cross section of a 400 mm internal diameter column from which liquid hold-up values can be deduced. It is observed that the liquid flow is homogeneously distributed for both packings, the structured packing giving better results. Correlations are proposed to estimate the liquid hold-up, the effect of the liquid flowrate and the liquid viscosity being taken into account. A non-negligible static liquid hold-up is considered for the structured packing, which can be explained by the texture on the packing walls. As long as there is a little effect of the counter current gas, then below the loading point, results can be extrapolated to larger columns.