涡轮搅拌萃取塔的模型研究

涡轮搅拌萃取塔是一种高效的液液萃取设备。介绍该塔型的两种数学模型:假设均相模型和液滴群模型。前者假设分散相为连续相,无法正确模拟实际流体特性;后者能精确地计算湍流区流体特性。同时描述了液滴群模型的求解及模型参数,包括液滴直径及其分布、液滴破裂与凝聚、滑动速度、传质系数和轴向扩散系数等的计算。     

往复振动筛板萃取塔放的大设计模型

对往复振动筛板萃取塔（RPEC）塔内的传质过程进行了理论分析，并在此基础上，从单液滴传质模型出发，应用数学统计方法建立了RPEC放大设计模型，即进行放大设计时应遵循通量、塔板间距、振幅和频率不变的原则计算表观传质单元高度H_OXP.采用林可霉素-正丁醇-酸水物系对塔径100 mm的RPEC实验塔研究表明：真实传质单元高度H_OX与体系物性、表观速度、输入能量（振幅A×频率f）有关，而与塔径无关，且不受轴向混合的影响，模型较好地预测了H_OX随输入能量的增加而减小，而通量的变化则对其影响较小;分散传质单元高度H_OXD是塔径D、输入能量、通量U_s和体系物性的函数，实验结果表明模型较好地描述了输入能量和通量增加强化传质起主导作用，有效降低分散传质单元高度H_OXD的传质过程部分，而不能描述轴向混合起主导作用部分.应用放大设计模型对直径325 mm的RPEC放大设计结果验证模型的预测误差在20％以内.     

CFD在精馏分离中的应用

计算流体力学(CFD)是研究精馏塔内气液两相流动和传质的重要工具.本文介绍了板式塔和填料塔内气液流动状况,塔板上和填料层的流体力学模型,论述了国内外CFD技术在精馏塔流场模拟方面的应用,指出了CFD技术在精馏领域的发展方向,对于板式塔,应充分考虑气液两相间的相互作用,对于填料塔,应根据填料的具体形状建立每个孔道的流体力学方程,进行更接近实际的三维两相流模拟.     

液液萃取塔研究的若干新进展及展望

液液萃取是应用广泛的分离技术,在石油化工、制药提取、金属分离等领域都有重要的应用。萃取塔作为常见的分离设备当前的设计还十分依赖于以往的经验,需要进行大量的实验。文章综述了萃取塔设备的研究现状,总结了对塔内流场、液滴和浓度场的实验测量技术,介绍了基于液滴的模型化方法和多尺度计算流体力学模拟方法,归纳了过程强化的相关研究进展。并对萃取塔未来的研究发展进行了展望,在数字化和可持续的发展背景下,未来在实验方面可以关注实时测量和优化,模型化方面关注于微观界面行为和传质影响的描述,在基于先进的实验和模拟技术基础之上,结合新萃取体系进行萃取设备和内构件的开发,从而实现过程强化,以解决化工过程面临的共同挑战。     

超临界流体萃取塔的应用设计及理论研究

设计了超临界流体萃取塔系统，并对其流体力学特性和传质性能进行了研究，为工业设计提供了理论依据。在连续逆流操作的超临界填料萃取塔、筛板萃取塔和喷淋萃取塔中，应用超临界二氧化碳-异丙醇-水、超临界二氧化碳-乙醇-水两种实验体系对流体力学模型和传质模型进行了实验验证，计算结果与实验数据符合较好。     

填料萃取塔的研究现状及进展

综述了填料萃取塔的特点、国内外对填料萃取塔中填料的选择与开发并且详述了部分填料的工业应用,同时详细阐述了研究者使用不同的理论模型和方法对填料萃取塔的传质特性和流体动力学特性的研究。其中研究方法包括实验方法、经验公式方法及模拟方法。通过实验,能获得准确的液滴直径、分散相体积分数、液泛速度与滑移速度等数据,再通过计算机模拟则能获得详细的流场、温度场、浓度场等微观信息。可以预见,实验方法、经验公式、计算机模拟的有机结合将成为解决填料萃取塔传质和流体动力学问题的有效手段。     

新型转盘萃取塔研究开发与工业应用

采用激光多普勒测速仪(LDV)和计算流体力学(CFD)软件,对转盘萃取塔(RDC)内的单相流流场进行了测量和模拟。发现塔内存在沟流和级间的旋涡流动,级间返混严重,为此发明了一种装有级间转动挡板的新型转盘萃取塔(NRDC)。NRDC与传统的RDC的区别在于安装了设计独特的转动挡板。这些转动挡板安装在2个转盘之间,固定在转动轴上,并与固定环处于同一水平面。LDV测量和CFD模拟结果发现,NRDC可有效抑制沟流和级间旋涡流动。传质实验和流体力学表明,NRDC的传质效率比RDC高20%—40%,而液泛速度大致相当。成功地将NRDC用于引进RDC的扩能改造和新塔的设计中。     

塔式萃取设备的研究综述

塔式萃取设备由于其密闭性好、处理能力大、适用范围广以及占地面积小等优点,广泛应用于液液萃取分离过程,并且得到了广泛的研究和发展。文章综述了近年来塔式萃取设备最新的研究进展,并对应用较广泛的填料萃取塔、振动筛板塔、脉冲萃取塔以及机械搅拌萃取塔的研究进行了详细介绍,同时介绍了各类塔式萃取设备实验与CFD模拟相结合的研究概况。浅析了未来萃取设备技术研究和发展的方向。     

轻重相交替进料筛板萃取塔中的传质性能研究

针对间歇操作萃取工艺生产能力低,而逆流连续操作萃取工艺返混严重等问题,研究提出了轻重相交替进料操作的萃取工艺,并对轻重相交替进料筛板萃取塔中的传质性能进行了研究。以煤油-苯甲酸-水为萃取体系,采用单个液滴的传质模型来计算萃取塔的分散相总传质系数,并研究了分散相流速、连续相流速、液滴上升速度以及塔板间距对分散相总传质系数的影响。实验得到分散相总传质系数Kod的数值在3.49?10?5~5.47?10?5 m?s?1,总分散相存留分数在1.63%~4.37%。结果表明轻重相交替进料筛板萃取塔的分散相总传质数高于Kühni搅拌萃取塔、脉冲萃取塔和振动挡板塔,并且流量变化对Kod的影响小,返混效应弱,总分散相存留分数小,不易液泛。     

空气搅动的填料萃取塔性能实验研究

引　言气体搅动是一种外加能量的萃取方法 .与机械搅拌相比 ,气体搅动的萃取塔内无运动部件 ,操作稳定 ,结构简单 ,能耗低 .过去已有数篇关于气体搅动的混合 -澄清槽[1] 、喷洒塔[2～ 4 ] 、多级连续萃取器[5] 等无填料的萃取过程水力学性能和传质性能的文献报道 .而在填料塔萃取过程中加入气体搅动技术 ,一方面继承了填料可以有效地降低轴向返混的优越性能 ;另一方面 ,通过外加能量进一步强化液 -液两相接触与传质 ,提高传质系数 ,综合了外加能量的萃取技术和填料萃取技术的优点 .关于这方面的内容目前少有报道[6] .1　实验装置与实验方法…     

Compartment-model for the simulation of the separation performance of stirred liquid–liquid-extraction columns

For detailed simulation and evaluation of stirred extraction columns a CFD based compartment-model was developed. Instead of simulating all effects in a computational expensive PBE-CFD-model, the velocity field calculation of the continuous phase is decoupled from the calculation of the dispersed phase (one-way coupling). In CFD only the continuous phase is simulated and the resulting velocity profile is used in the compartment-model to simulate the drop movement, coalescence, breakage and mass transfer for a representative number of drops (Monte-Carlo Method). This decoupling has a major impact on the calculated fluid-dynamics. Thus, the velocity profile of the CFD results is modified in the model to account for phase interaction. The compartment-model is applied for the simulation of a Kühni extraction column with the system toluene/water/acetone. The simulation results, namely holdup, drop size and concentration profiles over the column height, are in good agreement with experiments for different loads and different stirrer speeds.     

萃取柱内液-液两相流CFD-PBM模拟研究进展

对萃取柱内CFD-PBM模拟研究进行了较详细的综述,包括其基本理论、不同的求解方法及模拟研究现状等. CFD-PBM模拟的基本方程包括流动方程和群体平衡方程,其相互耦合,群体平衡方程涉及破碎与聚并2个关键模型. 群体平衡模型的求解方法包括直接离散化方法、矩量法、正交矩量法、直接正交矩量法、分段正交矩量法等,对这些方法的原理、优点和缺点进行了综述. 目前国际上关于萃取柱内CFD模拟采用较多的是简单的欧拉-欧拉两相流模拟,考虑液滴尺寸分布和进一步的浓度分布的群体平衡模型应用较少. 完善伴随传质的液-液分散体系的群体平衡模型,并将其应用于不同类型的萃取柱中,是萃取分离学科的重要任务.     

CFD Simulation of Liquid–Liquid Two-Phase Hydrodynamics and Axial Dispersion Analysis for a Non-Pulsed Disc and Doughnut Solvent Extraction Column

A two-phase computational fluid dynamics (CFD) simulation for a non-pulsed disc and doughnut solvent extraction column has been developed with commercial CFD software FLUENT. Simulated hydrodynamic results including phase distribution, velocity fields, and holdup are given, which enables predicted holdup to be compared with experimental data. Average absolute relative deviation (AARD) of experimental data and CFD prediction in this study is found to be 10.8%, which is comparable to the estimated error in the experimental data and the predictions from traditional correlations in the literature. To estimate the extent of axial dispersion, a species transport model is used for the continuous phase with a small amount of tracer introduced in the continuous phase, when Sauter mean diameter of the dispersed phase is set to be 3.5 mm. A two-point monitoring method is used to estimate a Peclet number. The tracer concentration distribution in the two-dimensional distance–time space is interpreted with MATLAB along with the experimental measurement. The simulated Peclet numbers are compared with column experiments, and in general the simulation underestimates the experimental data by 60%. Introducing a modified drag law improves the predictions. This work shows that CFD can successfully model the performance of a non-pulsed disc and doughnut solvent extraction column.     

填料塔基础理论研究新进展

规整填料塔具有效率高、压降低、放大效应不明显等优点,其成功应用有赖于对二相流动与传质的深入认识。文中综述了规整填料塔内的气液二相流动与分布、返混、气液二相在常压和高压下的传质特性、M arangon i效应以及计算流体力学(CFD)在规整填料塔中的应用等方面的国内外研究进展。填料塔内液体的分布与返混的研究较多,气相的流动分布与返混特性的研究较少,高压传质、M arangon i效应,特别是利用计算流体力学(CFD)模拟填料塔内的液体流动与传质等已逐渐成为研究的热点。     

Advanced prediction of pulsed (packed and sieve plate) extraction columns performance using population balance modelling

A bivariate population balance model (the base of LLECMOD program) for the steady state simulation of liquid extraction columns is extended to simulate pulsed (packed and sieve plate) extraction columns. The model is programmed using visual digital FORTRAN and then integrated into the LLECMOD program. As a case study, LLECMOD is used to simulate the separation performance of a pulsed extraction column. Two chemical test systems recommended by the EFCE (namely toluene-acetone-water and n-butyl acetate-acetone-water) are used in the simulation. Model predictions are successfully validated against steady state experimental data, where good agreements are achieved. The simulated results (holdup, mean droplet diameter and mass transfer profiles) compared to the experimental data show that LLECMOD is a powerful simulation tool, which can efficiently predict the performance of pulsed extraction columns.     

Numerical Simulation of Uranium Extraction from Nitric Acid Medium Using Hollow-Fiber Contactor

ABSTRACT

A two-dimensional axisymmetric computational fluid dynamics (CFD) model is presented to simulate uranium extraction from nitric acid medium using tri-n-butyl phosphate in n-dodecane in a hollow-fiber membrane contactor operated in non-dispersive solvent extraction mode. CFD model solves continuity and momentum-transport equations for the feed and shell sides and species transport equations for the feed side, shell side, as well as the membrane. Complex boundary conditions of flux continuity and concentration jump are implemented in the CFD model. The estimates of percentage of uranium extraction obtained from CFD simulations for different parametric conditions are compared with the experimental results, and a good agreement is observed. The validated CFD model is used to gain detailed insights into the hydrodynamics and mass transfer.

Abbreviations CFD: Computational fluid dynamics; NDSX: Non-dispersive solvent extraction; TBP: Tri n-butyl phosphate     

CFD simulation of acetone separation from an aqueous solution using supercritical fluid in a hollow-fiber membrane contactor

In the present study, separation and mass transfer of acetone using a polymeric hollow fiber membrane by a supercritical fluid as a dense solvent was simulated. The propane is used as supercritical fluid for extraction of acetone. The simulated hollow-fiber membrane contactor has three compartments: tube, porous membrane and shell. The aqueous solution and solvent pass in the lumen and shell sides, respectively. The model equations have been solved by CFD technique using a finite element as numerical method. The simulation results were compared with experimental data obtained from literature and showed great agreement with the measured values. The simulation results of acetone extraction also showed that reducing the feed rate and increasing the solvent velocity will enhance the separation of acetone.     

Prediction of dispersed phase holdup in pulsed disc and doughnut solvent extraction columns under different mass transfer conditions

Using experimental data from a number of pulsed disc and doughnut solvent extraction columns,a unified correlation for the prediction of dispersed phase holdup that considers the effects of mass transfer is presented.Pulsed disc and doughnut solvent extraction columns(PDDC) have been used for a range of important applications such as uranium extraction and nuclear fuel recycling.Although the dispersed phase holdup in a PDDC has been presented by some researchers,there is still the need to develop a robust correlation that can predict the experimental dispersed phase holdup over a range of operating conditions including the effects of mass transfer direction.In this study,dispersed phase holdup data from different literature sources for a PDDC were used to refit constants for the correlation presented by Kumar and Hartland [Ind.Eng.Chem.Res.,27(1988),131–138] which did not consider the effect of column geometry.In order to incorporate the characteristic length of the PDDC(i.e.the plate spacing),the unified correlation for holdup proposed by Kumar and Hartland based on data from eight different types of columns [Ind.Eng.Chem.Res.,34(1995) 3925–3940] was refitted to the PDDC data.New constants have been presented for each holdup correlation for a PDDC based on regression analysis using published holdup data from PDDCs that cover a range of operating conditions and physical properties and consider the direction of mass transfer.     

AI-Based Supervision for a Stirred Extraction Column Assisted with Population Balance-Based Simulation

Solvent extraction as environmental benign separation technique can be modeled in physical detail by population balance of the droplet size distribution. However, much information on the droplet generation and coalescence is necessary for representative results. In this contribution, we present a comparison of AI-evaluated experimental and simulated data on the behavior of a stirred solvent extraction column with an inner diameter of 32 mm. Lab experiments were performed using the standard test system with n-butyl acetate, acetone, and deionized water. A digital camera is placed in front of the middle section as well as the head of the column. Droplet size evaluation is performed using a retrained neural net (Mask R-CNN). The stirred DN32 extraction column is modeled and simulated using a 1D CFD population balance software. The simulation allows for behavior analysis, trends comparison, and validation of the hydrodynamics and mass transfer performances.     

Computational fluid dynamics simulation of reactive absorption of CO2 in a structured packed column

In this study, multiphase Eulerian computational fluid dynamics (CFD) modelling is developed to predict the hydrodynamics, mass transfer, and chemical absorption of CO₂ using a monoethanolamine (MEA) solution in a structured packed column. First, the hydrodynamic simulation of liquid dispersion in a structured packed bed using a two-dimensional CFD is performed. The simulation results of the radial distribution of the liquid holdup are compared with the literature experimental data. The model prediction matches the experimental data at the top position of the column, whereas a slight deviation is found at the bottom position of the column. Using a validated CFD model, the reactive mass transfer is modelled to study CO₂ capture in a structured packed column with Mellapak 500.X. The model results are compared to the literature experimental results of CO₂ mole fractions along the height of the column. It is found that the model results match the experimental findings. Furthermore, CFD modelling is extended to investigate the influence of operating conditions such as gas and liquid velocities on CO₂ removal efficiency. The present CFD model demonstrates the porous media approach for reactive absorption of CO₂ in a structural packed bed.