Modelling of liquid-liquid extraction columns: Use of published model correlations in design

Design of several liquid-liquid extraction columns — packed, pulsed-packed, pulsed-plate, Oldshue-Rushton columns and the rotating disc contactor — was attempted utilizing available correlations for drop size, holdup of dispersed phase, flooding velocities, mass transfer coefficients and axial mixing coefficients. Correlations in many cases were vaguely defined and often based on very limited data. Results indicated that for given flow rates and extraction efficiency, the height of a packed or Oldshue-Rushton column must be considerably greater than the predicted minimum heights of the other three columns, which were comparable considering the limited data utilized in the developed correlations. A critical evaluation of the correlations should be carried out to guide the further experimental effort required to confirm the utility of the axial dispersion model in liquid-liquid extraction column design. Extension of the theory to include drop size variation is highly desirable.     

往复振动板式萃取塔水力性能研究

以上－煤油为介质,在内径为０．０３１ｍ的往复振动板式萃取塔内研究了此塔的分散相持液量、轴向混合和液滴大小。研究表明分散相持液量与板振幅、频率、连续相流速和分散相流速有关;Ｓａｕｔｅｒ平均直径与板振幅、频率有关。应用脉冲响应法测试此塔的轴向混合,以无因次方程对轴向混合系数进行关联。     

DISPERSED PHASE HOLDUP AND DROP SIZE DISTRIBUTION IN A ROTATING PERFORATED DISK CONTACTOR

Hydrodynamic characteristics of rotating perforated disk contactor(RPDC)were studied with emulsionwater system.The emulsion was dispcrsed in water and its holdup was measured.The effects of columndimensions and operating conditions on holdup and characteristic velocity were studied.By using the methodof dimensional analysis,the authors obtained two experimental correlations for estimating holdup and characteristic velocity respectively.Drop size distribution was studied photographically.The experimental results showedthat drop size distribuiion could be described by upper-limit log-normal distribution.     

A NEWLY DEVELOPED LIQUID-LIQUID EXTRACTION COLUMN——The Open Turbine Rotating Disc Contactor(OTRDC)

The experimental study on hydrodynamics,axial mixing and mass transfer has been carried out in anewly developed liquid-liquid contactor,the open turbine rotating disc contactor(OTRDC).It has been foundthat the OTRDC is possible to be operated with higher hold-up of dispersed phase,larger interface and hencehigher efficiency of mass transfer comparing with the ordinary RDC.In correlating axial mixing data,a combinedmodel has been used in which both forward mixing due to the drop size distribution and backmixingof droplets are taken into account.The RTD curves of dispersed phase predicted by the model were fit wellwith the experimental data.The comparison of the experimental mass transfer data with thosc predicted by theaxial mixing model and theoretical single drop models shown they are in good agreement.     

Pressure drop,bed expansion and liquid holdup in a three phase spouted bed contactor

Data on the pressure drop, bed expansion and liquid holdup in a three phase spouted bed contactor with an initial bed height of 243 mm. were obtained as a function of the gas and liquid flowrate. Polyethylene spheres 10 mm. in diameter with a density of 320 kg/m³ were spouted in a 194 mm. column using a 30 mm. nozzle. The spouted bed contactor with gas and liquid mass flow-rates of 2.18 and 1.88 kg/m² sec, respectively had similar pressure drop per unit area of particle surface, total liquid holdup per unit volume of operating bed, and “active” holdup, as a fluidized contactor.     

Hydrodynamics,axial mixing and mass transfer in open turbine rotating disc contactor (OTRDC)

An experimental study of hydrodynamics, axial mixing and mass transfer has been carried out in a newly developed liquid-liquid extraction contactor, namely the open turbine rotating disc contactor (OTRDC). It has been established that the OTRDC can be operated with larger holdups of the dispersed phase, larger interfaces and, hence, more efficient mass transfer than the conventional RDC. In correlating axial mixing data, a combined model has been applied in which both the forward mixing due to drop size distribution and the backmixing of droplets are taken into account. The RTD curves of dispersed phase predicted by the model agree well with the experimental data. Comparison of experimental mass transfer data with those predicted by the proposed axial mixing model and the theoretical single drop model shows that they are in good agreement.     

由转盘塔内连续相溶质浓度轴向分布 估算传质系数和轴向混合系数的研究

根据转盘萃取塔内连续相溶质浓度的轴向分布进行了参数估算.在估算中应用液滴尺寸分布,将带轴向混合的柱塞流模型应用于塔内连续相,将前混模型应用于分散相.参数估算结果表明:应用d_(32)所获得的连续相轴向混合系数E_c和传质系数k_c的估算值比应用液滴尺寸分布所得的E_c、k_c的估算值偏高;如果忽略液滴生成过程传质的影响,k_c的估算值略有增加,而E_c的估算值则明显偏高.     

Scale-Up Study on the Performance of Annular Pulsed Disc-and-Doughnut Columns

Based on the previous work of the hydraulic, axial mixing, and mass-transfer performance of an annular pulsed disc-and-doughnut column (APDDC), the effects of scaling-up on its performance were studied in APDDCs with different annular space widths. The effect of scaling-up on holdup was discussed, and a more universal correlation was established. The effect of scaling-up on the Sauter drop diameter could be expressed by the previous obtained correlation. The effects of scaling-up on both the flooding holdup and throughput were mainly reflected in the correlation of the Sauter drop diameter. The equations of operating regimes were also independent of the scaling-up effect as demonstrated by experimental data. The scaling-up effects on the axial-dispersion coefficient of the continuous phase, the mass-transfer coefficient, and the height of a transfer unit were also discussed.     

“FORWARD MIXING” MODEL: APPLICATION TO PULSED PLATE EXTRACTION COLUMN OPERATION IN THE EMULSION REGION

The “Forward Mixing” model has been applied to data obtained from a 22 cm diameter pulsed plate extraction column. Measurements of drop size distributions, dispersed phase hold-up and concentration profiles for two systems (toluene-acetone-water and n-butanol-succinic acid-water) of quite different properties were made with the column operating in the emulsion region. Generated drop size distribution function parameters, size-dependent slip velocities and mass transfer coefficients, and continuous phase axial dispersion coefficients were accurate in predicting dispersed phase hold-up and extraction efficiencies (or the related plug flow number of transfer units). These parameters were correlated with phase superficial velocities and pulse velocities. The influence of continuous phase axial dispersion was much greater than the influence of drop size variation, and was not accurately predicted by most previous tracer-based correlations. An inlet dispersed phase distributor was beneficial to the performance with the high interfacial tension system.     

再分布板和径向挡板对淤浆鼓泡床流体力学特性的影响

研究了在以空气-水-石英砂为实验体系的淤浆鼓泡床中加入内构件?再分布板和径向挡板对床层气含率和固含率的影响,并与不加内构件的情况进行了对比. 实验结果表明,再分布板可明显提高床层的平均气含率,且开孔孔径越小,作用越显著;但径向挡板的作用不明显;再分布板和径向挡板均可改善气含率和固含率的轴向分布,且不会大幅度增加压降. 通过对Smith关联式进行修正,得到了带有再分布板的淤浆鼓泡床中床层平均气含率的经验关联式.     

Mass-transfer effects on droplet phenomena and extraction column hydrodynamics revisited

The effect of solute mass transfer between the two liquid phases on the drop size distribution and holdup profiles of the dispersed phase in a multistage extraction column is experimentally investigated in this article. Experimental results of the drop size distribution, dispersed-phase volume fraction (holdup), and concentration profiles are obtained for both directions of mass transfer. The drop size distribution is measured by a photomicrographic technique, the holdup profile is measured by an ultrasonic technique, and the concentration profiles are measured by refraction index measurements. A strong influence of the mass-transfer direction on drop size and holdup has been found. The results are in qualitative agreement with the observations of other investigators. Mass transfer of butyric acid from toluene (dispersed) to water (continuous) produced larger drop sizes and lower values of the dispersed-phase holdup than for the equilibrated toluene—water system. For mass transfer of butyric acid from water (continuous) to toluene (dispersed) smaller drop sizes and higher holdup values are observed than for the equilibrated toluene-water system. This behavior significantly affects the performance of the extractor and indicates the necessity for more studies to determine the physics of the phenomenon and to model these processes appropriately.     

New Approach in the Prediction of RDC Liquid‐Liquid Extraction Column Parameters

The liquid‐liquid extraction process is well‐known for its complexity and often entails intensive modeling and computational efforts to simulate its dynamic behavior. This paper presents a new application of the Genetic Algorithm (GA) to predict the modeling parameters of a chemical pilot plant involving a rotating disc liquid‐liquid extraction contactor (RDC). In this process, the droplet behavior of the dispersed phase has a strong influence on the mass transfer performance of the column. The mass transfer mechanism inside the drops of the dispersed phase was modeled by the Handlos‐Baron circulating drop model with consideration of the effect of forward mixing. Using the Genetic Algorithm method and the Numerical Analysis Group (NAG) software, the mass transfer and axial dispersion coefficients in the continuous phase in these columns were optimized. In order to obtain the RDC column parameters, a least‐square function of differences between the simulated and experimental concentration profiles (SSD) and 95 % confidence limit in the plug flow number of the transfer unit prediction were considered. The minus 95 % confidence limit and sum of square deviations for the GA method justified it as a successful method for optimization of the mass transfer and axial dispersion coefficients of liquid‐liquid extraction columns.     

High flux mass transfer: Comparison of liquid-liquid extraction column and drop (Handlos-Baron) model predictions with rotating disc contactor performance

High flux mass transfer measurements have been made in a rotating disc contactor and the results compared with model predicted results. Extraction column and drop model equations for single solute transfer were modified to include the influence of the interphase convective, or drift, flux, previously neglected. The Handlos-Baron drop model was utilized and found to predict the correct trends with changes in drop size. Continuous phase axial dispersion measurements were carried out by pulse tracer injection and by concentration profile measurements at low flux, when simultaneous measurements were made of the continuous phase mass transfer coefficient. When these values were used in the high flux model, high flux extraction efficiencies were accurately predicted but concentration profiles were not.     

Radioisotope tracer study in trickle bed reactors

The residence time distribution (RTD) of liquid phase in trickle bed reactors has been measured for air‐water system using radioisotope tracer technique. Experiments were carried out in a glass column of internal diameter of 0.152 m packed with glass beads and actual catalyst particles of two different shapes. From the measured RTD curves, mean residence time of liquid was calculated and used to estimate liquid holdup. The axial dispersion model was used to simulate the experimental data and estimate mixing index, ie. Peclet number. The effect of liquid and gas flow rates on total liquid holdup and Peclet number has been investigated. Results of the study indicated that shape of the packing has significant effect on holdup and axial dispersion. Bodenstein number has been correlated to Reynolds number, Galileo number, shape and size of the packing.     

DISPERSION OF GAS AND LIQUID IN BUBBLE COLUMNS OF HOMOGENEOUS BUBBLE FLOW REGIME

Mean gas holdup, lateral distribution of gas holdup and axial mixing of gas and liquid were measured in bubble columns of 12 and 19cm i.d. The lateral distribution of gas holdup was strongly dependent on the flow regimes in the column. The axial mixing of liquid in the homogeneous bubble flow regime was much smaller than that in the heterogeneous bubble flow regime, and was not expressed by existing correlations. The axial mixing of liquid in the homogeneous bubble flow and the intermediate flow regime was simulated with a flow model based on the lateral distribution of buoyancy force and the effective viscosity. The axial mixing of gas was larger than that of liquid.     

Hydrodynamic characteristics of a horizontal flow ejector in a rectangular chamber

The effects of the volumetric flow rate of primary motive water, water height, and the geometric parameters of the hydrodynamiccharacteristics of the gas suction rate and gas phase holdup were investigated in a rectangular chamber (0.22×0.26×1.2 m-high) with a horizontal flow ejector. Gas suction rate increased with increasing volumetric flow rate of the primary motive water, mixing tube length and diffuser length, but it decreased with increasing water height and nozzle diameter. The gas phase holdup was directly proportional to gas suction rate, indicating its corresponding increase with the volumetric flow rate of the primary motive water. Conversely, it decreased with increasing water height and nozzle diameter. However, the mixing tube length affected the gas phase holdup minimally compared to other operating parameters. Both the gas suction rate and gas phase holdup correlated with the dimensionless equations of operating parameters.     

THE INFLUENCE OF HELICAL FLOW ON WATER FUEL EMULSION PREPARATION

This study presents a method of preparing simple and multiple emulsions formed in a liquid-liquid contactor with Couette-Taylor flow (CTF). A Couette-Taylor flow contactor represents a mini-channel device, and due to its small dimension can be connected to a diesel engine for just-prepared emulsion injection. Stable simple W/O and multiple O/W/O emulsions have been prepared, both with quite narrow drop size distribution. The mean drop size of the inner phase of multiple emulsions is in range of 2-10 μm depending on the operating conditions. Simple and multiple emulsions will be considered as an alternative diesel fuel for improving engine performance and emissions characteristics.     

Direct extraction of Mo(VI) from sulfate solution by synergistic extractants in the rotation column

Direct extraction of molybdenum from sulfate solution with synergistic extractants (mixture of D₂EHPA and TBP) was studied in the rotation column. The influence of extractant concentration and initial pH of aqueous phase was studied in the bench scale experiments. The outcomes demonstrated that the synergistic solvent extraction enhances the constancy of the extracted complexes for transfer into the organic phase. In the continuous experiments, the effect of different operating parameters such as speed of agitation, inlet solvent flow rate and inlet aqueous flow rate on the holdup, mean drop size, drop size distribution, slip and characteristic velocities and extraction percentage were examined. Modified correlations were proposed for prediction of hydrodynamic parameters with consideration of reaction extraction condition in the rotation column. Furthermore, these correlations were compared with the experimental data. According to the results, the direct extraction of Mo (VI) from aqueous solution and sulfuric media with extraction efficiency of 90.4% was obtained at higher rotor speed (240 r·min^-1 rpm) in this column.     

Comparison of the Hydrodynamic Performance of Pulsed Solvent Extraction Columns with Tenova Pulsed Column Kinetics Internals and Standard Disc and Doughnut Internals for Copper Extraction Using the LIX 84 System

The dispersed phase holdup and droplet size are important parameters for understanding the hydrodynamic performance of pulsed solvent extraction columns. This study provides a comparison of the hydrodynamic performance between a Tenova Pulsed Column with Kinetics Internals (TPC-KI) and a pulsed column with standard disc and doughnut internals. The TPC-KIs are designed to improve the performance of systems with slow reaction kinetics, such as copper extraction with LIX 84, which was the focus of the current study. Holdup and drop size have been measured as a function of pulsation intensity and phase velocities for both types of column internals. Lower holdup and larger drop sizes were obtained with the TPC-KI, which indicates a higher flood point and a higher throughput. Correlations have been developed to predict the performance of these internals over a range of operating conditions.