Scheibel Extraction Column Research Articles

Reactive extraction of zinc ions in the Scheibel column; A case study by applying the mathematical modelling of mass transfer with forward mixing

An experimental and modeling study on the feasibility of the Scheibel extraction column is presented for heavy metal separation from chloride solution. In continuous experiments, the chemical reaction systems are considered zinc extraction by D2EHPA and stripping from the loaded organic phase by chloride solutions. The experimental results represent that the best extraction and stripping rates in the agitation speed of 155 rpm and the rate of inlet phases of 28 L/h are equal to 99.56% and 98.11%, respectively. The mass transfer modeling by applying the forward mixing is interpreted for solvent extraction systems in this column with the fitting technique. The calculated results from theoretical models compared with the experimental data, which good agreement was obtained using this model. The mathematical modeling on the reactive mass transfer data expresses that the axial dispersion coefficients based on the dispersed phase improve with increased agitation speed and dispersed phase rate. In contrast, these coefficients have an inverse relation with the continuous phase flow rate. This paper's experimental and numerical study provides beneficial information about the metallurgical industry to design solvent extraction columns.

Study on the feasibility of using a pilot plant Scheibel extraction column for the extraction and separation of lanthanum and cerium from aqueous solution

Batch and continuous experiments were carried out in a Scheibel extraction column to separate La(III) from Ce(III). Central composite design was used to evaluate the influence of pH, extractant concentration in the batch experiments, and the influence of rotor speed, phase flow rates in the continuous experiments. At optimum conditions (pH 3.5, D2EHPA extractant concentration 0.05 M, rotor speed 128 rpm, dispersed phase flow rate 32 L/h and continuous phase flow rate 18 L/h), high extraction efficiency and separation factor equal to 88.12% and 4.89, respectively, for cerium separation from lanthanum were reasonably well predicted by the model. At higher rotor speed, La(III) and Ce(III) ions move faster from aqueous to the organic phase, which retards the higher interaction between ions and D2EHPA extractant. The results showed that this extraction column could be a potential candidate for the extraction and separation of La(III) and Ce(III) ions or other industrial wastewater.

Prediction of Dispersed Phase Holdup in Scheibel Extraction Columns by a New Correlation

In this study, the effect of operating parameters on dispersed phase holdup in liquid-liquid extraction process has been investigated. Three chemical systems (Toluene/Water, Butyl acetate/Water, and n-Butanol/Water) were utilized and holdup was considered in a wide range of interfacial tensions through a Scheibel extraction column. Various rotor speeds were examined on the certain velocities of dispersed and continuous phases. It was found that with increasing rotor speed in a Scheibel extraction column, the drop size was reduced and drops were trapped inside the packed so that an increase in the dispersed phaseholdup happened. An obvious increasing trend of dispersed phase holdup was observed as a result of increase in dispersed phase velocity for all systems operating under 2 different rotor speed, namely, 100 and 140rpm. However, the results showed that increase in the velocity of continuous phase would not make significant effect on the holdup. During examining the effect of both rotor speed and dispersed phase velocity, it was found that the holdup would be higher in the chemical system with the lowest interfacial tension compared with two other systems. An empirical correlation was also proposed to predict the dispersed phaseholdup with AARE of 8.72%.

Effects of silica nanoparticles on the mean drop size and drop‐size distribution in a Scheibel extraction column

AbstractIn this study, the effect of hydrodynamic parameters such as rotor speed, dispersed phase velocity, continuous phase velocity on the drop size distribution and the Sauter mean‐drop diameter (d32) were studied in the absence and presence of silica nanoparticles with the different weight fraction of them (0.01, 0.03 and 0.05 wt%) in a Scheibel extraction column. The experiment was conducted in a toluene/water system, and the results indicated that the effect of the rotor speed on the Sauter mean‐drop diameter was far more significant than the effect of the dispersed and continuous phase velocities. Also, the effects of the hydrodynamic parameters are more significant in lower concentration of silica nanoparticles. The log‐normal probability distribution function was used to predict the drop‐size distribution. Furthermore, some correlations were presented to anticipate the parameters of this function and the mean drop size in terms of the operating parameters and the physical properties of the systems. These equations conformed well to the empirical data. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

A comparison between drop size distributions derived from the probability distribution functions and maximum entropy principle. Case study; pilot plant Scheibel extraction column

A new model for prediction of drop size distribution is proposed in an eleven stage Scheibel extraction column by the maximum entropy density approximation technique. In addition, the conventional probability distribution functions (Gamma, Inverse Gaussian, Weibull) have already been applied to estimate the drop size distribution. The experimental procedures were carried out by three different systems such as toluene–water, n-butyl acetate–water and n-butanol–water. The drop size distribution was measured with an image analysis technique as a function of the operating conditions and physical properties of the liquid–liquid systems. The results show that the agitation speed has the main effect on the drop size distribution in the column. However, the effects of phase flow rates are not significant. An empirical correlation is proposed for estimation of the Sauter mean drop diameter in terms of operating variables, column geometry and physical properties. The results show that the maximum entropy function describes the drop size distribution better than the conventional probability distribution functions. The Shannon maximum entropy method provided a novel prediction method for the drop size distributions in the liquid–liquid extraction columns. The latter that could be used for modeling approaches.

An Improved Correlation of the Mean Drop Size in a Modified Scheibel Extraction Column

AbstractThe drop size is of fundamental importance in the design of liquid‐liquid extraction columns, the drop size was measured as a function of the geometry, operating conditions, and physical properties of a liquid‐liquid system with no mass transfer in a five‐stage modified Scheibel extraction column. An improved correlation of the mean drop size in the Scheibel extraction column is presented. The correlation was divided into three sections in terms of the Reynolds number. It could be applied in a wide range and could be further used for the study of mass transfer performance of the modified Scheibel extraction column.

Correlation of the Drop Size in a Modified Scheibel Extraction Column

AbstractExperiments were designed to ascertain the main factors for the Sauter mean drop size (d32) of the dispersed phase in a three‐stage modified Scheibel extraction column with no mass transfer. A precise correlation applied to the liquid‐liquid systems with low interfacial surface tension was proposed for calculating d32. The maximum relative error for all data was 16.0 % and the mean relative error ±4.6 %.

Study on an ideal start-up model for a modified Scheibel column

The start-up process existed in every solvent extraction process. An optimal start-up strategy in the solvent extraction process can shorten the time to get to steady state greatly. In order to offer some useful methods for the study on the start-up in the extraction process, an ideal start-up model was developed for a modified Scheibel extraction column. The numerical solution for the multi-stage extraction system was obtained from solving the mathematical equations. From the calculated values, the relationships between variables and time were established. According to the relationships obtained above, suitable start-up strategy could be taken to drive the extraction system to the desired steady state.

Optimization‐Based Nonlinear Centralized Controller Tuning of Liquid‐Liquid Extraction Processes

The control problem of an agitated contactor is considered in this work. A Scheibel extraction column is modeled using the non‐equilibrium backflow mixing cell model. Model dynamic analysis shows that this process is highly nonlinear, thus the control problem solution of such a system needs to tackle the process nonlinearity efficiently. The control problem of this process is solved by developing a multivariable nonlinear control system implemented in MATLAB™. In this control methodology, a new controller tuning method is adopted, in which the time‐domain control parameter‐tuning problem is solved as a constrained optimization problem. A MIMO (multi‐input multi‐output) PI controller structure is used in this strategy. The centralized controller uses a 2×2 transfer function and accounts for loops interaction. The controller parameters are tuned using an optimization‐based algorithm with constraints imposed on the process variables reference trajectories. Incremental tuning procedure is performed until the extractor output variables transient response satisfies a preset uncertainty which bounds around the reference trajectory. A decentralized model‐based IMC (internal model control) control strategy is compared with the newly developed centralized MIMO PI control one. Stability and robustness tests are applied to the two algorithms. The performance of the MIMO PI controller is found to be superior to that of the conventional IMC controller in terms of stability, robustness, loops interaction handling, and step‐change tracking characteristics.

Modeling, simulation and control of a scheibel liquid–liquid contactor: Part 1. Dynamic analysis and system identification

The liquid–liquid extraction process is well-known for its complexity and often entails intensive modeling and computational efforts to simulate its dynamic behaviour. However, rigorous mathematical models are usually impractical or are of limited usefulness for control system design. Therefore, there is a need to derive simpler models for this process. Reduced-order linear models can be derived through applying system identification on the input–output simulation data. As a first step, a rigorous model for dynamic simulation of an extraction process is developed. This model employs an improved detailed stage-wise mixing stage with backmixing and it takes into account the variation in hydrodynamics, mass transfer, and physical properties throughout the length of the extraction column. It also approximates end effects by incorporating two mixing stages at both ends in addition to calculation of mass transfer within calming zones through the use of a mass transfer weight factor. The model is validated with dynamic experimental data for a nine stage Scheibel extraction column of type I. The simulation model is shown to be accurate for prediction of process behaviour under different operating conditions. Dynamic analysis of the process is conducted on the developed rigorous simulation model. Then, system identification is applied to derive linear time-invariant reduced-order models, which relate the input process variables ( agitator speed, solvent feed flowrate and concentration, feed concentration and flowrate) to the output process variables ( raffinate concentration and extract concentration). The identified model predictions are found to be in a good agreement with the rigorous ones.

Mathematical modeling and steady‐state analysis of a scheibel extraction column

AbstractThe steady‐state behavior of a nine‐stage Scheibel extraction column was modeled and simulated using a back flow stagewise model. Steady‐state experiments were conducted, using the system water‐acetone‐toluene, for three phase ratios and three agitator speeds. The mathematical model was validated with the experimental concentration profiles by a single parameter fitting technique with an unconstrained optimization algorithm.Steady‐stage analysis of the experiments was performed for a further control study. The calculated steady‐state gain matrices were used for interaction analysis using different steady‐state analysis methods, e.g. Bristol numbers, Condition numbers, Morari Indexes of Integral Controllability, and Niederlinski Indexes. The results indicate that both agitator speed and phase ratio have a substantial influence on the control structure. Dynamic analysis should therefore be performed to verify the optimum control method for this process.

Holdup measurements in a Scheibel column by means of an ultrasonic technique

AbstractAn ultrasonic technique developed by Bonnet and Tavlarides for dispersed phase holdup determination in liquid–liquid contactors has been applied in a 0·10 m diameter Scheibel extraction column. The column consists of three alternate mixing and packing sections of 0·03 and 0·055 m in height, respectively. The packings were built with polypropylene mesh with 96% voidage. The liquid–liquid systems were toluene (dispersed)/water (continuous) and MIBK (dispersed)/water (continuous); the Rushton‐type impellers were operated at 400, 500 and 600 rpm, and with four dispersed and continuous phase flow rates. In one of the mixing chambers two different holdup measuring devices were installed: two ultrasonic transducers and one controlled dispersion sampler. The values of dispersed phase holdup obtained by both methods were compared using statistical methods. It was found that at low agitation and for high interfacial tension, conditions for which the dispersion is not completely uniform, the difference was significant, whereas at high agitation and low interfacial tension the values obtained through both methods were statistically equal. This work demonstrates the applicability of the ultrasonic technique for holdup measurements to Scheibel columns, in which the only technique used so far was sampling. This ultrasonic technique allows us to solve the axial monitoring and control problems of these columns.

Measurement of concentration profiles in a liquid‐liquid extraction column

AbstractA novel experimental technique for withdrawing uncontaminated samples of each phase from a highly agitated two liquid phase system (primary dispersion) is presented. The technique has been applied in the study of the continuous and dispersed phase axial mixing characteristic of a mechanically agitated liquid Scheibel extraction column operating under different conditions treating the chemical system acetone‐toluene‐water. The column mixing compartments were separated by a mixed stainless steel‐polypropylene knitted mesh packed bed which was completely ‘wetted’ by the organic dispersed phase. Several concentration profiles are presented and the non‐ideal flow parameters as well as the mass transfer coefficients for the column and system under study are reported.