A study on hydrodynamic characteristics in a Φ38 pulsed extraction column by four‐sensor optical fiber probe

Accurate prediction of dispersed phase droplet behavior is crucial to the design and scaling‐up of an extraction column. In this article, the dispersed droplet velocity algorithm and the diameter algorithm in a liquid–liquid two‐phase flow have been developed based on the bubble velocity model in gas–liquid two‐phase flow of Lucas [Measurement Science & Technology. 749, 758(2005)] and Shen [International Journal of Multiphase Flow. 593, 617(2005)]. Hydrodynamic characteristics, including droplet diameter, holdup and droplet velocity, were measured using a self‐made four‐sensor optical fiber probe in a 38 mm‐diameter pulsed sieve‐plate extraction column. Water and kerosene were used as continuous and dispersed phases, respectively. The influences of the pulsed intensity, the continuous and dispersed phase superficial velocities on the hydrodynamic characteristics were investigated. The experimental results show that it is reliable to use a four‐sensor optical probe to measure the hydrodynamic characteristics of a pulsed extraction column. © 2016 American Institute of Chemical Engineers AIChE J, 63: 801–811, 2017     

鼓泡塔中气泡尺寸分布和局部气含率研究

在内径为0.38 m的鼓泡塔中采用双电导探针法对不同通气速率下的气泡尺寸分布和局部气含率进行了实验研究,分析了气泡尺寸的概率密度分布。结果表明:气泡尺寸随轴向高度的增加而增大,随径向距离增加而减小;鼓泡塔中气液流动可分为过渡流域和充分发展流域,在过渡流域气含率随轴向高度增加而增大,在充分发展流域气含率趋于均值,径向局部气含率分布呈抛物线型下降。高气速下气泡尺寸概率密度分布比低气速下宽,且随轴向高度的增加分布变宽。     

Testing of a spherical dual-tipped optical fiber probe for local measurements of void fraction and gas velocity in two-phase flows

An alternate and easy method of constructing an optical liber probe tip is presented for the study of different two-phase flow variables such as local time-averaged void fraction, gas velocity and interfacial bubble passage frequency. The proposed probe tip has similar response characteristics to the “U-bend” single fiber probe and is easier to construct than the 90° wedge tipped probe. The signal from the spherical tip seems to be insensitive to changes in bubble velocity as opposed to the 90° wedge and is more advantageous at higher velocities. The signal from the spherical tip has the same time duration as the signal changes from liquid to gas and vice versa for the same bubble velocity. A simplified model is presented to describe the balance of forces around the spherical tip when a bubble is penetrated. The model offers a qualitative explanation of why the non-dimensional response intensity decreases as the bubble velocity increases.     

Reactive extraction of propionic acid using tri‐n‐octylamine,tri‐n‐butyl phosphate and aliquat 336 in sunflower oil as diluent

BACKGROUND : Propionic acid is widely used in chemical and allied industries and can be produced by biocultivation in a clean and environmentally friendly route. Recovery of the acid from the dilute stream from the bioreactor is an economic problem. Reactive extraction is a promising method of recovering the acid but suffers from toxicity problems of the solvent employed. There is thus a need for a non‐toxic solvent or a combination of less toxic extractants in a non‐toxic diluent that can recover acid efficiently. RESULTS: The effect of different extractants (tri‐n‐butylphosphate (TBP), tri‐n‐octylamine (TOA) and Aliquat 336) and their mixed binary solutions in sunflower oil diluent was studied to find the best extractant‐sunflower oil combination. Equilibrium complexation constant, K_E, values of 4.02, 3.13 and 1.87 m³ kmol^?1 were obtained for propionic acid extraction using Aliquat 336, TOA and TBP, respectively, in sunflower oil. The effect of different modifiers (1‐decanol, methylisobutyl ketone, butyl acetate and dodecanol) on the extraction was also studied and it was found that modifiers enhance extraction, with 1‐decanol found to be the best. CONCLUSION: The problem of toxicity in reactive extraction can be reduced by using a non‐toxic diluent (sunflower oil) or a modifier in a non‐toxic solvent, with the extractant. The addition of modifiers was found to improve the extraction. Copyright © 2008 Society of Chemical Industry     

Drop size correlation and population balance model for an agitated-pulsed solvent extraction column

Agitated-pulsed column (APC) is a newly designed extraction column with excellent mass transfer performance. In this work, Sauter mean drop diameter d₃₂ and drop size distribution was investigated under different operation conditions in a 25 mm diameter APC. The results show that with an increase in pulsation intensity and agitation speed the drop size distribution is narrowed and d₃₂ is decreased significantly. With increasing dispersed-phase velocity, d₃₂ increased and drop size distribution become narrow, while there was no noticeable change with continuous velocity. The cumulative size distribution was found to be predicted well using the Inverse Gaussian function. A new correlation was proposed to predict the experimental d₃₂ data of the APC column used in this study. Furthermore, population balance model was applied to predict the drop size distribution with refitted parameters in the breakage, coalescence kernels functions.     

Drop behaviour characteristics in different operating regimes in an L‐shaped pulsed sieve‐plate column

In this study, the influence of different operating regimes on drop behaviour in an L‐shaped pulsed sieve‐plate column has been investigated and the effects of pulsation intensity and phase superficial velocities on drop diameters are evaluated. The toluene‐water system with 0.03 L/L (3 vol%) acetone as a mass transfer agent is used. Experimental observations reveal that with increasing pulsation intensity, drop sizes slightly decrease and by reaching to the end of mixer‐settler regime, they significantly decrease followed by a mild decrease in the dispersion regime. Moreover, it is observed that mean drop size firstly varies inversely as both phase superficial velocities change, while it slightly increases with further increase in superficial velocities. Finally, some of the most recommended correlations are compared to the experimental data. It is revealed that these correlations show the highest deviation in the lower end of the mixer‐settler regime (> 40 %), while in the dispersion regime it becomes < 15 %, indicating that they are only applicable in the region of practical regimes. Accordingly, two of these correlations are modified in order to cover different operating regimes by means of two correlations proposed to predict the transition regime in each section of the column. The AARE values of the modified correlations are found to be < 14.7 %.     

Valeric acid extraction with tri‐n‐butyl phosphate impregnated in a macroporous resin: II. Studies in fixed bed columns

Extraction and back‐extraction of valeric acid in a fixed bed packed with Amberlite XAD‐4 resin impregnated with tri‐n‐butyl phosphate were experimentally studied at 25 °C. The effects of the feed flow rate, acid concentration in the feed solution and extractant concentration in the impregnated resin on the breakthrough curves, were investigated. The bed saturation capacity was larger under the conditions of higher extractant concentration in the resin phase and higher acid concentration in the feed solution. A dynamic model that considers intraparticle diffusion and external liquid film diffusion as limiting steps in mass transfer rates was successfully applied. The intraparticle effective diffusivities (10^?9 dm² s^?1) were from one to three orders of magnitude lower than the diffusivities in the external liquid film (10^?8–10^?6 dm² s^?1). A fast and complete back‐extraction of valeric acid from the saturated bed was carried out with sodium hydroxide solutions. The operational life of the impregnated resin was also studied. Copyright © 2005 Society of Chemical Industry     

提升管中颗粒局部流率和速度的改进的光纤测量方法

在一套高约18 m、内径φ100 mm的提升管冷态实验装置上,根据PV-6D光纤探头的测量结果,提出了一种基于整个采样时间计算提升管颗粒局部流率和速度的改进方法,并与文献方法进行了对比。结果表明,两种方法计算的颗粒局部流率和速度相差较大,本文和文献两种方法计算的截面平均颗粒流率与实测值间的最大、最小和平均相对偏差分别为606.9%、241.3%,221.4%、89.5%和388.9%、145.6%,本文方法测量的颗粒流率偏差相对较小。文献方法计算的截面平均颗粒速度均大于操作气速,其气固间滑落速度和滑落系数分别在-1.6～-4.7 m·s^-1及0.56～0.90间变化,与提升管内的气固实际流动存在很大差别;本方法计算的截面平均颗粒速度均小于操作气速,其气固间滑落速度和滑落系数分别在0.6～9.6 m·s^-1及1.11～2.14间变化。反射型光纤探头在测量颗粒浓度时存在的一些问题是导致本文方法测量的颗粒流率、滑落速度和滑落系数偏大的主要原因。此外,根据光纤测量结果,提出了两个计算提升管颗粒循环强度的关系式,可以替代现有的容积法测量。     

Reactive extraction of itaconic acid using tri‐n‐butyl phosphate and aliquat 336 in sunflower oil as a non‐toxic diluent

Itaconic acid finds a place in various industrial applications. It can be produced by biocultivation in a clean and environment friendly route but recovery of the acid from the dilute stream of the bioreactor is an economic problem. Reactive extraction is a promising method to recover carboxylic acid but suffers from toxicity problems of the diluent and extractant employed. So there is need for a non‐toxic extractant and diluent or a combination of less toxic extractants in a non‐toxic diluent that can recover acid efficiently. Effect of different extractants: tri‐n‐butylphosphate (TBP) (an organophosporous compound) and Aliquat 336 (a quaternary amine) in sunflower oil was studied to find the best extractant–sunflower oil combination. Equilibrium complexation constant, K_E, values of 1.789 and 2.385 m³ kmol^?1, respectively, were obtained for itaconic acid extraction using TBP and Aliquat 336 in sunflower oil. The problem of toxicity in reactive extraction can be reduced by using a natural non‐toxic diluent (sunflower oil) with the extractant. Copyright © 2010 Society of Chemical Industry     

Bubble size and velocity measurement in gas—liquid systems: Application of fiber optic technique to pilot plant scale

A new fiber optic probe was developed for the detection and measurement of bubble sizes and velocities in a gas-liquid column. The probe is made of a single 1 mm plastic fiber with a sharp wedge tip. The calibration was carried out on a laboratory scale unit using a cine-photographic technique to verify the measurements. Bubble velocities were calculated using two identical parallel fibers and the cross-correlation technique. With the velocities and the passage time determined, it was then possible to determine the bubble diameter. Bubble diameters were within 10% of the measurements obtained with the cine-photographic technique. After calibration, measurements were carried out on a pilot scale unit.     

The effects of impeller speed and holdup on mean drop size in a mixer settler with spiral‐type impeller

An experimental investigation has been carried out in order to analyse the drop size distributions of liquid–liquid dispersion in a single stage mixer settler extractor. In this paper, the effects of the impeller speed and the holdup on mean drops size, D₃₂, have been investigated. D₃₂ was decreased with an increase in the impeller speed. Furthermore, D₃₂ was increased with an increase in the holdup. In addition, a new and modified correlation was established based on these results. The average absolute relative deviation is 3.36%.     

Multiphase hydrodynamics and distribution characteristics in a monolith bed measured by optical fiber probe

The optical fiber probe has been for the first time applied to investigate the hydrodynamics and gas‐phase distribution at high gas/liquid ratios in a two‐phase flow monolith bed with 0.048 m diameter and 400 cpsi. Local hydrodynamic parameters including gas holdup, bubble frequency, bubble velocity, and bubble length in single channels were measured by 16 inserted single‐point optical fiber probes within the bed under a nozzle as the liquid distributor. The following findings are reported. (1) The optical fiber probe can be used as an efficient and convenient technique for measuring local hydrodynamic parameters inside the channels of a monolith bed; (2) within the range of high gas/liquid ratios under which experiments were conducted, churn flow regime occurred. In this regime, the monolith bed radial distribution of gas holdup, bubble frequency, bubble velocity, and bubble length is nonuniform in nature. © 2013 American Institute of Chemical Engineers AIChE J 60: 740–748, 2014     

Effect of Rotor Disc Diameter on Holdup,Axial Dispersion and Droplet Size in a Taylor‐Couette Disc Contactor

Application of liquid‐liquid extraction is on a steady rise. Although there are considerable designs of extraction devices, equipment design and optimization is still on the research agenda. Utilization in the biorefinery industry or metallurgy requires robust technologies and equipment. The simple design and stable operation performance of the Taylor‐Couette disc contactor suffices the technical needs for these harsh operation conditions. The effect of different rotor disc diameter on the dispersed phase holdup, axial dispersion, and droplet size was investigated. It was shown that with smaller rotor disc diameter stable operation is still feasible but higher axial backmixing has to be expected.     

On the effect of gap size between baffle outer diameter and tube inner diameter on the mixing characteristics in an oscillatory‐baffled column

We report our experimental investigation on the effect of gaps between baffle outer diameter and inner tube diameter on the mixing characteristics, in terms of mixing time and axial dispersion coefficient, in a batch oscillatory‐baffled column. Local concentration profiles are measured using conductivity probes at two locations along the height of the column. The mixing time was determined based on the equilibrium concentration concept, and the axial dispersion coefficient was obtained by solving the axial dispersion governing equation. Comparison of mixing time between the ‘push‐fit’ and ‘loose‐fit’ baffle arrangements was carried out and the results showed that the existence of a gap of various sizes between the baffle outer and the tube diameters lengthened the time at which the state of uniform mixing is achieved in such a device. © 1999 Society of Chemical Industry     

Bubble size and radial gas hold‐up distributions in a slurry bubble column using ultrafast electron beam X‐ray tomography

Gas hold‐up and bubble size distribution in a slurry bubble column (SBC) were measured using the advanced noninvasive ultrafast electron beam X‐ray tomography technique. Experiments have been performed in a cylindrical column (D_T = 0.07 m) with air and water as the gas and liquid phase and spherical glass particles (d_P = 100 μm) as solids. The effects of solid concentration (0 ≤ C_s ≤ 0.36) and superficial gas velocity (0.02 ≤ U_G ≤ 0.05 m/s) on the flow structure, radial gas hold‐up profile and approximate bubble size distribution at different column heights in a SBC were studied. Bubble coalescence regime was observed with addition of solid particles; however, at higher solid concentrations, larger bubble slugs were found to break‐up. The approximate bubble size distribution and radial gas hold‐up was found to be dependent on U_G and C_s. The average bubble diameter calculated from the approximate bubble size distribution was increasing with increase of U_G. The average gas hold‐up was calculated as a function of U_G and agrees satisfactorily with previously published findings. The average gas hold‐up was also predicted as a function of C_s and agrees well for low C_s and disagrees for high C_s with findings of previous literature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1709–1722, 2013     

Equilibrium and kinetic studies on the extraction of gadolinium(III) from nitrate medium by di‐2‐ethylhexylphosphoric acid in kerosene using a single drop technique

The liquid–liquid extraction of Gd(III) from aqueous nitrate medium was studied using di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene. On the basis of the slope analysis data, the composition of the extracted species was found to be [Gd A₃(HA)] with the extraction equilibrium constant (K_ex) = (1.48 ± 0.042) × 10^?12 mol dm^?3. The results of the effect of temperature on the value of the equilibrium extraction constant indicated the endothermic character of the extraction system. The kinetics of the forward extraction of Gd³⁺ from nitrate medium by HDEHP in kerosene was investigated using the single drop column technique. The rate of flux (mass transfer per unit area) was found to be proportional to [Gd(III)], [H₂A₂]_(o), [NO₃^?], and [H⁺]^?1 in the liquid drop organic phase. The forward extraction rate constant, k_f, was 2.24 × 10^?3 m s^?1 using the equation: Copyright © 2005 Society of Chemical Industry     

Use of axial dispersion and plug flow models for determination of axial mixing and mass transfer coefficient in an l‐shaped pulsed packed extraction column

In this study, the volumetric overall mass transfer and phases axial mixing coefficients have been investigated in a pilot plant of an L‐shaped pulsed packed extraction column by using two liquid systems of toluene/acetone/water and n‐butyl/acetone/water. The mass transfer performance has been evaluated using two methods of axial dispersion and a plug flow model. The effect of the operational variables and physical properties, including the dispersed and continuous phases flow rates, pulsation intensity, and interfacial tension, on mass transfer and phases axial mixing coefficients have been considered. It has been found that the pulsation intensity and the continuous phase flow rate seriously affect the mass transfer coefficient, however, the dispersed phase flow rate has a weaker effect. Also, the axial mixing of a phase is strongly affected by the pulsation intensity and the flow rate of the phase itself and it is not affected by the second phase flow rate. Finally, new correlations are proposed to accurately predict the mass transfer and axial mixing coefficients.