折流板脉冲萃取柱水力学性能研究

以体积分数30%三烷基氧膦(TRPO)煤油溶液和1 mol/L硝酸溶液为体系,在100 mm折流板脉冲萃取柱中考察了折流板脉冲萃取柱的操作参数(脉冲振幅、脉冲频率、流速和流比)和结构参数(板间距)对其水力学性能(液泛通量、液泛存留分数和正常操作时分散相存留分数)的影响。实验研究表明:液泛通量随着脉冲强度的减小而增大,与流比和板间距无关,并给出其关联式;操作参数和柱结构参数对液泛存留分数的影响均可忽略;正常操作时分散相存留分数与连续相的流速、流比成正比关系,而与脉冲频率无关,并随板间距和脉冲振幅的增大而增大,并给出了分散相存留分数的经验关联式。     

Flooding and drop size in a pulsed disc and doughnut extraction column

The hydrodynamic behavior of a pulsed disc and doughnut column has been investigated using three different systems in the absence of mass transfer. Sauter-mean drop diameter (d₃₂), flooding velocity and holdup at flooding have been measured at different operating conditions. The following operating variables have been studied: pulsation intensity and flow rate of both liquid phases. As expected, smaller mean drop sizes are obtained with the increase of pulsation intensity. The results also show no significant effect of continuous phase flow rate on mean drop size, which increases with increase of dispersed phase flow rate for the operating conditions investigated. A single correlation for the prediction of d₃₂ in the mixer-settler, transition and emulsion regimes of operation is proposed with a mean deviation of 7.32%. The maximum throughput is influenced mainly by pulsation intensity and interfacial tension. Two precise correlations are proposed for predicting flooding velocities in this column. The first is based on operating variables, column geometry, and system physical properties. The second one considers the same variables, except column geometry. Good agreement between prediction and experiments is found for all operating conditions investigated.     

Drop size distribution and mean drop size in a pulsed packed extraction column

Drop size distribution and mean drop size are used for calculation of interfacial area available for mass transfer. In this study, the drop size distribution and Sauter mean drop diameter (d₃₂) have been investigated using three different liquid systems in the absence of mass transfer in a pilot plant pulsed packed column. The drop size was measured at four different points along the active column height. Three operating variables have been studied including the pulse intensity (af) and flow rates of both liquid phases. The effect of liquid properties and height of the active column were also investigated. A combination of the pulse intensity and interfacial tension had the largest effect on the drop size distribution while none of the flow rates were of significance. The height of the column played an important role at the bottom of the active column, but the associated effect was reduced with increase of the height. Finally, a normal probability function of number density was proposed for prediction of the drop size distribution with an Average Absolute Relative Error (AARE) of 8.8% for their optimized constant. Furthermore, two correlations were presented involving height or flow rates of the two phases along with operating variables and physical properties of the liquids. These correlations had AARE values of about 8.5 and 7.8%, respectively.     

Design aspect of a novel L-shaped pulsed column for liquid–liquid extraction applications: Energy consumption and the characteristics velocity concept

This article deals with the evaluation of the consumption of energy for a steady state solvent extraction in a novel L-shaped pulsed sieve-plate column,which is highly required for design and optimization of the periodic flow processes for industrial applications.In this regard,a comprehensive evaluation on the energy consumption in case of a pulsed flow for three different chemical systems is conducted and besides the influence of pulsation intensity,the effect of geometrical parameters including the plate spacing and the plate free area is investigated as well.Moreover,the concept ofcharacteristic velocity models at flooding points is evaluated with respect to the variation of pressure drop along the column at different operational conditions.     

Pressure drop in monolith reactors

A theoretical model for the computation of pressure drop in bubble-train flow inside capillaries of square cross-section was developed. The model is based on three contributions: hydrostatics, viscous pressure drop, and capillary pressure drop. Capillary pressure drop is related to the shape of the fronts and ends of the bubbles. The model does not include entrance or exit effects, has no adjustable parameters, and agrees very well with available experimental data.

For a given set of flow parameters, bubble velocity and liquid slug average velocity are computed as a function of gas and liquid superficial velocities. The length of the unit cell determines the number of bubbles inside the capillary for a given flow situation. The model requires experimental information of average bubble lengths to compute the length of a unit cell consisting of a bubble and a liquid slug.

The three pressure contributions for a unit capillary length are linear functions of the number of bubbles inside the capillary. The length of the bubbles in bubble-train flows is a critical parameter in the computation of pressure drop.     

Dispersed phase holdup and drop size distribution in pulsed plate columns

Dispersed phase holdup was measured in a pulsed plate column for the kerosene-water system under binary conditions and under solute transfer from dispersed to continuous and continuous to dispersed phases. The experimental data were satisfactorily modelled through a recirculation regime model. The drop size distribution, measured by a photographic technique, exhibited a multinodal character at low agitation rates and high dispersed phase flow rate. Sauter mean drop diameter was found to depend on the agitation rate, the dispersed phase flow rate, the mass transfer direction and the plate free area. Correlations for d₃₂ and the interfacial area were presented using Kolmogoroff's isotropic turbulence model.     

摇摆对气液并流模式立体旋流筛板压降的影响研究

以空气-水为实验介质,在喷淋密度78～182 m³·(m²·h)^-1、气相动能因子1.19～2.77 m·s^-1·(kg·m^-3)^0.5、摇摆幅值Θ=5°～15°、周期T=8～20 s的条件下,测定了气液并流模式下立体旋流筛板(TRST)的压降,考察了气液通量、塔板数量、位置和方式对压降的影响,并与直立和倾斜工况对比。结果表明：增加倾斜及摇摆角度干板压降略微下降;摇摆时的湿板压降介于直立和倾斜之间,受摇摆角度影响较大,基本不受周期影响;增大气量有利于抵抗倾斜及摇摆的影响,而增大液量会使倾斜及摇摆的影响作用加剧。整体上,塔板顺、逆向安装时的湿板压降分别在100 Pa和170 Pa以内,而逆向安装的变化率约为顺向的2倍,这是由于逆向安装下改变了气液流动方向,增大了能量损失。建立了气液并流摇摆工况下TRST的湿压降预测模型,相对误差在15%以内。     

Simulating the effects of liquid circulation in bubble columns with internals

Liquid circulation and mixing patterns in bubble columns may be significantly altered by the presence of bundles of vertical heat-exchange tubes. Unlike hollow vessels, the lack of unified geometrical standards for bubble columns equipped with internals complicates the deciphering efforts of fundamental studies. To unveil some of the refined features associated with internals-containing bubble columns, use was made in this work of two-fluid Euler continuum transient 3-D simulations to simulate five pilot-scale configurations: vessels of uniform filling (dense and sparse), vessels of non-uniform filling with large core and wall clearances, and equal cross-sectional hollow vessels. The study revealed that liquid circulation pattern was affected in various complex manners depending on the arrangement of implanted tubes and prevailing bubble sizes. The inter-tube gap represented a length-scale bottleneck which was shown to impede the growth of the larger structures in the flow at the expense of promoting smaller ones. Such forcing mesoscale length gave rise to 3-D effects on the time-averaged flow variables even in the fully developed region. Furthermore, a sharp decrease of the liquid kinetic turbulent energy was obtained upon insertion of the heat-exchange tubes even for low enclosure occlusions. The liquid gross flow structure was more or less of a core-annulus type for uniformly implanted heat-exchange tubes, whereas non-uniform, although geometrically regular arrangements yielded complex flow patterns with sometimes core liquid downward circulations.     

Pressure drop characteristics of flow in a symmetric channel with periodically expanded grooves

Pressure drop characteristics of flow in a periodically grooved channel are investigated experimentally. It is well known that a self-sustained oscillatory flow occurs from a steady-state flow at a certain critical Reynolds number in such grooved channels. The oscillatory flow enhances fluid mixing and leads to an increase in pressure drop. We measure the pressure drop with a pressure transducer. It is found that the pressure drop increases near the critical Reynolds numbers where the two- and three-dimensional oscillatory flows occur. In addition, the three-dimensional flow is confirmed by flow visualization.     

CFD simulations of single-phase flow in pulsed disc and doughnut columns: Axial dispersion and pressure drop

CFD simulations of pulsed disc and doughnut columns are performed to understand the effects of operating and geometric parameters on axial dispersion and pressure drop in single-phase flow. CFD simulations have been carried out using a two-step approach. In the first step, the flow field is obtained by solving the continuity and the momentum equations along with the equations of the standard k–ε model of turbulence. In the second step, the species transport equation is additionally solved to obtain the residence time distribution and hence the Peclet number and axial dispersion coefficient. The computational approach is validated by comparing its predictions with the experimental data reported in the literature and then used for detailed parametric analysis.     

Modelling of mass transfer in extraction columns with drop forward-mixing and coalescence-redispersion

The objective of this work is to model the effect of simultaneous drop forward-mixing and coalescence-redispersion on the hydrodynamics and mass transfer efficiency of a two phase countercurrent extraction process. Based on the flow mechanism and drop size distribution in extraction columns, a novel model with a simplified sequential algorithm is developed. It is much easier to use, and computationally less expensive, than a direct simulation technique which would typically be a tedious boundary-value iteration method. A new concept of Effective Mass Transfer Coefficient is presented, from which the effect of drop forward-mixing and coalescence-dispersion on extraction performance is directly evaluated from an analytical expression. The results calculated from the model are satisfactorily compared to experimental results obtained from three actual extraction system in two pulsed sieve-plate extraction columns. The relationship between the present model and the diffusion model is discussed and a parameter transformation equation for the two models is given.     

Calculation of the drop size in pulsed sieve-plate extraction columns

A new method for the calculation of drop sizes in pulsed sieve-plate extraction columns is reported. Under certain assumptions for the motion of the drops in the vicinity of the plates, it is possible to develop an equation that is confirmed by measurements in a much greater range, especially of the pulsation intensity, than other equations being known up to now. Additionally, a dependence of the drop diameter on the hole diameter at constant fractional free area results from that new equation, which has been proven so far only experimentally. Finally, with the developed equation under consideration of the time-dependent variations of the effective forces it is possible to make qualitative predictions on the type of the drop size distribution to be expected.     

Pressure drop and bubble-liquid interfacial shear stress in a modified gas non-Newtonian liquid downflow bubble column

A functional form of equation for predicting pressure drop in a modified non-Newtonian downflow bubble column has been formulated. The equation has been developed based on the bubble formation, drag at interface and the wettability effect of the liquid. Also the bubble-liquid interfacial shear stress in two-phase flow is analyzed and correlated with the dynamic, geometric and physical variables. The functional form of equation appears to predict the pressure drop satisfactorily for two-phase dispersed flow in the co-current modified downflow bubble column with carboxy methyl cellulose (CMC) solution in water with different concentrations.     

Very-viscous-oil/water/air flow through horizontal pipes: Pressure drop measurement and prediction

Core annular flow pattern, where a low viscosity liquid surrounds a very-viscous one, may be very interesting for heavy oil transportation. However, in oil production, oil and water rarely flow alone and gas is usually present. Despite several publications on liquid-liquid core annular flow, no much work has been done towards a proper characterization of the effect of gas on pressure drop. The aim of this paper is twofold: to provide a new data base on three-phase (very-viscous-oil/water/air) flow, and to propose a simple model for the determination of pressure drop.     

Study of mass transfer and determination of drop size distribution in a pulsed extraction column

A better understanding of pulsed liquid-liquid extraction columns was obtained by using an online digital image analysis system to characterize emulsion drop. The mass transfer of acetic acid from dispersed phase (ethyl acetate) to continuous phase (water) was studied under standard conditions. The system enabled drop size distribution (DSD) to be measured as a function of physical and thermodynamic parameters. The surface tension was investigated by static contact angle measurement. Mass transfer and energy transfer, characterized by the surface/volume ratio of the droplets were compared with the working parameters in order to interpret restrictive phenomena such as hold up and column efficiency. The experimental values of Sauter diameter (d₃₂) and those predicted by a correlation proposed in the literature are in good agreement. However, the adhesion work between liquid and PTFE plate surface indicates that interface property variations, as a function of solute concentration, must be taken into account in the theoretical correlations. It was found that hold up and separation efficiency depend mainly on the stirring rate. These results show that online image analysis can be used as a process control of a liquid-liquid extraction column in order to optimize the mixing phenomena and the DSD, the key parameter of extraction efficiency.     

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.     

Pressure drop through multiorifice gas distributors in fluidized bed columns

Good grid design is essential for the satisfactory performance of large gas fluidized beds and requires the accurate prediction of the grid pressure drop. Experiments conducted with various perforated plate distributors in a 0.6 m I.D. fluidized bed column showed that the presence of fluidized solids could increase the grid pressure drop by more than 100%. This increase was around 25% for a grid pressure drop to bed pressure drop ratio of 0.4. It was greatly affected by the bed height. An investigation of various possible causes for this increase demonstrated that it is primarily caused by the backflow of fluidized solids into the grid holes under the influence of waves at the bed surface.     

Pressure drop and gas bypassing in recirculating fluidized beds

The effect of different operating and design parameters on the pressure drop profile for a recirculating fluidized bed has been studied. A mathematical model was developed for the pressure drop in the recirculating fluidized bed. The different parameters considered were flow rate, inventory of solids and spacing between the draft-tube bottom and the distribution plate. Geldart D and B particles were used for the study. The gas bypassing from the jet towards the downcomer was calculated on the basis of the mathematical model and the effect of various parameters on gas bypassing were analyzed.     

Pressure drop modelling in cellular metallic foams

A theoretical model is presented for the prediction of pressure drop in a Newtonian fluid flowing through highly porous, isotropic metallic foams. The model is based on a rigorous assumption of piece-wise plane Poiseuille flow and a simplistic geometrical model, and shows promise to accurately predict the hydrodynamic conditions in both the Darcy and Forchheimer regimes, without a priori knowledge of the flow behaviour of the particular metallic foam.