一种由稳态浓度剖面计算萃取柱中轴向混合系数和“真实”传质单元高度的方法

本文提出了一种根据扩散模型用最优化方法拟合浓度剖面的计算方法,可以在有传质情况下,较准确地由实验测定的稳态浓度剖面,同时求得轴向混合系数和扣除了轴向混合影响后的“真实”质单元高度.并已成功地用于脉冲筛板萃取柱的传质性能研究中.     

梯形波脉冲筛板萃取柱传质性能

本文以UO_2(NO_3)_2—30％TBP(KO)为实验体系,进行了梯形波脉冲筛板柱传质性能的研究。实验中测量了两组分的两相稳态浓度剖面共13组,以扩散模型为基础,求得了梯形波脉冲柱的“真实”传质单元高度HTU_(ox),分散单元高度HDU及表观传质单元高度HTU_(oxp)。通过对实验结果进行分析,选择出了适于本实验体系的较好的操作条件。     

不同隙径比环形脉冲萃取柱的传质性能

以30%TBP(煤油)-HNO_3-H_2O为实验体系,在外柱内径为100mm的环形脉冲萃取柱中以4种不同隙径比进行了传质性能研究.实验测定了环形柱的稳态浓度剖面,以扩散模型为基础拟合求取了传质模型参数,建立了相应的关联式.研究结果表明,4种不同隙径比环形柱的“真实”传质单元高度H_(ox)值可以用相同关联式表述;分散单元高度H_(oxd)值则与隙径比的0.16次方成正比.与外柱内径为50mm的环形柱相比较,其H_(ox)值可采用相同关联式描述;其H_(oxd)值与环形柱外柱内径有关.这反映了外柱径对环形柱轴向混合的影响.     

脉冲筛板萃取柱中传质过程的研究

在内径40mm实验脉冲筛板柱中,用30%磷酸三丁酯-硝酸-水体系测定了各种操作条件下两相稳态传质浓度剖面、液滴直径分布和分散相体积分数.根据多级返流模型拟合实际浓度剖面推算得到真实的体积传质系数K_(oDa)和两相返混参数,并进而计算出相际传质系数K_(oD).对标准板和分散-聚合型板两种柱结构内的传质过程进行了分析和讨论.研究结果表明,在本实验范围内,脉冲筛板柱内相际传质系数可按单液滴湍流内循环传质模型来预测.     

脉冲筛板柱用于醋酸回收的研究

在内径40mm的实验柱中,用30％TBP(煤油)-醋酸-水体系研究了脉冲筛板柱的稳定操作范围和传质特性。按扩散模型的近似解法处理实验数据,讨论了表观传质单元高度H_(OXP)、真实传质单元高度H_(OX)、分散单元高度H_(OXD)和体积传质系数K_(OX)a随脉冲强度fA变化的规律。结合低浓醋酸废水的回收问题,讨论了脉冲筛板柱的优化操作条件。     

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.     

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.     

CO_2在13x分子筛上的吸附分离——总传质系数及数学模型

以CO_2在分子筛和活性炭上的吸附平衡理论为基础,用微分床层测定CO_2在13x分子筛上的吸附与解吸总传质系数K_0,对描述吸附柱操作的偏微分方程组,分别用Laplace变换和有限差分法直接求解,计算所得透过曲线与实验结果相近似。     

三相循环流化床中的气液相界面积和传质系数

采用溶氧法测量了三相循环流化床中液相溶氧浓度的轴向分布,并按轴向扩散模型处理实验数据,优化得到气液体积传质系数kLa,同时用光纤探头测量了体系中的气含率和气泡大小分布,计算得到了气液相界面积a和气液传质系数kL,并研究了主要操作条件(表观气速、表观液速和固含率)对气液传质系数的影响规律.     

脉冲萃取塔径向扩散系数的测定方法

引　言对于脉冲筛板萃取塔或脉冲填料萃取塔中的轴向混合 ,已有许多人用轴向扩散模型作了研究[1,2 ].但是 ,在脉冲萃取塔工业放大设计的过程中 ,径向混合程度是个不可忽略的重要因素 .然而 ,这方面的研究尚未见报道 .萃取塔中的混合情况会直接影响液液两相传质推动力的大小 .通常 ,希望塔内连续相出现尽可能小的轴向混合 ,使连续相的流形接近活塞流 ,以获得最大的传质推动力 .而对于连续相的径向混合 ,其混合程度越大越有利于径向浓度的均匀 ,有利于获得最大的传质推动力 .因此 ,径向扩散系数大小的确定 ,对于工业规模脉冲萃取塔的设计具有…     

“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.     

用动态响应曲线法研究脉冲筛板萃取柱的传质特性

用动态响应曲线法研究了内径150mm脉冲筛板萃取柱的传质特性,并考虑了轴向混合。实验体系采用30％TBP(煤油)-硝酸-水,操作条件:脉冲频率:1.0～2.5s~(-1),脉冲振幅=0.0067～0.030m,有机相/水相=1/1～3.3/1.实验结果表明,本法与稳态浓度剖面法同样可靠,且省时、省料,可在更宽流比范围内用于大柱径萃取设备的研究。     

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.     

Development of Two‐point Dynamic Method for Evaluating Extraction Columns

The steady‐state method by measuring the concentration profile along the column height is an effective way, but it is a time and material consumption method for large extraction columns. In order to investigate the axial‐mixing and mass transfer performances in a large pulsed‐sieve‐plate extraction column with the diameter of 150mm, a two‐point dynamic method with mass transfer based on the diffusion model has been developed. The results proved that the two‐point dynamic method has the advantages of good accuracy, simple boundary equations and flexible sampling position over the traditional single‐point dynamic method. It is a reliable tool for studying the axial‐mixing and the mass transfer performances.     

Modeling the axial distribution of mass transfer coefficient in an agitated-pulsed extraction column

The dispersed phase holdup and drop size in solvent extraction columns vary along the column height and this affects the mass transfer coefficient and interfacial area. In this article, mass transfer study was performed experimentally using a 25 mm diameter agitated pulsed column. The axial distribution of mass transfer coefficient was determined by coupling population balance equation and axial dispersion model by taking the longitudinal variation in hydrodynamic performance into consideration. Feasibility of different mass transfer models in predicting concentration profiles was evaluated and a novel correlation based on effective diffusivity was developed. The results showed that both overall and volumetric mass transfer coefficients have significant change along the column height and greatly depends on the agitation speed and pulsation intensity. Increasing dispersed phase velocity also augments the overall mass transfer coefficient. The maximum number of transfer unit was measured to be 10 m⁻¹ at agitation speed of 1000 rpm.     

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.     

On the effect of tracer density on axial dispersion in a batch oscillatory baffled column

In this paper, we report our modelling evaluation on the effect of tracer density on axial dispersion in a batch oscillatory baffled column (OBC). Tracer solution of potassium nitrite, its specific density ranged from 1.0 to 1.5, was used in the study, and was injected to the vertical column from either the top or bottom. Local concentration profiles are measured using conductivity probes at two locations along the height of the column. Using the experimental measured concentration profiles together with both ‘Tank-in-Series’ and ‘Plug Flow with Axial Dispersion’ models, axial dispersion coefficients were determined and used to describe the effect of specific tracer density on mixing in the OBC. The results showed that the axial dispersion coefficients evaluated by the two models are very similar in both magnitudes and trends, and the range of variations in such coefficients is generally larger for the bottom injection than for the top one. Empirical correlations linking the mechanical energy for mixing, the specific density of tracer and axial dispersion coefficient were established. Using these correlations, we identified the enhancements of up to 269% on axial dispersion for various specific tracer densities.     

Computational techniques for liquid-liquid extraction column model parameter estimation,using the forward mixing model

Here is presented the first step toward the practical application of a model of liquid-liquid extraction column performance which includes the influence of drop size distribution, or of ‘forward mixing’. The theory, previously developed and described, has been used successfully to obtain model parameter values from experimental extraction data, including drop size distributions and solute concentration profiles. The presence of a significant settling zone height complicates the theory and poses difficulties. These were overcome by the reduction of the settling zone height to an insignificant level. Values of the continuous phase mass transfer, and axial dispersion, coefficients for an assumed (Handlos-Baron) drop-side model are reported. The overall mass transfer coefficients are confirmed to increase with drop size.     

Prediction of Concentration Profiles in an L‐Shaped Pulsed Extraction Column

The L‐shaped extraction pulsed plate column is believed to be able to perform under operating conditions between those of the vertical and the horizontal pulsed plate columns. It has an extraction efficiency similar to the vertical pulsed plate column. Here, the mass transfer performance of this novel column type was investigated and the application of three different models, i.e., the plug flow, the axial dispersion, and the back flow models, was evaluated to predict the solute concentration profile along the column length. The water‐acetone‐n‐butyl acetate and the water‐acetone‐toluene systems were used. The influence of the operational parameters on the height of the mass transfer unit and the back flow coefficients was evaluated using the back flow model. New correlations were proposed to predict the height of the mass transfer unit along with the back flow coefficients in each phase, which were in satisfactory agreement with the experimental data.