核燃料后处理厂泵轮式混合澄清槽的选型与设计

核燃料后处理厂中通常采用混合澄清槽作为铀纯化流程和溶剂循环流程的液-液萃取设备。与普通的机械搅拌混合澄清槽相比,泵轮式混合澄清槽具有设备紧凑、易于进行放大设计等优点,因此在国外核燃料后处理厂中广泛使用。文章简要介绍了KAPL型、KREBS型、PowerGas型以及法国后处理厂使用的泵轮式混合澄清槽;通过比较几种混合澄清槽的优缺点,分析适用于我国核燃料后处理厂的泵轮式混合澄清槽的结构形式,并对泵轮式混合澄清槽进行简略设计。     

一种水分散型多隔层混合室混合澄清萃取器的设计及操作性能

从减小液滴内传质阻力、提高两相间传质速率和改善混合室中两相的停留时间分布等方面对油分散型单混合室混合澄清萃取器(OWSMMS)的设计进行了改进,设计了水分散型多隔层混合室混合澄清萃取器(WOMMMS)以提高混合澄清萃取器的分离效率.在实验中分别应用OWSMMS和WOMMMS进行稀土分离,比较了它们的操作性能.在实验条件下,通量为1.46～2.92m~3/(m~2·h)时,轻/重稀土的相对分离效率比β_(qz)为1.426,相邻元素的相对分离效率比β_(ab)一般都大于1,说明WOMMMS的操作性能明显优于OWSMMS.     

高效澄清萃取槽内搅拌对液液分离特性的影响

针对传统稀土萃取混合澄清槽存在的问题,提出了在澄清室增加搅拌装置以提高澄清效率的方法。通过对四斜叶搅拌桨、Intermig桨及框式搅拌桨等不同桨型搅拌对澄清度影响的研究,证实四斜叶桨是合适的桨型,经搅拌之后,澄清室两相分离效果明显优于传统混合澄清槽,澄清度平均提高30%以上。在转速20,30,40和50 r·min-1条件下,搅拌桨离底距离分别为4.0,5.5,7.0,8.5和10.0 cm,搅拌桨距溢流口距离分别为10,13和16 cm时,对四斜叶桨搅拌澄清度的研究结果表明,低转速下澄清效果更好,搅拌桨距离溢流口越近澄清效果越好,而搅拌桨离底距离8.5cm,即处于两相混合带附近时澄清效果最佳。在此基础上,根据因次分析原理和试验数据建立了澄清度因次公式。     

混合澄清槽研究进展

混合澄清槽是应用最早、使用最广泛的逐级接触式萃取设备,具有级效率高、适应性强、放大简单及操作性强等优点.文章综述了近年来研究者们普遍关注的新型混合澄清槽形式,介绍其工作原理,剖析了不同槽体的优缺点,总结了当前混合澄清槽的三大研究方向分别是高混合效率、低搅拌转速和小占地面积.此外,随着对混合澄清槽的研究不断深入,国内外学者利用先进的技术深入地剖析设备内部的流体力学特性,如桨叶的抽吸效应、分散相液滴直径分布等,文中对此也进行了介绍,提出计算流体力学方法是改进混合澄清槽混合与澄清性能的重要手段.     

液滴行为与液-液混合设备

总结了液-液非均相混合过程中的液滴运动速率计算模型,分析了液滴破碎及合并的机理。在结合各种工业应用的基础上,总结了搅拌釜、射流混合器、静态混合器、撞击流混合器及纤维液膜混合器等五种混合设备的混合原理及研究现状。展望了液-液混合设备的研究前景。     

膜分散式混合澄清萃取器性能研究

针对传统的混合澄清器存在的问题，将膜分散技术应用于萃取分离过程中，设计了新型的膜分散式混合澄清器，并选择正丁醇／丁二酸／水和正丁醇／磷酸／水两种研究体系，考察了该设备的传质及澄清性能。研究结果表明，膜分散式混合澄清器的传质效率高，单级萃取效率达到95％以上；处理量大，单位面积膜处理量最大可达225m3．m^-2.h^-1；澄清性能好，澄清时间低于20s。此外，膜分散式混合澄清器可以实现大相比操作。因此，膜分散式混合澄清器是一种高性能的萃取分离设备。     

气-液-液萃取的流体力学研究

在液-液萃取过程中,提高分散相的表面更新速率可有效提高萃取的传质效率。研究发现,在萃取过程中使用气体搅拌可以增加液液之间的接触面积,促进液相内的湍动和循环。本文研究了气-液-液三相下油滴的流动形态,并对不同填料的流体力学性能进行了测定。实验结果表明,气相速度的增加可导致气含率、液含率的增加,从而提高分散相在填料萃取塔中的停留时间,在一定的速度范围内明显降低萃取的表观传质单元高度,极大地强化传质效果。通过与散装填料对比,发现规整填料更利于强化萃取效果,其液泛速度平均增加25%。     

液-液萃取及新型液-液-液三相萃取机理研究进展

根据新型液-液-液三相体系的特点,对传统两相溶剂萃取、双水相萃取机理研究进展进行了综述,提出应用Lewis酸碱理论对两种萃取体系的萃取机理分别进行归类,评述了新型液-液-液三相体系研究进展并对其研究方向进行了展望。     

湍流旋液萃取器萃取性能的研究

描述了新型萃取设备—湍流旋液萃取器的原理和结构。应用磷酸三丁酯-煤油-ZnCl_2水溶液这一萃取体系对该设备的萃取性能进行了实验测定,并与传统的混合澄清槽作了比较,结果表明该萃取设备具有处理量大,萃取效率高以及分相能力强的优点,适于工业化生产应用。     

气-液-液萃取传质效率的研究

在液-液萃取过程中,提高分散相的表面更新速率可有效提高萃取的传质效率.研究发现,在萃取过程中使用气体搅拌可以增加液液之间的接触面积,促进液相内的湍动和循环.据此,本文在气-液-液萃取条件下对不同填料的传质性能进行了测定.实验表明,通入气相后分散相液滴呈现稳定的“油包气”空心状态,这种结构大大降低了分散相液滴的传质层厚度,减小了传质距离,极大地强化传质效率.在适宜气速下,气-液-液萃取效率较传统萃取效率提高20％～40％.通过与散装填料对比,发现规整填料更利于强化萃取效果,传质效率提高约50％.     

萃取器的研究进展

综述了萃取器的传质性能及强化的研究现状。论述了膜萃取器的传质特性和强化方法。指出了膜萃取器与撞击流-旋转填料床萃取器是现代新型高效的萃取分离设备。     

Neural network model-based predictive control of liquid-liquid extraction contactors

The inherent complex nonlinear dynamic characteristics and time varying transients of the liquid-liquid extraction process draw the attention to the application of nonlinear control techniques. In this work, neural network-based control algorithms were applied to control the product compositions of a Scheibel agitated extractor of type I. Model predictive control algorithm was implemented to control the extractor. The extractor hydrodynamics and mass transfer behavior were modeled using the non-equilibrium backflow mixing cell model. It was found that model predictive control is capable of solving the servo control problem efficiently with minimum controller moves. This study will be followed by more work concentrated on using different neural network-based control algorithms for the control of extraction contactors.     

CONTROL OF A PULSED LIQUID-LIQUID EXTRACTION COLUMN BASED ON A MULTILEVEL SYSTEM OF AUTOMATA

This paper presents the real-time application of the learning control theory to the control of a chemical pilot plant: a pulsed liquid-liquid extraction column.

The behaviour of an agitated liquid-liquid extraction column can be related to random mechanisms such as the phenomena of droplets breakage and coalescence. Previous studies on hydrodynamic and mass transfer aspects showed that a pulsed liquid-liquid extraction column had an optimal behaviour for operating conditions close to flooding. These results led to choose the following strategy to control the column in its optimal behaviour zone:

- the measure of the conductivity of the liquid medium below the distributor which gives a good information about flooding, is the controlled variable

-the pulse frequency is the control action.

The learning control algorithm is based on a multilevel system of automata which operates in a random environment. By means of an evaluation unit of the performances of the column which generates either penalty (inaction) or reward on the basis of heuristic rules, the automaton chooses a value of the pulse frequency. This approach is essentially connected to artificial intelligence in so far as human knowledge on the plant is included in these rules.

This algorithm has been implemented on a microcomputer for control purposes. The experimental results presented show the good performances of the approach.     

Determination and correlation of axial-mixing parameters in an agitated liquid-liquid extraction column

Dispersion coefficients were measured in a pilot-plant sized agitated liquid-liquid extraction column of the Kuhni type. Available techniques were considered, and the axial mixing in both phases obtained over a broad range of operating conditions, both with and without mass transfer and with two sets of stator plates. Earlier correlations for backmixing in the continuous phase were checked and improved, the final equation being successfully tested on available published data.     

Mass transfer coefficient in the eductor liquid-liquid extraction column

In this research gasoil desalting was investigated from mass transfer point of view in an eductor liquid–liquid extraction column (eductor-LLE device). Mass transfer characteristics of the eductor-LLE device were evaluated and an empirical correlation was obtained by dimensional analysis of the dispersed phase Sherwood number. The Results showed that the overall mass transfer coefficient of the dispersed phase and extraction efficiency have been increased by increasing Sauter mean diameter (SMD) and decreasing the nozzle diameter from 2 to 1 mm, respectively. The effects of Reynolds number (Re), projection ratio (ratio of the distance between venturi throat and nozzle tip to venturi throat diameter, R_pr), venturi throat area to nozzle area ratio (R_th-n) and two phases flow rates ratio (R_Q) on the mass transfer coefficient (K) were determined. According to the results, K increase with increasing Re and R_Q and also with decreasing R_pr and R_th-n. Semi-empirical models of drop formation, rising and coalescence were compared with our proposed empirical model. It was revealed that the present model provided a relatively good fitting for the mass transfer model of drop coalescence. Moreover, experimental data were in better agreement with calculated data with AARE value of 0.085.     

Efficient Shortcut Method for Determining the Process Window in Stirred-Pulsed Extraction Columns

Recent studies showed the superior separation performance of stirred-pulsed columns of different diameters in liquid-liquid extraction processes. Here, an efficient shortcut method will be presented, which is time and resource-efficient as well as cost-effective to determine the operational window of these columns for industrial separation tasks. Savings in time of less experiments and costs of materials consumption can be estimated with up to 30 %. The presented method is particularly suitable before the application of new chemical systems, which are particularly cost-intensive and scarce in material supply.     

Investigation of a two impinging-jets contacting device for liquid-liquid extraction processes

A two impinging-jets contacting device (TIJCD) for liquid-liquid extraction processes was proposed and tested through the standard test system recommended by the European Federation of Chemical Engineering (EFCE), toluene-acetone-water, as a typical example of liquid-liquid extraction processes. The results obtained for the overall volumetric mass transfer coefficient (capacity coefficient) were more than three times higher than those reported in the conventional contactors and in an air-driven two impinging-streams contactor. These experimental results clearly indicate the greater performance capability of TIJCD relative to those of conventional contactors. To have a perfect study on the pertinent parameters of the TIJCD, the influence of jets momentum, nozzles diameter and the inter nozzle distance have been investigated. In addition, the enhancing effect of the impingement zone has been studied using a non-impinging-jets contacting device. Based on the experimental data obtained, an increase in the liquid flow rates results in an increase in the extraction efficiency and overall volumetric mass-transfer coefficient, while increasing the distance between nozzles decreases the extraction efficiency. In addition, it was found that the effect of nozzle diameter on the extraction efficiency could be dependent upon the jets velocity.     

糠醛和水逆流萃取分离的研究

选择三氯乙烯为糠醛和水萃取分离的溶剂,采用逆流萃取法进行模拟计算,并进行萃取试验,为进一步逆流萃取中试试验提供可行性依据。     

液液萃取塔研究的若干新进展及展望

液液萃取是应用广泛的分离技术,在石油化工、制药提取、金属分离等领域都有重要的应用。萃取塔作为常见的分离设备当前的设计还十分依赖于以往的经验,需要进行大量的实验。文章综述了萃取塔设备的研究现状,总结了对塔内流场、液滴和浓度场的实验测量技术,介绍了基于液滴的模型化方法和多尺度计算流体力学模拟方法,归纳了过程强化的相关研究进展。并对萃取塔未来的研究发展进行了展望,在数字化和可持续的发展背景下,未来在实验方面可以关注实时测量和优化,模型化方面关注于微观界面行为和传质影响的描述,在基于先进的实验和模拟技术基础之上,结合新萃取体系进行萃取设备和内构件的开发,从而实现过程强化,以解决化工过程面临的共同挑战。