一个非局部组成型活度系数方程

根据前文提出的液体混合的通用Gibbs自由能模型,导得了一个两参数非局部组成型活度系数方程.它适用于各种小分子液体混合物和高分子溶液,并能由二元参数预测多元系汽液平衡.对小分子液体混合物的泡点计算结果表明,除了醇/烃系统外,计算准确度不逊于局部组成型活度系数方程.它对高分子溶液的适用性则明显地优于UNIQUAC等方程.     

一个非局部组成型活度系数方程

根据前文提出的液体混合的通用Gibbs自由能模型,导得了一个两参数非局部组成型活度系数方程.它适用于各种小分子液体混合物和高分子溶液,并能由二元参数预测多元系汽液平衡.对小分子液体混合物的泡点计算结果表明,除了醇/烃系统外,计算准确度不逊于局部组成型活度系数方程.它对高分子溶液的适用性则明显地优于UNIQUAC等方程.     

低温下混合物的汽-液平衡和焓的预测

在一个用于预测多组份混合物的汽-液平衡和焓的计算机系统中,对于汽相和液相采用了不同的关联式;维里状态方程式被用于描述汽相的非理想性而液相活度系数是用一个四尾标Margules方程式关联的。纯组份,液相逸度和焓的参考状态是调整到零压的饱和液体;但是,对于高度超临界组份,参考逸度是由亨利常数给出的。对液体混合物焓施加了混合热和压力校正。和低温系统(如在天然气液化和氢气提纯中所遇到的)的实验数据作了比较。所描述的计算程序是可调的并能很容易地推     

混合池模型推算气液返混对精馏效率的影响

精馏操作过程中 ,气液返混现象对精馏传质效率有重要影响。为预测其影响规律 ,文内针对含有错流塔板且气相预混合的精馏塔 ,提出了气液返混发生时计算精馏效率的混合池模型。所得计算结果与实验数据的比较说明模型是可靠的。在此基础上 ,根据计算结果 ,探讨了不同情况下气液相返混对精馏效率的影响 ,发现气体返混和液体返混的发生均导致板效率下降 ,且过程的汽提因子和点效率越大 ,板效率随返混的发生而下降的速度越快。     

抽提蒸馏与恒沸蒸馏

Ⅰ. 引言无论在实验室中或在工业上,蒸馏的目的是将液体混合物各组成物分离成纯粹的物质,或至少得到一种纯粹的组成物。普通的精馏可达此目的。用精馏方法以分离混合物,全赖在平衡时汽液两相间组成的不同。若溶液的沸点曲线上显示出最大或最小点,即生成汽相液相组成相同的恒沸混合物,或混合物的组成物沸点十分相近,一般的     

非理想溶液的相平衡和精馏计算——Prausnitz-Wilson模型的应用(一)

本文以Prausuitz-Wilson模型为基础研编了非理想溶液的相平衡和精馏计算程序,对十八个二元和多元精馏系统进行了考核,取得了较满意的结果。 本文(一)、介绍了汽-液平衡模型。     

核心技术介绍

正技术特点:1、微型阀(浮阀和固定阀)将流出单一阀孔的气流分割为多股小气束,从而极大地增加了气体暴露在液体中的比表面积,使得气/液接触面增大,提高传质效率。具有导向作用的三角形阀降低塔板上的液体梯度。2、鼓泡促进器将流出降液管底部的澄清的液体快速与气体混合成泡沫。3、倾斜式多折边降液管使液体在塔板上的流动均匀分布,同时大大增加了鼓泡区面积,加速汽液分离。     

气液鼓泡床内的液体流速分布

引言 鼓泡床是一种重要的气液或气液固多相反应器.液体循环流动是鼓泡床的一个重要流体力学特征,从20世纪50年代人们就开始对此进行了比较系统的实验研究[1-6].这个特征对鼓泡床的流体返混行为、气含率、气液界面积以及传热传质系数都有很大影响,特别是液体返混行为可以由液体循环特性直接决定.如何准确地描述和预测鼓泡床中的液体流速沿径向的分布,关系到鼓泡床反应器的设计、放大和优化.因此,许多年来它一直是人们致力探讨的重要课题之一[7-8].     

四种活度系数模型在汽-液平衡和精馏计算中的应用和比较

作者将最近十余年来发展的四种活度系数模型（Wilson、NRTL、McCann和UNIFAC）与维里方程及三对角矩阵法相结合,成功地应用于各类非理想溶液精馏过程的严格计算。所编的NIDISTL精馏计算程序曾先后对33个精馏系统进行过百余次考核运算。 为对这些活度系数模型作一平行的比较,本文选取了18组二元汽-液平衡实验数据,用非线性最小二乘法分别确定Wilson、NRTL和McCann方程中各对二元参数值。所得参数值被应用于预测18组二元系和8组由此导出的多元系泡点汽-液平衡数据,并与UNIFAC官能团模型的预测结果及实验数据作比较。 通过四个精馏计算的示例,可以说明采用下同活度系数模型时的收敛特性和计算结果是一致的。本文对各模型所算得的温度、流量和组成分布作了比较,并就某些情况下可能出现较大偏离的原因进行了讨论。     

非理想溶液间歇精馏的计算机辅助设计

为了提高二元非理想溶液间歇精馏的设计效率,提出了恒馏出液组成和恒回流比两种间歇精馏操作方式的计算机辅助设计法。采用由智能拟合法得到的汽液相平衡方程逐板计算求理论塔板数,高斯-勒让德数值积分法求有关积分,可视化的Visual Basic 6.0语言编制设计软件。将设计参数输入软件,可快速准确地求出二元非理想溶液间歇精馏的众多设计和操作参数,还可求出回流比与釜液温度的关系,实现由釜液温度前馈控制间歇精馏过程。计算机辅助设计法极大地提高了二元非理想溶液间歇精馏的设计效率。     

CALCULATING DISTILLATION EFFICIENCIES OF MULTICOMPONENT i-BUTANE/ n-BUTANE COLUMN

This paper presents experimental data and estimated distillation efficiencies of an industrial scale distillation column separating i-butane and n-butane. The data gathered from plant instruments and laboratory analysis were reconciled and compared to distillation simulations. The simulations were performed with a number of real plates using the point and the Murphree plate efficiency calculation model. This matrix model of efficiency at first estimates the point efficiencies using the two-film and multicomponent mass transfer theory. The point efficiencies are then converted into Murphree plate efficiencies using a liquid mixing model. The whole method is implemented in a computer program to simulate an industrial distillation column with real plates. Finally the calculated product compositions are compared with reconciled measurements. The values of overall, section, point and Murphree plate efficiencies of multicomponent i-butane/n-butane system are also calculated. The results show that point efficiencies are not adequate for large industrial scale columns. The results also imply that the plate efficiency calculation method can be utilized and employed in the design and simulation of industrial scale columns.     

GENERAL LINEARIZED MATRIX THEORY OF ELECTROCHEMICAL MASS TRANSFER WITH APPLICATIONS TO ELECTRODE PROCESSES AND ION EXCHANGE

A general linearized matrix theory for electrochemical mass transfer is presented. The accuracy of the theory when applied to cases where electric current exists is tested by comparing results with exact calculations of the effect of ionic migration on limiting currents at a rotating disk electrode with laminar flow and at a flat plate electrode adjacent to a stagnant fluid film. Application of the theory is further illustrated by using it to calculate the effect of ionic migration on limiting currents in a turbulent, law-of-the-wall boundary layer. Finally, the theory is used to evaluate commonly used “film-model” methods for generalizing binary mass-transfer correlations to multicomponent nonideal mixtures. For this last purpose, a film-model generalization method was developed for nonideal electrolyte mixtures. The method is equivalent to that used by Krishnamurthy and Taylor (1985) for mass-transfer in nonideal nonelectrolyte mixtures. Results using the film-model method are compared to matrix calculations of multicomponent ion-exchange mass transfer across a laminar boundary layer and in fixed and fluidized beds.     

Minimum-reflux regime of simple distillation columns

A general algorithm for calculating minimum reflux ratios in simple distillation columns used for the separation of ideal and nonideal (including azeotropic) homogeneous multicomponent mixtures is proposed. The algorithm deals with various splits: direct, indirect, intermediate, and with one distributed component. The algorithm is mathematically rigorous, developed on the basis of the geometrical theory of distillation, and makes it possible to consider the special features of nonideal mixtures (tangent pinch, necessity of using nonadiabatic columns).     

A modified “inside-out” algorithm for simulation of multistage multicomponent separation processes using the UNIFAC group-contribution method

A computational procedure using a modification of Boston and Sullivan's “inside-out” multistage multicomponent separation algorithm (1974) is developed. In order to improve convergence behavior for problems involving mixtures with highly nonideal liquid phases, a two-parameter model is used to describe liquid-phase compositional effects upon the K-factor. The quasi-Newton methods of Mehra et al. (1983) and Nghiem (1983) are applied to solving various sets of solution variables in the proposed algorithm. Activity coefficients are calculated using the UNIQUAC activity-coefficient model (1975) with parameters obtained from the UNIFAC group-contribution method (1975). The computational procedure is applicable to distillation, absorption and reboiled-absorption configurations. The proposed algorithm was implemented in a FORTRAN 77 program and tested on the Honeywell DPS 8/70M computer at the University of Calgary. Inclusion of the liquid-phase model resulted in improved convergence behavior for nonideal systems in which the original “inside-out” method failed to converge.     

非理想多组分混合物中质量传递过程基于Maxwell-Stefan扩散理论的建模及数值分析(英文)

The Intalox metal tower packing was used to simulate an industrial relevant extractive distillation column for purifying azeotropic multicomponent mixture.In order to explain the inconsistencies in the modeling of transfer process in nonideal multicomponent distillation column,a method was developed with equilibrium stage models(EQ)and non-equilibrium model(NEQ)incorporated with Maxwell-Stefan diffusion equations in the framework of AspenONE  simulator.Dortmund Modified UNIFAC(UNIFAC-DMD)thermodynamic model was employed to estimate activity coefficients.In addition,to understand the reason for the diffusion against driving force and the different results by EQ and NEQ models,explicit investigations were made on diffusion coefficients, component Murphree efficiency and mass transfer coefficients.The results provide valuable information for basic design and applications associated with extractive distillation.     

一种改进的多元精馏塔动态模型

综合了精馏塔的物料及能量平衡、塔板水力学方程、塔板效率及再沸器动态特性,给出一种改进的非理想多元物系精馏塔通用动态数学模型.增加了汽液平衡计算,从而弥补了文献[1]所提出的动态模型的缺陷,提高了其精度和通用性.模型仿真算法采用Gear积分方法,稳定性好,对解刚性比很高的精馏塔微分方程组十分有效.通过对某丙烯腈萃取精馏塔的仿真表明,该动态模型能够较好地反映对象的动态形为.     

A unified description of the distillation of ideal mixtures

It is shown that the distillation of multicomponent ideal mixtures may be regarded as a superposition of the distillation of ternary mixtures and that the equation describing the distillation of ternary mixtures may be reduced to one single fundamental equation. This fundamental equation contains the lightest, the heaviest and one intermediate boiling component and is equally valid for distillation based on theoretical trays as well as packings. It applies to the distillation at total and finite reflux and also includes the limiting cases of reversible distillation or distillation with a mass transfer resistance either on the gas or on the liquid side. This reduction of the distillation of multicomponent mixtures to the distillation of a ternary mixture and to one single equation greatly simplifies the understanding of the complexities of multicomponent distillation.     

A rigorous calculation method for the minimum stages in multicomponent distillation

A computer method is presented using stage by stage component material balances and nonideal vapor liquid equilibria to calculate the minimum stages for a given key component split in a multicomponent distillation. The calculated results also include an overall material balance and the distillate to feed ratio. These results are useful for optimal distillation column design.     

Prediction of multicomponent distillation efficiencies

The prediction of multicomponent distillation efficiencies from binary data is highly desirable as it is physically impossible to perform the experimental study of all the systems of industrial importance.In the present work a new method of predicting ternary efficiencies is presented. The validity of the method is assessed comparing experimental ternary distillation lines with predicted distillation lines. Experimental results obtained in a 38mm diameter seven plate sieve-plate column with the binary systems cyclohexane/n-heptane, cyclohexane/toluene and n-heptane/toluene and the ternary system cyclohexane/n-heptane/toluene are used for such comparison.Experimental results obtained with the ternary system show the existence of Murphree efficiencies greater than unity for the intermediate component. Such interesting physical situations are also predicted using the new method.     

Effect of two-pass trays on distillation efficiencies

Two important structural factors that affect distillation efficiencies, the outlet weir heigh and the liquid flowpath length, are investigated. Performance and efficiency data of an industrial scale i-butane/n-butane distillation column equipped with two-pass trays are used as a basis for the calculations. A mathematical development for a new method for predicting the numbers of vapor and liquid phase transfer units is given. This method together with some other NTU calculation methods is used to assess the effect of the outlet weir height on efficiencies. The effect of outlet weir height on the Murphree tray efficiencies is investigated using the observed point efficiencies and different point efficiency to the Murphree tray efficiency relation methods. The effect of varying liquid flowpath lengths on efficiencies is studied by calculating the Murphree tray efficiencies for one-pass and two-pass trays. The results obtained using the NTU calculation method presented in this study show that a certain outlet weir height point efficiency reaches its maximum. Most of the other methods give opposite results giving a minimum for point efficiency at a certain outlet weir length. The results also show that the Murphree tray efficiencies for one-pass trays are higher than for two-pass trays. Obviously, this is caused by the longer liquid flowpath length of one-pass trays. The Murphree tray efficiencies are also calculated for an industrial-scale MTBE purification column. The column is equipped with two-pass trays in the stripping section and with one-pass trays in the rectifying section. The Murphree tray efficiencies of one-pass trays are considerably higher than the two-pass tray Murphree tray efficiencies.