Dynamic simulation of a multicomponent distillation column with asymmetric dynamics

The dynamic behavior of an existing industrial distillation column with eight components and twenty trays has been investigated. The column exhibits “asymmetric dynamics”, since the time required to move from one steady state to another can vary significantly depending on the direction of the change. The column also exhibits highly nonlinear behavior and very long response times for intermediate ranges of step disturbances. These long response times are associated with the migration of key components through the column.     

规整填料塔多元蒸馏过程混合型模型的模拟

填料塔精馏过程的模拟设计大多采用平衡级模型,但由于单一板效率值的难以确定,很多场合模拟很不成功;而新提出的非平衡级模型认为塔内传质传热均处于非平衡状态,由于方程数和经验性参数多,模型求解非常困难。文章针对规整填料的特点,建立了规整填料塔蒸馏过程的一种混合型模型,模型的主要特征是认为气液二相传质处于不平衡状态,而传热处于平衡状态。模型建立在实际填料基础上,既舍去传统的平衡级模型不确定性,又省略了非平衡级模型中复杂的经验性传热系数和液相传质系数的计算。模型计算值和实验值符合较好,也证实混合型模型既反映实际,又使模型求解变得相对容易。     

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.     

基于SIMULINK系统的间歇萃取精馏动态模拟

间歇萃取精馏属于非理想性极强的非稳态过程,很难找到一种快捷有效且易于执行的求解方法.基于此,分别建立了全回流开工、加溶剂全同流及产品采出3个阶段的平衡级动态模型,编写S函数将该模型求解过程嵌套于SIMULINK模块中,并在此基础上开发了间歇萃取精馏的动态模拟平台.通过将不同解法与实验值进行对比,确定了该研究条件下动态模型的求解策略:ODE45解法适于求解全回流开工和加溶剂全回流动态模型;ODE 15s解法和ODE 23s解法适于求解产品采出动态模型,其中ODE 23s的计算过程相对更快捷.     

The solution of multicomponent distillation columns

The equations of A. J. V. Underwood for solution of distillation columns are arranged to give a solution in the form of a sum of difference products. For many distillation problems the present solution is much less tedious than the straightforward solution of Underwood's equations or the determinantal solution proposed by Alder and Hanson [1]. The solution is illustrated by an example employing a five-component system.     

A simple,reliable and fast algorithm for the simulation of multicomponent distillation columns

This work has developed a simple, reliable and fast algorithm for the simulation of multicomponent distillation columns, where any equilibrium stage can accept a feed-stream and/or a vapor-side-stream and/or liquid-side-stream. The new scheme considers internal molar overflows and constant relative volatilities to avoid the need of heat balances and vapor–liquid equilibrium calculations. The solution scheme is founded on a Newton-based formulation in block algebra, which relies in a simple, reliable and fast algorithm. Although the proposed calculation scheme can be classified as an approximate method, it is very useful when accurate phase equilibrium and enthalpy data are lacking. Numerical experimentations show good agreement with the results obtained with well-known rigorous simulation approaches.     

A computer-controlled pilot-plant distillation unit and studies on multicomponent distillation

A pilot-plant unit for distillation studies consists of a tray column, an on-stream process analyzer and a process computer. The analyzer system is based upon a quadrupole mass spectrometer, and provides means for on-line concentration measurements of both liquid and vapor samples with multicomponent mixtures. A study of multicomponent plate efficiencies is presented. Experimental results with water/ethanol/n-butanol mixture show that the Murphree vapor phase efficiencies of the components differ markedly.     

Dynamic simulation of steam distillation in a fatty acid esterification

In esterification processes, the process step which determines the time taken and which has the greatest impact on cost is often not the esterification reaction, but the subsequent work-up of the reaction mixture. In the fatty acid esterification described steam distillation is used as one step in the work-up to remove the fatty alcohol employed in excess. To describe the steam distillation, a simulation model was used to define and optimize the essential determining factors. Comparison with empirical operational data showed that a simple equilibrium model is sufficiently accurate for describing the steam-distillation process in the production plant. Varying the parameters allowed economically optimal conditions to be established in terms of vapor mass flow rate, pressure, and temperature.     

Dynamic modeling and simulation of an alembic pear wine distillation

In this research a phase equilibrium model to predict the recovery of several aroma compounds in spirits distilled in a traditional Charentais alembic has been developed. Due to the congeners’ quasi-infinite dilution, the properties of the mixture are assumed to be dependent on the ethanol mole fraction only. Thus, the system is treated as a quasi-binary mixture; the ethanol recovery, the dynamics of the condensation and the heat transfer processes are modeled independently of the congener's concentration. The model was calibrated with laboratory data obtained during the elaboration of pear distillates. The concentration of ethanol and 15 congeners in the distillate were measured with gas chromatography during the experiments. Fitting just two parameters, one for heating power and one for heat loss, was sufficient to reproduce the experimental ethanol recovery curves. This allowed an accurate prediction of most of the congener's recovery curves. The prediction of the concentration of five congeners, including acetaldehyde and methanol, are not significantly different from measured values. The prediction of the concentration of six congeners was biased but with relatively small errors (ranging between 8% and 25%). Significantly large prediction biases (more than 30%) were observed for ethyl hexanoate, ethyl decanoate and phenethyl alcohol.     

Dynamic simulation based fault detection and diagnosis for distillation column

The model-based fault diagnosis approach is characterized by a powerful process supervision capability with a priori knowledge about the system under consideration. Nevertheless, system complexity, high dimensionality, process nonlinearity and/or lack of good data often hamper its application in chemical engineering systems. A nonsteady state model based fault detection and diagnosis method for the distillation process was developed, using dynamic simulation to monitor the distillation process and identify abnormal sources when large deviations among measuring variables occur. It continuously updates the inner distillation parameters via on-line correction and predicts the trend of measuring variables and determines the existence of malfunctions simultaneously. The distillation model is dependent on transfer equilibrium, mass and heat balance, and is simulated by Euler and two-tier approach. This method was demonstrated with simulated data of a stripping tower collected from the Tennessee Eastman chemical plant simulator.     

一个半间歇催化蒸馏塔的动态模型及模拟

提出以环氧乙烷和正丁醇为原料,应用催化蒸馏法制乙二醇单丁醚的新工艺。建成一个中试规模的催化蒸馏塔,提出一种基于安全考虑的半间歇操作试验方案。建立了催化蒸馏塔的动态数学模型,通过模拟考察了环氧乙烷进料速率对反应物转化率和单醚选择性的影响,得到优化的操作条件。在此基础上,通过模型和模拟分析了塔内温度、汽液相流量及组分组成的动态分布特性,并与试验结果进行了比较。研究表明了模型和模拟方法的可靠性,同时表明了催化蒸馏制乙二醇单丁醚的优越性。     

A matrix method for multicomponent distillation sequences

We describe a simple‐to‐use “matrix” method for obtaining all the basic distillation configurations and additional thermally coupled configurations that separate a zeotropic multicomponent feed into essentially pure product streams. This provides an opportunity to rank‐list the configurations for a given application subject to criteria of interest. The only information needed to generate the configurations is the number of components in the feed. We have successfully enumerated all the configurations for feeds containing up to eight components. The method can also be used to generate nondistillation and hybrid separation configurations, and even easy‐to‐retrofit configurations. We illustrate the use of this method by applying it to the highly energy‐intensive problem of petroleum crude distillation. We have identified more than 70 new configurations that could potentially have lower heat duty than the existing configuration. A significant number of these could reduce the heat demand by nearly 50%. © 2009 American Institute of Chemical Engineers AIChE J, 56: 1759–1775, 2010     

Murphree and vaporization efficiencies in multicomponent distillation

A quantitative comparison between Murphree and vaporization efficiencies is presented based on ternary distillation data for the systems acetone/methanol/ethanol, acetone/benzene/chlorobenzene, benzene/toluene/mxylene and n-hexane/methylcyclopentane/benzene. The influence of experimental errors on calculated values of Murphree efficiencies is also analysed.It is shown that the vaporization efficiency model fails to describe the behaviour of distillation plates and it is suggested that Murphree's model gives a more useful representation of the behaviour of distillation columns.     

Horizontal reactive distillation for multicomponent chiral resolution

A novel horizontal reactive distillation apparatus and a new overall process scheme are proposed for continuous multicomponent chiral resolution via reversible enantioselective acylation of a chiral (racemic) substrate by a chiral (racemic) acyl donor. The process enables simultaneous production of up to four enantiomers with enhanced chiral purity. Kinetic studies, miniplant experiments, and process simulation results are described for a model lipase‐catalyzed reaction: (R)‐enantioselective transesterification of (R,S)‐1‐n‐butoxy‐2‐propanol with (R,S)‐1‐methoxy‐2‐acetoxypropane to produce (R)‐1‐n‐butoxy‐2‐acetoxypropane, (R)‐1‐methoxy‐2‐propanol, and the two unreacted (S)‐enantiomers of the (R,S)‐reagents. A horizontal, compartmentalized reactive distillation vessel is specified instead of a conventional reactive distillation column to provide longer liquid‐phase residence time needed for adequate conversion. Low vapor‐traffic pressure drop allows operation under vacuum at reduced temperatures for good enzyme stability and enantioselectivity. The general technology has potential as a means to producing a wide range of chiral synthons used in asymmetric syntheses of chiral pharmaceuticals and other biologically active products. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2603–2620, 2013     

Complex multicomponent distillation calculations by continuous thermodynamics

Complex multicomponent mixtures such as petroleum fractions, shale oils, coal-derived liquids etc. are usually characterized by continuous distribution functions which, for example, may be obtained from true boiling point distillations. Current methods for separation calculations, however, are based on the flows of discrete components. Hence, to apply these methods the continuous distributions traditionally are split into a number of pseudo-components. This is a crude and arbitrary procedure. Based on earlier work, the present paper shows how to perform distillation calculations for complex multicomponent mixtures by using the continuous distributions directly without splitting into pseudo-components.     

Estimates of energy consumption and selection of optimal distillation sequence for multicomponent distillation

An estimate has been obtained of the energy consumption on 1 mol of separated mixture based on thermodynamic balances for processes that use mechanical and heat energy. Only irreversible losses depend on the order of separation for mixtures in mechanical systems, while for the systems using the heat, the order of separation also affects the reversible energy consumption. In the latter case, in order to obtain a reversible estimate of the heat consumption, one should solve the problem of selecting the order of separation. An algorithm has been obtained for its solution that enables one to approximately choose the order of separation at the stage of preliminary calculations knowing only the properties of the feed.