甲缩醛合成流化催化精馏过程的非平衡级模拟

以酸性离子交换树脂为催化剂、在筛板塔内进行甲缩醛合成流化催化精馏过程，建立了非平衡级模型，采用ＮｅｗｔｏｎＲａｐｈｓｏｎ方法进行了模拟计算，得到了催化精馏塔内温度、浓度和流率等的分布规律，筛选了适宜的工艺条件     

Impact of mass transfer coefficient correlations on prediction of reactive distillation column behaviour

A significant part of the safety analysis of a reactive distillation column is the identification of multiple steady states and their stability. A reliable prediction of multiple steady states in a reactive distillation column is influenced by the selection of an adequate mathematical model.For modelling reactive distillation columns, equilibrium (EQ) and nonequilibrium (NEQ) models are available in the literature. The accuracy of the nonequilibrium stage model seems to be limited mainly by the accuracy of the correlations used to estimate the mass transfer coefficient and interfacial area.The binary mass transfer coefficients obtained from empirical correlations are functions of the tray design and layout, or of the packing type and size, as well as of the operational conditions and physical properties of the vapour and liquid mixtures.In this contribution, the nonequilibrium model was used for the simulation of a reactive distillation column. For prediction of the binary mass transfer coefficient for a sieve tray, four correlations were chosen to show their impact on the prediction of the reactive distillation column behaviour. As a model reactive distillation system, the synthesis of methyl tertiary-butyl ether (MTBE) was chosen. The steady-state analysis and the dynamic simulation of the model system were done. Qualitative differences between the steady states were predicted using the chosen correlations.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.     

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.     

多效反应精馏过程生产氯化苄的能量集成

以甲苯氯化生产氯化苄为研究对象,对带侧反应器的反应精馏与精制塔串联工艺(CSRRT)进行研究及能量分析,建立了分段反应精馏与精制塔串联生产氯化苄的新工艺。利用精制塔塔顶蒸汽潜热加热第一段反应精馏塔的塔釜,建立了多效反应精馏(MERD);进一步利用侧反应器的甲苯氯化反应热加热第一段反应精馏塔的塔板物料,建立了多效透热反应精馏(MEDRD)。在相同生产要求下,对3种工艺的能耗进行比较。结果表明,MERD和MEDRD过程实现了能量的优化利用,与CSRRT过程相比,塔釜总再沸器热负荷分别降低16.8%和33.7%。     

Application of the rate-based approach to three-phase distillation columns

For more reliable modelling of multiphase separation equipments the nonequilibrium approach has been recently recognised as superior if compared with the traditional equilibrium stage concept. However, for general three phase (V-L-L) distillation processes in a tray column the interaction between two liquid phases, continuous and dispersed, must be modelled as equilibrium according to insufficient knowledge about transport phenomena at the liquid-liquid interface. On the other hand, for the mass and heat transfer between vapour phase and continuous liquid phase the rate-based (i.e. nonequilibrium) approach is more appropriate (Eckert, 1997). The combined model was implemented in the AspenTech SPEEDUP environment using the SPEEDUP problem oriented language together with user supplied FORTRAN routines, selected SPEEDUP unit modules and ASPEN PLUS physical property libraries (i.e. PROPERTIES PLUS). Comparison with results from the equilibrium model is provided in this contribution.     

Overall efficiency evaluation of commercial distillation columns with valve and dualflow trays

The main objective of this work is to establish appropriated ways for estimating the overall efficiencies of industrial distillation columns with valve trays with downcomer and dualflow trays. The knowledge of efficiencies has fundamental importance in the design and performance evaluation of distillation columns. Searching in the literature, a tree of alternatives was identified to compose the tray efficiency model, depending on the mass transfer models, the liquid distribution and vapor flow models on the tray, the liquid entrainment model, the multicomponent mixture equilibrium model, the physical properties models, the height of froth on the tray model and the efficiency definition. In this work, different methods to predict the overall efficiency of distillation columns with valve and dualflow trays were composed and compared with data from three commercial distillation columns under different operating conditions. The models were inserted in the Aspen Plus 12.1 simulator, in Fortran language, together with tray geometrical data, fluid properties and operating data of the distillation columns. For each column, the best thermodynamic package was chosen by checking the temperature profile and overhead and bottom compositions obtained via simulation against the corresponding actual data of industrial columns. A modification in the fraction of holes evaluation that is jetting parameter of the Garcia's hydraulic model of dispersion above the tray was proposed. This modification produced better results than the original model to predict the fraction of holes that are jetting and in the efficiency of dualflow trays and similar results to Garcia model in the efficiency evaluation of valve trays. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Comparison between the design of experiments and simulation in the three-phase distillation in a sieve tray column for glycerine dehydration

Design of experiments (DOE) is a value scientific approach used to understand the processes in a better way and to determine how the inputs affect the response(s). In this work, this method has been applied to study the behavior of the three-phase distillation in a sieve tray column, through the effects of the process and geometrical variables. The experimental values were compared with predicted values obtained by simulation using the equilibrium and nonequilibrium models. Three-phase distillation has been used for glycerine dehydration using toluene as entrainer, in order to avoid the glycerol degradation by distillation at atmospheric pressure. The best conditions found were: vapor flow rate of toluene = 23.5 kg/h, feed flow rate = 2.2 kg/h and feed concentration = 50 wt% glycerol, using the layout L₄ with fractional hole area = 0.04 and weir height = 70 mm. The nonequilibrium model based on Eckert and Vanek's approach (2001) and Chen–Chuang's correlation (1993) have been used to estimate the binary coefficients of mass transport. The predicted values obtained by the experimental model and by the nonequilibrium model have represented the behavior of the dehydration in the sieve tray column studied. Both models underpinned the experimental results obtained for this column.     

蒸馏塔板上汽液传质系数的确定——非平衡池法(Ⅰ)模型的建立及求解

本文提出一种确定蒸馏塔板上汽液传质系数的新方法——非平衡池法.该法将塔板沿液流方向分为适当数目的串联非平衡池,通过联立求解每一池各相的物料衡算、能量衡算、相平衡和传质传热速率方程,可从塔板入口组成得到出口组成.调整汽液传质系数使计算的出口组成与实测值相等,从而可确定出两相传质系数.方程组用混合牛顿法求解.     

Nonlinear model based control of two-product reactive distillation column

Nonlinear feedback control scheme for reactive distillation column has been proposed. The proposed control scheme is derived in the framework of Nonlinear Internal Model Control. The product compositions and liquid and vapor flow rates in sections of the reactive distillation column are estimated from selected tray temperature measurements by an observer. The control scheme is applied to an example reactive distillation column in which two products are produced in a single column and the reversible reaction A+B=C+D occurs. The relative volatilities are favorable for reactive distillation so that the reactants are intermediate boilers between the light product C and the heavy product D. Ideal physical properties, kinetics, and vapor-liquid equilibrium are also assumed. It is shown that the proposed control scheme keeps tight product composition control.     

Design and control of reactive distillation for hydrolysis of methyl lactate

Esterification of raw lactic acid from fermentation broth and then hydrolysis of lactate ester in reactive distillation column is an effective process for purification of lactic acid. Reactive distillation for hydrolysis of methyl lactate is studied. First, the thermodynamic properties and reaction kinetics are analyzed; then the reactive distillation column is designed based on the objective function total annual cost. The effects of tray number of rectifying section, tray number of reactive section, and feed location on the total annual cost are investigated. And a dual-temperature control structure is proposed for the optimal reactive distillation column, and the results show that it works quite well for this hydrolysis system.     

计算传质法预测精馏塔效率(英文)

A computational mass transfer model is proposed for predicting the concentration profile and Murphree efficiency of sieve tray distillation column. The proposed model is based on using modified two equations formulation for closing the differential turbulent mass transfer equation with improvement by considering the vapor injected from the sieve hole to be three dimensional. The predicted concentration distributions by using proposed model were checked by experimental work conducted on a sieve tray simulator of 1.2 meters in diameter for de-sorbing the dissolved oxygen in the feed water by blowing air. The model predictions were confirmed by the ex-perimental measurement. The validation of the proposed model was further tested by comparing the simulated re-sult with the performance of an industrial scale sieve tray distillation column reported by Kunesh et al. for the strip-ping of toluene from its water solution. The predicted outlet concentration of each tray and the Murphree tray effi-ciencies under different operating conditions were in agreement with the published data. The simulated turbulent mass transfer diffusivity on each tray was within the range of the experimental result in the same sieve column re-ported by Cai et al. In addition, the prediction of the influence of sieve tray structure on the tray efficiency by using the proposed model was demonstrated.     

A novel type of equipment for reactive distillation: Model development,simulation, sensitivity and error analysis

A simulation study of heterogeneously catalyzed reactive distillation experiments carried out with the D + R tray, a novel type of laboratory equipment, is presented. One advantage of the D + R tray is that reaction and distillation are alternating stage‐wise, in a well‐defined way that can be modeled straightforwardly. An equilibrium stage model is used to describe the distillation and a plug flow reactor model to describe the catalyst bed reactors. The model parameters are derived from a systematic experimental characterization of the D + R tray both as a reactor and as a distillation unit. A validated physicochemical fluid property model is used. The primary experimental data are reconciled. Results from the predictive simulations are in good agreement with the experimental results. The influence of errors in the input parameters on the simulation results is investigated by means of a sensitivity and error analysis. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1533–1543, 2013     

Computing multi-species chemical equilibrium with an algorithm based on the reaction extents

A mathematical model for the solution of a set of chemical equilibrium equations in a multi-species and multiphase chemical system is described. The computer-aid solution of model is achieved by means of a Newton–Raphson method enhanced with a line-search scheme, which deals with the non-negative constrains. The residual function, representing the distance to the equilibrium, is defined from the chemical potential (or Gibbs energy) of the chemical system. Local minimums are potentially avoided by the prioritization of the aqueous reactions with respect to the heterogeneous reactions. The formation and release of gas bubbles is taken into account in the model, limiting the concentration of volatile aqueous species to a maximum value, given by the gas solubility constant.The reaction extents are used as state variables for the numerical method. As a result, the accepted solution satisfies the charge and mass balance equations and the model is fully compatible with general reactive transport models.     

A modified model of computational mass transfer for distillation column

The computational mass transfer (CMT) model is composed of the basic differential mass transfer equation, closing with auxiliary equations, and the appropriate accompanying CFD formulation. In the present modified CMT model, the closing auxiliary equations [Liu, B.T., 2003. Study of a new mass transfer model of CFD and its application on distillation tray. Ph.D. Dissertation, Tianjin University, Tianjin, China; Sun, Z.M., Liu, B.T., Yuan, X.G., Liu, C.J., Yu, K.T., 2005. New turbulent model for computational mass transfer and its application to a commercial-scale distillation column. Industrial and Engineering Chemistry Research 44, 4427-4434] are further simplified for reducing the complication of computation. At the same time, the CFD formulation is also improved for better velocity field prediction. By this complex model, the turbulent mass transfer diffusivity, the three-dimensional velocity/concentration profiles and the efficiency of mass transfer equipment can be predicted simultaneously. To demonstrate the feasibility of the proposed simplified CMT model, simulation was made for distillation column, and the simulated results are compared with the experimental data taken from literatures. The predicted distribution of liquid velocity on a tray and the average mass transfer diffusivity are in reasonable agreement with the reported experimental measurement [Solari, R.B., Bell, R.L., 1986. Fluid flow patterns and velocity distribution on commercial-scale sieve trays. AI.Ch.E. Journal 32, 640-649; Cai, T.J., Chen, G.X., 2004. Liquid back-mixing on distillation trays. Industrial and Engineering Chemistry Research 43, 2590-2597]. In applying the modified model to a commercial scale distillation tray column, the predictions of the concentration at the outlet of each tray and the tray efficiency are satisfactorily confirmed by the published experimental data [Sakata, M., Yanagi, T., 1979. Performance of a commercial scale sieve tray. Institution of Chemical Engineers Symposium Series, vol. 56, pp. 3.2/21-3.2/34]. Furthermore, the validity of the present model is also shown by checking the computed results with a reported pilot-scale tray column [Garcia, J.A., Fair, J.R., 2000. A fundamental model for the prediction of distillation sieve tray efficiency. 1. Database development. Industrial and Engineering Chemistry Research 39, 1809-1817] in the bottom concentration and the overall tray efficiency under different operating conditions. The modified CMT model is expected to be useful in the design and analysis of distillation column.     

酯化反应蒸馏过程的模型化及模拟研究

In this paper,a generalized model of the reactive distillation processes was developed via rate-based approach. The homotopy-continuation method was employed to solve the complicated nonlinear model equations efficiently. The simulation on the reactive distillation processes was carried out with the profiles of stage temperature,composition and flow rate for both vapor and liquid phases obtained. Based on careful analysis of the simulation results, the pitfalls in experimental design were detected. Finally, a software package for the simulation of reactive distillation processes was developed.     

考虑水力学可行性的反应精馏塔板持液量设计及优化

以筛板塔为塔板基础构型,以原料转化率最大为目标,以塔径和出口堰高为主要调节参数,以塔板水力学可行性为约束条件,建立了一种可优化塔板液相持液量的塔板结构设计方法. 塔模拟计算在Aspen Plus平台上进行,化学反应采用动力学方程表达,塔板水力学计算采用Cup-Tower软件. 结果表明,本设计方法应用于DPC反应精馏过程,在满足流体力学可行性条件下,塔板上液相持液量比基础设计提高了1.39倍,苯酚转化率提高了33.6%.     

Analysis of reactive distillation using the esterification of acetic acid as an example

The uncatalyzed esterification of acetic acid is described in the literature as a typical example of reactive distillation. Many rigorous models were validated using this esterification as an example. Process proposals for the production of pure ethyl acetate from ethanol and acetic acid have been determined using short-cut methods with the assumption of chemical equilibrium only. In this publication, the limitations of this esterification are clarified, using a rigorous model that was developed. The reasons why reactive distillation appears to be unfavorable for this esterification are explained. It is, however, theoretically possible to obtain ethyl acetate in high purity with different variants of the process. Different process variants are examined in this work. Construction variables that are important for the design of reactive columns, such as the number of reactive separation stages and the holdup in the column, are analyzed. Furthermore, the influence of variables dependent on the component system, such as the phase equilibrium of the reactive system and the reaction kinetics on the conversion in the column, are described. It can be shown that the short-cut methods published so far for reactive distillation, which assume chemical equilibrium, are inadequate.     

Modeling and Modernization of Tray Towers for Reactive Distillation Processes

The velocity, temperature, and concentration fields on a bubble tray were numerically modeled for a reactive distillation process using a two-dimensional mathematical model of momentum, mass, and heat transfer phenomena as a basis. The Murphree mass transfer efficiency matrix has been obtained. Some engineering solutions for modernizing an industrial plant for separating a ternary mixture with the possibility of increasing the initial mixture processing capacity by 25% and improving the efficiency of the reactive distillation process have been considered.