Feasibility of heterogeneous batch distillation processes

Synthesis of heterogeneous batch distillation is discussed, which aims at splitting azeotropic mixtures by adding an entrainer partially miscible with one of the initial binary mixture components. Key operational parameters are identified such as the amount of entrainer added in the ternary feed, the reflux policy, and the vapor line position by examples. Synthesis and operation are less straightforward for heterogeneous batch distillation than those for the homogeneous case, but offer many advantages: more design alternatives, simplified distillation sequences, a lower consumption of entrainer, and a crossing of distillation boundaries by the still path. Feasibility is assessed using simplified modeling and confirmed using a commercial batch process simulator package. Synthesis expectations and simulated results are verified throughout bench-plant experiments for the separation of the acetonitrile—water mixture using acrylonitrile as a light heterogeneous entrainer.     

间歇精馏过程模拟的发展与应用

介绍了间歇精馏模拟过程中常用的数学建模的经典方法以及近两年在数学建模及其算法领域的发展,讨论各模型的特点及其在精馏工业和试验中的应用实例。     

Heterogeneous extractive batch distillation of chloroform-methanol-water: Feasibility and experiments

A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform-methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike the well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform-water is obtained at the column top, condensed and further split into the liquid-liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in the extractive section for determining the proper range of the entrainer flowrate and the reflux ratio. The operating conditions and reflux policy are validated by rigorous simulation with ProSim Batch Column^® where technical features of a bench scale distillation column have been described. Six reproducible experiments are run in the bench scale column matching the simulated operating conditions with two sequentially increasing reflux ratio values. Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol.     

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.     

Generalised method for the determination of heterogeneous batch distillation regions

A new, general method for the calculation of residue curves and for the determination of batch distillation regions of heteroazeotropic distillation is suggested. The method proposed, which means the extension of the method of Pham and Doherty, takes into consideration the possibility of the withdrawal of any fraction of either liquid phase from the decanter as distillate. The simplified and rigorous simulation calculations were carried out for the mixtures dichloromethane-acetone (low α) + water (heavy, selective, heterogeneous entrainer), water-ethylenediamine (maximum azeotrope) + benzene (light, selective, heterogeneous entrainer) and isopropanol-water (minimum azeotrope) + benzene (light, non-selective, heterogeneous entrainer). The new method gives the right sequence of the cuts for all operation modes and strategies of heterogeneous batch distillation.     

A semicontinuous approach for heterogeneous azeotropic distillation processes

The separation of azeotropes has substantial energy and investment costs, and the available methods require high capital costs for reconstruction of process plants. As an alternative, a semicontinuous configuration that utilizes an existing plant with minor modifications has been explored. In this paper, a semicontinuous, heterogeneous azeotropic distillation process is proposed and acetic acid dehydration process is used as a case study. To carry out the simulation work, Aspen HYSYS^® simulation software is used along with MATLAB^® and an interface program to handle the mode-transition of the semicontinuous process. Sensitivity analyses on operating parameters are performed to identify the process limits. Comparisons are made to conventional heterogeneous azeotropic distillation, and dividing-wall distillation column on the annual cost. The results proved that the semicontinuous system is the best setup in terms of total annual costs and energy requirements.     

Discrete-event simulation of a sequence of multi-component batch distillation columns

The application of a discrete-event simulation system (GPSS) to modelling of a sequence of multi-component batch distillation columns, such as might be employed in a solvent recovery operation, is described. The primary objective of this simulation is to demonstrate the application of the GPSS system to determination of equipment and manpower utilization. The complete GPSS coding is included. Operating parameters corresponding to a particular installation are readily varied by an analyst.     

拟稳态模型用于间歇萃取精馏的数值模拟

Batch extractive distillation (BED) is a special method used in the distillation process by adding a solvent into the batch distillation column to alter the relative volatility of the components and improve the separation. A comprehensive design and simulation method is required due to the complexity of BED. In this study, a quasi-steady-state model for BED is proposed, the derivation and solution of the model are presented. This shortcut model can be used to simulate the composition and temperature of the reboiler, the top and other plates of the column in a batch extractive distillation operation. The calculated values are in good agreement with the experi-mental data. The results show that the quasi-steady-state model is a practical method because of some advantages such as high precision and fast calculation.     

异丙醇-水间歇共沸精馏模拟研究

运用两点隐含法求解间歇共沸精馏过程平衡级恒摩尔持液模型的非线性刚性方程组。以异丙醇-水-环己烷为例进行模拟计算,并将模拟计算结果同实验结果相比较。结果表明,当共沸剂塔顶回流的回流比为1∶5时,分离得到的异丙醇浓度可以达到99.5%(质量分数);异丙醇的收率最高,最大收率可达78%;模拟计算结果与实验结果吻合得较好,模拟计算可以反映实际过程。     

乙醇-苯-水非均相共沸精馏过程稳态模拟与动态控制

利用Aspen Plus流程模拟软件,以苯为轻夹带剂,建立了乙醇-苯-水三元非均相体系两塔共沸精馏工艺流程。对工艺流程中关键设备汽提塔和脱水塔进行了稳态模拟与优化,优化后的结果为:汽提塔共31块塔板,塔直径2.07 m,塔顶压力0.203 MPa,塔顶回流罐的温度313 K,回流比0.648,再沸器的热负荷9.149 MW;脱水塔共21块塔板,塔直径1.38 m,塔顶压力0.101 MPa,塔顶回流罐的温度347 K,回流比0.2,再沸器的热负荷4.57 MW。最终在汽提塔塔底可得到摩尔分数99.6%的乙醇产品。采用Aspen Dynamic建立了全工艺流程的控制结构,并对进料流量和进料组成的扰动进行了动态分析,结果表明:动态控制结构可满足对产品纯度的设计规定要求。研究结果对工艺与控制方案的选择具有重要的现实指导意义。     

带有中间储罐的间歇萃取精馏的模拟研究

本文提出了带有中间储罐塔间歇萃取精馏过程计算模型,将中间罐看成一块理论板,萃取剂看成第三组份进行建模,利用调节因子和泡点法相结合对整个塔进行迭代计算,经实例模拟表明,本模型只需较简单的赋初值,能以较快的速度收敛,本模型对带有中间储罐间歇萃取精馏操作及模拟具有一定的指导作用。     

Dynamic simulation,numerical control and analysis of a novel bottom flashing scheme in batch distillation

In this communication, the concept of bottom flashing under the mechanical heat pump system is introduced in the batch distillation columns. Proposing an operating strategy at transient state, a numerical control mechanism is formulated to simultaneously adjust the following variables aiming to ensure the optimal use of internal heat source: flow rate of reboiler liquid subjected to bottom flashing, operating pressure of throttling valve, compression ratio for pressure adjustment in the isentropic compressor and external heat input to the reboiler. The potential of this novel energy efficient batch distillation is numerically quantified in terms of the two performance indexes, namely energy savings and cost. Finally, a binary system is dynamically simulated to demonstrate the proposed configuration.     

An experimental simulation of distillation column concentration profiles using a batch apparatus

There has been a growing interest in the use of residue curves for the preliminary design and sequencing of distillation columns. Residue curves are used not only to predict composition changes in separation processes, but also to determine the feasibility of proposed separations, and flowsheet development (Chem. Eng. Sci. 33 (1977) 281).An experimental technique has been developed for the measurement of these residue curves. (Distillation & absorption ’97, Inst. Chem. Eng. 1 (1997) 187). It can be shown that the time-dependent composition profiles obtained in a modified form of this apparatus are mathematically equivalent to the position-dependent profiles in a continuous distillation column. Hence, it is possible to experimentally simulate a distillation column profile in a small batch apparatus using only small quantities of material.The modified apparatus consists of a still immersed in a heated oil bath so that a liquid feed is continuously supplied to the still. Samples of liquid are then analysed over time using a gas chromatograph. The results from an experimental system have been compared to available information and simulations to determine the accuracy of the apparatus.This technique has several advantages over working with distillation columns, firstly in the sample size required, and secondly in the ease of operation. The method allows quick and low-cost measurements of the concentration variables that model a distillation column. The information obtained this way could prove useful for the selection of feasible systems and for finding minimum reflux requirements. It could also be very valuable for screening of complex systems where only small amounts of material are available and simulations may be very difficult.     

Modeling of batch extractive distillation

New data on the concentration profiles in a packed column during extractive distillation of benzene–heptane mixture in the presence of N-methylpyrrolidone as a separating agent have been obtained. A calculation method for the process based on partial mass transfer coefficients in the vapor and liquid has been proposed. The calculated and experimental data have been compared. It has been shown that both continuous and batch extractive distillation are calculated more precisely using the proposed model compared to the equilibrium model.     

反应精馏过程模拟研究进展

对均相反应精馏和非均相催化精馏过程的各种模拟计算方法进行了评述，分析了各种算法的优缺点和适用范围，指明了目前研究中存在的不足和今后的发展方向。     

A systematic approach to SMB processes model identification from batch experiments

The optimization, monitoring and control of simulated moving bed (SMB) units require the use of a process model and the estimation of the model parameters. A systematic numerical procedure for determining parameters of SMB models from batch experiments is presented and evaluated. The unknown parameters are estimated by minimizing a cost function measuring the difference between experimental and simulated concentration profiles. In contrast with previous studies, parameter identifiability is studied and errors on the estimated parameters are calculated. A sensitivity analysis is used to design the experiments and to compare the identifiability of different chromatographic models. Then, the influence of local minima is evaluated by applying the numerical procedure on fictitious measurements generated from a model with known parameters.     

工业醋酸脱水过程五元体系非均相共沸精馏的流程模拟

针对以醋酸正丙酯为共沸剂的醋酸脱水过程,考虑醋酸溶剂中未反应的前体对二甲苯以及反应的副产物醋酸甲酯的影响及回收利用,分别选用HOC和UNIQUAC模型来修正体系中五元混合物系的汽液非理想性,通过拟合醋酸甲酯-对二甲苯和醋酸正丙酯-对二甲苯两体系的二元汽液平衡实验数据获得了该两组体系UNIQUAC模型的二元交互作用参数,借助模拟软件Aspen Plus,结合软件内置其他二元体系参数,对工业醋酸脱水塔系包括溶剂脱水塔、PX回收塔、共沸剂回收塔在内的三塔体系进行系统的分析模拟,得到了与工艺数据误差小于±6%的能正确描述工业醋酸脱水塔系操作特性的工艺机理稳态模型,为工业醋酸脱水过程工艺的进一步研究提供理论基础和依据。     

Synthesis of maximum energy recovery networks in batch processes

In the heat integration problem for batch processes, there are two differences in treatment from continuous operations. The first is the occurrence of cocurrent heat exchange, this case may happen when a process can not be transferred to another process. The second is that time must be considered as a variable. We divide the problem into two cases, namely co-current heat exchange and counter-current one, and then intend to find the rules to satisfy the requirement of each case. For the former, a matching rule and a MILP formulation had been proposed but any method did not obtain the optimal solution. The latter including the time as a variable often occurs in the practical industry. The limitation of time has been reduced by changing the schedule of processing or using the heat storages. However, the systematic rule considering the batch cycle time has not been presented for the rescheduling and heat storage is not usually practical although it is reasonable concept. Therefore this paper presents general method for optimal rescheduling to maximize heat recovery and reduce batch cycle time when heat exchanges occur as counter-current type. In the exchanges of co-current type, the heuristic, called the modified H/H which can be used to find the optimal match sequence of heat exchange between hot and cold tanks, is proposed. The proposed heuristics have the advantages of simple calculation and small computation time.     

间歇萃取精馏过程模拟计算

提出了一种可用于间歇萃取精馏过程模拟计算的快捷模型－准稳态模型，并对该方法的数学模型进行了推导。用此方法对间歇萃取精馏过程中塔顶、塔釜浓度，各塔板温度随时间的变化进行模拟，其结果与实验值吻合较好。它具有计算精度高、计算速度快等优点。