Optimal Design and Economic Evaluation of Dividing‐Wall Columns

In an effort to reduce costs, a systematic optimization approach is proposed to address the energy consumption of dividing‐wall columns (DWCs). This iterative optimization procedure begins by minimizing the overall heat duty using an innovative objective function within a constrained design space. A sensitivity analysis is then carried out on the manipulated variables to obtain their optimal ranges. Optimal operating parameters are obtained through the evaluation of the total annualized cost (TAC). For the separation process of benzene/toluene/o‐xylene, the optimal DWC flow sheet exhibits a significant decrease in TAC when compared to conventional flow sheet optimum designs. The applied optimization method and sensitivity analysis have proven to produce results at the global optimum. This method is both practical and easily applied to other systems, even to systems with more than three components.     

分壁式萃取精馏塔制取无水正丙醇的实验与模拟研究

采用分壁式萃取精馏塔制取无水正丙醇,以乙二醇为萃取剂,在溶剂比为3、主塔回流比为2.5时,实验测得塔顶正丙醇的质量分数达到96.03%,塔釜乙二醇的质量分数达到99.44%,可作萃取剂直接循环利用。利用Aspen Plus对该工艺进行模拟计算,其结果与实验基本一致。模拟对比该工艺和常规双塔萃取精馏工艺,结果显示分壁式萃取精馏塔节能22.5%,降低了能耗和设备投资。     

Design and Control of a Fully Thermally Coupled Distillation Column Modified from a Conventional System

A modified fully thermally coupled distillation column is proposed, with utilization of the existing distillation columns of the conventional system, and its control scheme is suggested here. The proposed distillation system is applied to a benzene‐toluene‐xylene (BTX) separation process, of which the system design and control performance evaluation are conducted using the HYSYS software. The performance of the suggested 3 × 3 control is examined in the set‐point tracking of product specification and the regulation for the changes of feed flow and composition. The pairings of three proportional‐integral control loops are the reflux flow and the specification of overhead product, the prefractionator vapor flow and that of the side product, and the vapor boil‐up rate and that of the bottom product. The multi‐variable controllability using various indices is investigated for the proposed control scheme, and the controllability is compared with that of the cross‐pairing between the control loops of the side and bottom products.     

Conceptual Design of Double‐Feed Reactive Distillation Columns

The feasibility and feasible range of operating parameters for double‐feed reactive distillation columns are evaluated, based on the combination of pinch point map analysis for the middle‐section in the compositional space and the feed angle method as an efficient shortcut design method. Limiting bounds for operating parameters are determined where the properties of singular points change. The existence and values of such bounds may vary in double‐feed reactive distillation columns depending on the nature of the system under study. The methodology is illustrated by production of methyl acetate and ethyl acetate. An efficient method is described to identify the most promising candidates of double‐feed reactive distillation columns and to study the design flexibility in terms of operating parameters.     

分壁塔响应面法优化分离芳烃混合物研究

以Hysys软件对分壁塔分离芳烃混合物进行研究,采用Box-Behnken方法对影响分离效果的因素进行了优化,并进行了数学模型的研究,建立了以组分分离纯度为目标值,各工艺参数为因素的二次多项式模型。结果表明:进料温度和液体分配比对整体分离效果的影响显著,气体分配比对苯的分离影响显著,进料温度和液体分配比对甲苯和二甲苯分离交互作用影响显著。分壁塔分离的最优工艺条件为:进料温度122℃、回流比7、液体分配比0.62、气体分配比0.45。     

Multiple Analysis in a Reactive Distillation Column for the Synthesis of tert‐Amyl Methyl Ether

tert‐Amyl methyl ether (TAME) is produced via reactive distillation. A simulation is set up and controlled on Aspen HYSYS v 8.0 for generating the highest purity of TAME. This simulation includes a plug‐flow reactor and a reactive distillation column. Emphasis was put on finding the optimal operating conditions of the reactive distillation column in order to get the maximum purity of TAME. The operational parameters were reflux ratio, number of reactive stages in the distillation column, and condenser pressure. The results indicated the optimal reflux ratio and condenser pressure which could be adapted to industrial scale.     

An Extensive Analysis on the Start‐up of a Simple Distillation Column with Multiple Steady States

The impact of start‐up procedures on the behaviour of simple distillation columns with multiple steady states is analyzed. A well‐known system with hysteresis is studied in this paper and transient responses for a binary distillation column yielding different steady states during the start‐up operation are shown. Several dynamic simulation results showing an interesting behaviour are presented. Through the examination of the profile evolutions corresponding to given start‐up policies, it can be seen how the column arrives to different steady states. It is shown that it is possible to identify a set of critical values for the start‐up supervision. Also, guidelines of general validity are achieved with the aim of finding the appropriate start‐up policy to obtain the desired solution.     

Dividing Wall Distillation Columns: Optimization and Control Properties

The optimal design of dividing wall columns is a non‐linear and multivariable problem, and the objective function used as optimization criterion is generally non‐convex with several local optimums. Considering this fact, in this paper, we studied the design of dividing wall columns using as a design tool, a multi‐objective genetic algorithm with restrictions, written in Matlab^TM and using the process simulator Aspen Plus^TM for the evaluation of the objective function. Numerical performance of this method has been tested in the design of columns with one or two dividing walls and with several mixtures to test the effect of the relative volatilities of the feed mixtures on energy consumption, second law efficiency, total annual cost, and theoretical control properties. In general, the numerical performance shows that this method appears to be robust and suitable for the design of sequences with dividing walls.     

A Short Note on Steady State Behaviour of a Petlyuk Distillation Column by Using a Non‐Equilibrium Stage Model

A Petlyuk distillation column, considering equilibrium and non‐equilibrium stage models, was studied. Rigorous simulations were conducted using Aspen Plus? RATEFRAC Module for the separation of ternary mixtures. According to the equilibrium model, the energy‐efficient design of the Petlyuk column requires that the intermediate component be extracted from the maximum point in the composition profile in the main column. It was found that, for the intermediate component, mass transfer occurs from the vapour to the liquid phase from the top of the column to the stage where the side stream is extracted, from this point mass transfer occurs in the opposite direction. This point, considering the non‐equilibrium model, corresponds to the stage in which the net mass transfer rate is zero. For the case of two segments per stage, it was found that the heat duties predicted by the equilibrium model are significantly lower than those obtained by using the non‐equilibrium model, which is consistent with previous reported results. However, it is important to say that despite the higher energy duty predicted by the non‐equilibrium model; both models predict significant energy savings.     

Experimental study on pressure drops in a dividing wall distillation column

Previous studies in the fields of process design and process control [1] have shown the potential benefits that can be achieved through the implementation of thermally coupled distillation sequences, in particular, the dividing wall distillation column. The dividing wall distillation column meets important goals of process intensification, including energy savings, reduction in carbon dioxide emissions and miniaturization. In this paper, an experimental study on the hydrodynamic behavior of a dividing wall distillation column is presented. Several different values for gas and liquid velocities were tested in order to measure pressure drops and identify operational regions; the air/water system was used as the basis for the experimental setup. Results regarding pressure drops (fitted to the model of Stichlmair et al.) provide operational limits for the operation of the packed dividing wall distillation column. According to the results, the experimental dividing wall column can be operated at turbulent regime that is associated to proper mass transfer.     

Predictions for Start‐Up Processes of Reactive Distillation Column via Artificial Neural Network

The time consumed in starting up the unit with appropriate holdups can form an important part of the total distillation time, particularly for reactive distillation systems with large holdups. Also, the products formed during the start‐up time are off specification, and are not easily recycled as for traditional distillation, but must be carefully disposed of, which can be very costly. A back‐propagation algorithm artificial neural network model is presented as a tool to assess the start‐up process for a given reactive distillation system. All the data required for training and testing the artificial neural network have been generated using the CHEMCAD simulator, version 5.2–0. The values for the learning rate, momentum term, and gain term of the artificial neural network have been taken as 0.01, 0.6, and 1.0, respectively. From the case studied in this work, it can be seen that a good start‐up policy can reduce both the energy and time requirements in the start‐up phase of reactive distillation processes. Results from predictions show the time consumed in the start‐up period has an average error of 2.833 %, and a maximum error of 7.600 %, for the case studied here. The accuracy of the model will depend upon the data available and the type of model being approximated.     

轻型高效精馏塔的计算机辅助设计

论述了在Win9x操作环境下,用Visual Baisc 6.0可视化语言设计界面,用Microsoft Access建立数据库,用Auto CAD VBA编辑绘图程序,以Auto CAD作为平台,开发设计轻型高效精馏塔辅助设计软件。通过对实际设计结果的检验与试用,该软件具有良好的用户界面、人机对活功能和图形功能,使用简单方便,输入初始条件即可设计并绘制出塔结构图。     

精馏塔节能优化措施研究进展

通过对精馏塔操作过程中的能耗进行了分析,提出了节能思路和能耗优化的措施;并对精馏过程中对能量的需求、精馏系统的热力学效率、高效分离技术以及精馏-膜分离和精馏-吸收混合系统等方面进行了详细的分析、阐述其利弊;同时也对节能措施进行了展望。     

焦油蒸馏塔的腐蚀与防腐

分析了焦油车间蒸馏塔腐蚀的情况，腐蚀的主要原因是固定铵盐、Cl^-、游离碳及过量的水分。采取了在焦油加工前加入Na2CO3溶液等多种防腐措施后，取得了良好的效果。     

全回流-全馏出与变塔压联合的间歇精馏过程

A novel operation of batch distillation-combination of varying colum pressure and total reflux-total efflux is studied experimentally. In the operation, the product is accumulated at the top of the column under total reflux and then drained off completely, and the column pressure is varying in the whole process. This process has been industrialized successfully with large profits. The conventional mode of batch distillation is improved by this method effectively: the separation eficiency and the yield of product are increased greatly, the operation time is shortened and the production cost is cut down. Moreover, the amount of condensation water is decreased and the over-high reboiler temperature is lowered.     

丁醛精馏塔流程模拟与优化

利用Aspen-plus流程模拟软件对丁辛醇装置丁醛精馏塔建立流程模拟模型,比较模拟结果与设计值,通过灵敏度分析,确定最佳操作参数条件.     

流程模拟软件Aspen Plus在精馏塔设计中的应用

以Aspen Plus流程模拟软件对精馏塔进行了简捷设计和严格核算,对精馏塔设计的影响因素进行了分析,并对精馏塔的经济核算进行了初步说明。     

Implementation of an Indirect Control Structure for Composition in a Hybrid Distillation Column

In this paper a PID controller is proposed to ensure the fuel ethanol composition at desired value, above 92.5°INPM, at the same time as saving energy through the minimal use of reboiler power. Due to the fact that composition analyzers are expensive and have a high response time, an inference model was developed in which the product composition is inferred from the product temperature and thermodynamics equations, enabling the monitoring and the indirect control a posteriori of this variable. In addition, the inference of composition allows defining the reference value of the product temperature, which ensures the fuel ethanol production at the desired composition.     

乙烯脱丁烷塔智能操作优化方法研究

考虑乙烯生产过程中实时操作优化特点,在建立精馏塔严格机理开放式方程优化模型的基础上,提出了基于简约空间序列二次规划(RSQP)算法的精馏塔智能操作优化方法.该法根据精馏塔优化操作的实际性和实时性要求,对简约空间SQP算法进行了一些特殊处理,对收敛条件加入了一些智能化规则,使得优化算法综合考虑优化效益、优化求解时间和质量约束等方面.计算结果表明该法的计算效率高于基于Snopt和一般简约空间SQP算法的精馏塔操作优化方法,并且该方法更符合实时操作优化的要求.