Evolutionary design of optimum distillation column sequence

Synthesis of the optimum distillation column sequence (DCS), which incorporates a huge search space composed of both conventional and complex arrangements, is a highly complicated combinatorial problem in the field of chemical process design and optimisation. In this study, a novel procedure for the synthesis of optimum DCS proposed by Boozarjomehry et al. [Boozarjomehry et al., Can. J. Chem. Eng. 87, 477–492 (2009)] is expanded to include the complex distillation arrangements. The method is based on evolutionary algorithms, and the total annual cost (TAC) is the main criterion used to screen alternatives. Efficient procedure has been proposed for encoding mechanism to include and classify various complex arrangements together with conventional distillation columns. All columns existing in each DCS alternative are designed using the most recommended short‐cut methods to estimate the TAC of the DCS. Four standard benchmark case studies are carried out to clearly demonstrate the excellent performance of the proposed method. The produced results for these problems indicate that the proposed method outperforms the other existing approaches in terms of flexibility, accuracy and comprehensiveness. © 2011 Canadian Society for Chemical Engineering     

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     

Automatic design of conventional distillation column sequence by genetic algorithm

Synthesis of the optimum conventional (with non‐sharp separations) distillation column sequence (DCS) is a challenging problem, in the field of chemical process design and optimization, due to its huge search space and combinatorial nature. In this paper, a novel procedure for the synthesis of optimum Conventional Distillation Column Sequence is proposed. The proposed method is based on evolutionary algorithms. The main criterion used to screen alternative DCS's is the Total Annual Cost (TAC). In order to estimate the TAC of each DCS alternative all columns that exist in the DCS are designed using short‐cut methods. The performance of the proposed method and other alternatives are compared based on the results obtained for four standard benchmark problems used by researchers working in this area. Based on the results of the comparison, the proposed method outperforms the other methods and is also more flexible than other existing methods.     

A combined method for the design and optimization of intensified distillation systems

The sequential design method (SDM) is a recently introduced distillation column design method based on the correspondence between the simple column and the alternative sequences design parameters. It can be defined as a method that combines the alternatives generation step with the design procedure. The Multi-Objective Differential Evolution (MODE) algorithm instead, is based on the minimization or maximization of a defined objective function; it is a strong method that allows the evaluation of a large number of alternatives.The SDM is characterized by a poor control of the error propagation among the sequences, the MODE algorithm by a high computational time. It was obtained that a proper combination of the methods allows the compensation of the drawbacks of the stand-alone procedures. For the case study considered, when the MODE algorithm is initialized with the SDM, a 39% reduction of the computational time was observed. If the combination between the methods is realised at the beginning of the design procedure, the reduction of the computational time was of about 28%. The time reduction was due to a narrower initialization of the MODE algorithm with the parameters obtained applying the SDM. Moreover, when some overestimated design values where used to initialize the MODE algorithm, it is still possible to identify a configuration very close to the optimum.     

A synthesis method for multicomponent distillation sequences with fewer columns

An easy‐to‐use matrix‐based method for the systematic synthesis of distillation configurations using less than n‐1 columns to separate any zeotropic n‐component feed into n product streams is described. The method is easily extended to obtain additional thermally coupled configurations. The only information needed to generate the configurations is the number of components in the feed, or equivalently, the number of distinct composition final product streams. We have successfully enumerated configurations for feeds containing up to eight components. This has resulted in a large number of hitherto unknown configurations even for four‐component separations. Some of the novel configurations generated using the method have substantially lower heat duty than the previously known fewer column configurations for a four‐component feed separation. Therefore, it is essential to include these novel configurations in the search space to find the optimal distillation configuration with fewer columns for a given application. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2479–2494, 2012     

A generalized method for the synthesis and design of reactive distillation columns

Owing to the combination between the reaction operation and the separation operation involved, it is extremely difficult to determine in advance the optimum configuration of a reactive distillation column and this makes process synthesis and design a great challenging task. Currently, no easy-to-use and yet effective methods are available to guide process synthesis and design, restricting considerably the applications and therefore the impacts of reactive distillation columns to the chemical process industry. In this paper, a generalized method is proposed for the synthesis and design of reactive distillation columns in terms of the insights from process intensification. The method is initiated from a simple process design with all feeds of reactants at the middle of the process and all stages as reactive ones. In terms of an economical objective function, it can be evolved into the optimum process design via sequential structure adjustments, including reactive section arrangement, feed stage relocation, feed splitting, and catalyst redistribution. The generalized method proposed is characterized by great simplicity in principle, the capability to tap the full potentials of process intensification, and the high robustness to the initial guess of process configuration as well as the thermodynamic properties of the reacting mixtures separated. Four example systems are employed to evaluate the generalized method proposed and the obtained outcomes demonstrate its effectiveness and applicability to the synthesis and design of various reactive distillation columns.     

Conceptual design of distillation processes for mixtures with distillation boundaries. II. Optimization of recycle policies

Geometric design methods for the conceptual design of azeotropic distillation processes are fast and efficient tools for the economic screening of different process alternatives. The second article of this two‐part series presents a novel optimization‐based conceptual design framework for azeotropic distillation processes, which allows a rapid screening of the different process alternatives with respect to feasibility and economic incentive. The design framework is based on the economic assessment of distillation columns by the rectification body method. The feasibility limits imposed by the azeotropes are incorporated using the split feasibility test introduced in the first part of this series. The application of the framework is highlighted with several ternary and quaternary process alternatives for the production of high‐purity alcohols. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

一种通用的反应蒸馏塔综合与设计方法

反应精馏是反应过程和分离过程耦合为一体的单元操作,已成为当今研究的重要领域。然而,到目前为止并没有一套通用简便的方法去指导反应精馏过程的综合与设计,严重限制了它的广泛应用。本文在过程强化原理的基础上提出了一种反应蒸馏塔通用的综合与设计方法,并利用2种反应蒸馏系统来评价所提出的设计策略。结果表明,该综合设计方法可以简便高效地搜索出反应蒸馏塔的最优结构,适用于不同类型的反应蒸馏塔的综合与设计。     

Conceptual design of distillation processes for mixtures with distillation boundaries: I. Computational assessment of split feasibility

Geometric design methods for the conceptual design of azeotropic distillation processes are fast and efficient tools for the economic screening of different process alternatives. This two‐part series presents a fully automated conceptual design method for finding an optimal recycle policy for the separation of mixtures with distillation boundaries. It does not require visualization and graphical inspection of residue curve or pinch maps and is, hence, not limited to ternary mixtures. The first part introduces a fully computational geometric split feasibility test based on bifurcation analysis. This bifurcation‐based feasibility test can be used as a valuable stand‐alone tool for the assessment of different separation options. It is also one of the core elements of the recycle optimization discussed in the second part of this series. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

A novel stochastic optimization method to efficiently synthesize large-scale nonsharp distillation systems

This study presents a novel stochastic optimization method for the efficient synthesis of large-scale nonsharp distillation systems, where heat integration and thermal coupling can be involved simultaneously. A new binary tree encoding method was developed to represent distillation sequences with no limits on the number of middle components in nonsharp splits to ensure a complete solution space. Thermally coupled structures were defined by 0–1 binary variables. Evolutionary rules were developed to generate neighboring distillation configurations randomly. Finally, an optimization framework was proposed, where simulated annealing (SA) algorithm was used to optimize distillation configurations; for a certain distillation configuration randomly generated by SA, its continuous variables were optimized using particle swarm optimization algorithm. Four cases—including the synthesis of six- and seven-component nonsharp heat integrated and thermally coupled distillation sequences—were studied to demonstrate that the proposed method was efficient and could obtain optimal and valuable suboptimal solutions with high probabilities.     

基于代码矩阵的精馏序列合成

提出了一种基于代码矩阵的精馏序列合成方法及其算法实现。该方法包括混合物组群划分、减塔配置基本搜索空间的创建、代码矩阵的生成和使用分离限制条件筛选4个步骤。由于代码矩阵衍生自矩阵法的0-1矩阵,且其元素代码包含了精馏塔分离编号和产品流股的采出位置等信息,因此,该合成法不仅能提供完整的精馏配置搜索空间,而且便于根据分离限制要求进行分离序列的筛选。文中给出该方法在乙二醇粗产品体系的应用,由VB计算共获得了8个三塔分离方案。结合Aspen模拟,得到总再沸器热负荷最小的三塔分离方案。     

A method for flexibility analysis of continuous processing plants

A methodology has been developed for the analysis of operational flexibility of a continuous processing plant. An application has been demonstrated for a multipurpose plant with uncertain operating conditions. A practical flexibility analysis procedure using a direct search optimization algorithm is proposed to solve the problem. The method provides a heuristic screening technique that makes it possible to avoid the exhaustive enumeration of every constraint vertex, while the direct search optimization offers a simple and effective means to identify bottlenecks. A refinery multiperiod plant problem has been investigated in order to highlight the procedures which lead to the construction of flexibility indices for each operating mode.     

A method for the design of distillation systems aided by ionic liquids

Ionic liquids (ILs) have recently been considered for several applications in chemical processes. Particularly, as they promote an evident salting-out effect over vapor–liquid equilibrium properties and integrate the advantages of a liquid entrainer with the benefits of a solid salt, the use of ILs for the ethanol–water separation has gained wider interest. In this work, a design method for distillation systems aided by ILs is presented. The method is based on tray-by-tray calculations from the outside to the inside of the column, and the feed stage is determined by using a minimum distance concept. The method is illustrated with an ethanol dehydration design. An analysis on the effect of ILs on the column composition profiles is also carried out. The method is shown to provide an effective tool for the conceptual design of these types of systems.     

Optimal retrofit design of extractive distillation to energy efficient thermally coupled distillation scheme

Design and optimization procedures employing the response surface methodology (RSM) for retrofitting the conventional extractive distillation sequence to a thermally coupled extractive distillation scheme (TCEDS—SR) is presented. The optimum TCEDS—SR structure can be found in a practical manner with minimal simulation runs. Furthermore, the RSM allows the interactions between variables to be identified and quantified. The separation of close boiling point mixtures and azeotropic mixtures was examined to test the proposed method. The predictions agreed well with the results of a rigorous simulation. The results showed that a retrofit of the extractive distillation sequence to TCED—SR can achieve significant energy savings compared to the conventional extractive distillation sequence. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1175–1182, 2013     

A note on an extended short-cut method for the design of multicomponent reactive distillation columns

Until now, few studies have proposed analytical short-cut methods for reliably designing multicomponent reactive distillation columns. Therefore, in this study we have improved and extended a design methodology for the design of RD columns of multicomponent systems. We have developed a graphical design method, based on distillation lines and tray-by-tray calculations defined in terms of reaction-invariant composition variables, to determine RD design parameters such as the number of theoretical stages, operating reflux ratio, the feed tray location and the top or bottom flow. In this note, we report our extended and improved method, which is analytical and useful for reliably determining the design parameters of multicomponent RD systems. We study the synthesis of TAME with inert components (with different feed thermal conditions) as case of study to show the effectiveness of the proposed strategy. Results obtained with our strategy show a significant agreement with those obtained using a rigorous model of commercial simulator AspenONE Aspen Plus^®.     

An iteratively refined distillation line method

The focus of this article is distillation design feasibility. It is shown that existing methods for determining feasibility can give incorrect results or produce feasible designs that waste energy due to over‐specification and mass balance errors. An iterative refinement procedure based on direct substitution is proposed within the distillation line method of Lucia et al. that automatically adjusts one product composition to determine feasibility. Direct substitution equations are presented in detail and 14 literature examples are used to illustrate the efficacy of iterative refinement. Numerical results show that iterative refinement can find feasible designs that other methods cannot find, often resulting in significant reductions in energy requirements, and that it is all product compositions, not just trace compositions that affect most shortcut methods for distillation design. Iterative refinement can also find minimum energy requirements and identify sets of specifications that give infeasible designs. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

A novel method for generating distillation configurations

An improved matrix method for generating distillation configurations with (N−1) and less than (N−1) columns was proposed for the separation of an N-component mixture into essentially pure product streams based on the concepts of streams matrix and 0–1 matrixes proposed by Agrawal. In contrast with the matrix method developed by Agrawal, the present method removes the intermediate process centered on the splits, and complex column configurations, allowing the direct generation of multi-feeds and multi-product streams. Furthermore, certain configurations that cannot be generated directly and that are missing in the matrix method are obtained. Through rigorous simulations and optimization, we have demonstrated that these configurations have the potential to outperform certain existing configurations.     

A new technique for recovering energy in thermally coupled distillation using vapor recompression cycles

Even though it has been proved that a fully thermally coupled distillation (TCD) system minimizes the energy used by a sequence of columns, it is well‐known that vapor/liquid transfers between different sections produce an unavoidable excess of vapor (liquid) in some of them, increasing both the investment and operating costs. It is proposed here to take advantage of this situation by extracting the extra vapor/liquid and subjecting it to a direct/reverse vapor compression cycle. This new arrangement restores the optimal operating conditions of some of the affected sections with energy savings of around 20–30% compared with conventional TCD columns. Various examples, including the direct and reverse vapor recompression cycles, are presented. Furthermore, in each example, all possible modes of distillation (direct, indirect and Petlyuk distillation) with and without vapor recompression cycles (VRC) are compared to ensure that this approach delivers the best results. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3767–3781, 2013     

A unified graphical formulation for synthesis of basic and subcolumn distillation sequences

In contrast to the different approaches currently adopted for generating basic and side-split subcolumn distillation sequence for separating zeotropic multicomponent feed mixture, we present a unified graphical method applicable towards both basic and side-split subcolumn distillation sequence. For a given number of components in the feed mixture, we enforce constraints on a base graph to eliminate violations of conservation principles and to preclude distillation sequences that demand higher heat duty in all appraised practical scenarios. A compact set of algebraic constraints is transfixed using the graph counterpart for generating basic-only distillation configurations. These algebraic constraints utilize binary variables to quantify existence of submixture streams and this considerably reduces the number of variables in generating distillation sequences. We also suggest extension of the formulation to enable the exploration of thermally coupled configurations.