89 research outputs found

    Logic hybrid simulation-optimization algorithm for distillation design

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    In this paper, we propose a novel algorithm for the rigorous design of distillation columns that integrates a process simulator in a generalized disjunctive programming formulation. The optimal distillation column, or column sequence, is obtained by selecting, for each column section, among a set of column sections with different number of theoretical trays. The selection of thermodynamic models, properties estimation etc., are all in the simulation environment. All the numerical issues related to the convergence of distillation columns (or column sections) are also maintained in the simulation environment. The model is formulated as a Generalized Disjunctive Programming (GDP) problem and solved using the logic based outer approximation algorithm without MINLP reformulation. Some examples involving from a single column to thermally coupled sequence or extractive distillation shows the performance of the new algorithm.Spanish Ministry of Science and Innovation (CTQ2012-37039-C02-02)

    Synthesis and design of integrated reaction-separation systems with complex configurations and rigorous models

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    Chemical engineering, and specially process design, synthesis and intensification, are well positioned to support both society and industry in overcoming present global challenges of environment degradation, energy supply, water scarcity and food supply. These challenges have been translated into industrial problems that involve the design of chemical processes with decreased water and energy consumption, and improved efficiencies. In this context the present study focuses on the simultaneous synthesis and design of reaction-separation systems including complex configuration distillation columns and using rigorous models. The study is considered a further step in this research area, as previous works have usually focused on the synthesis of sub-networks and have used shortcut models. Additionally, among complex configuration, thermally coupled distillation columns are reported to present significant savings in terms of the total annualised cost of the system. Among the available approaches to synthesis and design, a superstructure optimisation approach is used. The procedure involves the construction of a superstructure that includes a reaction superstructure, taken from Ma et al. (Ma et al. 2019) and a separation superstructure, proposed by Sargent and Gaminibandara (Sargent and K. Gaminibandara 1976). The modelling is performed using generalised disjunctive programming (GDP) to produce a logic-based model. This model is then reformulated into a mixed-integer nonlinear programming (MINLP) optimisation problem, where the objective is to minimise the total annualised cost of the process. For the reformulation convex hull and bypass efficiency methods are used. A modified version of the solving strategy presented by Ma et al. (Ma et al. 2019) is used, which involves using the solver SBB in General Algebraic Modelling System (GAMS). The proposed framework is applied to a case study previously addressed by Zhang et al. (Zhang et al. 2018) and Ma et al. (Ma et al. 2019). Economic models and assumptions made in those studies are maintained in order to evaluate the benefits of including complex configuration columns in the design possibilities. Results present a flowsheet with one PFR reactor and complex configuration distillation columns that are partially thermally coupled. The total annualised cost of the process is 5.85x105 $/yr, which is 6.3% and 4.7% less than the value achieved by Zhang et al. (Zhang et al. 2018)and Ma et al., respectively. Results show that it is both possible and beneficial to consider complex configuration distillation columns, including thermally coupled ones, in the simultaneous synthesis and design of reaction-separation systems using rigorous models.Chevening AwardsAgencia Nacional de Investigación e Innovació

    A Framework for Globally Optimizing Mixed-Integer Signomial Programs

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    Mixed-integer signomial optimization problems have broad applicability in engineering. Extending the Global Mixed-Integer Quadratic Optimizer, GloMIQO (Misener, Floudas in J. Glob. Optim., 2012. doi:10.1007/s10898-012-9874-7), this manuscript documents a computational framework for deterministically addressing mixed-integer signomial optimization problems to ε-global optimality. This framework generalizes the GloMIQO strategies of (1) reformulating user input, (2) detecting special mathematical structure, and (3) globally optimizing the mixed-integer nonconvex program. Novel contributions of this paper include: flattening an expression tree towards term-based data structures; introducing additional nonconvex terms to interlink expressions; integrating a dynamic implementation of the reformulation-linearization technique into the branch-and-cut tree; designing term-based underestimators that specialize relaxation strategies according to variable bounds in the current tree node. Computational results are presented along with comparison of the computational framework to several state-of-the-art solvers. © 2013 Springer Science+Business Media New York

    Synthesis and design of integrated reaction-separation systems with complex configurations and rigorous models

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    Chemical engineering, and specially process design, synthesis and intensification, are well positioned to support both society and industry in overcoming present global challenges of environment degradation, energy supply, water scarcity and food supply. These challenges have been translated into industrial problems that involve the design of chemical processes with decreased water and energy consumption, and improved efficiencies. In this context the present study focuses on the simultaneous synthesis and design of reaction-separation systems including complex configuration distillation columns and using rigorous models. The study is considered a further step in this research area, as previous works have usually focused on the synthesis of sub-networks and have used shortcut models. Additionally, among complex configuration, thermally coupled distillation columns are reported to present significant savings in terms of the total annualised cost of the system. Among the available approaches to synthesis and design, a superstructure optimisation approach is used. The procedure involves the construction of a superstructure that includes a reaction superstructure, taken from Ma et al. (Ma et al. 2019) and a separation superstructure, proposed by Sargent and Gaminibandara (Sargent and K. Gaminibandara 1976). The modelling is performed using generalised disjunctive programming (GDP) to produce a logic-based model. This model is then reformulated into a mixed-integer nonlinear programming (MINLP) optimisation problem, where the objective is to minimise the total annualised cost of the process. For the reformulation convex hull and bypass efficiency methods are used. A modified version of the solving strategy presented by Ma et al. (Ma et al. 2019) is used, which involves using the solver SBB in General Algebraic Modelling System (GAMS). The proposed framework is applied to a case study previously addressed by Zhang et al. (Zhang et al. 2018) and Ma et al. (Ma et al. 2019). Economic models and assumptions made in those studies are maintained in order to evaluate the benefits of including complex configuration columns in the design possibilities. Results present a flowsheet with one PFR reactor and complex configuration distillation columns that are partially thermally coupled. The total annualised cost of the process is 5.85x105 $/yr, which is 6.3% and 4.7% less than the value achieved by Zhang et al. (Zhang et al. 2018)and Ma et al., respectively. Results show that it is both possible and beneficial to consider complex configuration distillation columns, including thermally coupled ones, in the simultaneous synthesis and design of reaction-separation systems using rigorous models.Chevening AwardsAgencia Nacional de Investigación e Innovació

    Structural considerations in zeotropic distillation sequences with multiple feeds

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    The separation of multiple feed streams with some common components using sequences of distillation columns produces a rich space of alternatives that must be considered. In this work, we present the main structural characteristics of sequences generated when we want to take advantage of the synergies of common components in multiple feed streams to reduce both, energy consumption and the total number of distillation columns. In general, the sequence of separation tasks of the whole system can be obtained from the sequences of separation tasks of each one of the feeds. However, the integration in actual columns is not so straightforward and we must consider aspects like the optimal location of feeds in multiple-feed columns; and the alternatives of integration of common sub-mixtures (when possible) in actual columns. Besides, the optimal sequence of separation tasks for each feed is not necessarily the same when all of them are considered simultaneously. We show that the minimum number of actual columns, without considering further intensification, depends on the number of components in each feed and on the possibilities of integration of common sub-mixtures, so we extend the concepts of regular and basic column sequences to deal with these new situations. The examples show the potential savings in energy and number of columns compared to maintain isolated each feed; mixing the feed streams or an incorrect integration.The authors acknowledge financial support to the “Generalitat Valenciana” under project PROMETEO 2020/064

    Multiobjective Early Design of Complex Distillation Sequences Considering Economic and Inherent Safety Criteria

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    Inherent safety aspects are not usually considered as a driving force during the conceptual design stage of chemical plants. Instead, after the selection of the optimal economic flowsheet, safety is added to the design. However, this sequential design approach could be applied to inferior designs due to protection devices’ cost overrun. The objective of this work is to implement a strategy to simultaneously design a profitable and inherently safer distillation train. Two safety indexes, a disaggregated version of the Safety Weighted Hazard Index and Dow’s Fire and Explosion Index, have been adapted to quantify the inherent safety performance. A large-scale multiobjective MILP problem is formulated. Thus, two strategies of objective reduction are utilized: principal component analysis coupled with Deb’s algorithm and a method based on the dominance structure. The results prove the suitability of these safety index as inherently safer metrics, and showcase the ability of the objective reduction methods to discriminate among the inherent safety criteria.We acknowledge financial support from “Proyectos de I + D para grupos de investigación emergentes GV/2016/005” (Conselleria d’Educació, Investigació, Cultura i Esport, GENERALITAT VALENCIANA) Spanish “Ministerio de Economía, Industria y Competitividad” (CTQ2016-77968-C3-2-P, AEI/FEDER, UE)

    Rigorous design of distillation columns using surrogate models based on Kriging interpolation

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    The economic design of a distillation column or distillation sequences is a challenging problem that has been addressed by superstructure approaches. However, these methods have not been widely used because they lead to mixed-integer nonlinear programs that are hard to solve, and require complex initialization procedures. In this article, we propose to address this challenging problem by substituting the distillation columns by Kriging-based surrogate models generated via state of the art distillation models. We study different columns with increasing difficulty, and show that it is possible to get accurate Kriging-based surrogate models. The optimization strategy ensures that convergence to a local optimum is guaranteed for numerical noise-free models. For distillation columns (slightly noisy systems), Karush–Kuhn–Tucker optimality conditions cannot be tested directly on the actual model, but still we can guarantee a local minimum in a trust region of the surrogate model that contains the actual local minimum.The authors gratefully acknowledge the financial support of the Ministry of Economy and Competitiveness of Spain, under the project CTQ2012-37039-C02-02

    СИНТЕЗ СХЕМ РЕКТИФИКАЦИИ СО СВЯЗАННЫМИ ТЕПЛОВЫМИ И МАТЕРИАЛЬНЫМИ ПОТОКАМИ

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    Approaching a hypothetical thermodynamically reversible process is one of the main directions of energy saving in distillation. In practice, this is achieved by the use of systems with coupled thermal and material flows (STMP). Such systems have long been used in the separation of zeotropic mixtures. As follows from the analysis of literature data, they save energy costs by up to 30%. Recently, it has been revealed that the use of such systems is possible, expedient and energetically advantageous for separating the close-boiling and azeotropic mixtures by extractive distillation (ED). The article considers the main approaches to the synthesis of distillation schemes, including systems with STMP: 1) a method based on the construction of a "superstructure"; 2) a method based on the concept of thermodynamically equivalent configurations; 3) an evolutionary algorithm; 4) a method based on the transformation of distillation scheme graphs. As the analysis of the literature has shown, the first three methods are sufficiently well developed only for the synthesis of distillation schemes with STMP to separate zeotropic mixtures. There are a relatively small number of publications that consider the generation of ED schemes with STMP based on the concept of thermodynamically equivalent configurations for distillation of specific binary mixtures. The only current system approach to the synthesis of ED schemes with coupled thermal and material flows for multicomponent mixtures is the method of graphs (algorithm 4). At present, the first step has been taken to implement it in the form of a computer program. Thus, the article presents the current state of the problem of synthesizing highly effective, energy-saving distillation technologies, including extractive distillation, based on the analysis of publications over the past 20-25 years.Одним из основных направлений энергосбережения при ректификации является ее приближение к гипотетическому термодинамически обратимому процессу. На практике это реализуется за счет применения комплексов со связанными тепловыми и материальными потоками (СТМП). Комплексы с СТМП достаточно давно используются для разделения зеотропных смесей и, как следует из анализа литературных данных, обеспечивают экономию энергозатрат до 30%. В последнее время выявлено, что применение таких комплексов возможно, целесообразно и энергетически выгодно и для разделения близкокипящих и азеотропных смесей экстрактивной ректификацией (ЭР). Первый этап выбора оптимальной схемы разделения заключается в генерации полного множества возможных вариантов схем. В статье рассмотрены основные подходы к синтезу схем ректификации, включающих комплексы с СТМП: 1) метод, основанный на построении «суперструктуры»; 2) метод, базирующийся на концепции термодинамически эквивалентных конфигураций; 3) эволюционный алгоритм; 4) метод, основанный на трансформации графов, отображающих схемы ректификации. Анализ литературы показал, что первые три метода достаточно хорошо разработаны только для синтеза схем ректификации с СТМП зеотропных смесей. В зарубежной литературе имеется относительно небольшое число публикаций, в которых рассматривается генерация схем ЭР с СТМП для конкретных бинарных смесей на основе концепции термодинамически эквивалентных конфигураций. Единственным существующим в настоящее время системным подходом к синтезу схем ЭР со связанными тепловыми и материальными потоками для многокомпонентных смесей является графовый метод (алгоритм 4). В настоящее время сделан первый шаг к его реализации в виде компьютерной программы. Таким образом, в статье представлен анализ публикаций за последние 20-25 лет, который отражает современное состояние проблемы синтеза высокоэффективных энергосберегающих технологий ректификации, в том числе с применением экстрактивных агентов
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