Synthesis of Heat Exchanger Networks Taking into Account Cost and Dynamic Considerations

AbstractIn this work an approach is presented for the synthesis of near cost optimal heat exchanger networks with a high controllability. The presented methodology is based on a sequential approach utilizing different algorithms and mathematical models. The procedure is carried out in three steps. A genetic algorithm is used to produce a high diversity of promising structures that suffice the needs for cost reduction and controllability characteristics. For selected structures controllability evaluations are carried out, which are mainly based on relative gain array and condition number assessments. Therefore, a linear model is utilized which was further used to calculate the area adjustments and nominal bypasses for complete disturbance rejection for perfect control. As a last step simplified mathematical solution models are used to further extend insight gained for decision-making. These models are used to carry out dynamic simulations for testing the impact of different possible decentralized feedback control structure designs developed by previous methods. The application of the developed approach will be shown using an example from literature

A rewriting grammar for heat exchanger network structure evolution with stream splitting

The design of cost optimal heat exchanger networks is a difficult optimisation problem due both to the nonlinear models required and also the combinatorial size of the search space. When stream splitting is considered, the combinatorial aspects make the problem even harder. This paper describes the implementation of a two level evolutionary algorithm based on a string rewriting grammar for the evolution of the heat exchanger network structure. A biological analogue of genotypes and phenotypes is used to describe structures and specific solutions respectively. The top level algorithm evolves structures while the lower level optimises specific structures. The result is a hybrid optimisation procedure which can identify the best structures including stream splitting. Case studies from the literature are presented to demonstrate the capabilities of the novel procedure

A Simple Hybrid Approach for the Synthesis of Heat Exchanger Networks Involving Internal Utility Exchangers

This study aims to present a simple hybrid approach for synthesizing heat exchanger networks (HENs). The synthesis of HEN structures employs a genetic algorithm based on a modified node representation, closely resembling the stage-wise superstructure model. This modified representation allows for addressing the internal utility exchangers throughout the entire network. Despite the nonlinear nature of the model governing the continuous variables of each structure, a relatively simple linear formulation is developed to handle these variables. This novel formulation comprises a linear programming model for maximum energy recovery, a linear correction procedure (COP), and two search loops. The COP focuses on determining the optimal values of exchangers’ heat loads and stream split ratios to reach the minimum total annual cost of the network. The study investigates four extensively studied medium- to large-scale networks from the literature. Despite the simplicity of the proposed approach, a comparison of results demonstrates its potential effectiveness

Automatic synthesis of heat exchanger networks using pinch analysis and mathematical programming

Orientador: Roger Josef ZempDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Desde a crise energética dos anos 70, a otimização do consumo de energia se tornou uma importante tarefa para os engenheiros de processo. Duas diferentes metodologias têm sido aplicadas para minimizar o uso de energia em processos químicos. A primeira é a metodologia Pinch, que envolve a aplicação de análise termodinâmica do processo e baseia-se em metas de energia e custo para obter uma rede de trocadores de calor que opera com o mínimo consumo de energia. A segunda é a programação matemática, que consiste na elaboração de modelos matemáticos complexos resolvidos através de métodos numéricos. Neste trabalho, uma nova metodologia para a síntese de redes de trocadores de calor é apresentada. O procedimento proposto combina a abordagem sistemática da tecnologia Pinch com métodos de programação matemática (linear inteira mista) e procedimentos evolutivos. A nova metodologia é baseada na otimização de uma superestrutura cuja complexidade varia ao longo do procedimento de síntese da rede de trocadores, e que permite ao engenheiro de projeto a consideração das restrições do processo sem necessidade de formulação matemática das mesmas. Uma vantagem da metodologia é a possibilidade de considerar aspectos práticos como operabilidade e controlabilidade. O método proposto é ilustrado com a integração energética de três problemas típicos: um caso-teste com quatro correntes, o caso padrão em estudos de integração energética da planta simplificada de aromáticos e o caso recente do sistema de célula combustível a membrana trocadora de prótons. Foram obtidas redes alternativas para os casos estudados, que são energeticamente eficientes, mais baratas e simplesAbstract: Since the energy crisis of the 70s, the optimization of energy consumption has become an important task for process engineers. Two different methodologies have been applied to minimize energy use in chemical processes. The first methodology is the pinch method, which involves applying process thermodynamic analysis and it is based on energy and cost targets for a network of heat exchangers operating at the minimum power consumption. The second one is the mathematical programming, which is the development of complex mathematical models solved through numerical methods. In this work, a new methodology for the synthesis of heat exchanger networks is presented. The proposed procedure combines the systematic approach of Pinch technology with mathematical programming methods (mixed integer linear) and evolutionary procedures. The new methodology is based on the optimization of a superstructure whose complexity varies throughout the synthesis procedure of the network of exchangers, which allows the design engineer to consider the constraints of the process without having to include them into the mathematical formulation. One advantage of this methodology is the possibility of considering practical aspects such as controllability and operability. The proposed method is illustrated by the energy integration of three typical problems: a test case with four streams, the standard case in studies of energy integration simplified aromatics plant and the recent case of fuel processor system coupled to proton exchange membrane fuel cell. Alternative networks were obtained for the cases studied, which are energy efficient, cost-effective and simplerMestradoSistemas de Processos Quimicos e InformaticaMestre em Engenharia Químic

Mathematical Modeling and Optimization for Heat Exchanger Network Synthesis

Ph.DDOCTOR OF PHILOSOPH

Development of a Multi Criteria Process Design Framework for Sustainable Design and Synthesis of Processes

A framework is developed to address sustainability concerns with special intention to chemical process design. The platform consists of a novel rigorous multi-objective optimization algorithm in tandem with a commercial process simulator for rigorous design and optimization of the processes. A sustainability evaluator module is linked to the framework for evaluation of process alternatives in terms of sustainability criteria. In addition a novel decision making step is devised to reduce the cognition load on decision makers imposed by a multitude of objectives and solutions. This research contributes to sustainability development assessment in process design. Sustainable design of processes involves process design complexity compounded by several conflicting criteria. In this work, a systematic multi-criteria framework was developed to enable rigorous process design with many design criteria such as sustainability concerns. The proposed framework involved development of: a modified Particle Swarm algorithm to handle a multitude of objectives, a method for handling mixed integer optimization problems, an effective constraint handling methodology, an algorithm that incorporates multi-objective optimization a non-dominated methodology to enable process design with several objectives especially to satisfy social, economic and environmental objectives, a generic computer aided tool to assess process technologies in terms of sustainability, a decision making procedure for selecting the most sustainable process from multiple optimum alternatives that will remain sustainable in the future. This study addressed a major challenge in process design as engineers will now be able to design for multiple criteria, not restricted but specifically sustainability concerns. This work will develop approaches for the optimization of chemical processing technologies with sustainability considerations.School of Chemical Engineerin