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Crude oil distillation is an energy intensive and environmentally challenging process. To decrease the large energy demand of crude oil distillation, heat integration is implemented. The system (i.e. distillation unit and heat exchanger network, HEN) needs to perform an energy-efficient separation in a broad range of scenarios (e.g. changes in product yields or product specifications), without compromising overall profit. Operational optimisation and revamp projects are frequently implemented to adapt an existing system to such diverse scenarios. The present work provides a new approach for optimising crude oil distillation systems. The scope of this methodology consists of: 1) finding the operating conditions for the distillation system that maximise net profit, while 2) proposing retrofit modifications for the HEN that allow a feasible operation. Artificial neural networks (ANN) are used to represent the distillation process. In the proposed modelling strategy, results of rigorous simulations provide the data used to train the ANN models. The resulting ANN models have the advantages of overcoming convergence problems presented by both rigorous and simplified models, of handling fewer variables and performing calculations in less time. The HEN models used in this work consist of a retrofit model and a simulation model. The HEN retrofit model employed by Chen (2008) is extended to include constraints on heat transfer areas, utility consumption; and to optimise stream split fractions. In addition, the segmented linear data used by Chen (2008) to calculate temperature-dependent heat capacities are replaced by models tailor-made for each stream. This allows a more flexible and accurate representation of these properties, compared to the approach of Chen (2008). The HEN simulation model of de Oliveira Filho et al. (2007) is modified and extended in this work to simulate simple unit operations and to consider heat exchangers specified in terms of heat loads. Distillation, HEN and economic models are implemented in a two-level optimisation framework. The first level consists of a simulated annealing algorithm that optimises the operating conditions of the distillation unit (e.g. flow rates of products and stripping steam, pump-around duties and temperature drops, furnace exit temperature) and HEN topology (i.e. number and location of heat exchangers and stream splitters). The second level solves a non-linear least squares problem that addresses the violation of HEN constraints. Different objective functions can be considered, such as maximising net profit or minimising total annualised costs. The case studies presented in this work show that ANN models are suitable for their implementation in optimisation methodologies for crude oil distillation systems. Results indicate that interactions between the distillation process and HEN are captured, and that significant economic improvements can be achieved with the proposed optimisation approach.

Orientador: Roger Josef Zemp / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-16T10:03:36Z (GMT). No. of bitstreams: 1 Salviano_FlaviaRichterFernandez_M.pdf: 1544610 bytes, checksum: faf01181a27b65fd972f0e2414e7112b (MD5) Previous issue date: 2010 / Resumo: Originalmente a Análise Pinch foi aplicada em projetos de novas redes de trocadores de calor em plantas industriais. No entanto, com a ampliação de plantas ou modificação das condições de processos, surgiu a necessidade de se adaptar o conceito de integração de processos para modificar redes existentes. Diante da limitação de ferramentas para auxílio em círculos e a dificuldade de se desenvolver projetos de retrofit, foi desenvolvida uma planilha eletrônica de cálculo baseada nos programas Microsoft Excel e Visual Basic for Applications (VBA). Os dados da rede existente e/ou proposta são inseridos pelo usuário e a planilha utiliza os conceitos de balanço energético e Network Pinch para calcular temperaturas de saída dos fluidos nos trocadores e temperaturas finais das correntes de processo. A ferramenta também permite ao usuário a identificação dos limites de recuperação de calor da rede existente e a minimização do consumo de utilidades sem mudanças topológicas / Abstract: Pinch analysis techniques were originally developed for projects of new heat exchangers networks in industrial plants. However the increasing capacity of plants or modifications in process parameters generated the necessity of adaptation of the original concept of process integration to retrofit of existing networks. Due to the limitation of tools to support calculations and the difficulty in developing retrofit projects, an electronic worksheet based on softwares Microsoft Excel and Visual Basic for Application (VBA) was created. The information of the existing and/or proposed network is inserted in the worksheet by the user and the program uses the concepts of energy balance and Network Pinch to calculate the outlet temperature of fluids in each heat exchanger and the outlet temperature of each process stream in the network. This tool also allows the identification of limits of heat recovery and the minimization of utilities consumption with no topological changes / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

Orientador: Roger J. Zem / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-07-27T02:36:46Z (GMT). No. of bitstreams: 1 Santos_LucianaCristinados_M.pdf: 3430679 bytes, checksum: 28d163db7620c9a4ecc0df34b7ae538b (MD5) Previous issue date: 2000 / Resumo: Um novo procedimento de estimativa de área e custos de capital para sistemas sob integração energética é proposto. Este método permite que restrições de troca térmica e trocadores com mais de uma passagem nos tubos sejam utilizados. O método desenvolvido resulta em um modelo não linear onde, balanços de energia, restrições de troca térmica e o fator de correção para trocadores do tipo casco e tubo 1-2 (com 1 passagem no casco e duas ou mais passagens pares nos tubos) são incluídos. As dificuldades de convergência decorrentes da adição de restrições não lineares, devido a utilização de trocadores com múltiplas passagens nos tubos, levaram ao uso de uma estratégia nova. Esta estratégia é constituída pela resolução de dois problemas não lineares. O primeiro estima a área para trocadores contracorrente constituindo a primeira aproximação para obtenção dos fatores de correção para trocadores com múltiplas passagens nos tubos, e outro onde é estimado o capital para trocadores 1-2. Os fatores de correção dos trocadores com múltiplas passagens nos tubos são calculados externamente ao modelo e entram como parâmetro conhecido. Este procedimento é repetido até que uma diferença tolerável entre as estimativas de capital seja atingida. Para completar o projeto de recuperação de energia, uma metodologia que fornece o projeto da rede de trocadores de calor considerando restrições de troca térmica é proposto. O modelo de síntese resulta na formulação de um MIP (Mixed Integer Programming), onde o problema é dividido em estágios e submetido a balanços de energia para minimizar o número de trocadores.Uma comparação dos custos de capital entre os métodos da estimativa de área e o de síntese de rede mostrou bons resultados, já que a diferença de capital entre os métodos foi inferior a 10% / Abstract: A new procedure for estimating area and capital cost targets of constrained heat exchanger networks is presented. The method allows for match constrained networks and exchangers with more than one tube passo The procedure is based on modelling the problem as a non-linear formulation where the forbidden exchanger matches are included as constraints and the temperature difference correction due to multipass exchangers is included in the modeI. The difficulty of converging to a solution due to the additional non-linear constraints imposed by the multipass exchangers required the use of a two-Ievel approach: at the inner leveI, the area targets for simple pass exchangers are obtained, and at the outer leveI the temperature difference required for multipass exchangers are computed and fed back to the inner leveI. The procedure is repeated until an appropriate tolerance between two iterations was achieved. A procedure for the authomatic synthesis of contrained heat exchanger network was developed, using a mixed integer programming approach and minimising the overall number of heat exchangers. A comparison between the estimated exchanger areas and costs estimated by the new procedure and the area and costs obtained from the final heat exchanger design shows a very good agreement / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

Orientador: Roger Josef Zem / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T08:08:56Z (GMT). No. of bitstreams: 1 Novazzi_LuisFernando_D.pdf: 882915 bytes, checksum: b56c7f8ed1c61f78280d0e06dbdf2df6 (MD5) Previous issue date: 2007 / Resumo: A integração energética entre correntes num processo químico pode dar origem a redes de trocadores de calor bastante complexas, de dificil controle. Nesse trabalho foram discutidos aspectos dinâmicos e estacionários dessa rede, a fim de se propor uma estratégia de controle que minimizasse o consumo de utilidade e satisfizesse especificações impostas. Fez-se a modelagem em regime permanente da rede, através do método da efetividade, levando-se em conta condições operacionais como a temperatura de entrada das correntes, vazão e posição dos bypasses nos trocadores, e considerando a topologia da mesma, com a presença de trocadores, aquecedores ou resfriadores, divisores e misturadores nas correntes. Através da solução de um sistema linear de equações escrito a partir dessas condições, foram calculadas as temperaturas de saída das correntes. O modelo dinâmico de trocadores casco e tubo é descrito por equações diferenciais parcIaIs, que foram discretizadas e resolvidas pelo método das diferenças finitas, em Matlab. Foi verificado que nos trocadores 1-1 as respostas dinâmicas diante de perturbações nas temperaturas de entrada das correntes podem ser aproximadas por funções de transferência de primeira ordem associadas a tempo morto. No caso de distúrbios na vazão, as respostas são mais intensas nas correntes que foram diretamente perturbadas. Quando existe variação nos bypasses, as respostas são aproximadamente dadas por funções de transferência com atraso e avanço de fase. Mostrou-se que em trocadores 1-2 a dinâmica depende da configuração de escoamento, paralelo / contracorrente ou contracorrente / paralelo, e que quando ocorre uma perturbação na vazão, pode haver inversão temporária na resposta. O modelo dinâmico desses trocadores foi usado para descrever o comportamento dinâmico da rede e se concluiu que as perturbações são atenuadas ao longo da mesma. Promoveu-se a linearização do ,modelo dinâmico de trocadores aqui proposto, chegando-se à conclusão que a não linearidade do sistema não é muito acentuada. A partir de algumas considerações e equações de projeto de trocadores, provou-se que existem faixas típicas para a relação entre área de troca e volume do casco e entre área de troca e volume dos tubos. Isso é um resultado importante pois a relação entre área e voll).me surge naturalmente na modelagem dinâmica dos trocadores. Com as ferramentas desenvolvidas, foi proposta uma estratégia de controle ótimo de caráter antecipatório, que consistiu na minimização de uma função objetivo em regime permanente, ligada ao consumo de utilidade e tendo como restrição as especificações de temperatura de saída das correntes. O resultado desse problema de minimização dava a posição ótima dos bypasses nos trocadores, que foi dinamicamente implementada em rampa e depois em degrau. Verificou-se que a implementação em rampa foi mais adequada, com violações dinâmicas mais toleráveis. A fim de melhorar as respostas do sistema de controle, sugeriu-se também uma estratégia de controle ótimo antecipatório e com retroação, promovendo-se a otimização do consumo de energia. Ao se fazer o emparelhamento entre as variáveis, foram distinguidos objetivos de controle rígidos, ligados a controladores com ganho integral, e objetivos flexíveis, associados a controladores com ganho proporcionaL Através desse enfoque, conseguiu-se minimizar o consumo de utilidades, satisfazer as especificações de temperatura e ao mesmo tempo obter-se uma resposta dinâmica rápida. Palavras chave: 1. Redes de trocadores de calor 2. Modelagem 3. Controle ótimo 4. Dinâmica / Abstract: Energy integration among chemical process streams can lead to quite complex heat exchanger networks (HEN) with difficulties in terms of controI. In this work HEN dynamics and steady state aspects were addressed with the aim of proposing a control strategy that minimizes utility consumption and satisfies imposed specifications. A steady state model of the HEN was suggested using the effectiveness method and by taking into account some operational conditions like inlet stream temperatures and flow, bypasses position in the heat exchangers and by considering HEN topology, with the presence of heat exchangers, heaters 01' coolers, splitters and mixers. Based on these considerations a linear set of equations was written, solved and outlet stream temperatures were calculated. Shell and tube heat exchanger dynamic model is described by differential partial equations, which were discretized and solved by the finite difference method, in Matlab. When an inlet temperature disturbance occurs, it was verified that the dynamic response of a 1-1 heat exchanger can be represented by a first order transfer function associated with dead time. In the case of flow disturbances, the responses are more intense on the streams directly disturbed. When bypasses positions change, the responses can be approximated by . a lead Ilag system. It was shown that the dynamics of a 1-2 heat exchanger depends on flow configuration, i.e., paralle1 flow I counterflow or counterflow I parallel flow. When a flow disturbance happens in 1-2 exchangers, a temporary inversion on respons~ can take place. The dynamic models of isolated 1-1 and 1-2 heat exchangers were used to, describe the dynamic behavior of HEN and one could conclude that disturbances were damped along the network. The heat exchangers dynamic models were linearized and it was shown that system non linearity is not very accentuated. By, taking into account some heat exchanger design equations and assumptions, it was proved that there are typica1 intervals for the relation between heat exchange area and shell volume and heat exchange area and tubes volume. This is an important result since these relations appear naturally on heat exchangers dynamic models. With the tools developed in this work it was proposed a feedforward optimal control strategy which consisted in lhe minimization of a steady slate °7ve function connected to utility consumption and subjected to constraints in outlet stream temperatures. The solution of the minimization problem resulted in optimal bypasses positions in the HEN, which were dynamic~lly implemented using a ramp function and a step function. It was verified that ramp implementation was better, with tolerable dynamic violations. With the objective of getting better responses of the control system, it was also suggested a feedback / feedforward strategy, promoting energy consumption optimization. In this strategy, input and output variables were paired and rigid control objectives, connected to integral gain controllers, and flexible control objectives, associated with proportional gain controllers, were distinguished. Through this approach utility consumption was optimized, temperatures specifications were satisfied and at the same time a fast dynamic response was got. Key words: 1. Heat Exchanger Networks 2. Modeling 3. Optimal Contro14. Dynamics / Doutorado / Sistemas de Processos Quimicos e Informatica / Doutor em Engenharia Química

Orientador: Roger Josef Zemp / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T09:52:33Z (GMT). No. of bitstreams: 1 Santana_MarianaFraga_M.pdf: 1967335 bytes, checksum: 90f67a6bf06f7540d4dea0d84fc080bc (MD5) Previous issue date: 2012 / Resumo: 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 simples / Abstract: 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 simpler / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

The purpose of this project is to find an identification tag that can be used in a future automated pinch analysis tool. It can be used to further analyse composite curves and pinch results by tracking the original streams that was converted. In real life situations, retrofitting a process industries streams, can decrease heat demands and costs. A pinch analysis and a heat exchange network is created with fixed and flexible flows to show a recommendation on how the system model can handle this type of situations. The models have been created by hand with support from pinch literature and the calculations validated with mathematical software such as matlab and other graphing tools. The literature study and pinch modelling resulted in a recommendation of tagging Hstart and Hend for each individual stream. By using a geographical tag in a coordinate system the analyst will be able to find the original streams in the pinch analysis and composite curves. The project also resulted in a heating exchange network created from the fixed and flexible data set. The enthalpy differences between the ideal pinch result and the fixed data set is smaller than one might expect because of enthalpy abundance in the specific intervals.

This thesis focuses on the challenges that arise from the scheduling of heat exchanger network maintenance problems which undergo fouling and run continuously over time. The original contributions of the current research consist of the development of novel optimisation methodologies for the scheduling of cleaning actions in heat exchanger network problems, the application of the novel solution methodology developed to other general maintenance scheduling problems, the development of a stochastic programming formulation using this optimisation technique and its application to these scheduling problems with parametric uncertainty. The work presented in this thesis can be divided into three areas. To efficiently solve this non-convex heat exchanger network maintenance scheduling problem, new optimisation strategies are developed. The resulting contributions are outlined below. In the first area, a novel methodology is developed for the solution of the heat exchanger network maintenance scheduling problems, which is attributed towards a key discovery in which it is observed that these problems exhibit bang-bang behaviour. This indicates that when integrality on the binary decision variables is relaxed, the solution will tend to either the lower or the upper bound specified, obviating the need for integer programming solution techniques. Therefore, these problems are in ac- tuality optimal control problems. To suitably solve these problems, a feasible path sequential mixed integer optimal control approach is proposed. This methodology is coupled with a simple heuristic approach and applied to a range of heat exchanger network case studies from crude oil refinery preheat trains. The demonstrated meth- odology is shown to be robust, reliable and efficient. In the second area of this thesis, the aforementioned novel technique is applied to the scheduling of the regeneration of membranes in reverse osmosis networks which undergo fouling and are located in desalination plants. The results show that the developed solution methodology can be generalised to other maintenance scheduling problems with decaying performance characteristics. In the third and final area of this thesis, a stochastic programming version of the feasible path mixed integer optimal control problem technique is established. This is based upon a multiple scenario approach and is applied to two heat exchanger network case studies of varying size and complexity. Results show that this methodology runs automatically with ease without any failures in convergence. More importantly due to the significant impact on economics, it is vital that uncertainty in data is taken into account in the heat exchanger network maintenance scheduling problem, as well as other general maintenance scheduling problems when there is a level of uncertainty in parameter values.

Deposição é um fenômeno indesejável que ocorre na superfície dos trocadores de calor ao longo de sua operação, ocasionando redução na efetividade térmica e aumento da resistência ao escoamento nestes equipamentos. Estes efeitos trazem grandes consequências econômicas e ambientais, devido ao aumento dos custos operacionais (energia adicional é requerida), aumento dos custos de projeto (demanda por equipamentos de maior área de troca térmica), limitações hidráulicas (que pode levar a uma diminuição da carga processada) e aumento das emissões (aumento da queima de combustíveis fósseis para suprir a energia adicional requerida). Neste contexto, o presente trabalho tem por objetivo fornecer ferramentas computacionais robustas que apliquem técnicas de otimização para o gerenciamento da deposição em redes de trocadores de calor, visando minimizar os seus efeitos negativos. Estas ferramentas foram desenvolvidas utilizando programação matemática no ambiente computacional GAMS, e três abordagens distintas para a resolução do problema da deposição foram pesquisadas. Uma delas consiste na identificação do conjunto ótimo de trocadores de calor a serem limpos durante uma parada para manutenção da planta, visando restaurar a carga térmica nesses equipamentos através da remoção dos depósitos existentes. Já as duas outras abordagens consistem em otimizar a distribuição das vazões das correntes ao longo de ramais paralelos, uma de forma estacionária e a outra de forma dinâmica, visando maximizar a recuperação de energia ao longo da rede. O desempenho destas três abordagens é ilustrado através de um conjunto de exemplos de redes de trocadores de calor, onde os ganhos reais obtidos com estas ferramentas de otimização desenvolvidas são demonstrados / Fouling is an undesirable phenomenon that occurs over the surface of heat exchangers during its operation, causing reduction of thermal effectiveness and increase of flow resistance along these equipment. These effects bring large economics and environmental consequences, due to the increase of operational costs (additional energy is required), increase of project costs (demand of equipment with larger thermal exchange areas), hydraulic limitations (that can diminish the process throughput) and increase of emissions (increase of fossil fuel firing to supply the additional energy required). In this context, the objective of this work is to provide robust computational tools that apply optimization techniques for fouling management on heat exchanger networks, aiming to reduce its negative effects. These tools were developed using mathematical programming on GAMS software, and three distinct approaches for the resolution of the fouling problem were investigated. One of them consists in the identification of the optimal set of heat exchangers that have to be cleaned during a plant maintenance shutdown, aiming to restore the thermal load in these equipment through the removal of the existent deposits. The other approaches consist in to optimize the distribution of flow rates of the streams along parallel branches, using stationary and dynamic models, in order to maximize the energy recovery in the network. The performance of these three approaches is illustrated through examples of heat exchanger networks, where the real gains obtained with these optimization tools are demonstrated