A number of factors have contributed to increased pressure on plant operating efficiency in the chemical processing industry. These factors include more stringent environmental and safety regulations, global economic pressures and downsizing of many support services in order to save money. Control performance monitoring is a tool that is used to keep control systems performing as optimally as possible. Various performance metrics and methods exist to evaluate plant operation. In essence, however, they all refer to the same principle which is to indicate how far a plant is operating from its inherent optimum and what can be done to ensure that the gap between the optimum and the current operation is as small as possible over the longest possible period. Performance monitoring is, although well researched, not a generic, complete and specific application. Current shortcomings of monitoring applications include the following; they are process or unit operation specific and they provide local indications of performance and do not provide a plant wide evaluation of how close the plant is operating to its inherent optimum. Performance reports are usually in terms of statistical measures and graphics which are usually abstract and vague. For high level decisions making (on operation end economic investment) simple and quantifiable measures are needed that are repeatable and transparent. The focus of this project was to develop and implement a regulatory performance monitoring structure for real-time application on an industrial pilot scale distillation column. The structure was implemented by means of two graphical interfaces. The first interface provides a holistic plantwide indication of performance and indicates sources of poor performance in the regulatory control structure. The plantwide interface includes a proposed plant wide performance index (PWI) that reduces operational efficiency to one specific number. The second interface supplements the plantwide interface by providing statistical information on individual loop performance. The individual loop interface is a tool to locate causes of poor performance in the regulatory control structure to aid controller and plant maintenance. / Dissertation (MEng (Control Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

The problem of designing control systems for entire plants is studied. A review of previous works, available techniques and current research challenges is presented, followed by the description of some theoretical tools to improve plantwide control, including the proposal of an augmented lexicographic multi-objective optimization procedure. With these, an augmented hierarchical plantwide control design technique and an optimal multi-objective technique for integrated control structure selection and controller tuning are proposed. The main contributions of these proposed techniques are the inclusion of system identification and optimal control tuning as part of the plantwide design procedure for improved results, support to multi-objective control specifications and support to any type of plant and controllers. Finally, the proposed techniques are applied to industrial benchmarks to demonstrate and validate its applicability. / O problema de projetar sistemas de controle para plantas inteiras é estudado. Uma revisão de trabalhos anteriores, técnicas disponíveis e atuais desafios de pesquisa é apresentada, seguida da descrição de algumas ferramentas teóricas para melhorar o controle plantwide, incluindo a proposta de um procedimento de otimização multi-objetivo lexicográfico aumentado. Com tais elementos, são propostas uma nova técnica hierárquica aumentada de projeto de sistemas de controle plantwide e uma técnica multi-objetivo para seleção de estrutura de controlador integrada à sintonia ótima do controlador. As principais contribuições das técnicas propostas são a inclusão de identificação de sistemas e sintonia ótima de controladores como parte do procedimento de projeto de controle plantwide para melhores resultados, suporte a especificações multi-objetivo e suporte a quaisquer tipos de plantas e controladores. Finalmente, as técnicas propostas são aplicadas a benchmarks industriais para demonstrar e validar sua aplicabilidade.

Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-10-10T18:36:07Z No. of bitstreams: 1 TeseAOC.pdf: 3133234 bytes, checksum: fa3788cc1616002b40bb53fd23954c58 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-21T12:01:29Z (GMT) No. of bitstreams: 1 TeseAOC.pdf: 3133234 bytes, checksum: fa3788cc1616002b40bb53fd23954c58 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-21T12:01:36Z (GMT) No. of bitstreams: 1 TeseAOC.pdf: 3133234 bytes, checksum: fa3788cc1616002b40bb53fd23954c58 (MD5) / Made available in DSpace on 2016-10-21T12:01:42Z (GMT). No. of bitstreams: 1 TeseAOC.pdf: 3133234 bytes, checksum: fa3788cc1616002b40bb53fd23954c58 (MD5) Previous issue date: 2016-07-08 / Não recebi financiamento / Chemical plants are increasingly complex and integrated with recycle streams promoting energy integration and increasing process yield. This results in a complex dynamic behavior which can interfer in control systems design. Decentralized control systems are an alternative although this methodologie is not always e ective once that interactions between process units are not considered. In this work, decentralized coordinated optimization with severous methods of coordination is applied to a reactor- ash systems and Williams-Otto plant, getting satisfatory results for these chemical plants. Then, we develop a control system to complex chemical plants that are decomposed in subsystems, combine decentralized coordinated optimization with strategies of plantwide control theory to ensure that processes operate in conditions comply with global and local demands, minimizing the e ect of disturbances in the system and avoiding snowball e ect, characteristics of this type of systems since both methodologies consider the interconnections of the systems. The methodology is applied to design of control systems to Williams-Otto plant, because of complexity of its optimization problem and high f interaction between its process units. The result is a control systems of complex chemical plants with high performance and e ciency, with smooth actions in face of fast disturbances and minimizing their e ects along the plants. Futhermore, there is the importance of applying plantwide control theory in the proposed system, even if decentralized coordinate optimization is used that, alone, does not guarantee the performance and e ectiveness of the designed system. / As plantas químicas industriais estão cada vez mais complexas e integradas, com a presença de correntes de reciclo promovendo a integração energética e o aumento do rendimento do processo. Isto resulta em um comportamento dinâmico complexo, que pode dificultar o projeto de um sistema de controle eficaz para a planta. Sistemas de controle descentralizado são uma alternativa. Porém, esta metodologia nem sempre é eficaz uma vez que as interações entre as unidades de processamento da planta não são consideradas. Neste trabalho, a otimização descentralizada coordenada a partir de diferentes métodos de coordenação é testada para um sistema composto de um reator e um vaso flash e para a planta de Williams-Otto, obtendo resultados satisfatórios para as plantas químicas selecionadas. Posteriormente, desenvolveu-se uma estrutura de controle para Plantas químicas complexas que são decompostas em subsistemas, aliando a otimização descentralizada coordenada com estratégias de controle plantwide, de modo a garantir que o processo opere em condições que atendam as demandas globais e locais, minimizando o efeito das perturbações no sistema e evitando o “efeito bola de neve", característico deste tipo de sistema, uma vez que ambas metodologias consideram as interconexões do sistema que compõem a planta química. A metodologia é aplicada a planta de Williams-Otto em virtude da complexidade de seu problema de otimização e a alta influência das interações entre as unidades de processamento para o comportamento do sistema. Isto resulta em um sistema de controle de plantas químicas complexas com alto desempenho e eficiente, com respostas suaves às perturbações rápidas e minimização da propagação dos efeitos destas na planta. Além disto, verifica-se a importância de se aplicar heurísticas de controle plantwide na eficacia do sistema proposto, mesmo que este utilize a otimização descentralizada coordenada que, de maneira isolada, não garante o desempenho do sistema projetado.

The problem of designing control systems for entire plants is studied. A review of previous works, available techniques and current research challenges is presented, followed by the description of some theoretical tools to improve plantwide control, including the proposal of an augmented lexicographic multi-objective optimization procedure. With these, an augmented hierarchical plantwide control design technique and an optimal multi-objective technique for integrated control structure selection and controller tuning are proposed. The main contributions of these proposed techniques are the inclusion of system identification and optimal control tuning as part of the plantwide design procedure for improved results, support to multi-objective control specifications and support to any type of plant and controllers. Finally, the proposed techniques are applied to industrial benchmarks to demonstrate and validate its applicability. / O problema de projetar sistemas de controle para plantas inteiras é estudado. Uma revisão de trabalhos anteriores, técnicas disponíveis e atuais desafios de pesquisa é apresentada, seguida da descrição de algumas ferramentas teóricas para melhorar o controle plantwide, incluindo a proposta de um procedimento de otimização multi-objetivo lexicográfico aumentado. Com tais elementos, são propostas uma nova técnica hierárquica aumentada de projeto de sistemas de controle plantwide e uma técnica multi-objetivo para seleção de estrutura de controlador integrada à sintonia ótima do controlador. As principais contribuições das técnicas propostas são a inclusão de identificação de sistemas e sintonia ótima de controladores como parte do procedimento de projeto de controle plantwide para melhores resultados, suporte a especificações multi-objetivo e suporte a quaisquer tipos de plantas e controladores. Finalmente, as técnicas propostas são aplicadas a benchmarks industriais para demonstrar e validar sua aplicabilidade.