-Heat exchanger networks present an interesting control problem due to coupling among process streams. In this work, the linear quadratic regulator (LQR), a feedback optimal control technique, is used to control stream temperatures on a laboratory scale heat exchanger network, through bypass manipulation, in a multivariable system. The LQR design was based on a mathematical model of the plant and its performance was compared to traditional PID control and to dynamical decoupling. Experimental tests were performed to evaluate the controllers, involving regulatory and servo problems. The performance of the different controllers was quantitatively compared by using the integral absolute error. Although LQR is not a new control methodology, the results obtained in this work suggest that LQR is an interesting alternative to control HEN when compared to the PID and to the dynamic decoupler. Moreover, one of the main advantages of the LQR is its tuning simplicity, since only one parameter is sufficient for this application.

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O consumo de energia vem aumentando muito nos últimos anos, principalmente por conta do uso intensivo nas indústrias e também pelo aumento do padrão de vida. Nesse cenário, a matriz energética brasileira é bem diversificada e conta com importante uso de fontes renováveis. No presente trabalho, fez-se uma avaliação técnica e econômica do aproveitamento de energia solar, eólica e daquela proveniente da queima de bagaço de cana, num processo de cogeração. Para isso, foram levados em conta os investimentos necessários e as capacidades de geração de cada uma dessas fontes. O custo específico de geração da energia solar foi de R$0,98/kW∙h, o da eólica igual a R$0,12/kW∙h e aquele da biomassa foi de R$0,27/kW∙h. Esses números sugerem que a geração de energia a partir de fontes renováveis é interessante do ponto de vista econômico.Energy consumption has been increasing a lot recently because of the intensive use of energy in manufacturing processes and due to the modern lifestyle in our society. In this context, Brazilian energy sources are pretty diversified and they are mainly composed by renewable energy. A technical and economical assessment of solar, wind and biomass power generation was carried out in this work. With this aim, capital costs and generation capacities for each energy source were taken into account. Specific costs of solar generation resulted in R$0.98/kW∙h, wind power were equal to R$0.12/kW∙h and biomass power, obtained in a cogeneration process with sugarcane bagasse, resulted in R$0.27/kW∙h. These data suggest that renewable energy is quite interesting from an economical point of view.

A countless of different multivariable control techniques, ranging from decentralized PID to predictive controls, are presented in several literatures and applied to chemical plants. This work intends to present a study developed using a control solution based on optimal control, applied on a heat exchanger network (HEN) with bypasses. The HEN is frequently used in chemical processes to promote energy integration, reducing the utility consumption as its main objective. A H-Infinity model matching control was developed successfully to the network by using time domain specification instead of the traditional frequency domain specification. The results of the simulations have demonstrated that the proposed optimal control leaded to a reasonable control performance, i.e., process variables became almost totally decoupled, null offset, and the output responses presented a small time constant.

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