Multivariable Optimal Control of a Heat Exchanger Network (HEN) with Bypasses (original) (raw)
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Multivariable Optimal Control of a Heat Exchanger Network with Bypasses
Brazilian Journal of Chemical Engineering, 2016
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.
A myriad of different multivariable control techniques, ranging from the simplest isolated PID controllers to the most sophisticated model predictive controls, are presented in the literature and applied to chemical plants. This work intends to present an intermediate control solution between the simplest and the most complex control design, with a relative simplicity, in combination with a superior performance when compared to traditional PID controllers. The proposed strategy, based on a Linear Quadratic Regulator (LQR), was applied to a heat exchanger with bypasses, which is a typical equipment in industries' processes. Even though the LQR is relatively straightforward to design, with a simple tuning procedure, some simulations' results demonstrated that the proposed approach leaded to a reasonable control performance, i.e., process variables became almost totally decoupled, no offset was observed and the output responses presented an small time constant..
Multivariable control on a heat exchanger network with bypasses
2011
Atualmente, existe uma grande variedade de metodologias de controle que poderiam ser utilizadas e aplicadas a processos industriais. Algumas destas metodologias têm um projeto complexo, exigindo um estudo extra de engenharia para projetar um controlador com um desempenho excelente. Outros controladores não apresentam um desempenho tão bom, embora apresentem um projeto extremamente simples. Entre a mais simples e a mais complexa metodologia, existem soluções de controle intermediárias, baseadas nas teorias de controle ótimo, que apresentam uma relativa simplicidade de projeto combinada com um desempenho superior. A presente tese apresenta a aplicação de duas técnicas de controle aplicadas a uma Rede de Trocadores de Calor (RTC) com bypasses: o controle LQR (Regulador Linear Quadrático) e o controle H-Infinito, apresentando os resultados obtidos em simulação no Matlab/Simulink e também resultados experimentais. Além disso, foi desenvolvido um procedimento para a validação experimental...
Performance comparison of different control strategies for heat exchanger networks
Polish Journal of Chemical Technology, 2018
In this article, the dynamic responses of heat exchanger networks to disturbance and setpoint change were studied. Various control strategies, including: proportional integral, model predictive control, passivity approach, and passivity-based model predictive control were used to monitor all outlet temperatures. The performance of controllers was analyzed through two procedures: 1) inducing a ±5% step disturbance in the supply temperature, or 2) tracking a ±5 o C target temperature. The performance criteria used to evaluate these various control modes was settling time and percentage overshoot. According to the results, the passivity-based model predictive controllers produced the best performance to reject the disturbance and the model predictive control proved to be the best controller to track the setpoint. Whereas, the ensuing performance results of both the PI and passivity controllers were discovered to be only acceptable.
International Journal of Engineering & Technology, 2018
Heat exchanger plays a important role in many unitsas they have the capability to hold different temperarure and pressure range. In this paper the linear quadratic controller and Dynamic matrix controller is implemented for heat exchanger system. The out let temperature of the tube is controlled by monitoring the inlet flow rate by using different controllers. The model of the system has been obtained from experimental data using system identification technique. The LQR and DMC is compared by analyze the servo performance in the system in terms of settling time, overshoot and rise time.
On-line optimization and choice of optimization variables for control of heat exchanger networks
Computers & Chemical Engineering, 1997
The paper discusses optimal operation of a general heat exchanger network with given structure, heat exchanger areas and stream data including predefined disturbances. A method that combines the use of steady state optimization and decentralized leedback control is proposed. A general steady state model is developed, which is easily adapted to any heat exchanger network. Using this model periodically for optimization, the operating conditions that minimize utility cost are found. Setpoints are constant from one optimization to the next, and special attention is paid to the selection of measurements such that the utility cost is minimized in the presence of disturbances and model errors. In addition to heat exchanger networks, the proposed method may also be applied to other processes where the optimum lies at the intersection of constraints.
Optimal setpoint control of complex heat exchanger systems
Computers in Industry, 1985
This paper presents an approach for calculating the best way of distributing the streams following through a certain class of complex heat exchanger systems in order to achieve maximum heat recovery within the system. A computer code has been developed by which the described method is demonstrated, off-line, for two real cases. This program can be readily integrated into an overall , on-line computer control system for any complex process consisting of an exchanger system of this class. Using an accurate and detailed heat exchanger model, the exit temperatures of each exchanger are calculated by a simple mathematical procedure based on Gilmour's design method. This procedure has been included in a general model for the complete scheme of the system. The scheme is made up of a series of heat exchanger groups with parallel paths in each group. The optimal distribution of the streams within a group is found by the direct search method of Hooke and Jeeves, modified to include constraints; while the overall optimization of the system is achieved via dynamic programming.
Optimal operation of heat exchanger networks
Computers & Chemical Engineering, 1999
The paper discusses optimal operation of a general heat exchanger network with given structure, heat exchanger areas and stream data including predefined disturbances. A formulation of the steady state optimization problem is developed, which is easily adapted to any heat exchanger network. Using this model periodically for optimization, the operating conditions that minimize utility cost are found. Setpoints are constant from one optimization to the next, and for implementing the optimal solution special attention is paid to the selection of controlled variables such that the operation is insensitive to uncertainties (unknown disturbances and model errors). This is the idea of self-optimizing control. In addition to heat exchanger networks, the proposed method may also be applied to other processes where the optimum lies at the intersection of constraints. : S 0 0 9 8 -1 3 5 4 ( 9 8 ) 0 0 2 8 9 -0 J s for all cases of d u ,A = 0.55. It is clear that the nominal optimal value cannot be applied since this will result in infeasiblity for some unknown disturbances. Mathematically, if we have an objective function J (x, d) where the value of the variable (argument) x can be selected/manipulated and d represent the disturbances, we can write Nominal optimum: J nopt = opt(J(x, d= d 0 )) J ropt = opt(J(x, dD)) Robust optimum:
H ∞ Control with Time Domain Specifications Applied to a Heat Exchanger Network
Multivariable control techniques have been applied to chemical plants, ranging from multi-loop control up to predictive controls. This work intends to present a study developed using a control solution based on the H∞ design with time domains specifications applied on a heat exchanger network (HEN) with bypasses. The HEN is frequently used in chemical processes to promote energy transfer between hot/cold streams, reducing the utility consumption as its main objective. The H∞ control is used here to ensure a prescribed time domain response by means of a solution of model matching problem so that the closed loop dynamics are approximately the same as the ones of the reference model. The simulations results have demonstrated that the proposed control leads to a good performance with process variables decoupled, null offset and output responses with the prescribed dynamics.