Chemical Engineering and Processing 41 (2002) 87 – 98 Fuzzy temperature control of industrial refineries furnaces through combined feedforward/feedback multivariable cascade systems A.G. Abilov a, *, Z. Zeybek b , O. Tuzunalp a , Z. Telatar a a Department of Electronic Engineering, Faculty of Sciences, Uniersity of Ankara, Tandogan, Ankara, 06100, Turkey b Department of Chemical Engineering, Faculty of Sciences, Uniersity of Ankara, Tandogan, Ankara, 06100, Turkey Received 2 March 2000; received in revised form 1 December 2000; accepted 5 January 2001 Abstract The purpose of this paper is to improve and apply a multivariable advanced control structure on the basis of fuzzy logic technique for two flow tubular furnace having widespread applications in petroleum refinery industries. After analyzing the dynamic properties of furnaces, it has been concluded that these furnaces are the MIMO processes which have two inputs and two outputs. There are a lot of reciprocal interactions between input and output variables. For this reason, equivalent system methods were used to investigate and develop advanced control structures for these furnaces. According to this method, symmetric MIMO system was divided into two equivalent separate systems. Finally, the fuzzy model control design of combined multivariable symmetric cascade system and its results were given. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Industrial refineries furnaces; Fuzzy advanced control; Multivariable cascade; Feedback/feedforward control www.elsevier.com/locate/cep 1. Introduction Furnaces are the basic and the most important indus- trial units of petroleum refineries and petrochemical process. They are used in heated petroleum flows to the desired temperature through chimney gases obtained from burning processes The furnaces can have single or multiple flows ac- cording to their technological structures. They have been made up from the regions of convection and radiation. The heat transformation between chimney gasses and petroleum flows is realized in the regions of convection and radiation. Sufficient quantity of the oxygen required for the control of the burning process in these regions is obtained from the air. Also, an optimal amount of air is desired for economical and ecological clear burning in furnaces. There have been many studies in literature to control the burning process [1–7]. These works have shown that furnaces are nonlinear, multivariable, distributed, complex dynamic control systems. In multiple flow furnaces, there are also large delays in dynamic chan- nels and cross relationship between control parameters. In most applications, a linear model has been used to represent the dynamic behavior of the process (impulse/ step response function, transfer function, state space model). But, because of severe nonlinearities in some real-life processes, a fixed linear model for predictive control might not really result in the required performance. Because of these complexities, it is required to inves- tigate of the more effective control systems working on the basis of fuzzy advanced control algorithms. Fuzzy control is now well known as a method of implementing nonlinear controller. Although most in- dustrial applications of fuzzy controller have been based on rule-based controllers, there is a growing interest in model-based fuzzy designs. Many fuzzy modeling and control methods have been proposed in the literature [8 – 17]. In this paper, a combined multivariable cascade ad- vanced fuzzy control system has been developed for two flow industrial petroleum refinery furnaces. The following sections present the proposed algorithm in detail. The simulation results are then given. Finally, the conclusion is drawn. Abbreiations: AVF, Atmospheric vacuum furnace; MIMO, Multi- variable input – multivariable output. * Corresponding author. Fax: +90-312-2232395. E-mail address: abilov@science.ankara.edu.tr (A.G. Abilov). 0255-2701/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0255-2701(01)00119-2