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In this study it was proposed the application of a fuzzy-PI controller in tandem with a split range control strategy to regulate the temperature inside a fermentation vat. Simulations were carried out using different configurations of fuzzy controllers and split range combinations for regulatory control. The performance of these control systems were compared using conventional integral of error criteria, the demand of utilities and the control effort. The proposed control system proved able to adequately regulate the temperature in all the tests. Besides, considering a similar ITAE index and using the energetically most efficient split range configuration, fuzzy-PI controller provided a reduction of approximately 84.5% in the control effort and of 6.75% in total demand of utilities by comparison to a conventional PI controller.

This study intends to explore fuzzy logic control on clean water turbidity process with dissolved air flotation (DAF). Three different strategies were tested to regulate clean water turbidity by manipulating the saturator vessel flow output aiming for low actuators control effort. Saturator pressure was the manipulated variable (MV) in the first control loop named SISO I. The second control loop, SISO II, used recycle stream valve opening as MV. The third control loop (MISO) was developed applying fuzzy logic instead PID control. Several performance criteria were used to analyze the process control performance such as integral absolute error (IAE), recycle stream valve and saturator vessel pressure regulating valve control efforts, ECV01 and ECV02 respectively. Results from SISO I and SISO II strategies showed that recycle stream is a better MV than saturator vessel pressure for clean water turbidity control in the DAF process. Only SISO II and MISO strategies proved to be capable of regulating the process variable. However, MISO control showed better performance based on IAE value against SISO II, with a reduction of 11.24% on its value, even the recycle stream valve control effort for MISO control being fairly higher than that for SISO II. Nevertheless, fuzzy logic control application gave rise to better turbidity control, and consequently prevented the excessive use of clean water in the recycling stream.

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