Design of a robust fractional order controller for burning zone temperature control in an industrial cement rotary kiln

The control of the temperature of the burning zone of an industrial cement rotary kiln is addressed in this paper. An experimental identification of the process was carried out, which yielded a second order transfer function with no zeros but with a very large time delay. Moreover, it was detected that this time delay could change between ±8% of its nominal value. Then a robust controller had to be designed for this process. A standard PI controller, a PI controller embedded in a Smith Predictor scheme, and a fractional-order controller embedded in a Smith Predictor have been studied. A method to design the fractional-order controller is developed in this paper that yields better results than the other studied controllers. Simulated results are presented.