Comparative evaluation of advanced process control techniques for alumina flash calciners

Few examples of advanced control methods have been reported in the alumina processing industries. Alcoa of Australia Limited in its Western Australian operations has traditionally employed classical methods in its feedback strategies. Three control algorithms, proportional-integral-derivative (PID), dynamic matrix control (DMC) and self-tuning control (STC), were compared in the regulation of calciner furnace temperature at the Wagerup Alumina Refinery of Alcoa of Australia to assess the potential application of advanced control methods. The evaluation was carried out under both fixed and varying production conditions using process dynamic models obtained from identification experiments based on pseudo-random binary input (PRBI) disturbing signals. Measures were defined for controller performance, robustness and complexity. DMC delivered best performance, closely followed by the optimised PID controller. An explicit STC performed poorly, as the near minimum variance nature of the algorithm imparted too much control energy to the process. All the three controllers performed significantly better than the PID control achieved with tuning parameters currently implemented in the refinery.