An Intelligent Switching Control for the Intervals of Concentration and Flowrate of Underflow Slurry in a Mixed Separation Thickener

The mixed separation thickening process (MSTP) of hematite beneficiation is a strongnonlinear cascade process where the input is the underflow slurry pump speed and the outputs are theinner loop underflow slurry flow-rate (USF) and the outer loop underflow slurry concentration (USC).During its operation, some large random disturbances generated from the flotation middling would causethe underflow slurry flow-rate (USF) to fluctuate frequently, making it outside the technologicallyspecified range. This would decrease the flotation time and cause the unexpected level fluctuations offlotation machines, leading to the deterioration of the concentration grade. In this paper, a cascade controlstructure based upon the USC and USF intervals is proposed for such an un-modellable nonlinear cascadeprocess, where the fuzzy control, rule-based reasoning, switching control and cascade control arecombined together. A novel intelligent switching control method is established that includes a USFpresetting unit via system static model, a fuzzy reasoning based USF set-point compensator, a maintainerof USF set-point and a switching mechanism using rule based reasoning. The successful application to areal hematite concentration plant has shown the effectiveness of the proposed method. In particular, thereal application has shown that the proposed method can ensure the USC, the USF and the fluctuation ofits rate of change within their target ranges when the process is subject to the flotation middling randomdisturbance. As a result, the concentration grade has been much improved.