Simple mass balance controllers for continuous sedimentation

The rational use of water in the mineral processing industry has become an im-portant issue due to the geographical location of many plants. The increase of capacity in manycopper concentrators has lead to an increased effort for recovering the maximum amount ofwater in the solid-liquid separation process. Thickeners work continuously to produce a con-centrated underflow and a water overflow free from particulate matter. The behavior of manyprocesses can be represented by a set of intensive and extensive variables. In this case, practicehas shown that standard feedback control based on intensive variables has not been very easyto tune and effective in providing consistent operations. In many plants, thickeners operatewith poor standards, with high dosages of flocculants, overflows with high fine particles con-tents and highly variable underflows. This work presents a novel nonlinear PI controller whichis able to stabilize thickener operation using a simple control structure. An internationallyaccepted model and calibration using plant data is used to illustrate the design methodologyand the level of performance attained by the controllers. The analysis of the results points outthe improved performance by using extensive variables. In addition some guidelines concerningcontrollers tuning are also provided.