Turbidity Control in Sedimentation Columns by Direction-Dependent Models

Sedimentation is a crucial phenomenon in recovering water from slurries by separating solid-liquid. Thickeners and sedimentation columns are equipments widely used in the process industry to reclaim water from process slurries. This contribution addresses the problem of controlling the turbidity of the recovered water in a sedimentation column by manipulating the underflow. The phenomenological model describing the turbidity is too complex to be used in a control strategy, and it is difficult to identify its parameters using plant measurements. This work proposes an empirical piecewise time-delay model for modeling the turbidity at the top of the column to circumvent these problems. A systematic design procedure is developed to tune a proportional-integral (PI) controller guaranteeing closed-loop stability for systems modeled as a piecewise time-delay model. Experiments in a pilot plant validate the theoretical results and illustrate the control performance under various operational scenarios.