Cascade controller design for concentration control in a falling-film evaporator

Multi-effect falling-film evaporators are widely used in dairy industries. Achieving tight control of product concentration in evaporators is difficult due to disturbances, large time delays and other plant constraints. Experience has shown that the use of a single feedback PI controller is not sufficient for this application. This paper discusses the application and design of a cascade controller to control the product concentration in a two-effect falling-film evaporator at Fonterra Ingredients-Whareroa, Fonterra Co-op. Group Ltd. It has been shown that the disturbance rejection properties can be significantly improved with cascade control while still maintaining the tracking properties.