A minimum time operating policy for a liquid‐liquid extraction column

Abstract

Two methods, both based on linear programming techniques, have been applied to determining the minimum time control policy for effecting a grade change in the product from a liquid‐liquid extraction column. The method was made possible by the existence of a linear dynamic model for the column derived from a previous frequency response study of the laboratory unit. Both methods predicted policies of a partial bang‐bang nature. As expected the control paths were not the same; additional control criteria such as minimum control effort or minimum number of switchings are suggested as a means of further defining a best control policy. Suitable bounds on the controlled variables were found in the study so that physically realizable control policies were formulated.