Design of a combined control system incorporating knowledge based system and model predictive multivariable control system and its application to refining plant

This paper describes the implementation of the combined control system incorporating a knowledge based control system and a model predictive multivariable control system in a petroleum plant. The knowledge based control system is used to determine set points for the temperature of the reflux to regulatory controllers using 'if then' type rules based on skilled operators' know-how. The model predictive multivariable control system controls the flow rate of each reflux which is difficult for operators to control because of the large time-delay and interference among those manipulated variables. The implemented combined control system showed a satisfactory performance in controlling the pressure of the actual plant.