Application of a cooperative control system to residue fluid catalytic cracking plant using a knowledge based system and model predictive multivariable control

Describes the implementation of cooperative control system for a residue fluid catalytic cracking plant in a refinery using a knowledge based control system and a model predictive multivariable control system (PMC system). The PMC system is effective in the area of time-delay and interference process. However, due to their poor response to large time-delay and non-linearity, it sometimes fails to control actual plants in a refinery. On the other hand, expert operators control their plants with large time-delay and non-linearity fairly well by manipulating the setpoints of regulatory controllers. The proposed cooperative control system therefore combines their advantages. The knowledge based control system is used to determine set points of the reactor temperature, feed flow rate and recycle flow rate with large time-delays and non-linearity using 'if then' type rules based on expert operators' know-how. The PMC system sets the targets of PID controllers for other operation variables and keeps the process within constraints to achieve desired process conditions, which are difficult for operators to control because of time-delay and interference among those manipulated variables. The implemented cooperative control system showed a satisfactory performance in the actual plant.