Dynamic Modeling, Simulation and Multivariable Control Strategy Applied to Catalytic Cracking Unit

The control problem of fluid catalytic cracking (FCC) units is a challenging task due to its model complexity, on linear dynamics, constrained variables and cross coupling interaction between inputs and outputs. Mathematical Control of FCC is challenging and there is a strong incentive to use multivariable control schemes. In this paper, first principle Model of FCCU is developed after analysis of dynamic behavior of this complex process which was sufficiently complex to capture the major dynamic effects that occur in an actual system. Difficulties caused by the interactions are always encountered in the design of multi-loop control systems for MIMO processes like FCCU.The investigated control approach is the multivariable PID which uses BLT tuning. In this detuning method, each controller in the system is designed based on the corresponding diagonal element and ignore the interactions from other loops. The controllers are then detuned to take into accounts the interactions until some prescribed limit (e.g. the biggest log-modulus) is attained.