Optimal control of fluid catalytic cracking processes

Abstract

An investigation was made of the applicability of optimal control theory to the design of control systems for non-linear, multivariable chemical processes. A hypothetical fluid catalytic cracking process was selected as a typical representative of such a chemical process. Mathematical models describing the dynamic behavior of the process were developed from non-steady-state heat and material balances about the reactor and regenerator. The dynamic models were used to simulate the process on a digital computer. The simulations predicted most of the important dynamic characteristics that have been attributed to commercial units. A new approach to the design of control systems for highly non-linear multivariable chemical processes based on optimal feedback control theory was demonstrated. In the feedback control law which resulted, the regenerator temperature is controlled by the air rate and the oxygen level is controlled by the catalyst rate. This control scheme is quite different from that which is typically used in refinery operation where the reactor temperature is controlled by the catalyst rate and the oxygen level is controlled by the air rate. The performances of the resulted control scheme was demonstrated by dynamic simulation to be significantly better at controlling the hypothetical cracking process in the face of disturbances than was the conventional control scheme.