Approach to the analysis of the dynamics of industrial FCC units

Although it is known that FCC units are operated at a controllable steady state, it is commonly assumed that this state is pseudostable An ignited steady state, theoretically stable, outside the operable domain has also been reported for the same set of operating parameters. The aim of this work is to introduce a theoretical method for the preliminary analysis of the controllability of an industrial FCC unit, at any set of conditions, using a nonlinear model directly. An approach for the analysis of the stability of the system zero dynamics is used to investigate the dynamic behaviour of two common operating policies when the unit is operating either in the standard or in the ignited steady state. It is used to predict some particular characteristics of the process, such as the presence of inverse response after the change in catalyst circulation rate, a common control action. The results derived from the analysis developed are discussed in terms of physical responses and verified by performing open loop dynamic simulations of an industrial FCC unit. The operation of the unit is simulated for both the standard and the ignited steady states.