hi! FCC is well known as fluidized catalytic cracker. it involves all sort of complexity that is possible in the world.people are struggling to improve its performance with optimal catalyst and other operating variable.people are trying to use CFD to predict its performance.But my question is will it be reliable? because conducting experiments at larger scale is freightning one.

I would think that the particle dymanics could be modeled successfully, since circulating fluidized bed combustors have been modeled. The surface reactions would be complex (in addition to the composition of the reactant flow) because of the variety of cracking reactions that take place at the catalyst surface. Modeling catalyst deactivation due to S and N adsorbtion onto active sites would add an additional layer of complexity. Of course, all of these effects might not need to be included in the scope of your study.

Maybe you should speak to the guys at UOP to find out if this has been attempted before. Very complex physics on this problem.

Do you want to model the whole system, i.e. reactor, catalyst regenerator, catalyst cooler and flue gas?

yes of course!