The fluid catalytic cracking (FCC) process is at the heart of a modern refinery oriented toward maximum commercial (gasoline and diesel) production. In order to describe the large number of components present in heavy distillates and the kinetic models that are able to predict the profiles of heavy and light chemical fractions in industrial risers, the 12 lump approaches has been used. Gas acceleration inside the reactor due to molar expansion and catalyst deactivation were considered by simulating unsteady state cases over a time long enough to show that the variables had a cyclic behavior. The tracer particle was instantaneously injected following the tracer technique, to get an estimation of the residence time. The governing equations were solved numerically by finite volume method with a commercial CFD code, CFX version 14.0. Appropriate functions were implemented in the model by considering the heterogeneous kinetics, catalyst deactivation and function tracer. The simulation results were validated against the experimental results. This work was carried out in order to evaluate the predictions of product yields and to estimate the residence time distribution in industrial reactors.