Modeling of Gas-Liquid-Solid Multiphase Flow of FCC Riser Reactor

The Fluid Catalytic Cracking (FCC) is an important process for profitable conversion of heavy hydrocarbons into valuable products. In this study, a CFD simulation of hydrodynamic and heat transfer of FCC gas-liquid-solid riser reactor was carried out by considering the evaporation of liquid droplets. Since there is no symmetry in fluidizing steam, catalyst particles, and atomized liquid droplets, the reactor was modeled as a 3-D system. An Eulerian model was used for both gas and catalyst particles, which is comprised of continuity and momentum, species, heat transfer equations for gas and solid phases, and an equation for solid granular temperature. The hydrodynamic and heat and mass transfer (evaporating liquid droplets) were modeled using Lagrangian approach. The reactor hydrodynamic model predictions were compared with corresponding experimental data reported in the literature to validate the model. The distributions of gas and catalyst velocity are in good agreement with the experimental data. The multiphase results include flow field, distributions of volume fraction of each phase, temperature profiles of gas and solid phases as well as variation of atomized liquid droplet diameter and temperature. The simulation results indicate that the heating of liquid droplets takes place proportional to their initial size and immediately. Therefore, this step is not the controlling part of FCC riser operation. When the evaporation of the liquid starts, rate of droplet evaporation and reduction in droplet diameter are low. When the droplet temperature reaches the boiling point, the droplet diameter decreases faster and the total mass of liquid droplet evaporates in a fraction of riser reactor. In this research, a correlation for droplet evaporation time was also developed.