(279b) Numerical Evaluation of a Fluid Catalytic Cracking Unit with Internal Baffles

Authors: 
Utzig, J., University of Blumenau
Rosa, L. M., University of Blumenau
Martignoni, W. P., University of Blumenau
Meier, H. F., University of Blumenau
Martinez, T. S., University of Blumenau
Fluid Catalytic Cracking (FCC) units play a very important role in an oil refinery, because they convert heavy fractions (vacuum distillates or some vacuum residues) to gasoline, C3-C4 cuts and petrochemicals. These units and the catalysts used are in continuous evolution. They must adapt to market changes: gasoline yield and/or quality maximization, petrochemicals production, conversion of residues, environmental requirements. New riser configurations require that the phases have an increasingly short contact time, being separated after 1 s or 2 s of flow. Regenerators operating at a higher combustion temperature allow a higher recovery of the catalyst. The catalyst entering the reactor warmer requires that the mixture between the phases be extremely efficient, since a poor thermal exchange between the phases results in high temperature points and, consequently, the favoring of thermal cracking reactions. Products formed by thermal cracking have lower value than those formed by catalytic route, and therefore regions with temperatures too high must be avoided. Once the gas-solid flow in risers can develop a "core-anulus" pattern, in which catalyst particles are more concentrated near the walls of the reactor, the inclusion of internals can enhance the phases mixture. However, it can also increase its pressure drop, which is a limiting factor to the process. Therefore, the aim of this study is to evaluate the performance of an industrial riser type reactor, with the inclusion of airfoil-shaped ring-type baffles in order to improve the gas-solid flow. Computational fluid dynamics (CFD) techniques are applied to simulate in a three-dimensional geometry, in which the turbulent three-phase flow was calculated in a transient formulation. Gases (air and steam) and catalyst particles were the two Eulerian phases simulated, and a third Lagrangian phase was composed of liquid oil droplets which were evaporated during the process. Results indicate that it is possible to enhance the gasoline production without causing an expressive increase in the pressure drop of the unit.