Simulation analysis of oil droplet-catalyst collision, heat transfer and vaporization in residue fluidized catalytic cracking

Residue Fluidized Catalytic Cracking (RFCC) is the key process to convert heavy oil into light products. The feedstock enters the riser reactor and collides with the catalyst particle with high temperature, and then undergoes vaporization and cracking reactions. Fast vaporization is critical to prevent coking and increase the conversion of feedstock. In order to reveal the hydrodynamics, heat transfer and vaporization of oil droplets, a systematic study was performed to analyze the collision process between oil droplets and catalyst particles at the feeding section of the FCC riser with the Volume of Fluid (VOF) model and Lee vaporization model. The model was validated against the experimental results from high-speed camera. When oil droplet collides with the catalyst surface, the liquid film and vaporized gas film can cover the catalyst surface, in which the direct contact between the liquid film and catalyst can greatly increase the coking risk in the liquid phase. By studying the effects of boiling point and collision parameters, it was found that lower boiling point, higher initial oil droplet temperature, suitable collision velocity, and suitable oil droplet to catalyst diameter ratio can increase the gas film coverage area on the catalyst surface and prevent the direct contact between the liquid film with the catalyst surface. The collision eccentricity had significant effects on the vaporization rate and the highest oil droplet vaporization rate can be achieved when the dimensionless eccentricity is 0.75. The present results can provide important information for designing and optimizing the feeding section of the FCC riser reactor.