Optimizing droplet vaporization in the emulsified feeding technique of FCC: Impacts of operating conditions and reactor structures

Fluidized Catalytic Cracking (FCC) is a critical process in refineries for converting heavy oil feedstock into light products including olefins. High olefin yield requires rapid and uniform vaporization of feedstock, which is very challenging in an environment where the properties of the feedstock oil are deteriorating. This study focuses on a novel emulsified feeding technique that injects emulsion droplets into the FCC riser reactor, where micro-explosion occurs due to high temperature. This process breaks the droplets into smaller, secondary droplets, greatly increasing the specific surface area. The heat transfer and motion of both catalyst particles and droplets in this technique are largely different from the conventional atomized feeding. Therefore, optimal operating conditions need to be determined to accommodate the reduction in droplet diameter. Computational Fluid Dynamics (CFD) simulation was used in this paper in order to explore the effects of operating conditions and reactor structures on the droplet vaporization. Results indicate that when keeping constant heat carried by the catalyst particles, higher initial temperature can increase the droplet vaporization ratio, with an optimal catalyst temperature of 957 K and an optimal droplet temperature of 473 K. The contact between the oil droplet and the catalyst also strongly influences droplet vaporization. A two-layer nozzles arrangement at the inlet increases the vaporization ratio of heavy distillate fractions by 17.61 %. Moreover, enlarging the bottom diameter to 0.9 m can enhance the vaporization ratio of heavy distillates by 15.33 %, while the average oil vaporization ratio is improved by 3.07 %.