The Effects of Vaporisation Models on the FCC Riser Reactor

This work presents a steady-state one-dimensional model of the FCC riser considering the vaporisation of the gas oil feed and subsequent cracking reactions. The evaporation of droplets is studied using three models: the classical homogeneous model and the heterogeneous vaporisation models from the literature. Droplets are modelled using the Lagrangian framework model for particles moving through a fluid. This was coupled with the gas-solid flow field describing the catalyst particulate transport in the riser. Cracking reaction kinetics are modelled using a four-lumped model. The model was then validated against published plant data. The model performed well in terms of gas oil conversion, gasoline yield, pressure drop, and phase temperature profiles. Therefore, it is suitable for use in the design and optimisation of new and existing FCC unit risers, particularly in cost-benefit analysis considering the current push away from petroleum energy sources. It was found that vaporisation models are largely insignificant in terms of gas oil conversion profiles and gasoline yield for usual operation conditions of FCC risers, which is a finding that had yet to be proven in the literature. Vaporisation models are shown to only affect conversion and yield when the initial droplet exceeds 2000 mu m.

Automated summary

This study presents a one-dimensional steady-state model of the FCC riser that considers the vaporisation of gas oil feed and subsequent cracking reactions. Three different models were used to study the evaporation of droplets. The model was validated against plant data and showed good performance in terms of gas oil conversion, gasoline yield, pressure drop, and temperature profiles. The findings suggest that vaporisation models are largely insignificant for typical operation conditions of FCC risers, unless the initial droplet size exceeds 2000 μm.