A CFD model for the FCC feed injection system

Abstract

This paper presents a CFD model for steady-state simulation of the feed injection system in an FCC unit. The model assumes a non-isothermal gas-liquid flow through one feed nozzle and the injection zone in order to reproduce spray formation. Three different designs for the outlet orifices of the feed nozzle were tested to analyze their effect on the spray structure. A two-fluid Eulerian approach is selected for modeling the aforementioned phenomena considering that gasoil are droplets dispersed in steam. Then the realizable κ-ε model is applied to each phase to represent the turbulence effects. Model capabilities to represent the actual flow behavior are tested by comparing calculated gasoil pressures at the nozzle with experimental values obtained for different gasoil flow rates. Our flow analysis provides relevant information about the effect of internal components in the nozzle on the velocity field and phases distribution. It is observed that the impingement plug displaces the gasoil from the center of the main pipe to the walls of both the divergent and upward nozzle zones. Hence the cross baffle separates the main flow into four pie-shaped parts through the expansion nozzle zone. The multiphase flow dispersion analysis through the injection zone demonstrates that the present model provides a good agreement with available experimental data for the external characteristics of sprays generated by different outlet orifices configurations.