CFD simulation of gas–solid two-phase flow and mixing in a FCC riser with feedstock injection

• The secondary flow phenomenon is verified by using CFD simulation.
• The coke deposition problem above feed nozzles is analyzed with CFD.
• The uneven mixing in the feedstock injection zone is affected by the diffusion of feed spray.

The feedstock injection zone is a key section for Fluid Catalytic Cracking riser reactor. A 3-D Computational Fluid Dynamics simulation is performed by coupling the two-fluid model and the energy-minimization multi-scale (EMMS) drag. The prediction agrees well with the available data and the secondary flow phenomenon is captured. The simulation reveals that the M-shape distributed feed sprays interact with the W-shape distributed solid particles and then cause the undesirable W-shape distribution of the matching ratio of catalysts to feed. The transformation of such uneven distribution to the finally core-annular distribution heavily depends on the secondary flow, whereas its mechanism can be explained by using the Kutta–Joukowski lift theorem. The increase of the feed spray velocity facilitates the feed diffusion and reduces the transition region. However, excessively high jet velocity may intensify the back-mixing near the wall and causes intense attrition or breakage of catalysts and thereby an increase of costs.

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