The hydrodynamics of FLUID COKING (TM) units are investigated with computational fluid dynamics (CFD). The vaporisation of liquid feed is simulated by introducing limiting assumptions to simplify and bound the process: (a) liquid feed entirely vaporised at the entrance of the column; (b) liquid feed vaporised immediately upon contact with the coke particles; and (c) liquid coated uniformly on the particles, with vapour generated uniformly throughout the bed. Results predicted under these extreme scenarios are compared. Then, two cases with a relatively realistic description of liquidsolid interaction and feed vaporisation are simulated. The vaporisation rate is found to play an important role in affecting the flow hydrodynamics. Based on the local liquid-to-solid ratio and shear stress distribution, an agglomeration index is introduced to characterise the stability of agglomerates in the reactor. The vaporisation rate of liquid film on particles is shown to affect the distribution of the agglomeration index. The results indicate that a high vaporisation rate tends to decrease both agglomeration and stripper fouling. (c) 2011 Canadian Society for Chemical Engineering