Hydrodynamics of gas–liquid–solid three phase systems in ebullated beds and fluidized beds using computational fluid dynamics

The hydrodynamics of the three-phase system in an ebullated bed reactor (EBR) is investigated using computational fluid dynamics and compared with that in a fluidized bed reactor (FBR). For consistency in the comparison, the two reactors have the same dimensions (2.20 m length and 0.172 m diameter), except that there is no recirculation column in the FBR, and the same superficial velocities of liquid phase (0.057 and 0.095 m/s) and gas phase (0.04, 0.08, 0.12 m/s), particle diameter (300 μm), initial solids volume fraction of the bed (0.5), and initial packing height (0.3 m). It is found that the expansion of the bed is greater in the EBR than in the FBR under identical conditions of low liquid superficial velocity. In the FBR, the larger size of the voids formed in the expanded region causes decreased interactions between the three phases, whereas in the EBR, smaller voids are formed at lower simulation times, whereas slugs are formed at longer times. In addition, early stability of bed expansion is attained at lower gas superficial velocities, irrespective of the value of the liquid superficial velocity. In the EBR, there is no symmetry of bed expansion on each side of the recirculation pipe even at low liquid superficial velocities. It is found that at 0.5 m bed height, the radial distributions of gas, liquid, and solids indicate a more uniform and better distribution of the three phases in the EBR. The local solids fraction distribution along the radial position indicates that in the EBR, for most of combinations of gas and liquid superficial velocities, the solids fraction is properly distributed and that it is even more uniform for the combination of a higher liquid and lower gas superficial velocity.