Effect of fluidized bed diameter on fluidization dynamics

Abstract

The effect of the bed diameter on the gas-solids flow characteristics inside a cylindrical fluidized bed is investigated numerically using a two-fluid model based on the kinetic theory of granular flow. Particle bed diameters of 0.10, 0.15, 0.30 and 0.60 m are studied, containing particles of 1.1 mm diameter and a density of 800 kg/m3 (Geldart B), using an inlet gas velocity of 2.5Umf. The equivalent bubble diameter shows an increasing trend with height in the bed and bed diameter. Slugging behavior is observed in a smaller bed and/or above a bed height of approximately twice the bed diameter. The porosity near the axis is higher for a smaller bed and gradually decreases for a larger bed. Different particle circulation patterns are observed for different bed sizes. The center of circulation vortex at the bottom for a smaller bed lies approximately at r/R = 0.5 and this center is shifted to r/R = 0.8 for a larger bed. The upper particle circulation obtains a more elongated shape for a smaller and deeper bed in comparison to a larger bed diameter. The particle flow characteristics are nearly the same for the 0.30 and 0.60 m diameter beds, irrespective of the difference in bubble size. This shows that the bed size effect levels off beyond a 0.30 m diameter column for Geldart B particles.