Effect of solid loading and particle size on the phase holdup distribution and bubble behaviour in a pilot-scale slurry bubble column

Complexities in the hydrodynamics of slurry bubble columns lead to noticeable uncertainty in the design and scale-up of these multiphase reactors. Knowledge of local hydrodynamics can alleviate this problem. The effect of solids properties on the local hydrodynamic parameters isa critical subject where the lack of knowledge is undeniable. In the present study, optical fiber probes were used to study the effect of par-ticle size and concentration on the solids and gas distribution inside the bubble column. A pilot-scale cylindrical bubble column 270 cm in height and 29.2 cm in diameter was employed. Glass beads with various mean diameters (35, 71, 156 mm) and 1, 3 and 5 vol% were added to tap water in order to make the slurry phase. Air with a wide range of superficial gas velocities (up to 20 cm/s) was injected into the slurry phase. The results demonstrated that the solid particles' radial and axial distributions were not uniform in the column. Solids concentration showed a local maximum in the near-wall region. Gas holdup had a parabolic shape except for large particles at high solids concentration in which the maxi-mum of the gas holdup was observed at the sides rather than the centerline. The variations in the pres -sure fluctuations revealed that the particle size decrease led to an increase in the bubble size; however, the initial bubble size was independent of the particle size. Moreover, the increase in the solids concen-tration resulted in an increase in the gas holdup in the homogeneous flow regime; and a decrease in the heterogeneous one. Finally, a predictive model that can estimate the radial and axial solids distributions in the slurry bubble column is presented. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The complexities in the hydrodynamics of slurry bubble columns create uncertainty in reactor design and scale-up. Understanding local hydrodynamics can help alleviate this issue. The effect of solids properties on the local hydrodynamic parameters is a critical subject of study, with experiments showing non-uniform distribution of solid particles and gas holdup in the column.