Hydrodynamics and Gas-Liquid Mass Transfer Coefficient in a Slurry Bubble Column with High Solid Content

Abstract

Volumetric liquid-phase mass transfer coefficient, k_la, and axial variations of gas, liquid and solid holdups were measured in a slurry bubble column of 15 cm diameter and 1.05 or 1.55 m height containing concentrated solids supported by a concurrent upflow of a gas and a liquid. Gas and liquid media were air and water or air and aqueous glycerol solution. Slurry particles were glass beads with mean diameter of 0.16 and 0.23 mm and a density of 2500 kg/m³.
In beds of high solid content, the measured axial variations of solid holdup indicated that :
(1) At low gas velocity two slurry layers were formed in the column. The lower layer was the dense region with high uniform concentration of solids and the upper layer was the lean region where solid concentration decreased steeply with axial distance.
(2) At large gas velocity the solid concentration in the column decreased continuously with axial distance as a result of sedimentation and diffusion of solids.
On the other hand, gas holdup was fairly uniform from the bottom to the top of the column.
The value of k_la increased with gas velocity and decreased with solid concentration. k_la values obtained in this work were empirically correlated by the following equation with a term of apparent viscosity of slurry.
k_la=3.09×10^-7 {(1-φ_s/0.60) /μ_l} ^1.50 U_g
where, φ_s=ε_s/ (1-ε_g) [-], k_la [s^-1], μ_l [Pa·s] and U_g [cm/s]. This correlation covers the range of variables, 0.8≤U_g≤8.0, 0.001≤μ_l≤0.002 and 0≤φ_s≤0.4.