(666b) Entrainment-Sedimentation Model for Axial Solid Concentration Profiles in a Slurry Bubble Column

Slurry bubble columns are used as gas-liquid-fine particle contactors in a wide variety of processes such as syngas/coal conversions to liquid fuels, hydrogenation of unsaturated oils, gas liquid reactions with precipitation, fermentation, floatation etc. In slurry bubble columns, fine particles in the liquid are suspended by gas sparging alone. Axial solid concentration profile along the column height was observed to be not uniform. Sedimentation-Diffusion model is widely used to explain the observed axial solid concentration profiles and it assumes upward movement of solids is by diffusion due to solids concentration difference while downward movement of solids is by sedimentation. The estimated diffusion coefficients were observed to depend on gas velocity, column diameter and physical properties of gas-liquid-particle system; the sedimentation velocity was also observed to be a function of terminal velocity of particles, liquid volume fraction in the slurry as well as gas velocity.

Gas flow in bubble columns develops circulation of liquid. Particles in a slurry bubble column are suspended due to entrainment by the upflowing liquid and sediment along with downflowing liquid. The suspended particles always try to sediment by gravity. Based on this mechanism, Entrainment-sedimentation model is developed considering that at any cross section, upflowing solid flow rate is equal to downflowing sold flow rate. The model compares well with the literature data.