Volumetric Gas−Liquid Mass Transfer Coefficient in Aerated Stirred Tank Reactors with Dense Floating Solid Particles

Abstract

The effect of floating solid particles on volumetric gasÀliquid mass transfer coefficients was investigated using a stirred tank of 0.2 m inside diameter (i.d.) with dual four-flat blade disk turbines for solid concentrations up to 50 vol %. Two kinds of floating solids, synthetic adsorbent particles (particle size of 375 μm and wet density of 793 kg m À3 ) and polypropylene particles (particle size of 480 μm and wet density of 854 kg m À3 ) were used. At very low impeller speeds the floating particles formed a stagnant layer on the liquid surface, and none of the solids were dispersed. As the impeller speed was increased, particles were partially dispersed, and the stagnant layer volume was reduced. With further increasing impeller speed, all solids were ultimately dispersed throughout the tank. The gas hold-up and volumetric gasÀliquid mass transfer coefficient in a baffled or unbaffled stirred tank with dense floating solids particles are measured. The power consumption and gas hold-up decreased with an increase in floating solids concentration. It was found that the presence of floating solid particles significantly reduced the mass transfer coefficient at a given impeller speed. The presence of floating solids increased the apparent viscosity of the slurry and hence probably resulted in increased bubble coalescence tendency enhancing the formation of larger bubbles. They might lead to a decrease in gas hold-up or specific surface area and subsequently induce a significant decrease in the volumetric gasÀliquid mass transfer coefficient. The experimental data for gas hold-up and volumetric gasÀliquid mass transfer coefficient are satisfactorily correlated to power consumption, superficial gas velocity, and solid volume fraction.

Enhancing Impeller Power Efficiency and Solid–Liquid Mass Transfer in an Agitated Vessel with Dual Impellers through Process Intensification

“…The decrease in k SL for C V > 0.20 (v/v) was attributed by Bong et al to turbulence dampening due to increasing effective viscosity of slurry (η slurry ) and its effect on diffusional mass transfer. Also, particle–particle interactions become more frequent with increasing η slurry , which decreases the solid–liquid interfacial area thereby decreasing the mass transfer rate. , It is expected that the changes in turbulence intensities and consequent changes in the trends of k SL versus C V plots for denser particles will be similar to those found in this work, but they should be verified by carrying out further experimental work.…”

Joint effects of gas bubbles and solid particles on sonochemical inhibition in sonicated aqueous solutions

“…The inhibition in sonochemical activity caused by solid particles and gas bubbles can be attributed to several possible mechanisms: (a) the addition of solid particles increased the apparent viscosity of the mixture, which could in turn lead to increased bubble oscillation time [65] and the formation of larger bubbles due to coalescence [66] , thereby retarding the cavitation rates. (b) When the non-condensable argon gas diffused into cavitation bubbles, it could strongly influence the bubble dynamics, e.g., by decelerating the bubble collapse, weakening the shockwaves emitted, and reducing the intensity of cavitation [67] .…”

Correlating Mass Transfer Coefficients of O2 and N2 in Methanol in a Stirred‐Tank Reactor

“…In traditional solvents such as water [12,13], glucose solution [14], ionic liquid systems [15][16][17], and other solvents [18,19], the mass transfer characteristics in the stirred tank were studied extensively by experimental methods. As common reaction gases, the solubility and mass transfer coefficients k L 1)…”