Mass transfer phenomena in an airlift reactor: Effects of solids loading and temperature

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Abstract
Gas holdups and volumetric mass transfer coefficients were measured in a concentric tube airlift reactor designed for the microbial desulfurization of coal. The solutions studied were comprised of an acidified basal salts solution containing thirteen different weight percentages (0 to 40) of coal (74 μm Ohio #1) at three different temperatures (30, 50, and 72°C). Gas holdup ϵG decreased with solids loading for the entire range studied. An enhancement in the volumetric mass transfer coefficient KLa with respect to that in pure solution was observed from zero to approximately 5 wt % (solids volume fraction ϵs = 0.035), the maximum enhancement occurring at approximately 2 wt % (ϵs = 0.014). At higher solids fractions, the mass transfer coefficient decreased with further solids additions. Gas holdups and the mass transfer coefficients increased with temperature over the studied range. The KLa and ϵG were correlated to three process variables separately and the separate correlations combined to yield generalized correlations for the mass transfer coefficient and gas holdup for this system. The correlations may be used for design, operation, and ost estimation of such systems.