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

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 microm Ohio #1) at three different temperatures (30, 50, and 72 degrees C). Gas holdup epsilon(G) decreased with solids loading for the entire range studied. An enhancement in the volumetric mass transfer coefficient K(L)a with respect to that in pure solution was observed from zero to approximately 5 wt % (solids volume fraction epsilon(s) = 0.035), the maximum enhancement occurring at approximately 2 wt % (epsilon(s) = 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 K(L)a and epsilon(G) 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.

Overall volumetric mass transfer coefficient in a modified reversed flow jet loop bioreactor with low density particles

“…Similar effect was reported in the literature for an airlift reactor [21] and for fluidized bed reactors [22]. The reason for this type of behaviour can be explained as a disruption in the liquid-film surrounding the air bubble which reduced the resistance to mass transfer in the presence of solids.…”

Bioreactors: Airlift Reactors

“…This situation is not very frequent in biological processes, with the exception of biolixiviation (302) or the special case of microbial desulfuration of coal (303). In most of the biological processes that may take place in an ALR, the solids are either cells, clumps of cells, or supports that are not much denser than the medium.…”

Applications of yeast flocculation in biotechnological processes

“…However, no real data are available for flocculation bioreactors and so far, even when systems with similar properties have been used as models, only a few of them deal with solids loads as high as those found in flocculation bioreactors. In fact, solids load may affect gas-liquid mass transfer efficiency [132], gas hold-up [133,134], liquid velocity [135], mixing time [128] and solids hold-up in the different parts of the bioreactor [134], among other parameters.…”