Gas holdup in three-phase immobilized-cell bioreactors |
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Authors: | Bajpai Rakesh Thompson James E Davison Brian H |
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Institution: | 1.University of Missouri, 65211, Columbia, Columbia, MO ;2.Chemical Technology Division, Oak Ridge National Laboratory, 37831, Oak Ridge, TN ; |
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Abstract: | A number of studies in the published literature deal with gas holdup in three-phase reactors. However, very few address the
cases in which the solid density approaches that of the liquid phases and in which low gas velocities are involved. These
conditions are commonly encountered in immobilized-cell bubble columns and in fluidized-bed bioreactors. This paper reports
the effect of gas and liquid velocity upon gas holdup and bed expansion in fluidized-bed bioreactors.
For liquid-fluidization of low-density alginate beads in the absence of gas, the terminal sedimentation velocity (vT) of the
particles is a constant, and expansion of the bed follows Richardson and Zaki’s correlation. In the presence of gas, however,
the apparent terminal sedimentation velocity value is affected by the velocity of the gas and liquid phases. For gas velocities
above a minimum value, the calculated value of vT depends on liquid velocity only, and a constant bed expansion was observed
for a range of gas and liquid flow rates. For the gas-liquid interactions, a modified drift-flux model was found to be valid.
For superficial gas velocities between 5 and 17 cm/min, the modified drift-flux velocity was observed to be a function of
gas velocity, suggesting the prevalence of a coalescence regime. |
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Keywords: | Index Entries" target="_blank">Index Entries Hydrodynamics drift-flux wake-model multiphase fluidized bed |
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