Mixing Time Studies in Bubble Column Reactor with and without Internals

Abstract

Sectionalized bubble columns are finding a wide use in the case of FT synthesis, petroleum refining, wastewater treatments, extraction, absorption, leaching, ion exchange etc., due to their superiority in terms of reduced liquid phase back-mixing. The present work covers a mixing aspect in a 0.41 m id. sectionalized bubble column over a wide range of superficial gas velocity, liquid height to column diameter ratio, percent free area of the sectionalizing plates and electrolyte concentration for Air-water system. The acquired conductivity data was optimized using a compartmental and axial dispersion models and the model parameters have been estimated. For a given Hc/D ratio; mixing time was found to decrease with an increase in gas superficial velocity and free area of the sectionalizing plate. The compartmental model successfully predicts the tracer concentration profile and the longitudinal dispersion coefficient. The mixing time in a sectionalized bubble column was also compared with a non-sectionalized bubble column and was found to be order of magnitude higher.

Impact of Internals on the Gas Holdup and Bubble Properties of a Bubble Column

“…The reason is that it is common at low velocities to have a maldistribution of the gas flow through the sparger holes if the sparger was not designed properly for low velocities as in our case. This phenomenon has been reported in the literature. , In such cases, bubble swarms were to flow upward according to the active/inactive bubbling zones on the distributor which were found to be circumferentially shifting. Earlier studies showed in empty columns that the recovery of the above-mentioned maldistribution yielding a radially well-distributed gas plume occurred at higher axial locations or at higher gas velocities.…”

CFD-Facilitated Flow Field Analysis of Bubble Columns with Concentric Plates for Biological Applications

“…In literature [11][12][13], the increase in gas holdup is normally explained by bubble breakup. This renders the CFD predictions of an increase in gas holdup in the presence of plates very interesting; particularly as in our CFD formulation bubble breakup and coalescence were neglected.…”

“…The conformity between experiments and CFD simulation was remarkably good for mixing times that were of the order of 10 s. Rampure et al [10] measured and applied CFD to determine the mixing time in bubble columns and found that, for superficial gas velocities varying from 0.01 to 0.4 m s -1 , the mixing time decreased from 10 to 4 s. Although experiments and predictions corresponded well for the highest superficial gas velocities, the measurements were below predictions when the superficial gas velocity was less than 0.1 m s -1 . The introduction of internals, such as perforated plates, concentric solid plates, and other geometric irregularities, to bubble column reactors reduces the fraction of larger bubbles [11][12][13] and increases the residence time of the dispersed phase. When bubble columns are used as photobioreactors to cultivate microalgae, an increase in residence time of the gas phase and a smaller bubble size are desirable outcomes that grant more time to complete the mass transfer of CO 2 from the gas phase to the liquid phase.…”

Validation of a Computationally Efficient Computational Fluid Dynamics (CFD) Model for Industrial Bubble Column Bioreactors

“…Published hydrodynamic data for bubble columns operating in the homogeneous regime have generally been generated using a column with a symmetrical sparger (typically a perforated plate). ,,− Hence, one of the key aims of this work was to generate a comprehensive experimental data set (i.e., one that consists of measurements of the bubble size distribution (BSD) and the overall holdup, as well as profiles of the local holdup, liquid velocity, and gas velocity) for a column equipped with an asymmetric “tree” type sparger of the sort commonly used in the bioprocessing industry. Such knowledge is of interest because bubble columns used in bioprocessing typically have aspect ratios of 2–5, meaning that the volume of the column where the sparger design has an impact can be a substantial proportion of the total …”