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Analysis of gas holdup and bubble behavior in a biopolymer solution inside a bioreactor using tomography and dynamic gas disengagement techniques

Khalili, Fariba, Jafari Nasr, MR, Kazemzadeh, Argang, Ein‐Mozaffari, Farhad
Journal of chemical technology and biotechnology 2018 v.93 no.2 pp. 340-349
biopolymers, bioreactors, bubbles, electrical resistance, gases, impellers, liquids, mass transfer, mixing, rheology, tomography, viscosity
BACKGROUND: The interfacial mass transfer rate in an aerated system vessel in which the liquid phase is in contact with the gas phase is closely related to the interfacial area between two phases. The gas–liquid interfacial area strongly depends on the bubble size, bubble size distribution, and the gas holdup. For the first time, in this study the performance of the ASI impeller was assessed by determining the bubble classes, bubble size distribution, local gas holdup, and global gas holdup in an aerated mixing system containing a highly viscous and non‐Newtonian biopolymer solution. The effects of the volumetric gas flow, impeller speed, and fluid rheology on the gas dispersion attained by the ASI impeller were investigated. RESULTS: Electrical resistance tomography (ERT) was coupled with the dynamic gas disengagement (DGD) technique to determine the bubble classes, to measure the gas holdup, and to calculate the Sauter mean bubble diameter. The performance of the ASI impeller was compared with those of the pitched blade turbine and the Rushton impeller in terms of the bubble size distribution and gas holdup. The experimental data revealed that three classes of bubbles were formed within the aerated system. An empirical correlation for the gas holdup as a function of the gas flow number and apparent viscosity of fluid was developed for the aerated mixing tank equipped with the ASI impeller. CONCLUSION: The ASI impeller effectively enhanced the breakage of the bubbles and gas holdup at the higher gas flow rates in a yield‐pseudoplastic fluid. © 2017 Society of Chemical Industry