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CO2 Dissolution and Design Aspects of a Multiorifice Oscillatory Baffled Column

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posted on 05.11.2014, 00:00 authored by Filipa M. Pereira, Diana Z. Sousa, M. Madalena Alves, Malcolm R. Mackley, Nuno M. Reis
Dissolution of CO2 in water was studied for a batch vertical multiorifice baffled column (MOBC) with varying orifice diameters (d0) of 6.4–30 mm and baffle open area (α) of 15–42%. Bubble size distributions (BSDs) and the overall volumetric CO2 mass transfer coefficient (KLa) were experimentally evaluated for very low superficial gas velocities, UG of 0.12–0.81 mm s–1, using 5% v/v CO2 in the inlet gas stream at a range of fluid oscillations (f = 0–10 Hz and x0 = 0–10 mm). Remarkably, baffles presenting large do = 30 mm and α = 36%, therefore in the range typically found for single-orifice oscillatory baffled columns, were outperformed with respect to BSD control and CO2 dissolution by the other baffle designs or the same aerated column operating without baffles or fluid oscillations. Flow visualization and bubble tracking experiments also presented in this study established that a small do of 10.5 mm combined with a small value of α = 15% generates sufficient, strong eddy mixing capable of generating and trapping an extremely large fraction of microbubbles in the MOBC. This resulted in increased interfacial area yielding KLa values up to 65 ± 12 h–1 in the range of the UG tested, representing up to 3-fold increase in the rate of CO2 dissolution when compared to the unbaffled, steady column. In addition, a modified oscillatory Reynolds number, Reo and Strouhal number, St′ were presented to assist on the design and scale-up of gas–liquid systems based on multiorifice oscillatory baffled columns. This work is relevant to gas–liquid or multiphase chemical and biological systems relying on efficient dissolution of gaseous compounds into a liquid medium.