CO<sub>2</sub> Dissolution and Design Aspects of a Multiorifice Oscillatory Baffled Column
2014-11-05T00:00:00Z (GMT) by
Dissolution of CO<sub>2</sub> in water was studied for a batch vertical multiorifice baffled column (MOBC) with varying orifice diameters (<i>d</i><sub>0</sub>) of 6.4–30 mm and baffle open area (α) of 15–42%. Bubble size distributions (BSDs) and the overall volumetric CO<sub>2</sub> mass transfer coefficient (<i>K</i><sub>L</sub><i>a</i>) were experimentally evaluated for very low superficial gas velocities, <i>U</i><sub>G</sub> of 0.12–0.81 mm s<sup>–1</sup>, using 5% v/v CO<sub>2</sub> in the inlet gas stream at a range of fluid oscillations (<i>f</i> = 0–10 Hz and <i>x</i><sub>0</sub> = 0–10 mm). Remarkably, baffles presenting large <i>d</i><sub>o</sub> = 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 CO<sub>2</sub> 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 <i>d</i><sub>o</sub> 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 <i>K</i><sub>L</sub><i>a</i> values up to 65 ± 12 h<sup>–1</sup> in the range of the <i>U</i><sub>G</sub> tested, representing up to 3-fold increase in the rate of CO<sub>2</sub> dissolution when compared to the unbaffled, steady column. In addition, a modified oscillatory Reynolds number, <i>Re</i><sub>o</sub><sup>′</sup> and Strouhal number, <i>St</i>′ 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.