CO₂ Dissolution and Design Aspects of a Multiorifice Oscillatory Baffled Column

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 (K_La) were experimentally evaluated for very low superficial gas velocities, U_G 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 d_o = 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 d_o 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 K_La values up to 65 ± 12 h^–1 in the range of the U_G 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, Re_o^′ 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.