(591b) Predicting Mass Transfer and Liquid Holdup in a Vertical Droplet Array

Gas-to-liquid mass transfer is essential in many commercial processes. However, capacity and rate are often limited due to the insolubility of many gases in liquids and the small surface area-to-volume ratio over which mass transfer can occur in many system configurations. Although droplets and sprays have been suggested and proven to offer favorable hydrodynamics for mass transfer, widespread application has been limited due to the unpredictable performance of many spray systems arising from complex column hydrodynamics. This complexity makes development of generalized design tools difficult, restricting the widespread application of spray and droplet systems. Previous work in this area includes evaluations of simple models of gas-to-liquid mass transfer in singular falling droplets or development of complex and system-specific computational fluid dynamics models that are both financially and computationally expensive to develop and run. The presented work proposes to modify the standard spray tower to simplify the hydrodynamics and facilitate more accurate application of a first principles-based model for mass transfer prediction. This simplified system includes an array of vertically falling droplets with consistent hydrodynamics, building upon previous work studying singular falling droplets without requiring intense computations to track axial dispersion, droplet-droplet interactions, liquid sheets, or droplet-wall interactions that may convolute mass transfer in more complex spray patterns. A population balance model approach is taken to predict the overall column mass transfer and hydrodynamic characteristics based on controllable design parameters such as droplet size distribution, flowrates, and column geometry. Using these parameters, single droplet mass transfer correlations can be extrapolated to describe the mass transfer characteristics of the entire array as well as predicting the droplet residence times and overall column performance. These predictions can be experimentally validated by equipping a pressure vessel with a vertical droplet array manifold and measuring the dissolved gas concentration in the bulk liquid when it exits the vessel, confirming the applicability of this simplified model for early stage process design and system performance estimation.