Simulation of mass transfer in Bubble columns

Bubble column reactors are extensively used in a variety of industrial processes involving gas-liquid mass transfer along with chemical reactions. Despite intensive research, knowledge on the mass transfer is still limited in comparison with that on the fluid dynamics, which provides an open field of research.

In this study, mass transfer of CO2 between air bubbles and water in a bubble column is investigated using Euler-Euler simulations in OpenFOAM. Previously validated fluid dynamics models are applied and focus is put on the description of the mass transfer. Experimental data to validate the results are taken from the study of Deckwer providing axial profiles of gas fraction, and carbon dioxide concentration in both phases. Previous work considering only cases with co-current absorption is extended to also include the cases with counter-current flow and desorption. Some simplifications are made in accordance with the previous work, i.e. taking the bubble diameter to be constant and using the experimentally determined values for the mass transfer coefficient. Despite these simplifications, the simulation results show a quite good agreement with the experimental data.

As a second step, the change in bubble size due to the mass transfer is included in the simulations by means of a population balance equation discretized using the class method. The well-known model of Brauer is implemented as an example of a bubble size dependent mass transfer coefficient. Since experimental data including the development of bubble size are not available for comparison, an initial validation is provided by comparison of the polydisperse calculation with two monodisperse calculations corresponding to initial and final size in the former.