(48a) CFD Simulation of a Lab-Scale Bubble Column

Bubble columns are widely used in the chemical, petrochemical and biochemical industry for gas liquid contact due to their simple construction and absence of moving internal parts. The prediction of the fluid flow behavior, gas hold-up and bubble size distribution is of major importance for the development and design of such reactors. These characteristics directly affect the performance and eventually economics of the process. Experimental methods to investigate bubble columns are common. But numerical methods are also widely used to study bubble columns, since the numerical simulations has made significant progress in the last several years for such multiphase flow.

In this contribution we have numerically investigated a 3D lab scale bubble column to validate the predictive capabilities of the commercial STAR-CCM+ CFD solver by CD-adapco. For the simulation of the two phase flow, an Eulerian-Eulerian approach was used. The influence of several  forces which define the interactions between the continuous water phase and the dispersed gas phase is investigated, which includes,  amongst others, drag force, lift force, turbulent dispersion force, virtual mass force and turbulence induced by bubbles. Bubble size distribution as well as bubble break-up and coalescence is incorporated by using the S-gamma model proposed by Lo[1].

Validation is done with respect to the gas plume oscillation frequency, liquid and bubble velocity and gas holdup against published data by Pfleger[2] and Diaz[3]. A reasonable agreement between the numerical and experimental results was found. Further the importance of the different interaction forces could be shown. A mesh study was conducted to compare calculation time and accuracy of the results with respect to the used cell types, hexahedrons and polyhedrons.

In the second part of this contribution, the oxygen transfer from the gas bubbles to the continuous water phase is investigated. The overall mass transfer coefficient is compared with literature data and also shows a reasonable agreement.

[1] Lo, S. & Zhang, D. (2009); J. Comp. Multiphase Flows (1), pp. 23-38

[2] Pfleger, D.; Gomes, S.; Gilbert, N. & Wagner, H.G. (1999); Chem. Eng. Sci. (54), pp. 5091-5099

[3] Diaz, M.E.; Montes, F.J. & Galan, M.A. (2008); Chem. Eng. Proc. (47), pp. 1867 - 1876