Theoretical Prediction of Mass Transfer Coefficients in Two-Phase and Slurry Bubble Columns

Two-phase and slurry bubble columns are characterized with high volumetric mass transfer coefficients kLa at low energy input. The design, modelling, optimization and scale-up of these reactors require precise knowledge of the mass transfer parameters. The mass transfer coefficients determine the efficiency and dimensions of (slurry) bubble columns. Nedeltchev et al. (2007) developed a correlation for prediction of mass transfer coefficients in gas-liquid bubble columns operated in the homogeneous flow regime. It was based on experimental gas holdups. On the other hand, Nedeltchev and Schumpe (2008) developed a correlation for prediction of gas holdups in gas-liquid bubble columns operated in the homogeneous regime. In this work, the theoretically calculated gas holdups were substituted in the mass transfer model (in the correlation for the interfacial area) of Nedeltchev et al. (2007) and the mass transfer coefficients were recalculated by means of a purely theoretical approach. The same gases and liquids (18 pure organic liquids, 14 adjusted liquid mixtures and tap water) were used and 263 kLa values (only in the homogeneous regime) were successfully predicted at ambient and high pressures (up to 1 MPa).
The same approach was tested in a slurry bubble column. Nedeltchev et al. (2014) predicted successfully the experimental mass transfer coefficients in a slurry bubble column based on bubble sizes which depended on the experimental gas holdups. On the other hand, Nedeltchev (2014) established a new approach for predicting the gas holdups in a slurry bubble column. When these theoretical gas holdups were substituted in the mass transfer model (in the correlations for prediction of bubble size and interfacial area), a purely theoretical kLa values in a slurry bubble column were obtained. The predictions were good not only in the homogeneous regime but also in the heterogeneous regime. The theoretical approach was applicable up to relatively high (18 %) solids concentrations. Six different liquid-solid systems were used and 66 kLa values were successfully predicted. In both mass transfer models, correction factors (a function of Eӧtvӧs numbers) were introduced due to the non-spherical (ellipsoidal) shape of the bubbles.