Population balance modelling of bubble columns under the heterogeneous flow regime

Abstract

Industrial bubble columns generally operate under the so-called heterogeneous regime and with high gas volume fractions, implying a fundamental role of the coalescence and breakage phenomena. These columns are usually simulated thanks to Eulerian CFD modelling, whereas the local bubble size distribution can be estimated with population balance models. The coupling can be realized with the Quadrature Method of Moments in order to minimize the CPU time consumption. In this work, the CFD-PBM/QMOM approach is validated using experimental data. Various qualities of water and two spargers are investigated. Considering different additives and spargers allow studying separately the effect of breakage and coalescence. In particular, a perforated plate with many holes leads to the formation of small bubbles that hardly break. On the contrary, a perforated sparger with a few big holes induces the production of big bubbles in the lowest part of the column, enhancing breakage. In this second case, due to breakage, bubble size decreases quickly along the axial position until an equilibrium bubble size is reached. The presence of additives is used to further investigate coalescence and breakage phenomena, given that it generally suppresses coalescence and highlights the kinetics of breakage. In this work, a suitable set of breakage and coalescence kernels is proposed, capable of providing predictions in good agreement with experimental data for different bubble columns geometries, gas flow rates and additive concentrations.