LOCAL FLOW STRUCTURES IN INTERNAL LOOP AND BUBBLE COLUMN REACTORS

Internal loop reactors and bubble columns are used extensively in the bio- and petrochemical industry. Simulation of these reactors has traditionally been based on dispersion and cell type models. For design and scaleup purposes however, these models are not adequate and more detailed knowledge of the flow structure within the reactors is necessary. This paper presents the results obtained from a two phase fluid-dynamic model and how these results compare with experimental data. At ISCRE 11 a two fluid model based on a first principles approach was presented. To describe turbulence the single phase k-epsilon model was used. In this work a modified turbulence model based on the k-epsilon structure is used. The model takes into account the turbulent kinetic energy and dissipation caused by interaction between the gas and liquid phases. Furthermore the basic two fluid model has been modified to take into account terms arising from the volume fraction fluctuations including pressure gradients. For experimental verification local gas fractions have been measured using the five point conductivity method. The system investigated is air/water. Measurements have been performed both for an ordinary bubble column and an internal loop reactor, both with largest inner diameter 0.288m. Furthermore the model results for axial liquid turbulent intensity and axial liquid velocity profiles are compared with experimental data available in the literature for an ordinary bubble column. The new turbulence model is shown to be a significant improvement over the single phase one previously used.