A study on coalescence and breakage mechanisms in three different bubble columns

A study of the interfacial mechanisms focusing on the coalescence and breakage is carried out in the framework of a BRITE-EURAM project named ADMIRE. The main objective of this study is to develop a new methodology to analyse breakage and coalescence phenomena in bubble columns. For this purpose both detailed measurements of the bubble-size distribution and the development of population balance equation (PBE) model were carried out. An elaborate database is established which describes the evolution of the bubble-size distribution in three different columns at EniChem, Politecnico di Milano and DSM. The database contains a unique set of bubble-size distribution measurements: not only the evolution of this distribution as a function of height in the column has been investigated but also the influence of gas superficial velocity and different hydrodynamic configurations have been studied. The distribution curves were obtained by analysing a large amount of bubbles with a measurement based on a new image analysis technique. The experimental measurements showed a consistent trend on the three sites and the influence of the bubble size on breakage and coalescence rates has clearly been observed. Simultaneously, a novel model that describes bubble-bubble interactions was developed. The advantage of this new model with respect to models published in literature is that the physics of free rising bubbles (e.g. wake interactions, bubble swarm velocity and the shape of the bubbles) are also taken into account. Moreover, this model is especially tailored for bubble columns where the physics of the interfacial mechanisms is thought to play a major role. For this reason this model distinguishes itself from general-purpose models which usually describe less accurately the phenomena taking place in such particular systems. The validation of the model using the experimental data is satisfactory. (C) 1999 Elsevier Science Ltd. All rights reserved.