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

A study of the interfacial mechanisms focusing on the coalescence and break age 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 bot h 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 di stribution in three different columns at EniChem, Politecnico di Milano and DSM. The database contains a unique set of bubble-size distribution measur ements: not only the evolution of this distribution as a function of height in the column has been investigated but also the influence of gas superfic ial velocity and different hydrodynamic configurations have been studied. T he distribution curves were obtained by analysing a large amount of bubbles with a measurement based on a new image analysis technique. The experiment al measurements showed a consistent trend on the three sites and the influe nce of the bubble size on breakage and coalescence rates has clearly been o bserved. Simultaneously, a novel model that describes bubble-bubble interac tions 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. w ake interactions, bubble swarm velocity and the shape of the bubbles) are a lso taken into account. Moreover, this model is especially tailored for bub ble columns where the physics of the interfacial mechanisms is thought to p lay a major role. For this reason this model distinguishes itself from gene ral-purpose models which usually describe less accurately the phenomena tak ing place in such particular systems. The validation of the model using the experimental data is satisfactory. (C) 1999 Elsevier Science Ltd. All righ ts reserved.