Dispersive gas-liquid mixing in static mixers
Dispersing gaseous phases into liquid bulks is an often required operation in the chemical and process industry. Growing interest towards process intensification in chemical industries over the last decade promotes static mixers as an attractive contactor alternative to the bubble column and mechanically stirred vessels. Small space requirement, low equipment and maintenance costs, sharp residence time distributions and high interfacial area production are the main features of static mixers. Application examples of static mixers for dispersive mixing of gaseous phase into liquid phase are ozonation processes in waste water treatment processes, scrubbing ammonia, hydrogen chloride, hydrogen fluoride or cyanides with water and hydrogenation of vegetable oils.
Dispersive mixing and interfacial area production result from flow splitting and merging by a series of obstacles creating notable acceleration forces and providing an intimate contact. In the future, a careful optimization of the flow and design parameters can only be done with assistance by CFD simulations. However, reliable validation data are hardly available.
In this work, turbulent dispersion of co-current upward gas-liquid flow in a pipe packed with helical static mixer elements was investigated using ultrafast electron beam X-ray tomography. The imaging technique allows visualizing the gas-liquid flow morphology within the helical static mixer elements in a great detail. Beyond the number of static mixer elements, the effect of the variable operation parameters on the bubble size distribution, gas holdup profile and specific interfacial area upstream and downstream of the mixer elements was studied and correlated with pressure drop and power dissipation.
In addition, the bubbly gas-liquid flow in such helical static mixer devices has been studied by means of multiphase computational fluid dynamics simulations (CFD) using the Euler-Euler approach with a baseline closure. In the future, models for bubble coalescence and breakup as well as bubble-induced turbulence within a full Reynolds stress model will be implemented to further improve the prediction of the mixing process.
- S. Rabha, M. Schubert, F. Grugel, M. Banowski, U. Hampel (2015)
Visualization and quantitative analysis of dispersive mixing by a helical static mixer in upward co-current gas-liquid flow.
Chemical Engineering Journal 262, 527-540
- F. Zidouni, E. Krepper, R. Rzehak, S. Rabha, M. Schubert, U. Hampel (2015)
Simulation of gas-liquid flow in a helical static mixer.
Chemical Engineering Science 137, 476-486.