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Despite the widespread application of bubble columns and intensive research efforts devoted to understand their complex behavior, detailed knowledge on the fluid flow, mass transfer and chemical reactions as well as their interactions is currently very limited. Gas-liquid flow in bubble column reactors is characterized by a combination of inherently unsteady complex processes with widely varying spatial and temporal scales. The complicated interactions between the gas and the liquid phases comprising hydrodynamics, mass transfer and chemical reaction cause many challenging modeling problems to be solved. The Euler–Euler model is adopted throughout this thesis to investigate gas-liquid flow in bubble columns. In this study, efforts have been focused on the assessment of suitable closure laws for interfacial forces and for turbulence in the continuous phase. Furthermore, gas-liquid heterogeneous flow and reactive gas-liquid flows have been studied. All the numerical simulations were carried out with the commercial CFD package CFX-4.4 and all simulation results were compared with the available experimental PIV data of Deen (2001).

Spout-fluid beds find a widespread application in the process industry for efficient contacting of large particles with a gas. Since the spout-fluid bed configuration allows for the introduction of a liquid, spout-fluid beds are used for both coating and granulation applications, for example in the fertilizer industry. In this application, the spout-fluid bed has the advantage of producing strong granules over a wide range of particle sizes. However, the particle size distribution obtained in spout-fluid beds can be relatively wide resulting in large recycling requirements. The objective of this thesis is to improve the control over the particle size distribution resulting from spout-fluid bed granulation by gaining insight into the underlying fundamental processes. As detailed experiments in operating granulators are virtually impossible, it was decided to adopt a modeling approach. Since the flow behavior inside the spout-fluid bed was considered to be most critical, the modeling efforts were focused on the hydrodynamics.

In this thesis, a multi-scale modelling approach in combination with an advanced parallel computing strategy is used to study the phenomena prevailing at different scales. Two CFD models, namely a front tracking model and an Eulerian-Lagrangian model are used to study the relevant phenomena at different scales. The interactions between hydrodynamics, mass transfer and chemical reactions are treated directly in each model taking into account the relevant coupling.