Elongated particles in fluidized beds

Abstract

Gas-solid fluidized beds are widely used in various industries due to their favourable mixing, and mass and heat transfer characteristics. Fluid catalytic cracking, polymerization, drying, and granulation are a few examples of their applications. In recent years, there has been increased application of fluidized beds in biomass gasification and clean energy production. Fluidization has been extensively studied, experimentally, theoretically and numerically, in the past. However, most of these studies focused on spherical particles while in practice granules are rarely spherical. Particle shape can have a significant effect on fluidization characteristics. It is therefore important to study the effect of particle shape on fluidization behavior in detail. One of the main reasons we still do not completely understand the fluidization phenomenon is because of complex hydrodynamic interactions and its large separation of scales. Industrial fluidized bed reactors of tens of meters in diameter can have hydrodynamic scales varying from micrometers to meters. Experimental setups of such large size are extremely expensive and therefore not practical. On the other hand, theoretical and empirical correlations are not accurate for scale-up and are rarely available for non-spherical particle shapes. Because of this, we need a different approach. One that takes advantage of experimental measurements and numerical simulations. The tasks are divided into three parts based on scales, each focusing on a particular aspect : DNS (direct numerical simulation), CFD-DEM (computational fluid dynamics - discrete element model) and TFM (two fluid model) or MP-PIC (multi-phase - particle in cell). In this thesis, the focus is on CFD-DEM modelling, a ’bridge’ that connects the DNS and TFM/MP-PIC models.