Numerical study of collisions between particles in liquid fluidized bed

Abstract

Wastewater treatment using liquid fluidized bed anaerobic bioreactor is an effective and self-sustainable technology. The performance of this type of equipment is usually better than other technologies, like slurry and fixed bed, because of the increase in mass transfer between phases. However, it is quite challenging to determine how particles and fluid behave inside the equipment, leading to uncertainty in project optimization processes. In this respect, coupled unresolved Computational Fluid Dynamics and Discrete Elements Method (CFD-DEM) appears as a tool to simulate changes in fluidization due to variations in characteristics of particles and fluid, allowing the evaluation of not only global effects, such as pressure drop inside the equipment, but also local variances, like the velocity profile of individual particles. Nevertheless, CFD, DEM, and its coupling require advanced knowledge in fluid dynamics, granular flows, numerical methods, and computational programming; to ensure physical and reliable results. During the execution of the numerical part of the current project, numerous issues, mainly related to the proportion between the size of mesh and particles, were identified. As the simulated column is narrow in diameter and the particles are large, the unresolved simulations need a coarse mesh to reliably calculate the void fraction per cell in the mesh. This leads to an unrealistic representation of the fluid phase. The main accomplishment of the internship is to overcome the presented problem, determining the behavior of a liquid fluidized bed bioreactor with CFD-DEM coupled numerical computational method, applying different model sets, turbulence models, and numerical meshes. It is also intended to compare the performances of CFDEM coupling and the novel high-order Lethe open-source packages in the fluidized bed numerical representation. (AU)