Multi-scale Understanding of Agglomeration and Deagglomeration in Fluidized Beds
Falk Bunke, M.Sc.
Fluidized beds are often used in several Industries for gas-solid processes that include an additional liquid phase as e.g. granulation, agglomeration or coating processes. Due to collisions between wetted particles or particles which undergo the glass transition, the particles can stick together and form black-berry shaped agglomerates. This consolidation may be desired or undesired. Independent of the underlaying mechanism, the agglomeration will determine the quality and morphology of the product. Therefore, understanding, predicting and thereby controlling the agglomeration behavior are crucial for the design and optimization of the desired process performance. Thus, a fundamental understanding of the micro-mechanisms of agglomerations as well as deagglomeration of agglomerates is essential for the prediction and control of the mentioned processes.
The first goal is to obtain a comprehensive understanding of the micro-mechanisms of agglomerations as well as the deagglomeration of agglomerates. The second goal is to understand the influence of agglomeration and deagglomeration phenomena on macroscopic flow behavior in fluidized beds involving liquid injection or glass transition phenomena.
The objectives will be achieved via utilizing a multiscale approach consisting both experiments and simulations. On the experimental side, novel experiments on microscale for the investigation of collision mechanisms of wet particles and agglomerates will be performed. The first aim of the experimental work is to develop correlations that describe the micromechanics between colliding pairs of wetted particles. For these investigations, ideal spherical particles, e.g. porous γ-Al2O3 or non-porous glass breads of different size will be used in experiments as well as particles with quantifiable surface roughness. A high-speed camera in combination with florescent dyes in the surface liquid will be used to observe the liquid bridges. The second step are collision experiments with particles of visco-elastic behavior, like maltodextrin DE 21. After single collision experiments, agglomeration experiments with liquid binder in lab-scale fluidized bed will take place for ideal spherical glass and γ-Al2O3 particles as well as particles with visco-elastic behavior. The knowledges of the experiments will be used in CFD-DEM to simulate fluidized beds with agglomeration and deagglomeration.
Micro scale investigations of agglomeration and deagglomeration due to single collisions between wetted particles.
Video: Wetted binary particle collision between two spherical ZrO2 particles with a diameter of 1.5 mm.
Project funding and Start Date
We gratefully acknowledge for the ﬁnancial support the German Research Foundation (DFG) (Germany).
Project start: December 2020