Flow of Granular Materials

We investigate the flow dynamics of cohesive powders in rotating cylinders with an L : R ratio of 3 : 1 using experiments and DEM simulations. Flow onset and steady-state behavior are compared for free-flowing (cohesionless) dry glass beads, wet glass beads, and “dry” cohesive powders (lactose, microcrystalline cellulose). The avalanching dynamics of powders is substantially different from those observed for free-flowing or wet-cohesive glass beads. Dry cohesive powders exhibit history-dependent flow dynamics, significant dilation, aperiodic avalanche frequencies, and variable avalanche size. These behaviors also provide a route for effective characterization of cohesive forces under dilated conditions characteristic of unconfined flows.

Impregnation of Catalysts

The dry impregnation of catalyst supports is a widely used process in the preparation of heterogeneous catalysts, however there has not been a lot of work done computationally on this process. In this work, discrete element method (DEM) simulations coupled with an algorithm for the transfer of fluid to and between particles are used to study dry impregnation. We use a previously developed model, which has been further validated with geometrically equivalent experiments and the results show very good agreement. The effects of rotational speed, particle size and particle morphology are explored in order to achieve the best overall mixing and fluid content uniformity in the particle bed. We study spheres and cylinders of different sizes and aspect ratios. Axial mixing analysis and liquid distributions are used to investigate the propagation of the fluid throughout the particle bed with the goal of understanding the effect of operational and material parameters and ultimately to improve fluid content uniformity in systems with particles of different morphologies. The fluid content uniformity is characterized by the relative standard deviation (RSD) of the liquid content from all the particles in the system. Our results show that cylinders always take less time to mix than spheres of the same diameter and mixing times are also shorter for cylinders of higher aspect ratios when compared to cylinders of smaller aspect ratio. Likewise, the times to reach good fluid content uniformity are shorter for cylinders with higher aspect ratios as compared with cylinders with lower aspect ratios. We also observe that mixing time in the axial direction for both spheres and cylinders followed an exponential function of the surface area to volume ratio. We found an excellent linear correlation between the times to achieve good axial mixing and the times to achieve good fluid content uni- formity in the entire particle bed, which suggests that mixing in the axial direction controls fluid uniformity in the entire particle bed.

1. Y. Shen, W. Borghard, M. S. Tomassone, “Discrete Element Method Simulations and Experiments of Dry Catalyst Impregnation in a Double Cone Blender”, Powder Technology 318, 2017, 23–32

2. Dry catalyst impregnation in a double cone blender: A computational and experimental analysis; Romanski, F. S.; Dubey, Atul; Chester, A. W.; et al. POWDER TECHNOLOGY, Volume: 221Special Issue: SIPages: 57-69Published: MAY 2012.

3. Improved Mixing in Catalyst Impregnation Using a Double Cone Blender Incorporated With Baffles

Yangyang Shen and Maria Silvina Tomassone ( to be submitted)