Mechanistic model to simulate wet agglomerate breakage in a gas-solid fluidized bed

Abstract

A mathematical model that describes wet agglomerate breakage in a gas-solid fluidized bed was developed, utilizing the energy approach to assess agglomerate stability and the Kinetic Theory of Granular Flows (KTGF) to describe collisions between bed primary particles and agglomerates. Wet agglomerates are held together by liquid bridges that resist breakage due to capillary and viscous forces. The probability of breakage depends on the balance between the collisional energy and the energy required to break the necessary number of liquid bridges. The model considers two types of breakage: abrasion, characterized by individual primary particles being stripped from an agglomerate, and fragmentation, where an agglomerate breaks into two pieces, each containing multiple primary particles. Simulations were performed using the Eulerian-Eulerian method with either a monodispersed or a polydispersed approach to describe the size distribution of agglomerates during breakage. Comparison with available experimental data revealed good qualitative agreement between the predicted and measured abrasion and fragmentation rates, with some quantitative discrepancies that can be attributed to model limitations and experimental uncertainties. The effects of superficial gas velocity and liquid viscosity on agglomerate breakage are investigated in detail. The model can serve as a valuable tool to study breakage of wet agglomerates, and it can be extended to include agglomerate formation for a more comprehensive description of hydrodynamics of wet fluidized beds.