Granule efficiency evaluation process using two-way CFD-DEM coupling analysis

Abstract

Amino acid granulation using a fluidized bed is an important process that can improve the fluidity of powders and provide better process control. In this study, a granulation process evaluation procedure using numerical analysis is presented. Before analyzing the flow and particle behavior during the process, experiments and analyses such as pour angle of repose, drained angle of repose, and static angle of repose were performed to measure material properties and ensure the reliability of the numerical model. Material properties determined through experiments and numerical analyses were applied to an evaluation model of the granulation process. The granulation process is characterized by the interdependent behavior of a strong flow and large amounts of powder inside the equipment. A Computational Fluid Dynamics (CFD)-Discrete Element Model (DEM) coupled numerical model was presented for simulating particle and multiphase flow phenomena. Additionally, because there is a strong correlation between particle behavior and flow, a two-way coupling model was applied.The particle behavior characteristics are directly related to the granulation efficiency. Particle behavior was analyzed by setting four process conditions depending on the flow intensity. In this study, the concept of a dead zone was introduced to evaluate the kinetic performance of the particles under different process conditions. A dead zone is an area where the particles do not move actively and are unable to mix. The creation and size of the dead zone were compared based on the process conditions. Additionally, this study presents a procedure to evaluate the mass, volume, and size increase due to the granulation process based on the time spent in the granulation region. The granulation region is defined as the area in which the granulation of the particles is expected to proceed using the material sprayed from the nozzle. The granule quantity and uniformity were evaluated according to the process conditions. The granule amount refers to the mass and volume of individual particles that increase during the granulation process, and uniformity refers to the variation in granule amount between particles. The process efficiency can be evaluated as good when the granule amount of the work particles reaches the target value and is evenly distributed. Although the behavioral characteristics of the analyzed process did not represent all similar processes, it was confirmed that separate process conditions should be set according to the initial size distribution of the particles, target granule amount, and uniformity. Consequently, a series of processes was organized to obtain the properties of the target particles, effectively simulate the behavior inside the equipment, and reasonably determine the granulation region. Additionally, it presents a method to evaluate the amount and uniformity of granules rather than simply evaluating the time spent in the granulation region.