Identification of volatile cloudy zone in a liquid-injected fluidized bed by CFD–DEM simulation

Abstract

In liqud-injected fluidized bed processes, such as ethylene polymerization, it is crucial to quantitatively identify the cloudy zone consisting of gas bubbles, droplets, and wet particles. While various experimental methods exist for measuring relevant parameters, a comprehensive understanding of the characteristics of the cloudy zone remains challenging. This study introduces a particle-based method to identify the cloudy zone using CFD–DEM simulations, focusing on heat and mass transfer during liquid evaporation and particle-droplet collisions. Image analysis of simulation results reveals a horseshoe-shaped cloudy zone and elucidates the life cycle of wet particles, transitioning from dry to wet and back to dry. The investigation identifies five distinct stages characterized by changes in evaporation rate, temperature, and liquid mass during the core-annular flow of wet particles. Importantly, the temperature gap between dry and wet particles diminishes as thermal energy transfer during droplet-particle collisions weakens at higher liquid injection rates.