Modeling microwave heating in fluidized bed reactors: Revealing the interaction between microwave absorption and fluidization hydrodynamics

Microwaves present a promising solution for electrifying process heat in fluidized beds. The present study introduces a pioneering CFD-DEM (Computational Fluid Dynamics-Discrete Element Method) model coupled with electromagnetics, providing novel insights into microwave-particle–fluid interactions. The model utilizes a one-way frequency-transient algorithm, where Maxwell’s equation is solved in the frequency domain while coupling CFD-DEM equations in a two-way transient scheme. Results show that fluidization dynamics affects microwave power absorption and distribution. For instance, altering the fluidization regime from bubbling to sluggish helps mitigate hotspot temperatures by axially mixing particles between microwave-induced hotspot and cold spot regions. Notably, microwave-induced cold spot is heated at a rate of 0.7 °C/s which is unexpectedly higher than the heating rate of 0.02 °C/s resulting from direct microwave absorption. This is due to convective heat transfer from gas due to bubble dynamics, introducing new physics in microwave-matter interactions. Our findings imply that microwave heating in fluidized beds offers substantial flexibility in controlling the temperature profile as well as microwave power absorption and distribution, offering new opportunities for optimization, research, and development.