A CFD study on ultrasound-enhanced CFB riser with calcium oxide and activated coal for CO2 capture application

Abstract

This numerical study explores techniques for optimizing fluidization in circulating fluidized beds (CFB), which are of significant industrial interest. Various intrusive and non-intrusive approaches have been investigated to mitigate issues such as cluster formation, core-annulus profiles, and solid back-mixing. Specifically, this research focuses on non-intrusive methods, employing ultrasonic waves to enhance solids distribution within a CFB riser by Computational Fluid Dynamics (CFD) simulations. Particulate phases, including calcium oxide and activated carbon particles, were studied alongside a gas phase of air with a 10 % carbon dioxide concentration, commonly encountered in carbon capture processes. A radial ultrasonic device featuring 20 transducers at 20 kHz and 40 kHz was affixed to the CFB to disperse particle flow. Numerical experiments within a 3-D CFD domain employed the URANS-k-ε-KTGF-EMMS mathematical model. Findings reveal that ultrasonic waves significantly influence particle motion, modifying riser flow profiles and enhancing solids distribution. While ultrasounds increase pressure drop within the transducers' region, they decrease it above, reshaping the flow profile for both particle types. Distinct outcomes are observed for calcium oxide and coal particles regarding the radial Péclet number and solids volume fraction dispersion coefficient, suggesting that ultrasounds effectively improve coal particle distribution along the riser's height.