Evaluation of mixing of a secondary solid phase in a circulating fluidized bed riser

• Published in: Chemical engineering science Vol. 269; p. 118503
• Main Authors: Nikku, Markku, Myöhänen, Kari, Ritvanen, Jouni, Hyppänen, Timo
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 05.04.2023
• Subjects: CFD modeling; Circulating fluidized bed; Dispersion; Eulerian; Mixing; Circulating fluidized bed; CFD modeling; Mixing; Dispersion; Eulerian
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2023.118503

•Transient three-phase simulations to obtain the effect of hydrodynamic fluctuations.•Mixing of fuel in time-averaged flow fields of bed material and gas analyzed.•Averaged results compared with transient to obtain effect of drag and dispersion.•Parametric study for secondary solid phase properties on the mixing.•Two routes for mixing observed based on momentum and elutriation tendency. Mixing of the secondary solids phase, i.e. fuel or sorbent is crucial in fluidized bed reactors due to its effect on the performance of the reactor. Fluctuations in the gas-particle flow affect mixing, thus modeling this is essential for the analysis of mixing. However, simplified mixing models are used for large circulating fluidized bed (CFB) reactors, which causes uncertainties. A novel averaging method is presented to obtain representative results of transient secondary solid phase mixing in CFBs, acknowledging the effect of fluctuations. A parametric study is performed to investigate the effect of particle size, density, and inlet velocity on mixing and for insight into the mixing process. Additionally, the presented approach is used to compare different steady-state mixing methods to evaluate their applicability for modeling mixing in CFB reactors. Initial momentum and elutriation tendency of fuel were found to affect the mixing behavior, with two distinct routes identified.