Modeling the axial hydrodynamics of gas–solid counter-current downers_中国颗粒学会


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Partic. vol. 50 pp. 135-143 (June 2020)
doi: 10.1016/j.partic.2019.08.001

Modeling the axial hydrodynamics of gas–solid counter-current downers

Juanbo Liua,b, Xinhua Liua,*, Zhixin Zhanga, Hui Zhaoc, Wei Gea,b,*

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    • EMMS theory is used to simulate gas–solid counter-current downward flow. • The model predicts well the axial hydrodynamics of counter-current downers. • An inflexional voidage variation with gas velocity is computed in the downers. • The predictions are supported by a CFD–DEM simulation. • The flooding behavior is quantified further according to the model predictions.


Gas–solid counter-current downer reactors, in which particles move downward in an upward gas flow, can achieve high solid concentration for high heat and/or mass transfer rates. However, the particles may reverse their direction or even be carried out of the reactor as the gas flow rate increases. This is closely related to “flooding” in counter-current flows. The energy minimization multiscale (EMMS) model well describes multiscale heterogeneity in gas–solid cocurrent upward flows. It is further developed to simulate gas–solid counter-current downward flows because similar heterogeneity can also be found in downers. The model characterizes well the axial hydrodynamics and predicts an inflexional voidage variation with superficial gas velocity in the fully developed region. This is supported by a simulation based on computational fluid dynamics and the discrete element method. The flooding predicted by the model agrees better with experiment than previous models.

Graphical abstract


Mathematical modeling; Counter-current downer; Flooding; EMMS; Mesoscale