Modelling the hydrodynamics of gas–solid suspension in downers

We modify the model developed by Ocone et al. [AIChE J. 3(8) (1993)] to include gas phase turbulence and then we test its predictive capabilities in the down flow of air and sand particle suspensions. Subsequently the flow of a diverse solid, namely fluid catalytic cracking (FCC) catalyst, is studied; the computational results for FCC show poor agreement with the experiments obtained by Cheng et al. [Chem. Eng. Sci. 54 (1999) 2019] and Ball and Zhu [Powder Technol. 114 (2000) 96]. However, when a counter-diffusive solid concentration term [Trans. IChemE 78 (2000) 860] is considered in the solid stress tensor, very good agreement with experimental data is observed. Furthermore, the effect of gravity, fluid turbulence, pressure drop and drag force is explored.