(519j) Computational Investigation of Scale Effects in Spouted Fluidized Beds

Spout fluidized beds allow for high circulation rates and are commonly used in a wide variety of industrial applications. Among the key benefits of these devices is the facility to achieve high heat and mass transfer rates. Major applications comprise coating, drying, as well as hot melt granulation of coarse pharmaceutical powders (see, e.g., Epstein and Grace, 2011, Borini et al., 2011, Link et al., 2005). Fluidization processes are highly scale-dependent so that an in-depth understanding of the limits and the scope of a scaling approach based on the principles of hydrodynamic similarity is of paramount importance for prosperous production at an industrial scale. Furthermore reliable scale procedures offer a promising approach to overcome restrictions inherent to the in-silico modeling methodology.

The objectives of the present work are to assess the current scale-up methodology by utilizing a four-way coupled Computational Fluid Dynamics (CFD) and discrete element method (DEM) simulation approach. Providing a detailed evaluation of the applicability of the principles of hydrodynamic similarity shall finally contribute to establish a reliable scale procedure for in-silico modeling

First, the applicability of Glicksman’s full set (Glicksman, 1988) is evaluated considering four different scale-up scenarios. Second, the significance of the individual dimensionless groups is assessed by analyzing the effects of a change in one dimensionless characteristic group on the spouted bed dynamics. Finally, the applicability of reduced scaling sets is investigated.

The results indicate that following a scale-up procedure based on the principles of hydrodynamic similarity (Glicksman’s full set) results in a very good overall agreement between the base case and the scale-up case. Furthermore Glicksman’s inertia limit set is found to be applicable for the scale-up of single-spout fluidized beds. Regarding in-silico scale-up it was found that by applying a reduced scaling set, which omits the bed-to-particle diameter ratio from the full set, the CFD-DEM simulations are capable to capture the essential hydrodynamic features of the spout fluidized bed.

References

Borini, G.B., Andrade, T.C. & Freitas, L. a. P., 2009. Hot melt granulation of coarse pharmaceutical powders in a spouted bed. Powder Technology, 189(3), pp.520–527.

Epstein, N. & Grace, J.R., 2011. Spouted and Spout-Fluid Beds - Fundamentals and Applications, Cambridge University Press.

Glicksman, L. R., 1988. Scaling relationships for fluidized beds. Chemical Engineering Science, 43(6), 1419-1421.

Link, J.M. et al., 2005. Flow regimes in a spout–fluid bed: A combined experimental and simulation study. Chemical Engineering Science, 60(13), 3425–3442.