Densification behavior of dry spent coffee ground powders: Experimental analysis and predictive methods

Abstract

The knowledge of bulk properties and densification behavior of Spent Coffee Ground (SCG) powders can be useful in handling such powders through the typical processing units of the soluble coffee industries. In this paper we measured the bulk densities of SCG mixtures with mean sizes from 225 to 550 μm as a function of tapping and tested a number of selected equations to predict the densification behavior of these mixtures. Densification kinetics of SCG powders was found to be overwhelmingly driven by the mass fraction of fines in the mixture. The equations proposed by Kawakita and Ludde (1971), Knight et al. (1995) and Mallol et al. (2008) predicted well the variation of bulk density of SCG powders throughout tapping. Nevertheless, the Kawakita and Ludde's equation is recommended as the most suitable because the fitted parameters in this equation could be correlated to the powders' mean size and Hausner ratio. Besides, three methods to predict the densification curves were proposed. In the first method, the powders' mean diameter is used to predict the densification kinetics and in the second the angle of repose and the loose bulk density of the samples are used. Finally, the third method is based on coupling the densification equation to the Modified Linear-Mixture Packing Model. The three approaches led to predictions of bulk density with deviations <10% in comparison to the experimental data and can be recommended to estimate the densification kinetic behavior of industrial SCG powders.