The assessment of a model for particle transport in the absence of airflow through cascading rotary dryers

Abstract

The predictions of the holdup in cascading rotary dryers made by the particle transport model of Kramers and Croockewit, Chem. Eng. Sci., 1 (1952) 259, as applied by Afacan and Masliyah, Powder Technol., 61 (1990) 179, have been compared with the measurements of holdup made with no air flowing through the drum by Matchett and Sheikh, Chem. Eng. Res. Design, 8 (1990) 1. Matchett and Sheikh obtained their experimental data in two sizes of drum (0.385 m and 0.154 m diameter) with two materials, fine sand and wheat, and they also studied the effects of the number of flights, the flight type, the drum slope and the drum rotational speed, giving 1 050 data points. The comparison between the predicted holdups and those measured has shown large discrepancies of up to an order of magnitude. The disagreement may be due to the interaction between the flights and the particles in the rolling bed of solids in the bottom of the drum, which is ignored in the model of Kramers and Croockewit, to the simplification of the mechanisms for particle movement in this model. The disagreement suggests that the toldup model of Kramers and Croockewit should not be used and that the two-phase holdup model of Matchett and Baker, J. Separ. Process Technol., 8 (1987) 11 and 9 (1988) 5, and Matchett and Sheikh is preferable for predicting particle transport rates in cascading rotary dryers.