Spherical shaped particles can result in a low degree of interstitial air, as the small particles in the size distribution fill the void spaces between the large particles. Irregular shaped particles and agglomerates can lead to a lower bulk density (Walton and Mumford, 1999). Bulk density tends to increase with a decrease in air outlet temperature, and with an increase in feed solids (Nath and Satpathy, 1998; Walton,
2000).