The design of flights in rotary dryers

Rotary dryers for particulate solids commonly use flights along the length of the shell to lift solids and make them rain across the dryer section. Th ese flights are critical to dryer performance. Previous models for the pred iction of the solids holdup in rotary drums have assumed that the angle of the solids level in a flight is independent of the flight geometry. They ha ve considered only the case of extended circular flights and angular flight s with two segments. New equations were derived to predict the solids holdup in flights with thr ee segments. Their predictions were compared to measurements performed with a pilot plant rotary dryer. Theoretical equations provided estimates of th e flight holdup that were accurate enough to predict the power required to lift the solids. On the other hand, the model is not accurate enough to pre dict the variations in the flux of solids over the drum cross-section. This shows that the angle of the solids level in a flight can be affected by th e flight geometry. (C) 2001 Elsevier Science B.V. All rights reserved.