The design of flights in rotary dryers

Abstract 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. These flights are critical to dryer performance. Previous models for the prediction 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 have considered only the case of extended circular flights and angular flights with two segments. New equations were derived to predict the solids holdup in flights with three segments. Their predictions were compared to measurements performed with a pilot plant rotary dryer. Theoretical equations provided estimates of the 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 predict 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 the flight geometry.