The single or triple pass rotary drum dryers are characterized by continuity, reliability and long-term efficiency operation in treating different kind of materials, with high input moisture. The evaporation process happens thanks to the hot air, provided by the burner and conveyed through a centrifugal fan, that removes the moisture, surrounding the porous substance. The transportation of the processed material takes place through the combined effect of the rotation induced by deflectors housed inside the drum and the action exerted by the hot air flow. The advancement of solid particles is so characterized by cyclical movements of lifting, dropping, slippage and rebound, which facilitate contact and heat exchange with hot fumes. The material retention time inside the equipment as well as the process temperature, are the main operating parameters on which acting to obtain an optimal drying.