Drum dryer (including rotary calciner or kiln, rotary scraper dryer, etc.) is a kind of contact internal heat conduction type drying machinery.
The materials are in direct contact with the hot air and are dried by convection heat transfer. According to the flow direction between hot air and material, it is divided into parallel flow type and counterflow type. In the parallel flow type, the hot air and the material move in the same direction, and the hot air with higher temperature at the entrance is in contact with the material with higher wet content. The material is in the surface vaporization stage, so the product temperature still roughly maintains the wet bulb temperature.