Rotary dryers are commonly used in the minerals industry to dry a range of commodities including clay, gypsum, kaolin, limestone, mineral sand, potash and silica sand (Photo 54). They consist of a relatively long cylindrical shell, which ranges from 0.6 to 5 m in diameter and from 5 to 30 m long, supported by two riding rings running on a set of rollers (rotation speed up to 25 rpm). They are slightly inclined from the horizontal; the slope enables material to move from the feed to the discharge end under gravity. They are suitable for a wide range of materials with varying size and composition. The feed rate ranges from less than 1 tonne to 500 tonnes per hour. Internal lifters, or flights, are used to lift, distribute and transport the material. This produces a shower, or cascade, of wet feed material through the hot gas stream, which promotes.
