Indirectly heated rotary dryer

An indirectly heated rotary dryer, comprising:

• a rotating shell, which is provided with a driven gear arranged around the rotating shell so that the driven gear is engaged with a drive gear and a rotational force of a motor is transmitted to the drive gear, which is rotated about a shaft center thereof by the rotational force of the motor, and which is capable of feeding of a material to be dried from one end side thereof and discharge of the dried material from the other end side thereof,
• a feed unit, which feeds the material to be dried into the rotating shell,
• a cylindrical center cover, which has the same shaft center of the rotating shell, which is arranged in the vicinity of the shaft center of the rotating shell, and which has a size corresponding to a seal portion to seal a clearance between the feed unit and the rotating shell,
• a plurality of partition walls, which are arranged respectively in the rotating shell in parallel to the shaft center of the rotating shell and structured to connect an outer circumferential face of the center cover and an inner circumferential face of the rotating shell so as to partition an inner space formed between the rotating shell and the center cover into a plurality of small spaces respectively extended along the shaft center of the rotating shell, and
• a plurality of heating tubes, which are arranged in each of the small spaces in parallel to the shaft center of the rotating shell for heating indirectly and drying the material to be dried by feeding heated steam to inner spaces of the heating tubes, wherein
• the partition walls are solid partition walls,
• the plurality of heating tubes are substantially located along concentric circles of same shaft center of the rotating shell,
• the heated steam is fed only to the inner spaces of the heating tubes,
• the material to be dried is supplied as being distributed into the respective small spaces, and the material to be dried is moved only within each of the small spaces, and
• the ratio of the outer diameter of the center cover with respect to the inner diameter of the rotating shell, the outer diameter of the center cover/the inner diameter of the rotating shell, is in a range between 0.2 and 0.6,
• wherein the plurality of heating tubes and the outer circumferential face of the center cover have the same annular concentricity.