Indirectly heated rotary dryer
Provided is an indirectly heated rotary dryer which has achieved enhanced energy-saving performance by reducing heating tubes non-contacting with material to be dried and reducing power required for rotation even when a hold up ratio is increased. Specifically provided is an indirectly heated rotary dryer having four partition walls extended respectively along a shaft center in an inner space of a rotating shell at angle intervals of 90 degrees in the vertical and horizontal directions. The four partition walls partition the inner space of the rotating shell at a lateral section of the rotating shell into four approximately-sector-shaped small spaces respectively extended along the shaft center. Heating tubes are aligned in the rotating shell in three lines extended respectively in parallel to the shaft center of the rotating shell. The heat tubes heat and dry the material to be dried by supplying heated steam to the heating tubes and performing heat exchange with the material to be dried in the rotating shell.
1. 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.
2. The indirectly heated rotary dryer according to claim 1 , wherein
the center cover is extended to the vicinity of the feed unit, which feeds the material to be dried into the rotating shell,
a screw-shaped blade, which reaches the inner circumferential face of the rotating shell, is arranged at the outer circumferential face of the extended center cover, and
a cutout portion is formed so as to eliminate a portion of the center cover at a part where the screw-shaped blade is arranged.
3. The indirectly heated rotary dryer according to claim 1 , wherein the heating tubes are arranged apart from the shaft center of the rotating shell by a length being 15% or more of a radius of the rotating shell as being in parallel to the shaft center of the rotating shell.