Drying method for processing material and horizontal rotary dryer

1. A drying method for processing material using a horizontal rotary dryer provided with: a rotating shell having a feed port for processing material on one end side thereof and a discharge port for processing material on the other end side thereof, and capable of freely rotating around an axial center; and a group of heating tubes through which a heating medium passes, provided within the rotating shell, and configured in a manner that the processing material is lifted up in a rotational direction by the group of heating tubes in accordance with the rotation of the rotating shell, the drying method for processing material comprising

drying, through indirect heating, the processing material by using the group of heating tubes in a process of feeding the processing material to the one end side of the rotating shell and discharging the processing material from an other end side of the rotating shell, wherein

the rotating shell is rotated to make a critical speed ratio α defined by the following expression 1 and expression 2 become 30 to less than 100% to dry the processing material,

Vc= 2.21 D 1/2   Expression 1

α= V/Vc· 100  Expression 2

wherein Vc indicates a critical speed (m/s), D indicates an inside diameter (m) of the rotating shell, a indicates the critical speed ratio (%), and V indicates a rotation speed (m/s).

2. The drying method for processing material according to claim 1 , wherein

the processing material is fed into the rotating shell to make a hold up ratio η of the processing material defined by a following expression 3 become 20 to 40%,

η= Ap/Af· 100  Expression 3

wherein η indicates the hold up ratio (%), Ap indicates a cross-sectional area (m 2 ) occupied by the processing material with respect to a free cross-sectional area, and Af indicates a free cross-sectional area (m 2 ) as a result of subtracting a cross-sectional area of all of the heating tubes from the entire cross-sectional area of the rotating shell.

3. The drying method for processing material according to claim 1 wherein

when the processing material is coal whose median diameter is 50 mm or less, the rotating shell with an inside diameter of 1 to 6 m is used, and the rotating shell is rotated to make the critical speed ratio α become 40 to less than 100% to dry the processing material.

4. The drying method for processing material according to claim 1 , wherein

when the processing material is a resin-based material whose median diameter is 200 μm or less, the rotating shell with an inside diameter of 1 to 6 m is used, and the rotating shell is rotated to make the critical speed ratio α become 30 to 70% to dry the processing material.

5. The drying method for processing material according to claim 1 , wherein

a plurality of the heating tubes are arranged in a radial manner or on concentric circles, and a separation distance between adjacent heating tubes is 80 to 150 mm.

6. A horizontal rotary dryer, comprising: a rotating shell having a feed port for processing material on one end side thereof and a discharge port for processing material on an other end side thereof, and capable of freely rotating around an axial center; and a group of heating tubes through which a heating medium passes, provided within the rotating shell, configured in a manner that the processing material is lifted up in a rotational direction by the group of heating tubes in accordance with the rotation of the rotating shell, and drying, through indirect heating, the processing material by using the group of heating tubes in a process of feeding the processing material to the one end side of the rotating shell and discharging the processing material from the other end side of the rotating shell, wherein

the horizontal rotary dryer is configured to be able to operate to make a critical speed ratio α defined by the following expression 1 and expression 2 become 30 to less than 100%,

Vc= 2.21 D 1/2   Expression 1

α= V/Vc· 100  Expression 2 wherein

Vc indicates a critical speed (m/s), D indicates an inside diameter (m) of the rotating shell, a indicates the critical speed ratio (%), and V indicates a rotation speed (m/s).

7. The horizontal rotary dryer according to claim 6 , wherein

a plurality of the heating tubes are arranged in a radial manner or on concentric circles, and a separation distance between adjacent heating tubes is 80 to 150 mm.

8. The drying method for processing material according to claim 2 , wherein

when the processing material is coal whose median diameter is 50 mm or less, the rotating shell with an inside diameter of 1 to 6 m is used, and the rotating shell is rotated to make the critical speed ratio α become 40 to less than 100% to dry the processing material.

9. The drying method for processing material according to claim 2 , wherein

when the processing material is a resin-based material whose median diameter is 200 μm or less, the rotating shell with an inside diameter of 1 to 6 m is used, and the rotating shell is rotated to make the critical speed ratio α become 30 to 70% to dry the processing material.

10. The drying method for processing material according to claim 2 , wherein

a plurality of the heating tubes are arranged in a radial manner or on concentric circles, and a separation distance between adjacent heating tubes is 80 to 150 mm.