Drying method for terephthalic acid and horizontal rotary dryer

A drying method for terephthalic acid using a horizontal rotary dryer provided with:

• a rotating shell having a feed port for terephthalic acid on one end side thereof and a discharge port for terephthalic acid 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, and configured in a manner that the terephthalic acid is lifted up in a rotational direction by the group of heating tubes in accordance with rotation of the rotating shell, the drying method for terephthalic acid comprising
• drying, through indirect heating, the terephthalic acid by using the group of heating tubes in a process of feeding the terephthalic acid to the one end side of the rotating shell and discharging the terephthalic acid from the other end side of the rotating shell, wherein
• the rotating shell is rotated to make a critical speed ratio α defined by following expression 1 and expression 2 become 17 to less than 80% to dry the terephthalic acid,
• Vc=2.21D1/2 Expression 1
• α=V/Vc·100 Expression 2
• wherein Vc indicates a critical speed (m/s) of the rotating shell, D indicates an inside diameter (m) of the rotating shell, α indicates the critical speed ratio (%) of the rotating shell, and V indicates a rotation speed (m/s) of the rotating shell.