(24)
When the dryer operates at a load of 20%, the volume of the dryer is calculated by Eq. 25. The L / D ratio of the dryer should be known to determine the area of the dryer. Typical rotary dryers have an L / D ratio of 4-10. The L / D ratio was selected as the average value of 7. The diameter of the dryer can be expressed in equation of volume like Eq. (26), and then the area is calculated by Eq. (27) [dryer cost]