Fluorspar (CaF 2 ) is to be dried from 6 to 0.4 percent moisture (dry basis) in

Question:

Fluorspar (CaF₂) is to be dried from 6 to 0.4 percent moisture (dry basis) in a countercurrent adiabatic rotary dryer at a rate of 18.000 lb/h of bone-dry solids. The heating air enters at 1,000°F with a humidity of 0.03 and a wet-bulb temperature of 150°F. The solids have a specific heat of 0.48 Btu/lb-°F; they enter the dryer at 70°F and leave at 200°F. The maximum allowable mass velocity of the air is 2,000 lb/ft²· h.

(a) Assuming Eq. (24.8) applies, what would be the diameter and length of the dryer if N_i = 2.2? Is this a reasonable design?

(b) Repeat part (a) with N_i= 1.8.

Eq. 24.8