Question 2: (Drying) 20 marks A rotary drier is applied to dry produce 36 tons.hr! The moisture content of the gypsum needs to be reduced to from 25 wt% to 2 wt% in a rotary drier. The diameter of the drier should be 1.5 m. The hold up of solids in the drier at all times is 0.4. The total area for drying is 200 m2. The equilibrium and critical moisture content are 0.002 and 0.15 kg moisture / kg gypsum respectively. The initial rate of drying for the current conditions is 0.00002 kg.m?.s! The density of gypsum is 2300 kg.m? (0) Explain the drying mechanism of gypsum in this type of drier. (3) (ii) Draw the drying diagram and determine the total time needed to dry the material to the required Moisture content. (12) (iii) Calculate the length of the drier. (5) [20]