Tray drying is used for the drying of solids and pastes. Drying is accomplished by direct contact of the wet solid and the drying gas. Tray dryers are useful for small production rates. They operate in batch mode. Due to the labor required for loading and unloading, they are expensive to operate. Frequent applications include drying of valuable products, such as dyes and pharmaceuticals.
Tray dryers consist of a rectangular chamber of sheet metal containing trucks that support racks. Each rack carries a number of shallow trays that are loaded with the material to be dried. Heated air or inert gas is circulated between the trays. Tray dryers may be operated under vacuum, often with indirect heating.
The material balances are done based on the evaporation percentage of the solvent components. The specific heating requirement along with the amount of solvents that evaporate are used to calculate the total heating requirement. The specific power requirement is used to calculate the overall power requirement. The Drying Gas Requirement along with the amount of solvents that evaporate is used to calculate and adjust the flowrate of the drying gas.
In Design Mode, the user specifies the depth of wet cake and the program calculates the tray area by dividing the calculated wet cake volume by the wet cake depth. If the calculated tray area exceeds the maximum allowable tray area per unit, the program assumes multiple identical units operating in parallel with a total tray area equal to the calculated. In Rating Mode, the user specifies the number of parallel units and their tray area and the program calculates the wet cake depth. If the calculated wet cake depth exceeds the maximum allowable value, the user is warned.
The drying time is either specified by the user or calculated based on the evaporation rate (in kg evap./m2-h). The cake discharge time is either specified or calculated based on the discharge rate. The user always specifies the cake discharge set up time. The overall process time is the sum of the drying time, the cake discharge time and the cake discharge set up time.
See Vacuum Pump Auxiliary Equipment Calculations.
1. Perry R.H. and D.W. Green (1984). Perry’s Chemical Engineers’ Handbook, 6th ed. McGraw-Hill, section 20 pp. 19-22.
2. McCabe W. L., J. C. Smith, and P. Harriott. (1993). Unit Operations of Chemical Engineering, McGraw-Hill, 5th ed., pp. 792-793.
3. Coulson J. M. and J. F. Richardson, (1978). Chemical Engineering, Vol. 2, Pergamon Press, 3rd ed., pp. 725-727.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Tray Drying: Oper. Conds Tab
● Utility Data, see Drying Operations: Utility Data Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab