In freeze dryers, drying is accomplished indirectly under high vacuum and low temperatures (usually below 0 °C). This is done in special vacuum tray dryers. Freeze drying (also known as lyophilization), is frequently used for drying proteins vitamins and other heat sensitive products.
The material balances are done based on the sublimation percentage of the solvent components. The specific power requirement (based on tray area or sublimation amount) is used to calculate the overall power requirement.
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. The program also calculates the sublimation capacity (in kg H2O or other solvent per cycle) based on the percentage of components that sublimate. If the calculated sublimation capacity exceeds the maximum, the program assumes multiple units operating in parallel with a total sublimation capacity equal to the calculated. In Rating Mode, the user specifies the number of parallel units, their tray area and their sublimation capacity 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 sublimation rate (in mm/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. Geankoplis, C.J. (1983). Transport Processes and Unit Operations, Allyn and Bacon, 2nd ed., pp. 554-557.
2. Perry R.H. and D.W. Green (1984). Perry’s Chemical Engineers’ Handbook, 6th ed. McGraw-Hill, section 20 pp. 22-23.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Freeze 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