Freeze Drying

General Description

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.

Unit Procedure Availability

      Freeze Drying Procedure

Freeze Drying: Modeling Calculations

Material and Energy Balances

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.

Equipment Sizing

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.

Drying and Cake Discharge Time

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.

Vacuum Pump Power Consumption

See Vacuum Pump Auxiliary Equipment Calculations.

References

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.

Freeze Drying: Interface

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