Investigation on the Design Space of the Primary Drying Stage of Spray-Freeze-Drying Technology

Spray-freeze-drying technology has gained considerable interest worldwide. However, the high energy consumption and lengthy process duration have hindered its further development. The primary drying stage accounts for the largest proportion of both the total energy consumption and process duration. To improve the energy utilization efficiency of the drying stage, a mathematical model describing the drying stage was established. The obtained drying time and maximum product temperature were selected to represent the drying efficiency and the risk of failure, respectively. The design space of the drying stage was then constructed. The results show that the mathematical model gives an accurate description of the drying stage, and increasing the shelf temperature and decreasing the chamber pressure would be beneficial for improving drying efficiency but unfavorable for reducing the risk of failure. In addition, the drying efficiency shows higher sensitivity to the change in the operating conditions compared with the risk of failure. Moreover, the packing porosity is found to affect the design space. A lower packing porosity is found to expand the design space, allowing for a wider range of operating conditions. This study provides insights into the drying process and supports the optimization of operating parameters.