Freeze drying is a dehydration process enable use in almost all industries, it has always been considered a very expensive process compared with other dehydration methods. For this reason, it is used only in those processes in which the thermal stability of the products makes it the only possible choice like pharmaceutical and biological, or when the high added value of the product justifies the expenses like nutrients and food.
This post we will talk about the freeze drying cost and help operator find solutions to reduce it. Please note that since Nixtar is a commercial and industrial supplier, so our discuss will be on the basis of production scale freeze drying equipment.
Absolutely electric consumption plays a much larger role in the freeze drying. Freeze drying consists of three main steps: freezing, primary drying and secondary drying. The product is firstly frozen at low temperatures, to solid phase constituted by ice crystals. After that, ice is removed by sublimation under vacuum environment, primary drying removes physical water, secondary drying removes bound water.
Roughly calculate: Freezing cost 15%, primary drying cost around 65%, secondary drying cost 15% and condenser defrost cost 5% of the total electric consumption. Which means to reduce the primary drying duration is the feasible solution.
1, Control The Ice Crystal Growth During The Freezing Stage
Quite a lot of operators ignore the importance of freezing, which result the longer freeze drying time or low dried quality. Freezing is important because in this stage, freezing speed influence ice crystal size, later will influence drying speed, rehydrate speed and dried products quality.
During freezing, ice crystal quantity and size influenced by nucleation rate and growth rate. At 0C, ice crystal growth rate is ideal but nucleation rate is low. So, products freezing at 0C will cause larger size ice crystal but less quantity; products freezing below 0C will cause small size ice crystal but more quantity. Larger ice crystal is good for sublimation but dissolution rate is low. Generally, frozen products with smaller crystal and dried, the structure is very close to original and quality is high.
Slow Freezing: Ice Crystal and Product Looks
Rapid Freezing: Ice Crystal and Product Looks
2, Optimization of The Shelf Temperature During Primary Drying
A second approach to reducing primary drying cycles consists of a careful optimization of the shelf temperature and chamber pressure during the process, and maximizing the heat and mass transfer. The main constraint of this strategy lies in the maximum temperature that the product being dried cannot exceed during the process, the so-called target temperature. The target temperature is usually set 5 C below collapse temperature, and it is an intrinsic constraint of the raws.
However, the duration of the primary drying cannot be reduced indefinitely, and a specific analysis should be made for each product and formulation.