Freeze drying system
Freeze drying system is mainly composed of five parts: drying chamber, heating system, vacuum system, refrigeration system and electrical control system. The five major systems of the freeze drying system are completely under the control and monitoring of HMI and computer. First, the product is cooled and frozen in the drying chamber, and the water is frozen into ice crystals. The product is dispersed in this crystal structure. Under the condition of maintaining the frozen state, the pressure around the product is reduced by vacuuming, when it is lower than the saturated vapor pressure of water at this temperature, the ice sublimates directly into a gas.
The drying chamber of freeze drying system is a kind of airtight that can be vacuumized and heated. The sublimation process of fruits and vegetables is completed in the drying chamber. The food is loading in the tray on the shelf in the drying room according to 8~12 kg per m². There are probes for measuring the temperature of the material on each shelf to monitor the temperature of the material throughout the freeze drying process. The function of heating of the freeze drying system is to heat the products in the drying chamber, so that the materials can continuously obtain the heat of sublimation. The freeze drying system has different heating methods: contact heating and radiant heating. The vacuum system consists of rotary vane vacuum pump and roots pump.
The Roots pump cannot be used alone which is a booster pump. The rotary vane pump must be started first to make it work for a period of time. When it reaches below 3Kpa, the roots pump will be automatically started again. The refrigeration system of the freeze drying system is composed of compressor, condenser, oil separator, high-pressure pipeline, dry filter, expansion valve, evaporator, and low-pressure pipeline. The refrigeration system is used for quick freezing of products and vapor condenser. When the freeze drying system is in operation, the shelf temperature can be reduced to - 35°C in contact heating mode. The control system of freeze drying system is composed of automatic devices and circuits such as computer, recorders, control instruments, and adjustment instruments. Its function is to manually or automatically control the freeze drying system to work normal.
The requirements of the freeze drying process for the freeze drying system mainly include: practicability, safety, reliability and advancement. Energy saving, environmental protection, cost reduction, easy maintenance, and ease of use should be considered when designing and manufacturing freeze drying system.