Generally speaking, the freeze dryer is mainly composed of refrigeration system, vacuum system, heating system and control system. The main functions of each part are as follows:
1.Refrigeration SystemAs the name implies, it is used to cool down the freeze dryer. It is the core component of the freeze dryer, mainly including compressors, evaporators, condensers, throttle valves (also called expansion valves), pipelines, refrigerants, etc. Its principle is similar to the refrigeration principle of air conditioners and refrigerators. Generally, the lowest temperature of commonly used freeze dryers can be reduced to between -40°C and -55°C.
2. Vacuum SystemIt is also an important part of the freeze dryer, used to vacuum the freeze dryer. It is mainly composed of vacuum pump, Roots pump, valve, pressure control system, steam-water separator, pipeline, etc. The limit vacuum of general freeze dryer is about 3pa. Of course, when choosing a freeze dryer, it is not that the ultimate vacuum is as low as possible, just meet the requirements. In addition to vacuum degree, vacuum rate (pumping rate) and vacuum leak rate are also important indicators.
3. Heating SystemIt is mainly used to supplement heat in the sublimation process. If the sublimation process does not supply heat, then the product can only reduce the internal energy to compensate for the endothermic sublimation. Of course, temperature control is a very important process for the freeze dryer, which requires high control accuracy and ensures that the temperature of the product is lower than a certain range of its eutectic point temperature.
4.Control SystemLike all precision equipment, the control system is the soul of the whole equipment. Almost all operations of the freeze dryer are completed through the control system, including the automatic cooling, vacuuming, heating and other processes of the freeze dryer, and the control related parameters follow the characteristic changes of the ideal drying curve. The control system generally includes a controller (PLC), input and output modules, sensors, actuators, human-machine interface (HMI), etc.
Of course, in addition to the above, the freeze dryer also includes cabinets, drying ovens, airtight doors, electrical appliances, cleaning in place (CIP) and sterilizing in place (SIP), etc., which are all indispensable parts of the freeze dryer.
Because the freeze-drying box is still in a vacuum state when the drying is completed. Therefore, air must be put in when the product is out of the box, and the door of the box can be opened to take out the product. The air put in should be sterile dry air.
As storage requirements vary for each product, handling when out of the box also varies. Some products only need to be placed in sterile dry air, and then sealed and stored out of the box; Some products need to be filled with nitrogen for storage, put in nitrogen gas when they are out of the box, and then fill with nitrogen and seal them for storage after they are out of the box; Some products need to be stored in a vacuum, and then re-vacuum and sealed after being out of the box.
Once the dry product is exposed to the air, it will quickly absorb the moisture in the air and deliquesce; especially in humid weather, the already dry product will increase the moisture content. Therefore, as soon as the product is out of the box, it should be sealed quickly. If the sealing time is too long due to the large quantity, appropriate measures should be taken to transfer the products in batches or transfer them to another drying cabinet.
Since the freeze-dried product is dried under vacuum, when it is out of the box, the oxygen in the air will immediately invade the gaps of the dried product, and some active genes will quickly combine with oxygen, causing irreversible damage to the product. Even further vacuuming won't help because it's an irreversible oxidation.
If an inert gas, such as nitrogen, is put in when the product is out of the box, oxygen will not easily penetrate into the gaps of the product after it is out of the box. Then use nitrogen to drive away the air in the product capacity, and then seal, the degree of product damage by oxygen can be reduced. The most fundamental solution to drive away the product from the influence of moisture and oxygen in the air is to use the method of plugging in the box. This method needs to use a special freeze-drying box and a special bottle and stopper to cooperate with each other. The stopper needs to be placed on the bottle stably, but it is not tightly stoppered but half of the stopper is used, commonly known as half stopper.
The sublimation of the ice is not affected due to the notches and small holes in the plug that allow ventilation. After the product is dried, the mechanical device of the freeze-drying box can be activated under vacuum or under the condition of putting inert gas to make all the stoppers of the whole box tightly pressed,then put in the air, the product is out of the box, and then the stopper is pressed on the aluminum cap or sealing wax to make the seal better.
The mechanical device of plugging in the box is specially designed in the freeze-drying box. According to the power of plugging, it can be divided into two methods: hydraulic and pneumatic. There are two types of hydraulic pressure: manual hydraulic and electrohydraulic. Manual hydraulic pressure is to use the manual pressure jack to press the plug with the power of the jack. Electro-hydraulic uses the power of the motor; the pneumatic pressure has two types: compressed air and vacuum negative pressure, and the compressed air uses the compressed air force of the air compressor to press the plug.
Vacuum negative pressure is to use the vacuum state of the freeze-drying box to put the outside air into the special rubber bag in the box, so that the rubber bag will generate pressure under vacuum to plug. According to different designs, there are two types of plates in the freeze-drying box: fixed and movable. Fixed design: the product layer in the freeze-drying box does not move, and there is another plate that can move up and down to press the plug; movable design: the product layer in the freeze-drying box can move up and down, and the plug is also pressed the ply itself. Most of the domestic ones are internal plugging devices with hydraulic motor movable slabs.
In addition, the following points should be paid attention to when stoppering in the box:
Since there is a stopper on the top of each bottle, although there are gaps and small holes for ventilation, it increases the resistance of water vapor after all, so the freeze-drying curve needs to be changed appropriately, the heating needs to be slowed down appropriately, and the time needs to be increased appropriately .
Due to the large total force of stoppering, in order not to bend and deform the layers in the freeze-drying box, the products on each layer must be placed evenly and not on one side. If it is not full due to the lack of products, wooden blocks whose thickness is equal to the height of the bottle stopper must be placed on the empty board layer.
The power of the stopper should not be adjusted too large, and of course it should not be too small. Because every layer is connected in series for the pressurization mode of movable plate layer, promptly one layer is laminated one layer. Therefore, the total force is the same as the force of each layer, as long as the force required for one layer is calculated, it is the total force of plugging. The force for each layer is simply the force required for each bottle multiplied by the number of bottles placed on that layer.