Pilot freeze dryers are common in daily life. Air freeze-drying technology, referred to as freeze-drying, is also known as sublimation air drying. Freeze-drying is a specific method of pre-freezing water-containing materials and then subliming them in a vacuum state to obtain air-dried objects. The original biological and chemical properties of the freeze-dried objects are basically unchanged, and they are easy to be stored for a long time. After being soaked in water, they can be restored to the form before freeze-drying, and their original biochemical properties can be maintained. Therefore, freeze-drying technology is widely used in various fields such as industrial chemistry and medical equipment. However, many people are not very clear about how to use it specifically, and they are not very aware of the precautions. Next, let us learn more about the pilot freeze dryer. First of all, let's take a look at how it works and get ready to work.
Before use, place the object to be air-dried in a low-temperature refrigerator or liquid nitrogen to make the object freeze solid, and then freeze-drying can be performed. The main engine and the vacuum pump are connected with each other by a vacuum tube, and standard clamps are used at the connection. The clamp contains a sealing rubber ring. Before connecting, apply an appropriate amount of vacuum grease on the rubber ring, and then clamp it with the clamp. There is a power socket for the vacuum pump on the right-side panel of the main unit, and the power cord of the vacuum pump is connected well. Check the vacuum pump to confirm that the vacuum pump oil has been filled, and it cannot be run without oil. The oil level should not be less than the centerline of the oil mirror. The "o" type sealing rubber ring above the cold trap of the main unit should be kept clean. When using it for the first time, a thin layer of vacuum grease can be applied. The plexiglass cover is placed on the rubber ring and rotated a few times, which is conducive to sealing.
The main methods of pressure control of the pilot freeze dryer are: ① the control method of the septum valve; ② the control method of the water vapor condenser; ③ the control method of the small butterfly valve; ④ the aeration method.
1. Septum valve control method
Refers to the purpose of pressure control by adjusting the cross-sectional area of the passage between the drying box and the water vapor condenser of the pilot-scale freeze dryer to increase the partial pressure of water vapor in the drying box.
2. Water vapor condenser control method
Refers to the operation method for the purpose of pressure control by increasing the surface temperature of the water vapor condenser to reduce its condensation capacity, resulting in an increase in the partial pressure of water vapor in the drying box.
3. Small butterfly valve control method
The purpose of pressure control in the box is achieved by intermittently opening or closing the valve between the water vapor condenser and the vacuum pump. The small butterfly valve control method controls the opening and closing of the valve by the signal sent from the control system. When the pressure is higher than the set value (that is, the vacuum degree is too low), the valve is opened; when the pressure is lower than the set value (that is, the vacuum degree is too low) high), close the valve. However, if the temperature of the condenser is very low at this time, the temperature of the product shelf is also very low. Due to the slowing down of the sublimation speed, the partial pressure of water vapor continues to decrease. At this time, the pressure in the pilot freeze dryer is lower than the set value However, since this method cannot increase the indoor pressure, the purpose of adjusting the pressure cannot be achieved.
4. Aeration method
The operation method of introducing sterile air or nitrogen into the drying box by controlling the air intake through the micro-control valve. This method is commonly used in actual production, but it also has certain defects:
①Since the introduction of mostly non-condensable gas (air or nitrogen), the existence of this gas reduces the effective condensation area of the condenser, which makes the condenser prone to ice blockage, and the introduction of nitrogen will also increase the cost.
②Because the gas is introduced from the outside, the cleanliness of the gas directly determines the quality of the product, which is easy to cause pollution and cause the product to have hidden dangers in quality and safety.
③With the alternation of air aeration and high vacuum, the products with a lighter texture and less filling volume are constantly reciprocating up and down. During this process, the friction between the product and the bottle wall makes the formed product into powder. And being taken away not only affects the loading and content of the product but also affects the appearance of the product.
④Due to the direct introduction of gas from the filling room, the normal fumigation and disinfection work in the clean area cannot be carried out, and there are two identical ones that cannot be accelerated, thus hindering the production progress. Although the above methods can achieve the purpose of pressure control, they all have various disadvantages. The degree of vacuum is directly determined by the vacuum pump, so it is recommended to start with the vacuum pump, study the variable frequency vacuum pump, and then automatically control the switch and running speed of the pump through the indoor pressure, so as to fundamentally solve the problem of pressure control. At the same time, due to the power of the vacuum pump being Smaller, it can also save energy.
