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There are still many problems to be solved in the freeze dryers on the market. With the advancement and development of science and technology, these problems will be solved one by one. The function of the freeze dryer is to cool the material containing a large amount of water or other solvents in advance and freeze it into a solid, and then under a certain vacuum condition, the water or other solvents in it are directly sublimated from the solid in the form of vapor, and the material It is left in the ice shelf when it is frozen, and the material after the drying equipment has the same volume as before drying but is loose and porous, and has good rehydration.
Freeze dryer is mainly composed of control system, vacuum system, refrigeration system and circulation system. In addition to the above components, the pharmaceutical freeze dryer also has hydraulic system, in-place cleaning system and in-place sterilization system. As the key equipment in the production process of aseptic freeze-dried preparations, due to the particularity of drugs, relevant departments have made clear regulations on the materials and performance of freeze-drying machines. Although the current freeze dryer meets the production requirements, there are still some shortcomings in terms of economic benefits, product quality, and production operations. The most important point is that the vacuum is too high, which is not conducive to product sublimation.
In the freeze-drying process of the product, the vacuum degree of the environment has a direct influence on the length of the freeze-drying cycle. If the vacuum is too low, the sublimation rate will decrease significantly; if the vacuum is too high, the freeze-drying rate will decrease significantly due to poor heat convection conduction. Therefore, various methods must be adopted to control the pressure in order to achieve the best conditions for product drying. The main methods of pressure control are:
1. Separating valve control method
2. Water vapor condenser control
The water vapor condenser control method refers to an operation method that increases the temperature of the water vapor condenser surface to reduce the condensation capacity, resulting in an increase in the partial pressure of water vapor in the drying box, thereby achieving the purpose of pressure control.freeze dryers
3. Small butterfly valve control method
Small butterfly valve control method refers to the purpose of controlling the pressure in the tank by opening or closing the valve between the water vapor condenser and the vacuum pump intermittently. The small butterfly valve control method uses the signal from the control system to control the opening and closing of the valve. When the pressure is higher than the set value, the valve is opened; when the pressure is lower than the set value, the valve is closed. However, if the temperature of the condenser is very low at this time, the temperature of the product shelf is also very low. As the sublimation rate slows down, the partial pressure of water vapor continues to decrease. At this time, the indoor pressure of the freeze spray drying equipment is already lower than the set value. , But because this method cannot increase the indoor pressure, the purpose of adjusting the pressure cannot be achieved.
4. Aeration method.
