Vacuum drying technology is to freeze the material to the temperature below the eutectic point in advance, and create a vacuum space with a certain degree of vacuum, and then remove the moisture in the product through sublimation reaction. This drying technology is composed of three parts: refrigeration, heating and vacuum. Moreover, the products processed by vacuum drying technology can effectively prevent the impact of high temperature on food, and can effectively maintain the nutritional value and color taste of the products. Because of the low water content and good rehydration, the products are widely used in the industry. In recent years, the dry vacuum pump drying technology has been widely used in food, medicine, health products and other industries, and there are many high-value products such as sea cucumber, ginseng, scallop, etc. are exploring the use of dry vacuum pump drying technology for processing, effectively maintaining the quality of products.
In the process of application of dry vacuum pump in food processing industry, several important problems and technical directions should be paid attention to, and the technology of vacuum pump drying technology in product quality, drying rate and energy saving and emission reduction are described.
In the application of vacuum pump technology, the vacuum pump manufacturers think that the following issues need to be focused on;
1. Eutectic point and melting point of products
The eutectic point of the product refers to the temperature of the product material when the moisture in the product material is completely frozen. The pre freezing temperature of the vacuum drying technology should be set according to the eutectic point of the material. In order to make the product completely frozen, the pre freezing temperature of the product material is generally set 5-10 ℃ lower than its eutectic point. The co melting point of the product refers to the temperature at which the frozen product melts from the beginning of the ice crystal. Generally, when the food materials are dried, the heating temperature should not be higher than the co melting point of the product materials, otherwise it will directly affect the moisture content and quality of the freeze-dried products.
2. Microwave vacuum drying technology
Microwave vacuum drying technology is established by combining microwave radiation heating technology and vacuum freeze drying technology. This technology mainly uses the product materials which are frozen by microwave radiation to transform electromagnetic energy into heat energy, so that the moisture in the materials can be sublimed. This technology is mainly used in high value food industry due to the high cost of machinery and equipment.
3. Combination of freeze-drying and vacuum microwave drying
Vacuum microwave combines the advantages of vacuum environment and microwave drying, so that the product materials can be dried quickly. However, because the drying speed is too fast, the product materials may deform greatly, and the appearance quality of the product can not be guaranteed. Researchers combine freeze-drying and real space microwave drying, learn from each other, improve the product quality, and energy loss can be achieved Lower.
4. Setting adjustment vacuum
The energy consumption of vacuum degree accounts for about 1 / 4 of the total energy consumption of freeze-drying. The lower the vacuum degree is, the more effective the energy transfer is. At the same time, it increases the diffusion resistance of water vapor, thus increasing the energy consumption. In the process of sublimation drying, the best vacuum degree should be optimized according to the temperature of the cold well. The vacuum degree of the freeze dryer is determined by the temperature of the well and the performance of the vacuum pump. In the stage of sublimation drying, the lower the temperature of the cold well and the higher the vacuum degree can promote the condensation of water vapor and effectively promote the speed, but the high vacuum degree has special requirements for the vacuum pump. If the vacuum degree is too high, it will increase the ability to maintain the vacuum degree At this time, choose a good and suitable dry vacuum pump.