With the development of science and technology, vacuum technology is more and more widely used in the food industry. Vacuum technology is known as the sunrise industry in the 21st century. As a comprehensive interdisciplinary subject, it has a wide range of applications in transportation, environmental protection, drying, storage, processing, and other fields. Various new processes, new methods, New technologies, and new equipment have shown their unique advantages and characteristics.
At present, the application of vacuum technology in the grain industry is mainly reflected in a series of production activities such as cleaning, drying, storage, transportation, and processing of grain after production, which is conducive to increasing the effective output of grain, improving or protecting the quality of the grain, and improving the efficiency of the system processing.
Work is done using the force generated by the pressure difference between the vacuum and the atmospheric space. Because this mechanical energy has the characteristics of uniform pressure everywhere, this vacuum equipment is widely used in the grain, flour, and feed industries. The vacuum pump installed at the end of the conveying system is used to suck the air in the system so that a negative pressure airflow below atmospheric pressure is formed in the conveying pipe. , the material particles are separated from the airflow by gravity or centrifugal force, and the gas is discharged into the atmosphere through a vacuum pump or centrifugal fan after dust removal, which is green and environmentally friendly.
Vacuum conveying equipment is mainly used for grain loading and unloading in the grain industry. It can be placed in ports, wharves, silos or bulk material storage points to suck up the materials and send them to receiving points such as silos. , vehicles, etc. do not need special modification, it is an ideal equipment for the transportation of bulk materials in grain and other powder and granule systems. It can realize long-distance vertical transportation and is easy to operate. The whole machine has reliable performance, dust-free operation, small loss of loading and unloading materials, and high work efficiency. And small in size, lightweight, simple and compact structure, easy installation, low noise, no vibration, and easy maintenance. The use of negative pressure conveying to handle and transport can improve the working environment of various grain facilities, reduce the wear and tear of equipment due to dust, protect operators from dust damage to the body, prevent dust explosions, and reduce the impact on the surrounding environment. of dust pollution. It has huge social and environmental benefits.
Vacuum conveying has the following characteristics: ① The equipment is simple in structure, easy to manufacture, process, and install, with less control cost and short construction time. The main components of the vacuum conveying system are the welded structure of profiled steel plates, which are composed of components in the shape of pipes and tanks. The relative movement and maintenance operations between the components are relatively easy. If some control equipment is installed, it is easy to realize automatic operation. . ②The transportation efficiency is high, and the equipment has no return transportation. Other means of transport all have the disadvantage of empty-way return, and the transport medium of vacuum transport is air, which only needs to be discharged into the atmosphere at the terminal. During the transport process, the feed port can be continuously fed to achieve continuous transport. ③Good labor sanitation conditions, the material runs in the tube during vacuum conveying, the tube is under negative pressure, the dust will not leak out and fly, and the material will not scatter and pollute the environment. During the conveying process, intermediate treatments such as sorting and drying can also be performed. If the material is conveyed under negative pressure because the moisture is easy to evaporate under the negative pressure, even if other drying methods are not used, the material with high moisture will get a certain drying effect during the conveying process, and the difference in the weight of material particles will be used. , The material can be sorted by designing the appropriate reeling port. ④ In addition, the conveying pipeline of vacuum conveying is convenient to set up the pipeline network according to local conditions, the layout is simple and flexible, the site area can be fully utilized, and it is easy to adapt to the working environment.
The main problem with vacuum conveying is that the power consumption is large and the conveying distance is limited. There are certain requirements for the volume, shape, and physical properties of the suctioned materials. It is not suitable for conveying cohesive and sticky materials. It is forbidden to input charged powder. Whether it is appropriate to use vacuum conveying should be determined by comprehensively considering economic benefits.
In the process of grain entering and leaving the warehouse, dumping, production, and processing, especially in the process of grain transfer, the dust generated is large and the working environment is harsh. What is more serious is that a large amount of dust is very likely to produce a powder explosion, which will bring people's lives to life. And national property security has brought serious hidden dangers. In the modern production field of the grain industry, the requirements for dust are getting higher and higher. The cleanliness of the production environment is not only a necessary prerequisite to ensure the high quality of certain products, but also is of great significance to improving the production environment, protecting personal health, and avoiding secondary pollution.
The use of vacuum dust removal is green and environmentally friendly, which not only improves the working environment of various grain facilities, protects personal health, prevents dust leakage and dust explosions, but also reduces dust pollution to the surrounding environment. Vacuum dust removal has the characteristics of flexible layout, convenient use, high collection rate, wide effective collection range, and strong operation reliability. It can greatly reduce the labor intensity of workers and the harm of dust to the body while reducing secondary pollution.
Vacuum packaging is a packaging method in which items are put into an airtight container and vacuumed before the container is sealed so that there is basically no air in the sealed container. The vacuum packaging method is also called the decompression packaging method or the exhaust packaging method. This kind of packaging can prevent the water vapor from the outside from entering the packaging container, and can also prevent the moist air in the airtight moisture-proof packaging from condensing when the temperature drops. When using the vacuum packaging method, care should be taken to avoid an excessive vacuum.
General raw grains and grain-processed commodities can be vacuum-packed. Vacuum-packing can not only avoid or reduce the oxidation, discoloration, and staleness of grains but also inhibit the growth of certain molds and bacteria.
In addition to controlling the external temperature and sterility of vacuum packaging, it is more important to control the appropriate gas environment of the food to achieve the expected fresh-keeping purpose. The main methods are mechanical extrusion, straw degassing, and other methods. Either way, the air inside the bag is evacuated and then heat-sealed. Its main features are: reducing the oxygen content in the bag, inhibiting the growth and development of mold and bacteria, controlling the deterioration of grains, and achieving the purpose of freshness and quality preservation. In addition, vacuum packaging, can resist mechanical pressure and reduce vibration, which is beneficial to long-distance transportation and sales.
Vacuum storage technology is also called low-pressure storage and decompression storage. Vacuum storage is to use the method of air extraction and decompression. The air in the well-sealed grain pile is extracted by the air extraction device, and the oxygen concentration in the grain pile is reduced or even close to the anaerobic state and maintained for a long time to achieve storage. The purpose of food preservation, insecticide, and insect control. Different from modified atmosphere storage, decompression storage only changes the total content and density of air in the storage environment but does not change the air composition and combined ratio. Vacuum storage is essentially a pressure-controlled storage method. It is beneficial to inhibit the occurrence and spread of enzymes, bacteria, diseases, and insects.
Vacuum storage is to place the grain in a closed warehouse (container), and in the process of cooling, the air in the warehouse (container) is drawn out to decompress and reduce oxygen. It also reduces or basically disappears, creating favorable conditions for the long-term storage and preservation of grain. The decompression warehouse can simultaneously and continuously complete the process of vacuum pre-cooling and decompression refrigeration during normal operation, which reduces the storage process links; because the grain stored in the warehouse does not need air-tight packaging, it has a wide range of applications and has become a research hotspot for grain researchers.
The hard shell agricultural products (such as chestnuts, sunflower seeds, etc.) are rinsed and selected (mainly to pick out moldy and insect-infested raw materials) and then put into a vacuum shell blaster. Under vacuum conditions, wet materials with considerable moisture are When heated to a certain temperature, under the action of the vacuum pump, the material absorbs heat so that the moisture in the shell is continuously evaporated and removed, its toughness and strength are reduced, and the brittleness is greatly increased. The vacuum effect can also reduce the pressure outside the shell, and the inside of the shell will be in a relatively high-pressure state. While the shell will be heated and dried to generate stress and strain, the nut is also heated and the moisture inside is vaporized. The nut shrinks due to water loss, making it separate from the inner skin and the outer shell; because the moisture of the nut cannot be vaporized. Escape from the outer shell further increases the pressure inside the shell, and when it reaches a certain value, the outer shell and inner skin will burst.
The vacuum blasting processing technology is not only efficient but also hygienic. It is not only suitable for large-scale production but also can maintain the original shape, original color, and original flavor of the nut. Compared with the processing techniques such as grinding, rolling, and squeezing, the crushing and loss of the nut are greatly reduced. , the shell burst rate is more than 90%, which improves the product quality and has broad application value.
The vacuum drying process is to place the material to be dried in a closed drying room and use the vacuum system to vacuumize the material to be dried continuously at the same time so that the moisture inside the material diffuses to the surface through the pressure difference or concentration difference, and the water molecules are on the surface of the material. After obtaining enough kinetic energy, after overcoming the mutual attraction between molecules, it escapes to the low-pressure space of the vacuum chamber and is pumped away by the vacuum pump. Vacuum drying can easily recover useful and harmful substances, and can achieve good sealing. In the sense of environmental protection, some people call vacuum drying "green drying".
In the vacuum state, the boiling point of the material moisture is lowered and the vaporization process is accelerated, so it is especially suitable for materials that are sensitive to temperature and easily decomposed. Vacuum drying is mainly carried out in the low vacuum area. During the vaporization process of grain moisture, its boiling evaporation temperature is proportional to the environmental pressure. The high-moisture grains are placed in a closed drying cylinder to form and maintain a certain degree of vacuum, and at the same time, the grain in the drying cylinder is continuously heated. The moisture inside the grain is diffused to the surface through the pressure difference, and after being vaporized, it is evacuated by a vacuum pump, so that the high-moisture grain can be continuously dehydrated and dried under a vacuum and low-temperature state. Vacuum drying reduces the boiling evaporation temperature of water from 100 °C to below 40 °C. Since the evaporation temperature is lower than the gelatinization temperature of starch, it will not cause damage to the grain. It avoids the swelling and bursting of the grains, and can ensure the quality of the dried grains. It ensures that the original color, aroma, taste, nutritional content, and quality of the material remain basically unchanged after drying.
Vacuum freeze-drying technology is to make the material first freeze, and then heat up under vacuum conditions so that the ice sublimates to achieve the purpose of final drying. The heating methods used include infrared heating, microwave heating, etc. The heat provided should not only quickly sublime the ice, but also not damage the surface of the product. Vacuum freeze-drying technology can maintain the original color, aroma, taste, shape and nutritional components of the product, especially for the drying of heat-sensitive materials, it is a promising drying method for the production of green food.