With the development of science and technology, the use of vacuum technology in the food industry is becoming more widespread. 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, etc., and various new processes and methods closely related to vacuum technology. New technologies and new equipment show their unique advantages and features.
The term "vacuum" is translated from the Latin vacuo, and its meaning is nothingness. In fact, vacuum should be understood as a space where gas is thin. In a given space, the state of the gas below one atmospheric pressure is collectively referred to as vacuum. The degree of gas thinness in a vacuum state is called a degree of vacuum, and is usually expressed by a pressure value.
According to the national standard GB3163 formulated by China, the vacuum area is roughly divided as follows:
Low vacuum area 105~102Pa (760~1torr)
Medium vacuum area 102~10-1Pa (1~10-3torr)
High vacuum area 10-1~10-5Pa (10-3~10-7torr)
Ultra-high vacuum area <10-5Pa (<10-7torr)
At present, the application of vacuum technology in the grain industry is mainly concentrated in the middle and low vacuum areas. It is reflected in a series of production activities such as grain clearing, drying, storage, transportation and processing after grain production, which is conducive to increasing the effective output of grain, improving or protecting food quality and improving system treatment efficiency.
2, vacuum handling
The work is done by the force generated by the pressure difference between the vacuum and the atmospheric space. Due to the uniformity of pressure in this kind of mechanical energy, these vacuum equipments are used more in the grain, flour and feed industries. The vacuum air pump (vacuumpumps) installed at the end of the conveying system is used to suck the air in the system to form a subatmospheric negative pressure airflow in the conveying pipe, and the material enters the pipeline from the starting nozzle together with the atmosphere, and the airflow is sent to the end separator. The material particles are separated from the gas flow by gravity or centrifugal force, and the gas is dedusted and discharged into the atmosphere through a vacuum pump or a centrifugal fan, which is green and environmentally friendly.
Vacuum conveying equipment is mainly used for grain handling in the grain industry. It can be placed at the port, dock, silo or bulk material storage point, pumping the material up and feeding it to the receiving point such as silo, for ships carrying bulk materials. Vehicles, etc., do not need special modification, and are ideal equipment for conveying bulk materials in food and pellet systems. It can realize long-distance vertical transportation and is easy to operate. The performance of the whole machine is reliable, dust-free operation, small loss of loading and unloading transmission materials, and high work efficiency. The utility model has the advantages of small volume, light weight, simple and compact structure, easy installation, low noise, no vibration and convenient maintenance. The use of negative pressure conveying method for handling and handling can improve the working environment of various food facilities, reduce the wear and tear on the equipment caused by dust, protect the operator from dust damage to the body, prevent the occurrence of dust explosion, and reduce the surrounding environment. Dust pollution. It has enormous social and environmental benefits.
As early as 1958, Shanghai Port and Changsha began to test the use of vacuum grain absorbing machines to lift food from ships. Taking the food industry sector as an example, more than 1,000 flour mills in China use vacuum transport, and the vacuum transport used in the port has reached 200 tons/h. As a new delivery technology, vacuum delivery is expected to be further developed in areas where it can be adapted.
Vacuum conveying has the following characteristics:
1 The equipment has simple structure, is convenient to manufacture, process and install, has low control cost and short construction time. The main components of the vacuum conveying system are the welded structure of the steel plate. It consists of tubes and cans. The relative movement and maintenance between the components are relatively easy. If some control equipment is installed, it is easy to automate. .
2 The conveying efficiency is high, and the equipment has no backhaul transportation. Other transportation vehicles have the disadvantages that the transportation means have a return of empty space, and the transportation medium for vacuum transportation is air, and only needs to be discharged into the atmosphere at the terminal. During the transportation process, the feeding port can be continuously fed to realize continuous transportation.
3 The sanitary conditions are good. When the vacuum is delivered, the material runs in the tube, the tube is under negative pressure, the dust will not leak and fly, and the material will not fly and pollute the environment. In the transportation process, intermediate processing such as sorting and drying can also be performed. If the material is transported under negative pressure, because the water is easy to evaporate under negative pressure, even if other drying means are not used, the material with higher moisture will have a certain drying effect during the transportation process, and the weight of the material particles will be different. The material can be sorted by designing an appropriate material port.
4 In addition, the vacuum conveying pipeline facilitates the installation of the pipe network according to local conditions, and the arrangement is simple and flexible, which can make full use of the site area and is easy to adapt to the working environment.
The main problem of vacuum transportation 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 material to be sucked. It is not suitable for conveying cohesive and adhesive materials. It is not necessary to input charged powder. The whole system should be airtight, and it is more difficult to do this completely. Whether it is appropriate to use vacuum transportation requires a comprehensive consideration of economic benefits.