Grain drying technology is one of the important processing technology for the storage and preservation of agriculture, grain drying equipment is an important part of achieving full mechanization of food production. According to statistics, China's grain harvest in threshing, drying, storage, transport and process the loss of up to 15%, far more than 5% of the standard provisions of the Food and Agriculture Organization of the United Nations. Food each year because of the climate is humid, wet valley too late to dried or do not meet the safety moisture causing mildew, germination losses up to 5%, and an annual output of 500 million tons of grain, equivalent to the loss of 25 million tons of grain. Shows that the importance of food crops drying technology applications in agriculture. Since the seventies in China, and actively carry out trials and studies of grain drying equipment the recent drying technology is more and more used in agriculture. Grain drying equipment the relatively common in the United States, the Commonwealth of Independent States, Japan and other countries. The main models in the United States, small low-temperature drying warehouse and large, medium-sized high-temperature dryer, diesel and liquefied petroleum gas as a heat source, the use of direct heating and drying. Equipment in general has: level control, the wind temperature control and a the grain moisture control system. Japanese food drying equipment developed from the World War II, the major development is suitable for drying rice in small devices. Models: a small fixed bed grain dryer, in small circulating grain dryer and large grain dryer. The heat source used in diesel and kerosene, and a small amount of a rice husk as fuel. Drying equipment, mostly equipped with automatic control system. The development of China's grain drying equipment machinery imitation Japan, the Soviet Union and other foreign grain dryer from the early days of liberation began. Due to the complex structure, the consumption of steel, high cost, was not suitable for rural economic and institutional situation, been applied only in large farms and grain storage. 1970s, Guangdong Province Agricultural research units are suited to China began to develop small and medium sized drying models, Guangdong Province Agricultural successfully developed using direct heating stacked dryer; 1980s, China's rural economic system reform drying machinery developed mostly multi-purpose, and the miniaturization direction. In 1981, organized by the Ministry of Agriculture, Nanjing Agricultural Mechanization where Subei comparative test of 13 models of grain drying equipment production, initially recommended a number of models. Closely associated with dry mechanical dry heat source has also made progress in the meantime, have successfully developed a thermal gas furnace, the LHV gasification furnace, rice husk gas furnace, solid fuel gas furnaces, tube stove , liquefied gas stove and solar drying device.
Since the 1990s, with the in-depth development of the rural reform, China's rural economy and agricultural productivity faster development, specialization, the intensive scale operation also has a new development. Especially large state-owned farms, grain storage, seed and grain production base, gradually equipment from the set of grain drying equipment, supporting Jackie Chan and warehousing, processing facilities, the main application on behalf of China's grain drying machinery. There has also been a lot of grain drying equipment, specialized production factory, the emergence of many new results. 1996, Taiwan and foreign seed dedicated dryer and Universal Dryer also enter the Chinese market, and led the southern rice-producing areas dry mechanization technology development. These grain drying equipment, despite high prices, but because of the use of a good performance, reliability, high degree of automation, attentive service, and still be welcomed by farmers, market prospects. At present, such as Jiangsu, Zhejiang, Guangdong and other grain drying equipment ownership has reached 1,000 units. With the development of science and technology, has appeared in the hot air, steam, electricity, heating and food drying method, to solve some problems, but because of their need to slow the Soviet Union and a long time after the dry food quality decreased significantly, and it is difficult to control, drying process and equipment requirements, and increase the cost of grain drying. The microwave is a high-frequency electromagnetic waves 7O's from the 20th century, China began to carry out the microwave technology research and development in the field of gold, chemicals, food processing, drying, preservation and pellet packing machine , drying of agricultural products, sterilization insecticidal has been a wide range of applications, the use of microwave drying food not only greatly shorten the drying time and improve processing quality and eating quality grain drying, lower food costs. Therefore, the microwave technology has broad application prospects in grain drying. Vacuum microwave food drying equipment is a new microwave microwave energy combined with vacuum technology applications, it is a series of advantages of both the microwave and vacuum grain drying equipment, to overcome the conventional vacuum grain drying equipment cycle, low efficiency shortcomings, with high yield, good quality, processing, and low cost, the vacuum microwave food drying equipment equipment is a set of electronics, vacuum science, mechanics, thermodynamics, programmed learning and other disciplines as one high-tech products, the physical changes of matter in the grain drying process, based on in-depth study of the internal and external heat and mass transfer and moisture migration process under vacuum conditions, development of a new technology, new processes. Industrial mass production, many of the items can not be dried in high temperature conditions, such as pharmaceuticals, chemicals, nutritional food, as well as ginseng, velvet and other high-end Chinese herbal medicine materials, in order to ensure the quality of products, the sawdust dryer process must be less than 100 ℃ or under room temperature conditions, known pressure reduced, the boiling point of water is also reduced, as in a of atm (101.3kpa), the boiling point of water is 100 ° C, under 0.073 atm (7.37kpa), the bing point of water is 40 ℃. Under vacuum conditions, the heating of the objects to object internal moisture can be evaporated without heating state. Convective heat transfer due to air in the vacuum conditions difficult, only rely on the thermal conductivity of the way to provide heat to the material. Conventional vacuum grain drying equipment the heat transfer rate is slow, inefficient, and temperature control difficult. Microwave heating is a radiant heating, microwave and materials directly interact, and its inside and outside is heated at the same time without the need to transfer heat by convection or conduction, so the heating speed, high efficiency, the temperature control is easy.