There are many kinds of vacuum drying equipment, which are widely applied and developed rapidly. The development of several vacuum drying equipment at home and abroad is expounded in this paper in order to realize the exchange of information, find out the problems to be solved in the development of vacuum drying equipment, and improve the purpose of the vacuum drying equipment in China.
  Vacuum drying has many advantages: low oxygen content at low pressure can prevent dry material from oxidizing and deteriorating, and can dry inflammable and explosive dangerous goods. It can vaporize moisture in material at low temperature, easily dry heat sensitive material; can recover valuable and useful ingredients in dry material; can prevent dry material. The emission of toxic and harmful substances can become the "green" drying of environmental protection type. Therefore, the application of vacuum drying equipment is more and more extensive.
  The main disadvantage of vacuum drying is the need for a set of vacuum system which can pump steam, which makes the investment cost of the equipment high, the operation cost is high, the production efficiency of the equipment is low, and the output is small. In order to overcome these shortcomings, many scientific and technological workers have made many efforts. At the same time, because vacuum drying has many advantages, some products have to use vacuum drying equipment. Therefore, the development of vacuum drying equipment will have a bright future.
1．Unbalanced development of continuous vacuum drying equipment at home and abroad
  In order to improve the output of equipment and ensure the quality of products, a variety of continuous vacuum drying equipment was developed abroad ten years ago. But in China, the development of technology and people's knowledge is slow.
1）Continuous vacuum drying equipment with belt type
  The WL-VAQ type continuous vacuum drying equipment produced in Japan's Japan sakaka production is suitable for liquid materials, mud like, paste paste and high viscosity and boring drying. The BV-100.5 type vacuum strip continuous drying device in the original plant of Da Chuan, Japan, uses steam and conduction heating. The temperature of each section is adjustable, and the tightness and speed of the conveyor belt are adjustable. Buck GAD, Switzerland, has developed a series of belt type continuous vacuum drying equipment with automatic cleaning device.
  Since 1995, we have been engaged in the design, manufacture, installation and service of belt type continuous vacuum drying equipment, and the technology is relatively mature.
  The domestic continuous vacuum drying equipment is rarely seen. In 2004, the Institute of Agricultural Sciences in Guangdong province developed a small test equipment for the drying of banana powder, and the effect was very good.
2）Continuous vacuum drying equipment for grain
  Grain drying is very large and continuous drying equipment must be used. Many grain drying equipments have been developed all over the world before, but vacuum drying is often used in seed drying because of the high cost of vacuum drying. In fact, this is a misunderstanding, according to the Zhengzhou food science research and Design Institute Hsiang senior engineer introduced, they developed a continuous corn vacuum drying equipment, production capacity of 60t/d, fixed investment is slightly higher than hot air drying, operation costs and hot air drying is flat. The total cost of vacuum drying at low temperature is not higher than that of hot air drying if the quality of drying products, breakage rate and waist burst rate are considered.
 
3）Continuous vacuum freeze-drying equipment
  Food raw materials are abundant, and the products that need freeze drying are very large. Therefore, continuous food freeze-drying equipment appeared earlier. In 1985, the Danish ATLAS company produced a CONRAD - 800 continuous freeze-drying equipment for the production of freeze-dried coffee with a production capacity of 13T per day. Figure 2 is a schematic map of the equipment. Figure 3 is a continuous freeze-drying machine produced in Germany.
 The first continuous vacuum freeze-drying equipment made in China was successfully developed by Shenyang Refrigeration Technology Research Institute in 2000. A rectangular structure is used in the vacuum chamber. An isolator is set between the barn and the drying chamber. The automatic weighing system is set in the barn, which can determine the drying rate of the frozen dried food, the amount of water and the final degree of drying. Two external water traps work alternately to achieve continuous water capture and ice melting.
  There is a big gap between domestic and international sales of continuous freeze drying equipment. The Danish ATLAS company sold 18 continuous freeze-drying equipment from 1985 to 1990, of which 1 units were purchased in Taiwan in China, and the provinces and cities in mainland China have not imported this equipment so far. Only 1 domestic equipment have not been sold yet.
2．The variety of vacuum drying equipment at home and abroad is increasing
  Various new vacuum drying equipments have been developed for different purposes.
1）Microwave vacuum drying equipment saves energy and improves drying rate.
2）The combination of spray freeze drying and freeze-drying is determined by the properties of the material and the production of the products. The material must be liquid slurry, which is frozen by spray to form micro and nanoscale particles, increasing the drying rate and improving the production of the products.
3）Vacuum vapour phase drying equipment is specially used for large oil immersed transformers and other similar electrical equipment drying equipment. Switzerland developed this product in 1970s. This kind of equipment was introduced in China in the 1980s. After the 1990s, it has basically completed the introduction and digestion. Now it can be produced in a complete set.
4）In order to meet the needs of schools and scientific research institutes, several kinds of freeze-drying equipment with different functions have been developed at home and abroad. Figure 4~7 is a small freeze-drying machine manufactured by Martinchrist company in Germany. It is small in size, light in weight and has many functions. Basically, it can meet the freeze-drying experiments of various materials. Several manufacturers, such as the Fourth Factory of Haimen Light Industry Machinery, have begun to digest, absorb and import designs in China, and have developed new products, but the performance is not stable enough.
Single cavity system
  Under sterile conditions, pre freezing and drying are carried out in the condensing chamber.
Double cavity system
  Pre freezing is carried out in a low temperature refrigerator or freezer, drying in a drying chamber above the condensing chamber.
5）Freeze dry separation type medical freeze-drying machine
  Food freeze-dryers are carried out separately by freezing and drying to save energy, time and increase production. Traditional medicine freeze-drying machine is frozen and dried in the machine once completed. Western European and American companies freeze medicines in advance for the same purpose as freeze-drying and then send them to dryers for drying. Figure 8 shows a photo of a continuous drug prefreeze equipment.
3．The function of the vacuum drying equipment is increasing
  The function of vacuum drying equipment is increasing. With the development of electronics and computer technology, the control system and display function of vacuum drying equipment are generally increased. The corn vacuum drying equipment developed by the Zhengzhou Academy of grain science has the function of automatic control and simulation screen display; the vacuum freeze drying machine produced by Shanghai East Fulong and Beijing tachyoriginal has the freeze-drying end point judgment, the design of freeze-drying curve, the operation condition, the storage of multiple freeze-drying curves, the printing of production information and many other functions.
  The vacuum drying equipment abroad has more functions, most of which have mechanical hands, and can be sampled in the drying process; some rotary types of vacuum drying equipment have the function of crushing and granulation, and the medicine freeze-drying equipment can also be granulated.
4．Some views on the development of vacuum drying equipment
1)Innovation is the fundamental way to develop vacuum drying equipment
  At present, the development of vacuum drying equipment is relatively slow. One important reason is that the vacuum drying equipment imitates each other, hovers in the same technical level and lacks innovation. The ability of imitation is strong, the speed is fast, the idea of innovation is poor, and the investment is few. The focus of competition is on grabbing the market, pulling ties and price wars. A better way is to put some effort into quality and after-sales service. But these are not good ways to develop vacuum drying equipment. We must invest in manpower, material resources and financial resources to innovate.
2)Energy saving is the key to the development of vacuum drying equipment
  Energy shortage has attracted worldwide attention. Traditionally, vacuum drying equipment is considered to have high energy consumption because it needs vacuum pumps. But no real energy consumption has been seen when drying the same material to the same wet content. In fact, vacuum drying is low temperature drying in enclosed space, and energy waste is relatively less. Nevertheless, the energy saving of vacuum drying equipment is still the key to development. Compared with other types of drying equipment, the energy saving of vacuum drying equipment should focus on the rational design, selection and use of vacuum system.
 There are not many vacuum systems for pumping steam. There are two main types of vacuum systems, one is the pump that can pump water directly, mainly water jet pump, steam jet pump, water ring pump and wet roots pump, and the other is to use condensing method to catch water. The energy consumption of these two methods is high. The direction of the former type of energy saving should be to improve the pumping efficiency of the pump; the direction of the latter type of energy saving is to design the structure and thermal efficiency of the gas solid phase transform heat exchanger.
3)Continuous vacuum drying equipment is an important way to increase the output of products and save energy.
  Compared with the periodic vacuum drying equipment, the continuous vacuum drying equipment has less auxiliary time, saves time and improves production. At the same time, he does not have to produce a cycle like periodic vacuum drying equipment, and the temperature of the equipment changes once, causing some energy to be wasted on the repeated heating of the equipment components. Thus, energy is saved.
4)The combination of vacuum drying equipment and other drying methods is a mode of production that should be advocated.
 The combination of vacuum drying and other drying methods can increase production efficiency and reduce product cost. For example, the products such as vegetables, aquatic products and fruits, and other products, vacuum drying can guarantee the quality of the product. If before the vacuum drying, after the cleaning and blanching, the surface water is removed by centrifugal dehydration, the cold air drying is removed, and then sent into the vacuum drying equipment, the high production efficiency can be achieved and the production can be reduced. Ben. The combination of spray and freeze-drying is also one of the combination methods. This kind of similar combination can be found through experiments, of course, it takes a certain amount of time, energy and financial resources.
5．Concluding remarks
  Vacuum drying equipment is constantly innovating. There are still many problems. If production, learning and research work closely, the effect will be even more significant.