There are many types of vacuum drying equipment, with a wide range of applications and rapid development. This article only elaborates on the domestic and international development trends of several types of vacuum drying equipment, in order to exchange information, identify the difficulties that need to be solved in the development of vacuum drying equipment, and improve the level of vacuum drying equipment in China.
Keywords: vacuum drying; Drying equipment; freeze drying
Vacuum drying has many advantages: low oxygen content when drying under low pressure, which can prevent the dried material from oxidizing and deteriorating, and can dry flammable and explosive dangerous goods; It can vaporize the moisture in the material at low temperatures, making it easy to dry heat sensitive materials; Can recover valuable and useful components from dried materials; It can prevent the discharge of toxic and harmful substances in dried materials, and can become an environmentally friendly type of "green" drying. Therefore, the application of vacuum drying equipment is becoming increasingly widespread.
The main disadvantage of vacuum drying is the need for a vacuum system capable of pumping steam, which results in high equipment investment and operating costs; The equipment has low production efficiency and small output. To overcome these shortcomings, many technology workers have made many efforts. Meanwhile, due to the many advantages of vacuum drying, some products have to use vacuum drying equipment. Therefore, the development of vacuum drying equipment will have great prospects.
1. Uneven development of continuous vacuum drying equipment at home and abroad
In order to increase equipment output and ensure product quality, various continuous vacuum drying equipment were developed abroad more than a decade ago. However, due to the limitations of technological level and people's cognitive concepts in China, the development is relatively slow.
1) Belt type continuous vacuum drying equipment
The WL-VAQ belt type continuous vacuum drying equipment produced by Nippon Nippon Manufacturing Company is suitable for drying liquid materials, slurries, paste with high concentration and high viscosity. The BV-100.5 vacuum belt continuous drying device produced by Japan's Okawa Original Plant adopts steam and conduction heating, with adjustable temperature in each section and adjustable conveyor belt tension and speed. Swiss company Buchner Gerd has developed a series of belt type continuous vacuum drying equipment with automatic cleaning devices.
I have been engaged in the design, manufacturing, installation, and service of belt continuous vacuum drying equipment since 1995, and the technology is relatively mature.
Domestic belt type continuous vacuum drying equipment is not common. In 2004, the Guangdong Agricultural Science Research Institute successfully developed a small-scale experimental equipment for drying banana powder, which achieved good results.
2) Continuous vacuum drying equipment for grains
The drying capacity of grains is large, and continuous drying equipment must be used. Previously, many countries around the world had developed grain drying equipment, and vacuum drying of grains was mostly used for seed drying due to the high cost of vacuum drying. In fact, this is a misconception. According to Senior Engineer He Xiang from Zhengzhou Grain Science Research and Design Institute, their continuous corn vacuum drying equipment has a production capacity of 60t/d, a fixed investment slightly higher than hot air drying, and operating costs are on par with hot air drying. If we consider the quality of the dried product, the damage rate during the drying process, and the burst rate, the total cost of vacuum drying at low temperatures is not higher than that of hot air drying.
3) Continuous vacuum freeze-drying equipment
Food ingredients are abundant, and there is a large production of products that require freeze-drying. Therefore, continuous food freeze-drying equipment appeared earlier. ATLAS, a Danish company, produced the CONRAD-800 continuous freeze-drying equipment in 1985 for the production of freeze-dried coffee, with a production capacity of 13 tons per day. Figure 2 is a schematic diagram of this equipment. Figure 3 shows a continuous freeze-drying machine produced in Germany.
The first domestically produced continuous vacuum freeze-drying equipment was successfully developed by Shenyang Refrigeration Technology Research Institute in 2000. The vacuum chamber adopts a rectangular structure, and there are isolation plates between the inlet and outlet silos and the drying silo. Both the inlet and outlet silos are equipped with an automatic weighing system, which can determine the drying rate, water output, and final drying degree of freeze-dried food. Two external water traps work alternately to achieve continuous water harvesting and ice melting.
There is a significant difference in sales volume between domestic and international continuous freeze-drying equipment. Denmark's ATLAS company sold 18 continuous freeze-drying equipment from 1985 to 1990, of which one was purchased in Taiwan. However, mainland provinces and cities have not yet introduced this type of equipment, and only one domestically produced equipment has not been sold yet.
2. The variety of vacuum drying equipment both domestically and internationally is increasing
Various new and different vacuum drying equipment have been developed for different purposes.
1) Microwave vacuum drying equipment saves energy and improves drying rate.
2) Spray freeze-drying equipment The combination of spray and freeze-drying is determined by the nature of the material and the output of the product. The material must be liquid slurry. After being frozen by spray, it forms micro and nanoscale particles, which increases the drying rate and improves the output of the product.
3) Vacuum vapor drying equipment is a device specifically designed for drying large oil immersed transformers and other similar electrical equipment. Switzerland developed this product in the 1970s. China introduced this type of equipment in the 1980s, and after the 1990s, the introduction and digestion have been basically completed. Now, it can be produced as a complete set.
4) In order to meet the needs of schools and research institutions, several small experimental freeze-drying equipment with different functions have been developed both domestically and internationally. Figures 4 to 7 show several small experimental freeze-drying machines produced by Martin Krist in Germany, which have small volume, light weight, and multiple functions. Basically, it can meet the freeze-drying experiments of various materials. Several domestic manufacturers, including Haimen Light Industry Machinery Factory No. 4, have started to digest and absorb, introduce designs, and develop new products, but their performance is not yet stable enough.
Single cavity system
Under sterile conditions, both pre freezing and drying are carried out in the condensation chamber.
Dual cavity system
Pre freezing is carried out in a low-temperature refrigerator or rotary freezer, and drying is carried out in a drying chamber above the condensation chamber.
5) Freeze drying separation type pharmaceutical freeze-drying machine
Food freeze-drying machines are designed to separate freezing and drying processes, in order to save energy, time, and increase production. Traditional medical freeze-drying machines are used to freeze and dry in one go. Some companies in Western Europe and the United States, in order to achieve the same purpose as food freeze-drying, pre freeze drugs and then send them to dryers for drying. Figure 8 shows a photo of the continuous drug pre freezing equipment.
3. The functions of vacuum drying equipment are increasing
With the advancement of electronic and computer technology, the control system and display functions of vacuum drying equipment have generally increased. The corn vacuum drying equipment developed by Zhengzhou Grain Science Research Institute has automatic control and analog screen display functions; The vacuum freeze-drying machines produced by manufacturers such as Shanghai Dongfulong and Beijing Suyuan have various functions such as determining the end point of freeze-drying, designing freeze-drying curves, checking operating conditions, storing multiple freeze-drying curves, and printing production information.
Foreign vacuum drying equipment has more functions, most of which have robotic arms that can be used for sampling and testing during the drying process; Some rotary vacuum drying equipment has functions of crushing and granulation; Medical freeze-drying equipment can also be used for granulation.
4. Several opinions 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, and one important reason is mutual imitation, hovering at the same technological level, and lacking innovation. Strong imitation ability, fast speed, poor innovation concept, and low investment. I have focused my competitive energy on grabbing the market, building relationships, and engaging in price wars. A better approach is to put some effort into quality and after-sales service. But these are not good methods for developing vacuum drying equipment, and it is necessary to invest manpower, material resources, and financial resources to innovate.
2) Energy saving is the key to developing vacuum drying equipment
The energy shortage has attracted global attention, and traditional beliefs believe that vacuum drying equipment has high energy consumption because it requires the addition of a vacuum pump. But I haven't seen a real comparison of energy consumption for the same material when dried to the same moisture content. In fact, vacuum drying is low-temperature drying in enclosed spaces, with relatively less energy waste. Nevertheless, energy conservation in vacuum drying equipment remains the key to development. Compared with other types of drying equipment, the energy-saving focus of vacuum drying equipment should be on
It should be focused on rational design, selection, and use of vacuum systems.
There are not many vacuum systems that can pump steam, and currently there are mainly two categories. One is pumps that can directly pump steam, mainly including water jet pumps, water vapor jet pumps, water ring pumps, and wet Roots pumps; Another method is to capture water by condensation. Both of these methods consume relatively high energy, and the first type of energy-saving direction should be to improve the pumping efficiency of the pump; The latter type of energy-saving direction is to design the structure and thermal efficiency of gas-solid phase heat exchangers.
3) Continuous vacuum drying equipment is an important method to increase product yield and save energy
Compared with periodic vacuum drying equipment, continuous vacuum drying equipment has less auxiliary time, saves time, and improves production. At the same time, he does not need to produce each cycle like periodic vacuum drying equipment, where the temperature of the equipment changes once, resulting in some energy being wasted on the repeated heating of the equipment components. Therefore, energy is saved.
4) The combination of vacuum drying equipment and other drying methods should be advocated as a production method
The combination of vacuum drying and other drying methods can improve production efficiency and reduce product costs. For example, products such as vegetables, aquatic products, and fruits can be dried under vacuum to ensure product quality. If they are cleaned and blanched before vacuum drying, dehydrated by centrifugation, then dried with cold air to remove surface water, and then sent to vacuum drying equipment, significant improvements in production efficiency can be achieved while reducing production costs. The combination of spray and freeze drying is also one of the combination methods. This kind of similar
There are many combinations that can be found through experimentation, but it also requires a certain amount of time, effort, and financial resources.
5. Conclusion
Vacuum drying equipment is constantly innovating. There are still many existing problems, and if industry, academia, and research can work closely together, the results will be even more significant.
The information available is limited and the insights may not be accurate. Please feel free to correct.
