Development Trends of Vacuum Drying Equipment at Home and Abroad
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 problems 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: it has 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 thermosensitive materials; Capable of recovering valuable and useful components from dried materials; It can prevent the emission of toxic and harmful substances from dried materials and can become an environmentally friendly "green" drying method. 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 production efficiency of the equipment is low and the output is small. To overcome these shortcomings, many technology workers have made a lot of 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 both domestically and internationally
In order to improve 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 continuous vacuum drying equipment produced by Nippon Paint Co., Ltd. in Japan is suitable for drying liquid materials, slurries, pastes with high concentration and viscosity. The BV-100.5 vacuum belt continuous drying device produced by Ogawa Hara Co., Ltd. in Japan uses steam and conduction heating, with adjustable temperature in each section and adjustable tension and speed of the conveyor belt. Swiss company Bucher 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 type continuous vacuum drying equipment since 1995, and my technology is relatively mature.
There are not many domestically produced belt type continuous vacuum drying equipment. In 2004, Guangdong Agricultural Science Research Institute successfully developed a small-scale experimental equipment for drying banana powder, which had a good effect.
2) Grain continuous vacuum drying equipment
The amount of grain drying is large, and continuous drying equipment must be used. Many countries around the world have developed grain drying equipment in the past, and vacuum drying grains are mostly used for seed drying because the cost of vacuum drying is too high. In fact, this is a misconception. According to He Xiang, a senior engineer at Zhengzhou Grain Science Research and Design Institute, the continuous corn vacuum drying equipment they developed has a production capacity of 60t/d, with slightly higher fixed investment than hot air drying and operating costs on par with hot air drying. If considering the quality of the dried product, the damage rate and waist failure rate during the drying process, the total cost of vacuum drying at low temperatures is not higher than that of hot air drying.
3) Continuous vacuum freeze-drying equipment
The food ingredients are abundant, and the production of products that require freeze-drying is large. Therefore, continuous food freeze-drying equipment appeared earlier. The Danish company ATLAS produced the CONRAD-800 continuous freeze-drying equipment in 1985 for freeze-drying coffee production, with a production capacity of 13 tons per day. Figure 2 is a schematic diagram of the equipment. Figure 3 shows a continuous freeze dryer 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, with isolation plates between the inlet and outlet silos and the drying silo. Both inlet and outlet silos are equipped with automatic weighing systems, 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 capture and ice melting.
There is a significant gap in sales volume between domestic and international continuous freeze-drying equipment. From 1985 to 1990, Danish company ATLAS sold 18 units of continuous freeze-drying equipment, of which Taiwan purchased 1 unit. However, no provinces or cities in mainland China have yet introduced this type of equipment, and only 1 domestically produced equipment has not been sold.
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 is energy-saving 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 equipment in the 1980s, and after the 1990s, it has basically completed the introduction and digestion. Now it can be produced as a complete set.
4) In order to meet the needs of schools and research institutions, several types of small-scale experimental freeze-drying equipment with different functions have been developed both domestically and internationally. Figures 4-7 show several small experimental freeze-drying machines produced by Martinchrist company 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 4, have begun to digest, 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 dryer
Food freeze dryers are designed to separate freezing and drying processes in order to save energy, time, and increase production. Traditional pharmaceutical freeze-drying machines are all completed by freezing and drying in one machine. 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 a dryer 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 simulation screen display functions; The vacuum freeze dryers produced by manufacturers such as Shanghai Dongfulong and Beijing Suyuan have multiple functions, including 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 crushing and granulation functions; Pharmaceutical freeze-drying equipment can also pelletize.
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 slow, and one important reason is that they imitate each other and hover at the same technical level, lacking innovation. Strong ability to imitate, fast speed, poor innovation concept, and low investment. We have focused our 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 worldwide attention, and traditional beliefs believe that the energy consumption of vacuum drying equipment is high because it requires the addition of a vacuum pump. But I have never seen a true comparison of energy consumption for the same material when dried to the same moisture content. In fact, vacuum drying is a low-temperature drying process in a closed space, with relatively less energy waste. Nevertheless, energy efficiency of 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 the rational design, selection, and use of vacuum systems.
There are not many vacuum systems that can pump steam. Currently, there are two main types: one is pumps that can directly pump steam, mainly including water jet pumps, steam jet pumps, water ring pumps, and wet Roots pumps; Another method is to capture water by condensation. Both of these methods consume a relatively high amount of energy, and the first type of energy-saving direction should be to improve the pumping efficiency of the pump; The direction of the latter type of energy-saving is to design structures and thermal efficiency such as gas-solid phase shift heaters.
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 yield. At the same time, he does not have to waste some energy on the repeated heating of equipment components, as the temperature of the equipment changes once every production cycle, like periodic vacuum drying equipment. Therefore, it saves energy.
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 ensure product quality by using vacuum drying. If they are cleaned, blanched, centrifuged, dehydrated, and then dried with cold air to remove surface water before being sent to vacuum drying equipment, it can significantly improve production efficiency and reduce production costs. The combination of spray and freeze drying is also one of the combination methods. This similar combination method 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 problems that exist, and if industry, academia, and research can work closely together, the results will be even more significant.
The information consulted is limited, and the insights may not be accurate. Please feel free to correct me.
