Development of vacuum drying equipment at home and abroad

There are many kinds of vacuum drying equipment, which are widely used and developed rapidly. In this paper, the development trends of several vacuum drying equipment at home and abroad are described 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 level of vacuum drying equipment in China.

Key words: vacuum drying; drying equipment; freeze drying

Vacuum drying has many advantages: low oxygen content in drying under low pressure can prevent the drying materials from oxidation and deterioration, and can dry inflammable and explosive dangerous goods; it can vaporize the moisture in the materials at low temperature, so it is easy to dry heat sensitive materials; it can recover valuable and useful components in the dried materials; it can prevent the discharge of toxic and harmful substances in the dried materials, so it can become an environmental protection class Type "green" drying. Therefore, vacuum drying equipment is widely used.

The main disadvantage of vacuum drying is that it needs a set of vacuum system which can pump steam, which makes the equipment investment cost high and the operation cost high; the equipment production efficiency is low and the output is small. In order to overcome these shortcomings, many scientific and technological workers have made a lot of 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. The development of continuous vacuum drying equipment at home and abroad is unbalanced

In order to improve the output of equipment and ensure the quality of products, many kinds of continuous vacuum drying equipment were developed abroad more than ten years ago. However, due to the limitation of technical level and people's cognition, the development is relatively slow in China.

1) Belt type continuous vacuum drying equipment

Wl-vaq belt type continuous vacuum drying equipment produced by Nippon Osaka Production Co., Ltd. is suitable for drying liquid materials, slurry, paste concentration and high viscosity boring. The bv-100.5 vacuum belt continuous drying device produced by Japan's Dachuan original plant adopts steam and conduction heating. The temperature of each section is adjustable, and the belt tension and speed are adjustable. A series of belt type continuous vacuum drying equipment with automatic cleaning device has been developed by Buch Gade company in Switzerland.

Since 1995, we have been engaged in the design, manufacture, installation and service of belt continuous vacuum drying equipment.

In 2004, Guangdong Institute of Agricultural Sciences successfully developed a small-scale experimental equipment for banana powder drying, and the effect was very good.

2) Continuous vacuum drying equipment for grain

Because of the large amount of grain drying, continuous drying equipment must be used. In the past, many grain drying equipments have been developed all over the world, and the vacuum drying grain is mostly used for seed drying because of the high cost of vacuum drying. In fact, this is a misunderstanding. According to He Xiang, a senior engineer of Zhengzhou grain science research and Design Institute, the continuous vacuum corn drying equipment developed by them has a production capacity of 60t / D, fixed investment is slightly higher than that of hot air drying, and the operating cost is equal to that of hot air drying. The total cost of vacuum drying at low temperature is not higher than that of hot air drying if the quality of drying products, damage rate and burst waist rate are considered.

3) Continuous vacuum freeze drying equipment

The production of freeze-dried food is very large. Therefore, continuous food freeze-drying equipment appeared earlier. Atlas company of Denmark has produced conrad-800 continuous freeze-drying equipment in 1985, which is used for the production of freeze-dried coffee. The production capacity is 13T per day. Figure 2 is the schematic diagram of the equipment. Figure 3 is a continuous freeze-drying machine made in Germany

The first domestic continuous vacuum freeze-drying equipment was successfully developed by Shenyang Institute of refrigeration technology in 2000. The vacuum chamber is of rectangular structure. There are isolation plates between the inlet and outlet bin and the drying bin. The automatic weighing system is set in the inlet and outlet silos, which can judge the drying rate, water output and final drying degree of freeze-dried food. Two external water traps work alternately to realize continuous water harvesting and ice melting.

There is a big gap in the sales volume of continuous freeze-drying equipment at home and abroad. Atlas company of Denmark has sold 18 sets of continuous freeze-drying equipment from 1985 to 1990, among which one was purchased by Taiwan in China. However, all provinces and cities in mainland China have not imported such equipment, and only one domestic equipment has not been sold.

2. The varieties of vacuum drying equipment at home and abroad are increasing

For different purposes, a variety of new vacuum drying equipment have been developed.

1) Microwave vacuum drying equipment can save energy and improve drying rate.

2) the combination of spray freeze drying equipment and freeze-drying is determined by the nature of the material and the output of the product. The material must be liquid slurry, and after spray freezing, the micro nano scale particles are formed, which increases the drying rate and improves the output of the product.

3) Vacuum vapor phase drying equipment is specially used for drying large oil immersed transformers and other similar electrical equipment. Switzerland developed this product in the 1970s. This kind of equipment was introduced into China in the 1980s. After 1990s, it has been basically completed and can be produced in complete sets.

4) In order to meet the needs of schools and scientific research institutions, several kinds of freeze-drying equipment with different functions have been developed at home and abroad. Figures 4 ~ 7 show several small experimental freeze-drying machines produced by German martinchrist company. They are small in size, light in weight and versatile in function. All kinds of freeze-drying materials can basically meet the requirements. Several domestic manufacturers, such as Haimen No.4 Light Industry Machinery Factory, have begun to digest, absorb, introduce design and develop new products, but the performance is not stable enough.

Single cavity system

Under aseptic condition, both pre freezing and drying were carried out in the condensation chamber.

Dual cavity system

Pre freezing is carried out in low temperature refrigerator or rotary freezer, and drying is carried out in the drying chamber above the condensation chamber.

5) Lyophilization separation type freeze-drying machine for medicine

In order to save energy, save time and improve output, freeze-drying machine is used to freeze and dry food separately. Traditional medicine lyophilizers are all freeze and dry in the machine once. Some companies in Western Europe and the United States, in order to achieve the same purpose as food freeze-drying, drugs are pre frozen and then sent to the dryer for drying. Figure 8 shows the photos of continuous drug pre freezing equipment.

3. The function of vacuum drying equipment is increasing

With the development of electronic and computer technology, the control system and display function of vacuum drying equipment have been increased. The corn vacuum drying equipment developed by Zhengzhou Academy of grain sciences has the functions of automatic control and simulation screen display; the vacuum freeze-drying machines produced by Shanghai dongfulong, Beijing Suyuan and other manufacturers have the functions of judging freeze-drying end point, designing freeze-drying curve, checking operation status, storing multiple freeze-drying curves, printing production information, etc.

Foreign vacuum drying equipment has more functions. Most of them have manipulators, which can be sampled and tested during the drying process; some rotary vacuum drying equipment has the function of crushing and granulation; the freeze-drying equipment for medicine can also granulation.
4. Some views on the development of vacuum drying equipment

1) Innovation is the fundamental way out for developing vacuum drying equipment

At present, the development of vacuum drying equipment is slow. One important reason is that they copy each other, hover at the same technical level and lack of innovation. The ability of imitation is strong, the speed is fast, the concept of innovation is poor, and the investment is less. The energy of competition is focused on seizing the market, pulling relations and price war. A better way is to put some effort into quality and after-sales service. But these are not good methods to develop vacuum drying equipment, we must invest human, material and financial resources to innovate.

2) Energy saving is the key to develop vacuum drying equipment

The energy shortage has been paid attention to all over the world. The traditional idea is that the energy consumption of vacuum drying equipment is high because it needs to add vacuum pump. However, there is no real energy consumption comparison for the same material when it is dried to the same moisture content. In fact, vacuum drying is a kind of low-temperature drying in closed space, which wastes less energy. However, the energy saving of vacuum drying equipment is still the key to development. Compared with other types of drying equipment, the key points of energy saving of vacuum drying equipment should be

The design, selection and use of vacuum system are discussed.

There are not many vacuum systems that can pump steam. At present, there are two main types: one is the pump that can directly pump steam, mainly including water jet pump, steam jet pump, water ring pump and wet roots pump; the other is to collect water by condensation. The energy consumption of these two methods is relatively high. The former energy-saving direction should be to improve the pumping efficiency of the pump; the latter is to design the structure and thermal efficiency of gas-solid phase heat exchanger.

3) Continuous vacuum drying equipment is an important method to improve the output of products 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, it does not have to be like the periodic vacuum drying equipment, the temperature of the equipment changes once every production cycle, resulting in part of the energy wasted on the repeated heating of equipment components. Therefore, energy is saved.

4) The combination of vacuum drying equipment and other drying methods should be advocated

The combination of vacuum drying and other drying methods can improve production efficiency and reduce product cost. For example, for vegetables, aquatic products, fruits and other products, vacuum drying can ensure product quality. If before vacuum drying, after cleaning and blanching, after centrifugation dehydration, and then cold air drying to remove surface water, and then sent to the vacuum drying equipment, the production efficiency can be significantly improved and the production cost can be reduced. The combination of spray and freeze-drying is also one of the combination methods. This kind of similar

Many combinations can be found through experiments. Of course, it also takes a certain amount of time, energy and financial resources.

5. Conclusion

Vacuum drying equipment is constantly innovated. There are still many problems. If the industry, University and Research Institute cooperate closely, the results will be more remarkable.

The information you have consulted is limited, and your opinions may not be accurate. Your comments are welcome.