Vacuum drying equipment is widely used in many fields, and has developed rapidly. The several vacuum drying equipment at home and abroad development dynamic carries on the elaboration, in order to achieve the exchange of information, to find out the problems to be solved in the development of the vacuum drying equipment, improve the level of vacuum drying equipment in China.
Keywords: vacuum drying; drying equipment; freeze drying
Vacuum drying has many advantages: drying under low pressure, low oxygen content, can prevent dry material oxidative deterioration, drying the inflammable and explosive dangerous goods; material in the water vaporization under low temperature, easy to dry heat sensitive materials; can be recycled material drying in the valuable and useful ingredients; can prevent dry materials, toxic and harmful substances in emissions, can become a environmental protection type "green" drying. Therefore, the application of vacuum drying equipment has become increasingly widespread.
Vacuum drying main disadvantage is the need a capable of pumping the vacuum system of steam, the equipment investment cost is high, the high cost of running; low efficiency of production equipment, production of small. In order to overcome these shortcomings, many scientific and technological workers have made a lot of efforts. At the same time, because there are many advantages of vacuum drying, some products have to use vacuum drying equipment. Therefore, the development of vacuum drying equipment will be very promising.
1. The development of continuous vacuum drying equipment at home and abroad
In order to improve the production of equipment to ensure the quality of the products, in more than a decade ago foreign developed a variety of continuous vacuum drying equipment. But in the country by the technical level and people's understanding of the concept of restrictions, the development of relatively slow.
1) belt type continuous vacuum drying equipment
Japan Japan Osaka produced by the production WL-VAQ belt type vacuum continuous drying equipment, suitable for liquid material, slurry, paste sued concentration and high viscosity boring dry. Japan Okawa original plant production of BV-100.5 type vacuum belt continuous drying device, the use of steam and conduction heating, district temperature can be adjustable, belt tension and speed adjustable. The Swiss - Booher gaide company has developed a series of belt type continuous vacuum drying equipment with automatic cleaning device.
Began to engage in design, cinctured continuous vacuum drying equipment manufacture, installation and service from 1995, mature technology.
Domestic type continuous vacuum drying equipment does not see more, 2004 Guangdong Province agricultural scientific research developed successful small test equipment for banana powder dry, the effect is very good.
2）Continuous vacuum drying equipment Grain drying capacity is very large, must use continuous drying equipment. Before the world has developed a lot of grain drying equipment, and vacuum drying of grains used in the seed dry, the reason is that the cost of vacuum drying is too high. In fact this is a misunderstanding, according to Zhengzhou grain science research and Design Inst ho Cheung, senior engineer introduction, they developed the corn continuous vacuum drying equipment, production capacity 60t/d, fixed investment slightly higher than hot air drying, operation cost and hot air drying flat. If the quality of the drying product is considered, the damage rate of the drying process and the waist rate of the drying process, the total cost of the vacuum drying at low temperature is not higher than that of the hot air drying.
3）Continuous vacuum freeze drying equipment Rich food raw materials, the need for a large quantity of freeze-dried products. Therefore, the continuous food freeze drying equipment appears earlier. Denmark ATLAS company in 1985 on the production of CONRAD - 800 continuous freeze drying equipment, used for freeze dried coffee production, production capacity of 13T per day, figure 2 is a schematic diagram of the device. Figure 3 is a continuous freeze drying machine made in Germany.
The first vacuum freeze drying equipment made in China was successfully developed in 2000 by the Shenyang Institute of refrigeration technology. Vacuum chamber with rectangular structure, import and isolation piece is arranged between the silo and dry warehouse, import and silo are equipped with automatic weighing system, can judge the drying rate freeze dry food, water and final drying. Two external water traps work alternately to achieve continuous water capture and melting of ice.
Sales gap between domestic and foreign continuous freeze drying equipment. Denmark atlas company from 1985 to 1990 5 years sales of 18 sets of continuous freeze drying equipment, which our country Taiwan to buy one, and the mainland provinces and cities has not introduced the equipment, only one domestic equipment has yet to sell.
2．The variety of vacuum drying equipment is increasing at home and abroad.
For different purposes, various new types of vacuum drying equipment were developed.
1) Microwave vacuum drying equipment, energy saving, improve the drying rate.
2) Spray freeze drying equipment spray and freeze drying combination is determined by the properties of the materials and the product yield, essential material is liquid slurry, by spray freeze after the formation of micro / nano scale particles and increased the drying rate, improve product yield.
3) Vacuum vapor phase drying equipment is designed for large oil immersed transformers and other electrical equipment drying device. Switzerland developed this product in 1970s. Our country introduced this kind of equipment in 1980s, after 90s has been basically completed the introduction of digestion, and now can complete sets of production.
4) In order to meet the needs of the school and scientific research units, a small experiment with freeze drying equipment has been developed at home and abroad for several different functions. Figure 4~7 is the German Martinchrist company production of several small-scale experiments with the freeze drying machine, its small size, light weight, multiple functions. Basically can meet the freeze drying experiment of various materials. The country has a few Haimen Light Industry Machinery Factory and other manufacturers began to digestion and absorption, the introduction of design and develop new products, but performance is still not stable enough.
Single chamber system
Under aseptic conditions, the pre freezing and drying were carried out in the condensation chamber.M
Dual chamber system
The pre freezing is carried out in a low temperature refrigerator or freezer, and the drying chamber is carried out on the top of the condensing chamber.
5) freeze dry separation type freeze drying machine for medicine
Food freeze drying machine for is frozen and dried separately, to achieve energy conservation, save time, increase the yield. Traditional Chinese medicine is frozen and dried in a machine. Some companies in Western Europe and the United States, for the purpose of achieving the same freezing and drying of food, the drugs in advance, and then sent to dry. Figure 8 shows a picture of a continuous pharmaceutical 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 are generally increased. Zhengzhou Grain Science Research Institute, has developed a corn vacuum drying equipment with automatic control and simulation screen display function; Shanghai tofflon, Beijing speed and other manufacturers of vacuum freeze a freeze-dried endpoint determination, design freeze drying curve, view the operation status, storage a plurality of freeze-drying curve, print production information for multiple functions.
Foreign vacuum drying equipment function more, most of the manipulator, in the drying process can sampling test; some type of rotation vacuum drying equipment with the functions of smash and granulation; pharmaceutical freeze drying equipment to granulation.
4．Some views on the development of vacuum drying equipment
1) innovation is the fundamental way for the development of vacuum drying equipment
At present of vacuum drying equipment development is slow, one important reason is mutual imitation, hovering at the same level of technology, lack of innovation. Imitation of the ability of strong, fast, innovative ideas, less investment. The focus of the competition in the market to grab the market, pull relations, price war. A good point of practice is in the quality and after-sales service, the next few. But these are not a good way to develop vacuum drying equipment, must invest human, material and financial resources to innovation.
2) energy saving is the key to the development of vacuum drying equipmentEnergy shortage has been the world's attention and traditional concept that vacuum drying equipment of high energy consumption. The reason is that it needs a vacuum pump. But not seen for the same kind of material, dry to the same moisture content, the real energy consumption contrast. In fact, vacuum drying is a low temperature drying in the closed space, and the energy waste is relatively small. In spite of this, the vacuum drying equipment is still the key to the development of energy conservation. Compared with other types of drying equipment, vacuum drying equipment, the focus should be energy saving
The on a reasonable design, selection and use of vacuum system.
Pumping the vacuum system of steam is not a lot. At present, there are mainly two categories, a class is directly pumping steam pump, main water jet pump, steam jet pump, water ring pumps and wet roots pump; another kind is by way of condensation water catching. These two methods are relatively high energy consumption, the first type of energy saving direction should be to improve the pumping efficiency of the pump; after a type of energy saving direction is designed such as gas solid phase transformation of the structure and thermal efficiency of the heat exchanger.
3) continuous vacuum drying equipment is an important method to improve product yield, energy saving
Compared with the continuous vacuum drying equipment and the cycle type vacuum drying device, less auxiliary time, saving time and improve the yield. At the same time, he does not have to be like the cycle of vacuum drying equipment, each production cycle, equipment temperature changes once, causing some of the energy wasted in the repeated heating of the device components. Therefore, saving energy.
4) combined vacuum drying equipment and other drying methods should be promoted mode of production
Vacuum drying and other drying methods combined can improve production efficiency and reduce the cost of products. For example, vegetables, aquatic products and fruits products by vacuum drying can guarantee the quality of the products, if before the vacuum drying, cleaning, blanching after, centrifugal dewatering, and then cold dry removal of the surface water is then fed into vacuum drying equipment, will be able to achieve significantly higher production efficiency, while reducing the production cost. The combination of spray and freeze drying is one of the combination methods. This similar
Combination, through the test, find many, of course also want to spend some time, energy and money.
5．Concluding remarks Vacuum drying equipment in continuous innovation.
There are still a lot of problems, if production, learning, research can work closely together, the results will be more significant.