Drying Technology Status and Development Trends in China (2)

Third, application
(a) Chemicals
The chemical industry has a large number of materials to process, and a large number of inorganic salts and organic materials have not only different characteristics, but also various types. Their traits vary greatly, and their quality requirements vary. In terms of morphology, there are solutions, suspensions, slurries, pastes, powders, granules, large pieces, fibers, unorganized materials, and the like; in terms of properties, there are loose and cohesive, resistant Hot and highly heat-sensitive, dehydrated when heated without deformation and easy to crack deformation; moisture in the material also has surface water, pore water and crystal water and other different forms of occurrence. In addition to complying with the most basic requirement for moisture content, the quality standard for dried products generally requires chemical, biochemical, and even electrical and magnetic properties to remain unchanged; many products have specific physical properties such as bulk density, particle size, and color. Requirements; some materials also require no deformation, breakage, etc. during the drying process. Due to these reasons, different types of materials require different technologies and equipment to solve their drying problems.
In chemical production, there are more than a dozen kinds of commonly used drying equipment, nearly 100 specifications. The commonly used types of dryers are: box type, tunnel type, belt type, airflow, spray, fluidized bed and vibrating fluidized bed, internal heating fluidized bed, fluidized bed spray granulation, rotary, drum, vacuum rake type There are also some organic combinations of two of these methods, vacuum double cone rotation, paddle type, flash evaporation, microwave and far infrared dryers.
After more than 30 years of development, most of the industrialized models of drying equipment can be processed in China, reversing the situation in which drying equipment simply relies on imports, and some equipment manufacturing levels have even reached the international advanced level. However, there is still a certain gap between China's drying technology in terms of basic theoretical research, processing quality, self-control level, experimental conditions and capabilities, research on special material drying processes, and large-scale equipment, complete sets, and standardization.
(b) Petrochemical
Petrochemical equipment is a complete set of equipment with advanced technology, great difficulty in development, complete sets, and high degree of correlation. It is a knowledge-intensive, technology-intensive and capital-intensive product.
Since the 1980s, great achievements have been made in the development of China's petrochemical major technological equipment and localization. The localization rate of oil refining equipment has reached more than 90%, and the localization rate of chemical equipment has reached about 70%. A number of major equipment The level of development has reached or approached the international advanced level, and the overall strength of the petrochemical equipment industry has also greatly improved.
The dryers widely used in the petrochemical industry include fluidized bed dryers (normal beds, vibrating beds, dual-mass vibrating beds, internal heating fluidized beds), flash dryers, paddle dryers, steam rotary dryers, and rotary dryers. Drum knot dryers, etc. Currently, many products in this industry have replaced imports.
(III) Pharmaceuticals
The extensive use of box-type drying ovens or hot-air circulating ovens from the 1960s, vacuum drying equipment in the 1980s, and boiling bed and spray drying, coating, and granulation equipment in the 1990s. Until the end of the 20th century, vacuum freeze dryers, microwave dryers in the country's own production, the pharmaceutical industry's drying equipment has basically met the requirements of the industry. In particular, the GMP certification of the pharmaceutical industry at the beginning of this century has promoted the development of medical equipment.
(d) Food
The lyophilized products under the freeze-drying technology can maintain the original shape, the original color, flavor and nutrient components, and have a long shelf life. Therefore, this technology is used in fruits and vegetables, condiments, sugars, solid beverages, bovine colostrum The range of applications for convenience foods, flavors, etc. is very wide.
Food freeze-drying equipment was born in Denmark in about 1943. Today, almost every industrially developed country in the world can produce food freeze dryers. Divided from the freeze-dried area, there are experimental lyophilizers as small as 0.1m2 and production freezers as large as 200m2; square, round, and tunnel-type in view of the shape of freeze-dried boxes; Manual, semi-automatic, and fully automatic; intermittent, semi-continuous, and continuous in terms of working methods; and in terms of freezing methods, they can be divided into two types: freeze-dried and freeze-dried, and freeze-dried ones. It is divided into several types, such as direct-cooling direct heating, direct-cooling interheating, inter-cooling direct heating and inter-cooling interheating. At present, the most influential food freeze-drying equipment manufacturers in the world are Danish Atlas Company and Japan Republic Vacuum Co., Ltd.
The future development direction of food freeze-drying technology is: to improve product quality and reduce product costs. The research direction of the freeze-drying process is the research of the best freeze-drying process curve and the inspection method of the freeze-dried product quality quality.
Drying of fruits and vegetables is a very active research direction. The dehydration of fruits and vegetables can reduce the moisture content, increase the concentration of soluble substances in raw materials, hinder the propagation of microorganisms, and inhibit the activity of enzymes contained in vegetables, so that the dehydrated vegetables can be stored at room temperature for a longer time, and are easy to transport and carry.
(5) Food
According to its structure and drying principle, grain dryers currently used in foreign countries are classified into forward-flow, cross-flow, mixed-flow, counter-flow, and internal-cycle mobile dryers.
In terms of drying mechanism and applied basic research, China Agricultural University, Northeast Agricultural College, South China Agricultural University, and Jiangsu University of Technology have done a lot of research work, and established experimental measurement devices such as grain thermal characteristics, moisture diffusion characteristics, and drying rates. The China Agricultural University took the lead in carrying out research on computer simulation of grain drying, which has enabled domestic drying technology research to continue to shorten the gap with the international advanced level.
(6) Timber
Industrialized common artificial wood drying methods include: conventional drying, high-temperature drying, desiccant drying, solar drying, vacuum drying, high-frequency drying, microwave drying, and smoke drying.
The development trend of wood drying technology is that conventional steam drying still dominates, and dehumidification, vacuum, microwave and high-frequency drying will show an increasing trend. Combination drying technology is still the focus of future development, such as dehumidification and microwave combined drying technology.
(The author is the Secretary-General and Deputy Secretary-General of the Drying Technology Professional Group of the Chemical Engineering Committee of the China Chemical Industry Society)