Characteristics of drying technology

Drying equipment technology has a wide range of services. In the face of many industries, different physical and chemical properties of materials, product quality and other requirements, drying equipment technology is an interdisciplinary, interdisciplinary and experimental science technology.

Generally, there are three aspects of knowledge and technology in the development and application of drying technology. The first is to understand the physical and chemical properties of the dried materials and the use characteristics of the products. The second is to be familiar with the principles of transfer engineering, that is, mass transfer, heat transfer, hydrodynamics and aerodynamics. The third is to have the means of implementation, that is to be able to carry out the engineering design of drying process, main equipment, electrical instrument control, etc. Obviously, these three aspects of knowledge and technology do not belong to one discipline area. In practice, one of the three aspects of knowledge and technology is indispensable. So drying technology is a cross industry, interdisciplinary technology.

Although modern drying equipment technology has a history of more than 100 years, it still belongs to the category of experimental science. Most of the drying equipment technology is still lack of scientific theory and design methods that can accurately guide the practice. In practical application, relying on experience and small-scale test data to guide is still the main way. The reasons for this situation are as follows:

One of the reasons is that some basic disciplines of drying technology (mainly subject to the category of transfer engineering) have the characteristics of experimental science. For example, the research and development of aerodynamics need to be promoted by "wind tunnel" tests, which shows that it is not out of the scope of experimental science. The development level of these basic disciplines directly affects and determines the development level of drying technology.

The second reason is that many drying processes are the process of multi-disciplinary technology convergence, involving a wide range of variables, complex mechanism. For example, in the field of spray drying technology, the running track of droplets in the drying tower is the key to engineering design. The trajectory of droplet is related to its volume, mass, initial velocity and direction, and the flow velocity of other droplets and hot air. But these parameters are changing all the time because of the mass and heat transfer process. In addition, both the droplet size and the distribution of hot air can not be uniform in the initial state. Obviously, for such a complex and changeable process, it is not reliable to carry out engineering design only by theoretical calculation.

The third reason is that the types of materials to be dried are various, and their physical and chemical properties are also different. The rate of mass transfer and heat transfer of different materials may vary greatly even under the same drying equipment. If it is not treated differently, it may result in unsatisfactory results. For example, although some Chinese herbal medicines belong to the same kind of medicinal materials, the drying conditions must be changed only because of the differences in the origin or harvest time of the medicinal materials, otherwise the product quality will be unqualified.

The above three reasons determine that the development and application of drying technology should be based on experiments. But these characteristics of drying equipment technology are often ignored intentionally or unintentionally. Due to the lack of test equipment or incomplete types (which is a common phenomenon in our country), manufacturers often avoid the drying experiments that should be done, and users often give up the requirements of necessary tests because they do not understand the characteristics of drying technology. The result is that the device is not effective, even scrapped. In China, such cases are common. There was a lesson that a set of industrial drying device worth 20 million yuan was idle because it could not meet the requirements. Therefore, before the construction of industrial drying device, especially the larger device, we must carry out sufficient and convincing test, and take the test results as the basis of industrial device construction. This is the remarkable characteristic of drying technology application.

In addition, a variety of different uses are also a feature of drying equipment technology. Each technology has its own suitable application field. In engineering practice, it is necessary to select the suitable drying technology according to the specific situation. This will have a significant impact on investment costs, operating costs, product quality, environmental protection requirements and so on. For example, in a certain enterprise, there are three models of drying technology of silica cake, namely, box drying, spray drying and swirling airflow drying. ^In the end, they realized that each of the three technologies had its own advantages. Although the production efficiency is low and the labor intensity is high, the product quality is good. The tensile strength of the product after mixing with rubber is higher. The rotary airflow drying equipment is compact, low investment and high production efficiency, but the strength index of the rubber products produced is poor among the three. Spray drying produces white carbon black. The products are centered among the three, but have good fluidity and low dust pollution. They are welcomed by users and operators. In the 1990s, the problem of which drying method is more advanced in the production of silica was once debated in China's drying industry. In fact, each of the three types of equipment has its own characteristics. Which type of technology to choose depends on the user's own conditions and product requirements. There is no conclusion that the technology is more advanced. There are many similar examples, which show that there are many kinds of drying technology and each has its own characteristics. Therefore, we should carefully compare and carefully select the technical scheme in the application, and it is also an essential step to evaluate the technical scheme through the drying test.