Characteristics of drying technology

Characteristics of drying technology

Drying equipment technology has a wide range of services. In the face of numerous industries, physicochemical properties of different materials, product quality and other diverse requirements, drying equipment technology is a cross-industry, interdisciplinary, experimental scientific nature of technology.
Generally, three aspects of knowledge and technology are required in the development and application of drying technology. The first is to understand the physical and chemical properties of the material being dried and the characteristics of the product. The second is to be familiar with the principles of transfer engineering, namely the principles of energy transfer such as mass transfer, heat transfer, fluid mechanics and aerodynamics. Third, there must be means of implementation, that is, engineering design for drying processes, main equipment, and electrical instrument control. Obviously, these three aspects of knowledge and technology do not belong to a subject area. In practice, these three aspects of knowledge and technology are indispensable. So drying technology is a cross-industry, interdisciplinary technology.
Although modern drying equipment technology has a history of more than one hundred years, it still belongs to the field of experimental science. Most drying equipment technologies currently lack scientific theories and design methods that accurately guide practice. In practical applications, relying on empirical and small-scale trial data to guide or the main way. The reasons for this situation are as follows:
One of the reasons is that some basic disciplines relying on drying technology (mainly subject to the discipline of transfer engineering) have the characteristics of experimental science. For example, the development of aerodynamic research is driven by the “wind tunnel” test, indicating that it has not left 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, many variables, and complex mechanisms. For example, in the field of spray drying technology, the trajectory of the atomized droplets in the drying tower is the key to engineering design. The trajectory of the droplet is related to its volume, mass, initial velocity and direction, and the flow velocity of other droplets and hot air around it. However, due to the mass transfer and heat transfer processes, these parameters change all the time. Moreover, in the initial state, neither the size of the droplet nor the distribution of the hot air is uniform. Obviously, engineering design based on theoretical calculations for such complex and varied processes is not reliable.
The third reason is that the types of materials to be dried are various, and their physical and chemical properties are also different. The mass transfer and heat transfer rates of different materials may vary greatly even under the same drying equipment conditions. If not treated differently, it may have unsatisfactory consequences. For example, the drying of some Chinese herbal medicines, although the same medicinal materials only need to change the drying conditions because of the difference in the origin or harvest period of the medicinal materials, the quality of the products will be unqualified.
The above three reasons determine that the development and application of drying technology should be based on experiments. However, these characteristics of drying equipment technology are often ignored by people intentionally or unintentionally. Manufacturers often avoid the drying experiments that should be done because of the lack or incomplete type of test equipment (which is a common phenomenon in China), 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 working well or even scrapped. In China, such cases are not uncommon. There has been a set of lessons learned from the industrial drying unit worth 20 million yuan because it could not be used. Therefore, before constructing an industrial drying device, especially a larger one, it is necessary to conduct a sufficient and convincing test, and use the test results as the basis for the construction of the industrial device. This is a distinctive feature of drying technology applications.
In addition, a wide variety and various uses are also a feature of drying equipment technology. Each technology has its own field of application. In engineering practice, the type of drying technology to be applied should be selected according to the specific situation. This will have a major impact on investment costs, operating costs, product quality, environmental requirements and other aspects. For example, in a certain enterprise, in the drying technology of silica filter cake, three modes of chamber drying, spray drying and rapid drying of rotary airflow have been selected. In the end, they realized that each of these three technologies has their own strengths. The production of white carbon black by box drying has low production efficiency and high labor intensity; but the product quality is good. The product produced after kneading with rubber has a high breaking strength value. Rotating airflow rapid drying equipment is compact, low investment, high production efficiency, but the strength index of the rubber products produced is the worst among the three. Spray drying produces white carbon black. The products are in the middle of the three indicators, but have good product fluidity and low dust pollution, which is very popular among users and operators of the factory. In the 1990s, the question of which drying method was more advanced in the production of white carbon black had caused controversy in the dry world of China. In fact, each of the three devices has its own characteristics. Which type of technology is used depends on the user's own conditions and product requirements. There is no conclusion that any technology is more advanced. There are many similar examples that show the wide variety of drying technologies and their individual uses. Therefore, in the application, it is necessary to carefully compare and carefully select the technical solution, and it is also an indispensable step to evaluate the technical solution through the drying test.