On the application of desiccant in drying industry

Drying is a very important and general unit operation in many industrial fields The drying of materials is often due to one or several reasons as follows: good fluidity of materials, easy loading and unloading, easy preservation and storage, reduced transportation costs, and desired product quality There are many kinds of materials that need to be dried They need different drying time and have different physical shape and quality requirements Improper drying will lead to poor product quality, product cannot be sold, and irreparable loss More than 400 types of dryers are recorded in the literature, of which more than 100 are commonly used Because of the high latent heat of vaporization and the inherent low efficiency of using hot air as drying medium (Zui is common), drying becomes a unit operation with high energy consumption compared with distillation The research shows that in the United States, Canada, France and the United Kingdom, the energy consumption of industrial drying accounts for 10% - 15% of the total energy consumption of the country, while in Denmark and Germany it accounts for 20% - 25% (the latter data comes from industry's forced energy audit, so it is more reliable.) Such high energy consumption is the result of extensive application of drying operation in various sectors of the national economy The energy needed in the drying process usually comes from the combustion of fossil fuels, which will cause harm to the environment With the prosperity of the global economy, the energy consumption needed for drying will increase correspondingly, and the contradiction between drying and the environment will become more and more obvious Therefore, it is necessary to improve the drying process and reduce the drying energy consumption as much as possible within the scope of market economy Drying technology innovation means that at least one of its attributes can replace the original products, operations or methods: products or methods that have not been manufactured or invented before; higher productivity than the existing technology; better quality or quality control is more feasible and effective; reduce the environmental space occupied by equipment; safer operation; higher efficiency; and lower total cost The new technology can be used to establish a new product type, such as microwave drying, dielectric drying and so on It can also be a moderate improvement of existing products and processes, such as jet impact drying, cyclone drying, etc.; and then a major improvement of existing technologies, such as organic superheated steam drying, desiccant drying, etc Desiccant drying is contact adsorption drying Its drying principle is based on the moisture transfer between the dried material and the solid that can absorb moisture when they are in direct contact The drying form includes two drying technologies One is the typical contact drying: the evaporation of moisture here is at the cost of the heat transferred on the surface of the hot solid The second is adsorption drying: the moisture transfer is driven by the mass concentration gradient Due to the different interaction between materials and adsorbents, contact adsorption drying can be divided into inert adsorbent drying and active adsorption drying Inert adsorbent is a solid material which does not constitute the final product of Zui The active adsorbent can be a part of the final product, and does not need to be separated after the drying process Due to the addition of desiccant, compared with conventional convection drying, desiccant drying technology has the advantages of good product quality, uniform quality, easy to maintain biological activity, short drying time, low operating cost, simple system, relatively small equipment, low civil engineering investment, etc It is a promising drying technology, which can be widely used in chemical, food, medicine, textile, biology and other industries.