Due to the wide variety of wet materials in the drying process and the different drying characteristics, different types of drying equipment and methods are required. This brings about the selection of drying methods and equipment. If you choose improperly, it will inevitably lead to excessive investment in equipment, or increase in operating costs, or product quality does not meet the requirements, and in extreme cases, it is impossible to operate. Therefore, we must pay enough attention to the selection problem.

1. Material properties and drying characteristics

(1) Form of material

Wood and ceramic products as well as flakes, fibers, granules, fine powders, pastes and liquid materials are all industrially dry materials. Therefore, the choice of dryer should be based on the shape of the material. (2) various physical properties of the material

Including density, bulk density, particle size distribution, heat capacity and adhesion properties of materials. Adhesive performance has a great influence on the operation of the feed and discharge and some forms of dryer. When the adhesion is serious, the drying process cannot be carried out. (3) Characteristics of materials during drying

Including thermal sensitivity of heat, some materials will change color and decompose after being heated. In addition, the shrinkage of the material during the drying process will cause the molded article to crack or deform, thereby degrading or even scrapping the product. (4) The state of combination of material and moisture

It determines the ease of drying, the level of energy consumption, and the length of time required to stay in the dryer, which has a lot to do with the selection. For example, materials that are difficult to dry are primarily given a longer residence time than enhanced dry external conditions.

2. Requirements for dry products

(1) Requirements for dry product form

This is especially important in some cases. For example, in food drying, the requirement for product geometry is the key to making the moisture content of the product meet the drying requirements. If detergents, dyes, etc. are used to facilitate instant dissolution and avoid dust flying, spray granulators must be used when selecting a dryer. (2) Requirements for drying uniformity (3) Hygienic requirements for products (4) Some special requirements for products

For the drying of coffee, mushrooms, vegetables and other materials, the product is required to maintain its unique aroma, so it can not be quickly dried with high air temperature.

3. Fluctuation of water content of wet materials and dehydration before drying

The moisture content of the material entering the dryer should avoid large fluctuations as much as possible. If the water content becomes larger, the output of the dryer will decrease or the dry product will not reach the moisture content requirement. If the water content becomes smaller, the outlet exhaust temperature will rise. Excessive drying of the product will not only reduce the thermal efficiency of the dryer, but also cause the temperature of the product to rise, thereby affecting the quality of the product.

For high-humidity materials (water content above 60%), pre-dewatering should be applied to mechanical dewatering (pressure filtration, centrifugal dewatering, etc.) as much as possible before drying. Although the cost of mechanical dewatering equipment is relatively high, the low operating cost is incomparable to hot air drying.