The dryer can be classified according to different characteristics such as operation process, operation pressure, heating method, wet material movement or structure. According to the operation process, the dryer is divided into intermittent (batch operation) and continuous two types
According to the operation pressure, the dryer is divided into atmospheric pressure dryer and vacuum dryer two types, the operation under vacuum can reduce the partial pressure of the moisture vapor in the space and accelerate the drying process, and can reduce the boiling point of the moisture and the drying temperature of the material, the steam is not easy to leak out, so the vacuum dryer is suitable for drying the heat-sensitive, easily oxidized, explosive and toxic materials as well as moisture vapor needs to be recovered occasions
The dryer can be classified according to different characteristics such as the operation process. Therefore, the vacuum dryer is suitable for drying heat-sensitive, oxidizable, explosive and toxic materials as well as wet steam need to be recovered
According to the heating method, the dryer is divided into convective, conductive, radiant, dielectric type and other types. Convection dryer is also called direct dryer, is the use of hot drying medium and wet material direct contact, convection way to transfer heat, and will generate steam away; conduction dryer is also called indirect dryer, it uses conduction by heat source through the metal wall to the wet material to transfer heat, the generated moisture steam can be used to decompression suction, through a small amount of blowing gas or in the separate setting of the surface condensation of low temperature condenser condensation method to move away. Methods to remove. This kind of dryer does not use drying medium, high thermal efficiency, the product is not polluted, but the drying capacity by the metal wall heat transfer area limitations, the structure is also more complex, often operated in a vacuum; radiation dryer is the use of a variety of radiators to emit a certain range of wavelengths of the electromagnetic wave, the surface of the wet material is selectively absorbed by the transformation of the heat into the drying; dielectric dryer is the use of high-frequency electric field, so that the wet material The dielectric dryer utilizes high-frequency electric field to make wet materials dry by internal thermal effect.
According to the movement of wet materials, the dryer can be divided into fixed-bed type, stirring type, spraying type and combination type; according to the structure, the dryer can be divided into chamber dryer, conveyor dryer, drum dryer, vertical dryer, mechanical stirring dryer, rotary dryer, fluidized bed dryer, air dryer, vibrating dryer, spray dryer, and the combination of dryer and so on. There are many kinds of dryers.
Drying equipment for wet materials. Various production processes need to be dried by the material is a variety of different drying requirements are also different, so a wide range of dryer, according to the heating mode, there are the following four categories: 1 convection dryer
The most widely used class of dryers, including fluidization dryer, air dryer, chamber dryer, spray dryer, tunnel dryer, etc. The main features of such dryers are:
The main features of such dryers are:
The main features of such dryers are:
The drying equipment for wet materials. The main features of this type of dryer are: ① hot air and solid direct contact, heat transfer by convection heat transfer to the wet solids from the hot air stream, the resulting water vapor by the air stream away; ② hot air temperature can be raised to the highest temperature that ordinary metal materials can withstand (about 730 ℃), at high temperatures, the radiation heat transfer will become the main mode of heat transfer, and can achieve high heat utilization; ③ the humidity of the air stream on the drying The humidity of the airflow has influence on the drying rate and the final moisture content of the product; ④ When using low-temperature airflow, it is usually necessary to dehumidify the airflow first; ⑤ The energy consumption of vaporizing the unit mass of moisture is higher than that of the conduction dryer, and this is especially true when the final product has lower moisture content; ⑥ A large amount of hot airflow is needed to guarantee the heat required for the vaporization of the moisture, and the dust removing device is huge and more costly if the particle size of the material to be dried is very small; ⑦ It is preferable to be operated in the near-atmospheric pressure condition. 2 conduction dryer
Including spiral conveyor dryer, drum dryer, vacuum rake dryer, freeze dryer, etc., the main features of this type of dryer are: ① heat through the wall (usually metal wall), by heat conduction to the wet material; ② the surface temperature of the material can be less than freezing (freeze drying) to 330 ℃; ③ to facilitate the operation of the pressure and inert atmosphere, the volatile solvents can be recovered. The evaporated solvent can be recovered. Commonly used in easy to oxidize, easy to decompose material drying, also suitable for handling powdery materials.3 Radiation dryer
Through the radiation heat transfer, the wet material will be heated for drying. Electric heating radiation dryer with infrared light bulb irradiation of the material to be dried, so that the material temperature rises and dry. Gas heating dryer is burning gas will metal or ceramic radiation plate heated to 400 ~ 500 ℃, so that the infrared radiation, used to heat the material being dried. Radiation dryer has high production intensity, compact equipment, flexible use, but large energy consumption. It is suitable for drying materials with large and thin surfaces, such as plastics, cloth, wood, painted products, etc. 4 Dielectric dryer
Place the material to be dried in the high-frequency electric field, and utilize the alternating effect of the high-frequency electric field to heat the object for drying. This heating is characterized by the higher water content of the material in the part, the more heat obtained. Because the water content inside the material is higher than the surface, so the energy obtained inside the material is more, the internal temperature of the material is higher than the surface temperature, so that the temperature gradient and the direction of moisture diffusion is the same, which can accelerate the vaporization of water and shorten the drying time, this dryer is especially suitable for the drying process is easy to shell and the internal moisture is difficult to go to the end of the material (such as leather). Dielectric heating drying power consumption is very large, at present mainly used in food and light industry production. The design calculation of the dryer, the first must choose the appropriate type of dryer. At present, the selection of the dryer also has a great deal of empirical, should mainly consider the following aspects: ① material and product characteristics, such as the form of the material (such as slurry, paste, powder, block particles, flakes, etc.), solid particles of the particle size and strength, the initial water content and the existence of water in the form of the material is poisonous, flammable, easy to oxidize the product requirements of the final water content, the product is allowed to be a little contaminated, whether or not the form Whether to allow a slight change in the maximum permissible temperature of the product and the price of the product and so on. ② The conditions related to the production process, such as the amount of materials to be processed, pre-treatment and post-treatment of drying, volatile solvents, whether or not to recycle, and so on. ③ Operational performance and economic indicators of the dryer. After the above aspects of the comprehensive consideration of the various types of dryer comparison screening, generally only a few types of dryer, and then a small test to find the most appropriate operating parameters and structural parameters, and finally according to the price of the equipment and the small test, decide to use what kind of dryer.