Pressure swing vacuum drying equipment is used for drying operation. There are many types. According to the operating pressure, it can be divided into atmospheric pressure and decompression (decompression dryer is also known as vacuum dryer). According to the operation method, it can be divided into intermittent type and continuous type. According to the drying medium, it can be divided into air, flue gas or other drying medium. The material can be divided into countercurrent flow and staggered flow according to the movement mode of the material.

According to the operating pressure, dryers are divided into atmospheric dryers and vacuum dryers. Operating under vacuum can reduce the partial pressure of wet vapor in the space and accelerate the drying process, and can reduce the boiling point of wet vapor and the drying temperature of materials. Steam is not easy to leak out. Therefore, vacuum dryers are suitable for drying heat sensitive, easily oxidized, explosive and toxic materials and occasions where wet vapor needs to be recovered.

According to the heating mode, the dryer is divided into convection type, conduction type, radiation type, dielectric type and so on. Convection dryer, also known as direct dryer, uses the hot drying medium to directly contact with wet materials to transfer heat by convection and take away the generated steam; The conduction dryer, also known as the indirect dryer, uses the conduction method to transfer heat from the heat source to the wet material through the metal partition wall. The generated wet steam can be removed by decompression suction, introducing a small amount of purge gas or condensing on the surface of the separately set low-temperature condenser. This kind of dryer does not use drying medium, has high thermal efficiency and products are not polluted, but its drying capacity is limited by the heat transfer area of metal wall, and its structure is complex. It is often operated under vacuum; Radiation dryer uses various radiators to emit electromagnetic waves in a certain wavelength range, which are selectively absorbed by the surface of wet materials and then transformed into thermal drying equipment for drying; Dielectric dryer uses high-frequency electric field to dry wet materials with thermal effect.

According to the movement mode of wet material, the dryer can be divided into fixed bed type, stirring type, spray type and combined type. According to the structure, dryer can be divided into box dryer, conveyor dryer, drum dryer, vertical dryer, mechanical stirred dryer, rotary dryer, fluidized bed dryer, air dryer, vibrating dryer, spray dryer and combined dryer.