vacuum drying equipment working principle and classification
vacuum drying equipment working principle :
In order to better understand the drying equipment, we briefly introduce the principle of the drying equipment. The drying process of the drying equipment needs to consume a lot of heat energy. In order to save energy, some materials with high moisture content, suspensions or solutions containing solid substances can be mechanically dehydrated or heated for evaporation, and then dried in the dryer to dry the solid.
In the drying process, heat and mass (moisture) transfer should be completed simultaneously. The moisture partial pressure (concentration) on the surface of the material is higher than that in the external space, and then the heat source temperature is higher than the material temperature. Through heat transfer from high temperature heat source to wet materials in various ways, the moisture content on the surface of materials can be vaporized and dissipated to the external space, thus the difference of moisture content between the surface and the internal of materials appears. The internal moisture diffuses to the surface and vaporizes, so that the moisture content of the material is continuously reduced, and the overall drying of the material is gradually completed. The drying rate of the material depends on the vaporization rate of the surface and the diffusion rate of the internal moisture.
Generally, the drying rate in the early stage of drying is controlled by the surface evaporation rate. As long as the external conditions of drying remain unchanged, the drying rate and surface temperature of the material will remain stable. This stage is called constant speed drying stage. When the moisture content of the material decreases to a certain extent, the diffusion rate of the internal moisture to the surface will decrease, and is smaller than the surface evaporation rate, the drying rate is the main one It is determined by the internal diffusion rate and decreases with the decrease of moisture content. This stage is called the rate reduction drying stage. In addition, technological progress will also reverse the current situation of domestic drying equipment export.
vacuum drying equipment type:
There are many types of equipment for drying operation. According to the operating pressure, it can be divided into normal pressure and reduced pressure (also called vacuum dryer). It can be completely selected according to its own needs. According to the operating 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. According to the movement (material movement and drying medium flow), it can be divided into parallel flow, counter flow and cross flow. Classification of drying equipment.
1. By operating pressure
According to the operating pressure, the dryer can be divided into two types: atmospheric dryer and vacuum dryer. Operating under vacuum can reduce the partial pressure of the wet steam in the space and accelerate the drying process, and can reduce the boiling point of the wet steam and the drying temperature of the material. The steam does not Therefore, vacuum dryer is suitable for drying heat sensitive, oxidizable, explosive and toxic materials as well as occasions where wet steam needs to be recovered.
2. By heating
According to the heating mode, the dryer can be divided into convection type, conduction type, radiation type and dielectric type. Convection dryer, also known as direct dryer, uses the hot drying medium to directly contact with the wet materials to transfer heat by convection and take away the generated steam; conduction dryer, also known as indirect dryer, uses the conduction mode to transfer heat from the heat source through the metal wall to the wet materials, and the generated wet steam can be vacuumed and pumped into a small amount by decompression Remove the purge gas or condense on the surface of the low-temperature condenser separately. This kind of dryer does not use drying medium, with high thermal efficiency and pollution-free products, but its drying capacity is limited by the heat transfer area of metal wall, and its structure is also complex, and it is often operated under vacuum; radiation dryer uses various radiators to emit electromagnetic waves of certain wavelength range, which are selectively absorbed by the surface of wetted materials and then converted into heat for drying; The dielectric dryer uses high frequency electric field to dry the wet materials.
3. By sport
According to the movement of wet material, the dryer can be divided into fixed bed, stirring, spray and combination. According to the structure, the dryer can be divided into box dryer, conveyor dryer, drum dryer, vertical dryer, mechanical stirred dryer, rotary dryer, fluidized bed dryer, air dryer, vibrating type dryer. Dryers, spray dryer and combined dryer.