Drying equipment

Drying equipment, also known as dryers and dryers. The equipment used for the drying operation vaporizes the moisture (generally refers to moisture or other volatile liquid components) in the material by heating to obtain a solid material with a predetermined moisture content. The purpose of drying is for material use or further processing needs. For example, the drying of wood before the production of wooden molds and woodware can prevent the deformation of the product. The drying of the ceramic blank before calcining the two drying equipments can prevent the finished product from cracking. In addition, the dried material is also easy to transport and store, such as drying the harvested grain below a certain moisture content to prevent mildew. Since natural drying is far from meeting the needs of production development, various mechanized dryers are increasingly being used.

Drying equipment working principle

Ideal drying equipment for paste cakes requires large amounts of thermal energy during the drying process. In order to save energy, certain high moisture content materials, suspensions or solutions containing solid materials are generally mechanically dehydrated or heated to vaporize, and then dried in a desiccator. To get a dry solid. During the drying process, the heat and mass (moisture content) transfer must be completed at the same time to ensure that the moisture partial pressure (concentration) of the moisture on the surface of the material is higher than the moisture partial pressure of the moisture in the external space and the heat source temperature is higher than the material temperature. The heat is transferred from the high temperature heat source to the wet material in various ways, vaporizes the surface of the material and escapes to the external space, so that the difference in moisture content occurs on the surface and inside of the material. The internal moisture spreads 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 surface vaporization rate and the diffusion rate of internal moisture. Generally, the drying rate in the early drying stage is controlled by the surface vaporization rate; then, as long as the external conditions of drying are not changed, the drying rate and surface temperature of the material remain stable. This stage is called constant-rate drying stage; when the moisture content of the material is reduced to a certain level To a certain extent, when the diffusion rate of internal moisture to the surface decreases and is less than the surface vaporization rate, the drying rate is mainly determined by the internal diffusion rate, and decreases continuously with the decrease of the moisture content. This stage is called the deceleration drying stage. Air drying equipment In addition, technological progress will reverse the current domestic export situation of drying equipment. At present, China's drying equipment has not yet formed an export scale, and its export volume is still less than 5% of the total, and it is mainly exported to Southeast Asia. However, according to authoritative forecasts, with the development of technology, the proportion of China's export drying equipment in total output will increase from 5% to 10% in the next few years, and the export market will also expand from Southeast Asia to Europe and the United States. The large gap between the domestic large-scale drying equipment manufacturing and the international level is expected to improve.

Classified <br> <br> drying apparatus for the drying operation. There are many types. According to operating pressure can be divided into normal pressure and decompression (vacuum dryer also known as vacuum dryer). According to the operating method can be divided into intermittent and continuous. According to the drying medium can be divided into air, flue gas or other drying medium. According to the movement (material movement and drying medium flow) can be divided into co-current, countercurrent and cross-flow.

According to the operating pressure according to the operating pressure, the dryer is divided into normal pressure dryers and vacuum dryers. Operating under vacuum can reduce the partial pressure of moisture in the space and accelerate the drying process, and can reduce the boiling point of the moisture and the drying temperature of the materials. Steam is not easy to leak, so the vacuum dryer is suitable for dry heat-sensitive, easily oxidized, explosive and toxic materials and wet steam recovery. The microwave flour sterilization drying equipment is heated according to the heating method, and the dryer is divided into the convection type, the conduction type, the radiation type, and the dielectric type. Convection dryer, also known as direct dryer, is the use of hot dry media in direct contact with wet materials, heat transfer by convection, and the generated steam away; conduction dryer, also known as indirect dryer, which uses conduction The method transfers heat from the heat source to the wet material through the inter-metal walls. The generated moisture vapor may be removed by vacuum suction, blowing a small amount of purge gas, or condensing on the surface of a separately provided low-temperature condenser. Dryers of this type do not use drying media and have high thermal efficiency. The product is not contaminated, but the drying capacity is limited by the heat transfer area of ​​the metal walls. The structure is also complex and often operates under vacuum. The radiation dryer uses various types of radiation. The device emits a certain wavelength range of electromagnetic waves, which is selectively absorbed by the surface of the wet material and converted into heat for drying. The dielectric dryer uses high-frequency electric fields to effect the drying of heat inside the wet material.

According to the movement mode of the wet material, the dryer can be divided into a fixed bed type, a stirring type, a spray type, and a combined type according to the movement mode of the wet material; according to the structure, the dryer can be divided into a box type dryer and a conveyor type dryer. Drum dryers, vertical dryers, mechanical stirring dryers, rotary dryers, fluidized bed dryers, air dryers, vibratory dryers, spray dryers, and combination dryers .