1、 Working principle of drying equipment

Intermittent dryerThis type of dryer is suitable for drying small batches and multiple varieties of materials, and the operation process is periodic. For example, in a box dryer (small ones are called ovens, large ones are called drying rooms), materials are placed in shallow trays, and hot air is used to dry the wet material surface. The commonly used method is partial circulation of exhaust gas. Its advantage is strong adaptability to materials, and the drying conditions can be flexibly adjusted according to the characteristics of different materials; The disadvantages are low thermal efficiency, uneven product quality, long preparation time for loading and unloading, and low equipment utilization.

Continuous dryerCapable of achieving large-scale, continuous production with high production efficiency. Like a rotary dryer, the main body is a slightly inclined and rotatable cylinder, which is equipped with several cutting plates inside. The material is picked up and scattered during the rotation of the cylinder, and fully contacts with hot air to achieve drying. The continuous dryer has a large production capacity, can be operated continuously, has a relatively simple structure, is easy to operate, and is suitable for large-scale production occasions, but the equipment investment is relatively high.

Atmospheric pressure dryerOperating under normal pressure, the structure is relatively simple and the cost is low. Widely used in situations where drying conditions are not demanding, materials are not easily oxidized, or have low thermal sensitivity. For example, tunnel dryers, some fluidized bed dryers, etc.

Vacuum dryerOperating in a vacuum environment can reduce the moisture vapor pressure in the space, accelerate the drying process, and lower the moisture boiling point and material drying temperature, reducing steam leakage. Suitable for drying heat sensitive, easily oxidizable, explosive and toxic materials, as well as situations where wet steam needs to be recovered. Common vacuum dryers include vacuum rake dryers, double cone rotary vacuum dryers, etc.

Convective DryerAlso known as a direct dryer, it uses a hot drying medium (such as hot air, flue gas, etc.) to directly contact wet materials, transfer heat through convection, and take away the generated steam. This kind of dryer is widely used, including fluidized dryer, airflow dryer, box dryer, spray dryer, tunnel dryer, etc. Its characteristics are direct contact between the hot air flow and the solid, rapid heat transfer, high drying rate, but relatively high energy consumption, and the humidity of the airflow has an impact on the drying rate and the final moisture content of the product.

Conductive dryerAlso known as indirect dryer, it transfers heat to wet materials through metal partition walls through a heat source (such as steam, hot water, thermal oil, etc.), and the generated wet vapor can be removed by vacuum suction, introducing a small amount of purge gas, or condensing on the surface of a separately set low-temperature condenser. This type of dryer has high thermal efficiency and the product is not contaminated, but its drying ability is limited by the heat transfer area of the metal wall, and its structure is relatively complex, often operated under vacuum. Common conductive dryers include spiral conveyor dryer, drum dryer, vacuum rake dryer, etc.

Radiation dryerUsing various radiators (such as infrared bulbs, gas heating radiation plates, etc.) to emit electromagnetic waves within a certain wavelength range, which are selectively absorbed by the surface of wet materials and converted into heat for drying. The radiation dryer has high production intensity, compact equipment, and flexible use, but it consumes a lot of energy and is suitable for drying materials with large and thin surfaces, such as plastics, fabrics, wood, painted products, etc.

Dielectric dryerUsing high-frequency electric fields to induce thermal effects inside wet materials for drying. The characteristic of this heating method is that the higher the moisture content in the material, the more heat is obtained, which can accelerate the vaporization of water and shorten the drying time. It is particularly suitable for materials that are prone to crust formation and difficult to remove internal moisture during the drying process, such as leather. However, the electrical energy consumption of dielectric heating and drying is high, and it is currently mainly used in food and light industry production.

Fixed bed dryerThe material is in a relatively fixed position during the drying process, such as placing the material on a shallow tray in a box dryer, and hot air is used to dry the surface of the material. Suitable for drying small batches and multiple varieties of materials, with strong adaptability to materials.

Agitated dryerBy stirring, raking, and other methods, the material is constantly flipped during the drying process, fully contacting with the heat medium to improve drying efficiency. For example, in a vacuum rake dryer, the horizontal mixer rotates alternately in both directions every few minutes to scrape off and mix the material adhered to the wall, in order to achieve uniform drying of the material.

Spray dryerDisperse the dilute liquid into droplets through an atomizer, freely settle and rapidly evaporate in a hot air flow (air, nitrogen or superheated steam), and finally dry into solid particles separated from the airflow. Suitable for drying liquid materials, capable of continuous and automated production, with short material retention time, suitable for heat sensitive materials.

Combination dryerCombine multiple drying methods or different types of drying equipment together, leveraging their respective advantages to meet the drying needs of complex materials. For example, fluidized bed spray granulation dryer is an organic combination of fluidization technology, atomization technology and drying technology.