Modern dryers initially used intermittent, fixed-bed dryers. In the mid-19th century, the use of tunnel dryers marked the shift from intermittent to continuous operation. Rotary drum dryers effectively agitated particulate materials, improving drying capacity and intensity. Some industries developed continuous dryers tailored to their specific requirements, such as drum dryers in the textile and paper industries.
In the early 20th century, spray dryers began to be used in dairy production, providing a powerful tool for large-scale drying of liquid materials. Starting in the 1940s, with the development of fluidization technology, high-intensity, high-productivity fluidized bed and airflow dryers emerged. Freeze-sublimation, radiation, and dielectric dryers provided new means to meet special requirements. Far-infrared and microwave dryers began to be developed in the 1960s.
There are many types of mechanical equipment used for drying operations. Based on operating pressure, they can be divided into atmospheric and vacuum dryers (vacuum dryers are also called vacuum dryers). Based on operating method, they can be divided into intermittent and continuous dryers. Based on the drying medium, they can be divided into air, flue gas, or other drying media. Based on the motion (material movement and drying medium flow), dryers can be classified into co-current, counter-current, and cross-current types.
Based on operating pressure, dryers are divided into atmospheric pressure dryers and vacuum dryers. Operating under vacuum reduces the partial pressure of moisture vapor in the space, accelerating the drying process. It also lowers the boiling point of the moisture and the drying temperature of the material. Vacuum dryers are less prone to vapor leakage, making them suitable for drying heat-sensitive, easily oxidized, explosive, and toxic materials, as well as for applications requiring moisture vapor recovery.
Advantages:
1. Well-designed adsorption tower
2. High-performance activated alumina adsorbent
3. Effective silencer
4. Imported pneumatic controller with high power and durability
5. Precisely adjustable regeneration gas regulating valve
Based on the heating method, dryers are classified into convection, conduction, radiation, and dielectric types. Convection dryers, also known as direct dryers, utilize direct contact between a hot drying medium and wet material, transferring heat through convection and carrying away the generated steam. Conductive dryers, also known as indirect dryers, use conduction to transfer heat from a heat source through a metal partition to the wet material. The generated moisture vapor can be removed by methods such as reduced pressure suction, introducing a small amount of purge gas, or condensation on the surface of a separately installed low-temperature condenser. These dryers do not use a drying medium, have high thermal efficiency, and produce uncontaminated products, but their drying capacity is limited by the heat transfer area of the metal walls, and their structure is more complex; they are often operated under vacuum. Radiation dryers utilize various radiators to emit electromagnetic waves within a specific wavelength range, which are selectively absorbed by the surface of the wet material and converted into heat for drying. Dielectric dryers utilize a high-frequency electric field to induce a thermal effect within the wet material for drying.
Advantages:
1. Employs a high-performance evaporator with an ultra-large heat exchange area, resulting in a smaller temperature difference and more stable evaporator outlet air temperature.
2. Utilizes a high-efficiency gas-water separation structure for high oil-water separation efficiency.
According to the movement of wet materials, dryers can be classified as fixed-bed, agitated, spray, and combined types. According to structure, dryers can be classified as chamber dryers, conveyor dryers, drum dryers, vertical dryers, mechanically stirred dryers, rotary dryers, fluidized bed dryers, airflow dryers, vibrating dryers, spray dryers, and combined dryers, among others.
Common knowledge about drying equipment: Common pre-dryers in my country include spray dryers, air dryers, fluidized bed dryers, flash dryers, and fluidized bed dryers, such as spray granulation. Flash dryers and spray drying are among the most advanced types of drying equipment. Traditional methods include three types of atomization: rotary atomization, pressure atomization, and airflow atomization. Rotary atomization spray drying has a large capacity (spray volume up to 200 tons/hour), which will be responsible for easy control, operational flexibility, and wider application. Pressure atomization spray drying is characterized by the creation of coarse particles for future maintenance. Due to the small nozzle orifice, it is easy to clog, and the liquid must be strictly filtered. The nozzle orifice is easily worn, so wear-resistant materials are used. There is also a new structure of nozzle pressure called pressure-flow nozzle. Its characteristics are nozzle pressure and air gap nozzle in the surrounding environment. Atomization is divided into two stages: the first is the liquid film forming pressure nozzle, and the second is air atomization, which makes more small water droplets.
The advantages of this type of nozzle are: (1) the pressure of compressed air can be adjusted to adjust the droplet diameter, and the operation is simple; (2) it can produce high viscosity liquids, which can be atomized into fine droplets; (3) if you disable compressed air, the original pressure nozzle can be used. Atomized airflow is used in laboratories and in the Middle East, and its power consumption is low. The first two nozzles cannot atomize liquids, so air-atomizable nozzles are used. High viscosity adhesive, adhesive and filter cake materials can be used for three-fluid nozzle atomization. Drying technology using relatively dry airflow is mature, and if the operational data can be directly designed.
Fluidized bed dryers, spray dryers, and feed settings are divided into partial fluidized bed dryers with agitators and heat transfer fluidized bed dryers. When the aggregated material is easy to dry in a fluidized bed dryer, or when the powdered feed material accumulates and more water flows in, the aforementioned difficult phenomenon occurs. In this case, a feed agitator is used to eliminate the aggregation problem and achieve normal flow. The latter is a combination of heat conduction and convection heat transfer. When using normal flow, the amount of hot air is far from sufficient to meet the required heat drying. A heat exchanger is used to supply part or most of the heat, and this type of operation can greatly save energy. Various forms of heat exchangers are adopted. Fluidized bed dryers are also frequently used in combination drying for secondary and higher education. Ordinary vibrating fluidized beds are also mentioned. Vibrating fluidized beds have a vibration source that can be divided into two categories: one is driven by a vibrating motor, and the other is a regular motor that generates vibration through a vibrating box, causing a spring. The size of the bed during vibration is important; the latter is better. The fluidized bed spray granulation dryer organically combines fluidization technology, atomization technology, and drying. It introduces atomized spray liquid into the fluidized bed of seeds, allowing the seeds to continue growing and drying to reach the desired size, beyond the time required for ejection. This device has both small and large production capacities, capable of creating large particles. The industrial application of this equipment is increasingly evident.
