Dryer Development And Classification

Modern dryers began to use fixed-bed dryers with intermittent operation. In the middle of the 19th century, the use of tunnel dryers marked the development of dryers from intermittent operation to continuous operation. The rotary drum dryer better realizes the agitation of the granular materials, and the drying capacity and strength are improved. Some industries have developed continuous operation dryers that meet the requirements of the industry, such as drum dryers in the textile and paper industries.

At the beginning of the 20th century, the production of dairy products began to use spray dryers, which provided powerful tools for large-scale drying of liquid materials. Since the 1940s, with the development of fluidization technology, fluidized beds and airflow dryers with high strength and high productivity have appeared one after another. The freeze sublimation, radiation and dielectric dryers provide new means to meet special requirements. In the 1960s, far infrared and microwave dryers were developed.

There are many types of mechanical equipment used for drying operations, which can be divided into normal pressure and reduced pressure according to the operating pressure (decompression dryer is also called vacuum dryer). According to the operation method, it can be divided into batch 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 co-current, counter-current and cross-flow.

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