Rotary dryer working principle

Rotary dryer introduction

Rotary dryer (also known as rotary drum dryer, drum dryer, etc.) is a kind of contact internal heat transfer type drying machinery. In the drying process, heat is transferred from the inner wall of the drum to its outer wall, through the material attached to the outer wall of the drum to be dried. The moisture on the material evaporates is a continuous drying of production machinery.

rotary dryer

Rotary dryer working principle

The rotary dryer’s drum is a slightly angled and rotatable cylinder with wet material entering from one end up and dry material collecting from the other end down. Hot air enters at the inlet or outlet end and exits at the top of the other end. The barrel is equipped with a forward-running plate, which makes the material to be continuously run up and down in the process of turning the barrel, so that it can fully contact with the hot airflow to improve the drying efficiency and make the material move forward. The heat source of dry materials is generally hot air, high temperature flue gas, water vapor, etc.

The working process of the drum dryer is as follows: the material and liquid to be dried and processed will flow from the high level tank into the receiving tank of the drum dryer, the material will be thinly attached to the surface of the drum by the cloth film device, there is a heating medium inside the drum, most of the food industry uses steam, the pressure is generally 0.2~6MPa, the temperature is between 120~150℃, the material will be vaporized by the heat transfer from the simple wall in the rotation of the drum, the drum will complete the process of cloth film, vaporization, dehydration, etc. in one rotation cycle, the dried material will be scraped down by the scraper, then conveyed to the finished product storage tank by spiral, and finally crushed or directly packed. The moisture evaporated in the heat transfer can, depending on its nature, be introduced into the corresponding treatment unit through a hood for dust capture or discharge.

rotary drum dryer

Rotary dryer specifications

The rotary dryer has a high capacity, low fuel consumption and low drying costs. The drum dryer is high temperature resistant and can use high temperature hot air to dry the material quickly. Scalable and rotary dryer design with production margins in mind, there is no need to replace equipment, even if production increases marginally. 

The equipment adopts the spherical tractor structure, the tractor and the rollers cooperate well, which greatly reduces the wear and power consumption. The specially rotary dryer designed retaining wheel structure significantly reduces the horizontal thrust caused by the tilting of the equipment. Strong overload resistance, smooth operation and high reliability of the cylinder.

High thermal efficiency

Since the dryer is heat transferring, the direction of heat transfer remains basically the same throughout the heat transfer cycle, so most of the heat supplied in the drum is used for the wet vaporization of the material with a thermal efficiency of 80% to 90%.

High drying rate

The heat and mass transfer process of the wet material film on the wall of the barrel, from inside to outside, the direction is the same, the temperature gradient is large, so that the surface of the material film maintains a high evaporation strength, generally up to 30 ~ 70 kg/(m.h).

Stable dry quality

Because the heating method is easy to control, the temperature inside the barrel and the heat transfer rate of the wall can remain relatively stable, so that the material film in the heat transfer state drying, product quality can be guaranteed. However, drum dryers also have their drawbacks, mainly the high surface humidity of the drum, which can damage the flavor or abnormal color of some products due to overheating. In addition, if a vacuum dryer is used, it is more costly and is only suitable for handling materials with very high thermal sensitivity.

drum dryer

Rotary dryer application

Chemical, mining, metallurgical industries such as ore, slag, coal, metal powder, clay, diatomaceous earth, kaolin.
Agriculture, fodder, fertilizer industry such as straw, forage, leaves, fishmeal, corn paste, starch residue, wine lees, medicine residue, fruit residue, soy sauce residue, bagasse, grass charcoal, organic compound fertilizer, sludge, water product waste, food factory waste, slaughterhouse waste, organic fertilizer, inorganic fertilizer, phosphate fertilizer ammonium sulfate.
Dryers for powder and granular materials with special requirements. Such as various crystals, light calcium carbonate, active white clay, magnetic powder, graphite, inorganic mud, clay, lime slurry, ore slurry, phosphate slag, aluminum plant red mud.

sand rotary dryer