The rotary dryer furnace contains a cylinder that rotates in the proper direction and it is merely horizontal.
The length of the cylinder is 4 to 10 times of the diameter, which may vary from 0.3 to 3 meters. Solids feed to the end of the cylinder and due to three factors of rotation, the difference in height and Cylinder slope, the finished product is removed from the other side.
Rotary dryers are divided into two groups:
A direct method is that when direct heat exchange occurs between solids, the temperature of solids increases or decreases but in indirect method the heat released from physical collision of solids goes to metal pipe.
Rotating drying furnace machine is one of the most important dryers used to dry granular solids that can have free flow and do not split in a significant amount of crushing. If the rotary dryer is equipped with a special machine that breaks solid
cakes, they can dry very sticky materials well. It is not suitable for drying thick liquids, glutinous materials, very sticky and gummy materials and materials that are slow to dry also sulfur content or lightweight materials that could easily be transported by airflow.
Rotating drying furnace machine is suitable for drying Chemical fertilizers such as sulfate, phosphate, and ammonium nitrate and potassium salts, as well as materials like minerals, gravel, limestone, clay.
The drying time in these dryers usually varies from 5 minutes to 1 hour and their capacity varies from several hundred kilograms to several hundred tons.
Schematic structure of a rotary dryer furnace consists of a horizontal rotating cylinder shell that is slightly inclined towards the outlet. The moist feed enters from one end of the cylinder and dried product exits from the other end. When the cylinder rotates, elevator blades lift solid materials and spray it into the hot air flow and the surface of solids is completely exposed to hot air therefor Drying is done more efficiently. At the entrance to the feed there are several spiral blades that help feed forward to reach the main curtain.
In humid environments, it is necessary that the inlet air be partially dehumidified and this can be done by the Absorption tower and adjacent to calcium chloride. Other related devices to this dryer include: Air warmer with direct or indirect flame, air flow adjusting channel, Dust collector and fans.
Rotary dryer theory
If the heat transfer directly occurs from the gas phase to the solid phase, it is called direct heat, and if the heat transfer from steam pipes to solids, it is called indirect
heat. If the direction of the gas phase and the solid phase are the same, it is called “favari” and if they are opposed to the direction, it is called mutual.
For materials that need to be heated to a higher temperature, such as minerals, sand, limestone, clay, etc., direct hot gas is used. For materials that should not be heated to a much higher temperature such as aluminous sulfate and sugar and chemical crystalline products, hot air is used.
Solid matters that are not concerned of contamination with combustion gas but they should not warm up to high temperatures such as Iron sulfide, gypsum and organic materials such as uncooked coal and agricultural materials, should cool in the parallel dryer.