Rotary kilns are typically used in thermal processing applications. The machine is used to heat solids to a certain temperature so as to create the desired physical and/or chemical reaction. Rotary kilns are utilized to process various types of materials starting from waste products to high-value minerals.
There are two major types of rotary kilns; the direct fired rotary kilns and indirect fired rotary kilns. Although both types are employed with the same thermal processing disciplines, they differ in the way heat is applied on the material. They are also suitable for two separate applications.
Direct Fired Rotary Kiln
This type of rotary kiln works by pushing the heat through the interior of the kiln. This way, the material comes in direct contact with the heat source. This type of rotary kiln is reliable and efficient for heat transfers and pyroprocessing applications. It is commonly used in metal recovery and waste combustion for processing waste products such as those containing nickel. Examples of these products are electronic gadgets such as mobile phones, tablets including batteries, among others. These electronic wastes contain a certain amount of nickel, which is a type of valuable mineral. To recover this mineral, the waste product is burned off or oxidized through rotary kilns with direct fire removing the organic materials while leaving behind ash and the nickel content. With an effective recovery process, nickel contents are recycled and reused in other forms.
Indirect Fired Rotary Kiln
This type of rotary kiln is also called a calciner. It is typically used for materials that are not suitable for direct contact with combustion gases. This kind of rotary kiln boasts of its ability to control its temperature within the entire machine. In indirect fired rotary kiln, the heat is applied to the material from the outside of the machine through a gas burner or electric heaters. This way, the material is protected from getting direct contact from the heat source. With the two rotary kilns, the indirect fired type has the advantage of being able to closely monitor and control the temperature thereby achieving the desired chemical or physical reaction without difficulty.