Another aspect of rotary kiln design is deciding whether to go with a direct fired rotary kiln, or an indirect fired rotary kiln. The difference between the two is how the heat is introduced. In a direct fired rotary kiln, the heat is introduced directly into the internals of the rotary kiln, via a stream of hot gas. This means there is high heat transfer between the material and the heat. However, it also means that there is more gas exiting the rotary kiln that needs to be processed. In an indirect fired rotary kiln, the heat comes through the shell of the rotary kiln, and the heat transfer comes from the material being in contact with the rotary kiln shell. One of the big advantages to an indirect fired rotary kiln is that the temperature can be tightly controlled along the length of the rotary kiln. For example, if a material needs to reach a certain temperature, and be held there for a specific amount of time, an indirect fired rotary kiln is ideal, because it is easy to control this. Another advantage to using an indirect fired rotary kiln is that there are fewer exit gases that need processing, because less gas is going into the rotary kiln. To read more on how indirect fired rotary kilns compare to direct fired rotary kiln, see Direct Fired Rotary Kiln vs. Indirect Fired Rotary Kiln: What’s the Difference?
FEECO Rotary Kiln Series: