Rotary Kilns

Rotary kilns (sometimes called calciners or rotary furnaces) are used for thermal treatment processes such as calcination, sintering, pyrolysis and firing, as well as for oxidation and reduction. These treatments can be applied to powders, granulates, suspensions and green bodies. A rotary kiln consists of a cylindrical, rotating body mounted between stationary material feed and outlet housings. The constant turning of the kiln body mixes the material, ensuring that it is processed homogeneously. Rotary kilns are heated either directly (inside the kiln chamber) or indirectly (from outside), depending upon the requirements of the application.

In a direct-fired rotary kiln, the burner is situated inside the kiln body, that is, inside the reaction chamber. The material is heated directly by the burner flame and the stream of hot gas produced by the burner. These kilns are usually lined with refractory (heat-resistant) material so that they can be operated at higher temperatures than kilns with plain metal tubes. Directly fired kilns are highly robust and easily scalable and can be used to achieve high throughput rates with relatively low production costs.

• 4 direct heated rotary kilns
• Temperature range: 100 – 1,550°C
• Residence time: 15 – 180 minutes
• Reaction modes: continuous, batch, co-current, counter-current
• Typical Processes: calcination , sintering , reduction , oxidation and drying

In contrast to directly fired kilns, indirect fired rotary kilns (also called rotary calciners) are equipped with natural gas burners or electric heating elements located outside the reaction chamber, so that the heat is transferred to the interior through the kiln shell. This arrangement makes it easy to operate the kiln with a controlled gas atmosphere in the reaction chamber (e.g. inert or reducing). Because combustion gases are kept out of the reaction chamber, the gas volume flow in an indirectly fired kiln is generally lower than in directly fired kilns. This means the indirect rotary kilns are excellent for treatment of very fine powders. They are also easier to clean, so that cross-contamination of materials can be more effectively prevented.

• 12 indirect heated rotary kilns
• Temperature range: 100 – 1,400°C
• Residence time: 15 – 180 minutes
• Reaction modes: continuous, co-current, counter-current, batch
• Typical Processes: pyrolysis, calcination, reduction and surface treatment of catalyst supports