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The Rotary Kiln in the Ferronickel Production
One of the ferronickel production forms is by the RKEF process. In this process, run-of-mine ore is extracted, crushed, dried before being fed into rotary kilns . The main role of rotary kilns is to transform chemically the ore into calcine by heating it up to around 900 °C over the time needed to calcination process. The rotary kilns for this process are usually long, extending over 100 m, leading the material to take hours to cross the entire kiln, therefore resulting in a temperature gradient over the kiln and three defined zones: drying, heating and reduction zones (Fig. 1).
Other processes, such as cement and lime calcining, also apply rotary kilns . The length should be compatible to a proper heating and reduction time, wherein rotation acts as a significant component to the material passage. A burner is located at a lower level to provide heat throughout the kiln, and gas exhausters account for the flame extension and a smother temperature gradient. An exhauster pulls out the hot gas through a bag filter, cleaning it before throwing into atmosphere. This exhauster helps also in the flame length due to the pressure drop. A blower injects additional (secondary) air into the kiln, to help combustion. Figure 2 shows a schema of the whole process.
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