The Calcine Temperature Challenge
In every rotary kiln application (not only for ferronickel production), calcine temperature is the most important KPI (key performance index). Insufficient calcine temperatures lead to bad calcine quality [6, 7]. On the other hand, a very high temperature can cause problems to the refractory lining at the hot end . For those reasons, there is an optimum range for the calcine temperature. However, it is influenced by many factors in the kiln, including:
Fig. 1 Kiln scheme with three zones
Fig. 2 The rotary kiln full system
- • Pressure drop
- • Temperature profile
- • Chemical profile
- • Kiln rotation
- • Primary, secondary and tertiary air flows
- • Material inflow and outflow rate.
The kiln rotation is tightly linked with the material flow. Kiln should rotate faster as ore load increases. However changes in rotation cause changes in temperature profile. Thereby calcine temperature responds to control actions only after a variable time. This fact makes both the modelling and control of the rotary kiln very complex tasks [8, 9]. Current approaches are just approximations of the time-varying plant. However, artificial intelligence and data mining based models are able to give good results .