Heat transfer conditions in a plasma-heated rotary kiln and the effect of coating layer formation

Other conference contribution, 2026

Reducing emissions from the cement industry is necessary for mitigating the effects of global warming. One potential electrification option is replacing traditional fossil-fuel flames with electrically generated thermal plasma as the heat source in the rotary kiln. Such a change in heating mode will however drastically change the heat transfer conditions in the kiln, potentially impacting the formation of a protective and insulating coating layer on the inner kiln wall. The buildup of the coating layer is linked to the temperature conditions at the rotating inner wall, which cyclically cools and reheats as it passes under the colder bed material. These temperature fluctuations can shift the axial position where the coating layer forms and, consequently, alter the temperature and heat transfer conditions within the kiln. To assess how the coating layer influences both the inner and outer wall temperatures, a 3D heat transfer model is employed. The modelling work focuses on an axially varying coating layer thickness profile, estimated from experimental measurements in a pilot-scale plasma-heated kiln, using recorded shell temperatures. During the experiments, large cyclic wall temperature variations were observed in the pilot kiln, which are further examined using the heat transfer model.

Inclusion of the insulating coating layer in the kiln model improved the accuracy of the model, producing inner and outer wall temperatures comparable to recorded temperatures. Further, the simulations reveal a wall temperature fluctuation of similar amplitude as observed during the measurements, confirming the strong cooling effect on the wall from the bed material. A parameter sensitivity study with the model reveals that a changed kiln rotational speed and bed feed rate has a notable impact on the wall temperature fluctuations, as do the physical properties of the wall material, specifically the thermal conductivity and heat capacity.