Towards electrified cement production: Modelling studies of heat transfer conditions in plasma-heated rotary kilns

Licentiatavhandling, 2026

Fossil fuel combustion is the dominant heat source in energy-intensive industries, why electrification of these industries is essential for mitigating global warming. A major challenge is the electrification of the cement industry rotary-kiln heat-treatment process, which has a high energy demand and requires high temperatures. Thermal plasma technology presents a suitable alternative for electrifying the rotary kiln. Plasma torches use electricity to produce a high-enthalpy gas plume, capable of providing high temperature conditions. However, a change from conventional burners to plasma torches entails a change in the complex heat transfer conditions governing the rotary kiln process.

The heat transfer in combustion-based rotary kilns is dominated by radiative heat transfer, with particle radiation from soot, ash and fuel particles being a major contributor. Hence, the lack of suspended particles in the plasma heated gas poses a challenge for the implementation in rotary kiln. Further, high peak temperatures near the torch expose the kiln refractory to new temperature conditions. To facilitate implementation of plasma torches in industrial kilns, modeling and experimental work on pilot- and demonstration scale is needed.

This thesis concerns modelling of a pilot-scale plasma-heated kiln, simulating industrial conditions. The work assesses heat transfer conditions in plasma-heated rotary kilns to identify how operational conditions may be adjusted to ensure sufficient heat transfer from the gas domain to the bed material. Potential issues, such as overheating of the wall and impact on the regenerative heat transfer, when implementing plasma heating are also assessed. Within this work, two models are employed: a three-dimensional kiln heat transfer model that obtains details on the heat transfer conditions and temperatures of the surfaces in plasma-heated kilns, including a moving product bed, incorporating plasma torch measurement data to estimate the gas temperature profile. The second model applies a one-dimensional conduction model that is developed and coupled to the kiln model to assess the radial and angular temperature distribution within the rotating wall.

By adapting operational parameters like directing the plasma torch towards the bed, increasing bed feed rate, and particle injection, this thesis concludes on the potential for plasma torches as the heat source in cement rotary kilns. While particle injection and tilting of the plasma torch is shown to achieve sufficient heat transfer conditions for producing cement clinker, potential overheating of the wall may be mitigated by increasing shell cooling and bed feed rate.