Heat Transfer Enhancement of a Thermal Plasma in a Rotary Kiln for Cement Production

Other conference contribution, 2024

Electrification of heavy emitting industries, such as the cement process, will be necessary to reduce greenhouse gas emissions and mitigate global warming. One promising option is to use an electrically generated thermal plasma as the heat source for cement production, replacing fossil fuel flames. However, the combustion of fossil fuels is not the only carbon dioxide source in the process as carbon dioxide is inherently formed in the calcination reaction, being the most energy demanding step of the cement process. The process peak temperatures are achieved in a rotary kiln, with product temperatures of about 1450°C, and the overall heat transfer in the kiln is dominated by radiation. One major challenge switching for a thermal plasma in the rotary kiln is therefore the lack of radiating particles in the plasma heated gas, expected to result in a lower radiative heat transfer compared to a fossil fuel flame.

In this work, an 8MW_el demonstration scale rotary kiln, heated with a thermal CO₂ plasma, is modelled using an in-house heat transfer modelling tool. Due to limited measurements of the temperature fields in the plasma, measurement data gathered on a 50kW_el plasma torch is used to estimate the temperature conditions of an up-scaled plasma torch. The heat transfer conditions in the kiln are examined, as well as ways to enhance the heat transfer from the plasma to the bed material. Additionally, this work presents modelled heat transfer conditions at a pilot scale rotary kiln of 300kWel, as is to be experimentally examined during the spring of 2024 in a constructed experimental rotary kiln. This experimental kiln is modelled using similar principles as for the demonstration scale kiln. It was found that the most promising approaches to enhance the heat transfer are tilting the flame towards the bed and adding radiating particles to the plasma volume.