A modelling study of coating layer effects and cyclic wall temperature variation in a plasma-heated cement rotary kiln

Other conference contribution, 2025

The cement industry is a large global emitter of CO2, with the heat treatment of the raw material being the most energy intensive step. Heat is conventionally supplied to a rotary kiln via combustion of fossil fuels to achieve the elevated temperature levels required for clinker formation. A potential electrification option for the kiln is to replace the traditional burners with electrically generated plasma, utilizing the CO2 inherently formed during calcination. Moving from a combustion flame to a plasma causes a significant change in the heat transfer conditions in the kiln, mainly from the lack of particles in the plasma heated gas reducing the radiative heat transfer, as well as increased peak gas temperatures. Another key factor affecting the heat transfer conditions in the kiln is the formation of an insulating coating layer on the inside of the kiln wall, formed as the melt resolidifies and sticks to the wall. Being highly dependent on the refractory surface temperature, the heat supply conditions directly impact the coating formation.
Experimental measurements on a plasma-heated pilot kiln, at 2.9m length and 0.58m inner diameter, show a cyclic variation in the wall temperature, coinciding with the kiln rotational speed of the kiln. This work aims to assess whether the cyclic temperature variation can be captured by an in-house built heat transfer modelling tool, as well as how the operational conditions and including an insulating coating layer affects the cyclic temperature variation.