AVT - Research - Research project

Modelling enrichment of minor compounds in cement rotary kilns by means of thermochemical and flow simulation tools

In cement production a powdery raw meal is heated up to approx. 1400 °C in a rotary kiln plant. At that temperature the actual cement phases are formed. The rotary kiln is heated by a coal, oil or gas flame. Due to combustion air and solid raw meal flow being conducted in counter current mode throughout the entire plant, volatile compounds of the fuel and the raw meal, that vaporise in high temperature regions, are transported back to cooler regions by the gas phase flow. There they precipitate and form a liquid melt, that makes the raw meal stick to the kiln walls and form coatings. Moreover, volatile compounds do not leave the plant but enrich in vaporisation precipitation cycles, which further promotes formation of coatings.

Applying the modelling concept for high temperature processes to the cement rotary kiln plant enables a detailed description of the process. Due to long residence times at high temperatures, the complex chemical conditions can be adequately modelled by thermochemical equilibria. The plant behaviour can be simulated for different raw meal and fuel compositions at different operation parameters. A steady state solution for the process model is calculated iteratively. Buildup of alcali and sulphur cycles is described in good agreement to measurement results. Thus, by applying the developed modelling concept it is possible to characterize operating points for new raw materials or fuels.