In cement production, a significant amount of thermal energy is used to burn the cement clinker in the rotary kiln. Nowadays, alternative fuels (AF) are used in parallel with fossil fuels, replacing the former. Cement manufacturers are striving to increase the share of AF in order to secure or improve their competitive position. In addition to economic advantages, ecological advantages should also be mentioned. For example the use of AF can contribute to the reduction of climate-relevant CO2 emissions.
The quantities of AF being used in the rotary kiln firing are limited by the fact that certain AF fuel particles can fall into the clinker bed and cause local disturbances in the clinker granules during the burning of the clinker. In order to further increase the use of AF, it is necessary to optimise the fuel input so that the clinker properties and kiln operation are not impaired even at high AF input rates.
The aim of the research project was to identify those fuel particles which potentially cause the greatest disturbances and to determine their rate of conversion in the flame and in the clinker bed. A further goal was to derive quality criteria for AF, to elaborate recommendations for the optimisation of fuel feeding systems and to develop a tool to estimate the suitability of an AF. The results were worked out by a combination of laboratory tests, fuel investigations as well as CFD/DEM simulations and subsequently checked on the basis of a kiln trial. Operators of cement plants are thus provided with knowledge and tools to further increase the use of AF.