The selective non-catalytic reduction (SNCR) process is currently employed in nearly all rotary cement kilns in Germany to reduce the level of nitrogen oxides (NOx). The SNCR process has already been the subject of research projects. These revealed that it permits the reliable attainment of an abatement level of 500 mg/m³. Reduction down to 200 mg/m³ is basically also possible, however so far only if the initial NOx level is already low. In addition, this requires over-stoichiometric use of the reducing agent (generally ammonia solution). This leads to both higher material costs and unwanted high ammonia emissions (NH3 slip).
The aim of the research project was to obtain general NOx emission abatement to 200 mg/m3 with a minimal NH3 slip of max. 30 mg/m3 in cement industry rotary kiln plants with precalcination. The research goal presupposed a detailed scientific and technical understanding of the complex interactions between the SNCR process with staged combustion and the decarbonation reaction in calciners with high secondary fuel rates. Models and tools were to be created on the basis of this detailed understanding to permit the specific technical design of rotary kiln plants with calciner and optimisation of plant operation with a view to maximum NOx reduction with minimal NH3 slip. The tools used were experimental studies and CFD simulation.
VDZ accompanied this research project in association with the Department of Energy Plant Technology (LEAT) at the Ruhr University in Bochum and the Department of Environmental Process Engineering and Plant Technology (LUAT) at the University of Duisburg-Essen.