REDUCTION OF NOx EMISSIONS FROM AUTOMATED BOILERS BY MULTIPLE AIR STAGING

Within recent years the utilisation of "new" biomass fuels (e.g. agricultural residues and energy crops) in biomass combustion processes has gained relevance. Unfortunately, most of these new biomass fuels are characterised by elevated contents of i.e. N resulting in higher NOx-emissions. Currently available biomass heating systems for the combustion of non-wood biomass fuels have a high system complexity and cost intensive secondary measures have often to be applied. Thus, emission reduction by primary measures can be a meaningful and economically attractive solution for the development and design of biomass combustion systems. In order to investigate the influence of multiple air staging on NOx emissions, test run series with different biomass fuels have been performed at a pilot-scale biomass combustion plant specially designed for the application of multiple air staging. The experimental investigations were accompanied and supported by CFD simulations in order to gain more detailed information regarding NOx formation. The results show that the potential to reduce NOx emissions by multiple air staging is considerable (up to 50% lower NOx emissions compared to Austrian emission limits achievable). Thus, NOx reduction by multiple air staging is of relevance for the development and design of Low-NOx combustion technologies. The application of multiple air staging may provide a cost attractive alternative to secondary measures and thereby contributes to a significant widening of the feedstock potential for heat and power production from biomass and the reduction of NOx, which is a primary contributor to photochemical smog.