Boiler design with solid-gaseous fuel staging to reduce NOX-emissions and optimize load flexibility

Stricter emission limits and low prices for fossil fuels are considerable challenges for biomass combustion technologies. Fraunhofer UMSICHT provides solutions for these challenges with an innovative boiler concept developed within the last years. The prototype was tested in the combustion center at Fraunhofer UMSICHT. Due to its design the boiler can be operated in different modes as a combi-boiler for solid and gaseous fuels. In the standard mode solid biomass is used as fuel. In case of higher NOX-emissions, switching to the fuel staging mode enables the reduction of these emissions. The experiments described in this article show that reduction rates of up to 50% are possible. In low load times or if it makes sense from an economic point of view, the boiler can also be operated with gas only. In this paper mainly the results from combustion experiments in fuel staging mode are discussed. Based on these results a model has been designed to develop a control unit and to support upscaling process.