6 th International Conference “SCIENCE IN THERMAL AND CHEMICAL BIOMASS CONVERSION” Victoria, Vancouver Island, BC, Canada 30 August to 2 September 2004 CFD modelling of NO x formation in biomass grate furnaces with detailed chemistry Robert Scharler 1,2,3 , Emil Widmann 1 , Ingwald Obernberger 1,2,3 1 Institute for Resource Efficient and Sustainable Systems, Graz University of Technology; Inffeldgasse 21b, A - 8010 Graz, Austria; Tel.: +43 (0)316 481300 34; Fax: +43 (0)316 481300 4; E-mail: scharler@rns.tugraz.at 2 AUSTRIAN BIOENERGY CENTRE GmbH; Inffeldgasse 21b, A - 8010 Graz, Austria 3 BIOS BIOENERGIESYSTEME GmbH; Inffeldgasse 21b, A - 8010 Graz, Austria 4 Technical University of Eindhoven, Department of Mechanical Engineering, Section Process Technology, Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, the Netherlands ABSTRACT: This paper presents the development and testing of a new CFD NO x postprocessor for biomass grate furnaces with detailed reaction kinetics. A self- developed empirical fixed bed model was extended in order to describe the release of the most important nitrogen species from biomass fuel beds (NO and NH 3 as well as HCN in small concentrations). The data obtained were used as boundary conditions for gas phase NO x modelling based on the results from the preceding CFD simulation of the turbulent reacting flow in the combustion chamber. The Eddy Dissipation Concept (EDC) was combined with detailed reaction kinetics for NO x postprocessing. The ISAT algorithm for the tabulation of reaction kinetics during runtime was used in order to reduce computation time by up to two orders of magnitude per iteration. Simulations were performed for a 440 kW th pilot-scale (fuel: fibreboard) and for a 7.2 MW th industrial-scale biomass grate furnace (fuel: waste wood). The calculation results showed good qualitative and quantitative agreement with measurements. The developed CFD NO x postprocessor was successfully tested. 3D simulations of biomass grate furnaces with detailed reaction kinetics were performed for the first time in an engineering application. Continued tests and comparisons with measurements are necessary, however, in order to improve and validate the model. In conclusion, it can be stated that the newly developed NO x postprocessor allows NO x reduction measures in biomass grate furnaces to be investigated in detail and, therefore, is a powerful tool for the optimisation of furnace design and process control. INTRODUCTION A technical and economic optimisation of biomass combustion plants is necessary in order to establish them in the heat and power generation market. In that context,