Towards a quantitative understanding of NOx and N2O emission formation in full-scale circulating fluidised bed combustors

A math. tool is being developed for studying the nitrogen oxide emission formation in circulating fluidized bed combustors.  The model is based on detailed homogeneous and heterogeneous chem. kinetics and a simplified, reasonable description of CFB hydrodynamics with presumed temp. distribution.  With the model different fuels and fuel mixts. can be compared in regard to their nitrogen oxide emission formation tendency at typical CFBC conditions.  In this paper the structure of the CFBC model and its submodels are shortly described in present form.  The CFBC model is tested for nitrogen oxide prediction at normal air staging conditions in a 12 MW CFB with bituminous coal and wood chips as the fuel, resp.  Comparisons of modeling results with detailed gas concn. profiles measured inside the furnace are made.  The relative importance of homogeneous and heterogeneous reactions on NO and N₂O concn. profiles is illustrated based on a quant. reaction rate anal. at different parts in the combustor.  The importance of effects of radical removal on particle surfaces, and thus, a decreased CO burnout and, simultaneously, enhanced rates of catalytic bed/char reactions on nitrogen oxide destruction are discussed.