NOx and N2O formation mechanisms - A detailed chemical kinetic modeling study on a single fuel particle in a laboratory-scale fluidized bed

NOx (i.e., NO and NO2) and N2O are known as harmful pollutants. In fluidize d bed combustion these are formed front the nitrogen in the fuel. To develo p effective primary measures reducing the emissions, more knowledge on the mechanism of formation and destruction ongoing in fluidized beds has to be obtained. lit this work, a detailed chemistry model is combined with a two- phase model for a stationary fluidized bed to calculate the emissions of a single fuel particle in a laboratory-scale stationary fluidized bed. The si ngle particle model consists of a simple model for the H2O release during d rying, a model for the volatiles composition, and a model for the nitrogen chemistry during char combustion. The detailed reaction mechanism consists of a homogeneous part, heterogeneously catalyzed reactions on the bed mater ial, and radical recombination reactions oil the solids' surface. The resul ts confirm that devolatilization and char combustion are of nearly equal im portance for NO and N2O formation. During devolatilization, NO is formed fr om HCN and NH3, while N2O is formed almost exclusively front HCN. During ch ar combustion, NO is mostly formed by heterogeneous oxidation of char nitro gen, while N2O is formed from homogeneous oxidation of HCN. On the other ha nd, there is also a back coupling of NO on the homogeneous burnout of the c arbon containing species, by sensitizing the oxidation of CH4.