Numerical simulations of staged biomass grate fired combustion with an emphasis on NO_x emissions

In the present paper NO_x emissions from biomass combustion was studied, with the objective to demonstrate the applicability of stationary computational fluid dynamics simulations, including a detailed representation of the gas phase chemistry, to a multi-fuel lab-scale grate fired reactor using biomass as fuel. In biomass combustion applications, the most significant route for NO_x formation is the fuel NO_x mechanism. The formation of fuel NO_x is very complex and sensitive to fuel composition and combustion conditions. And hence, accurate predictions of fuel NO_x formation from biomass combustion rely heavily on the use of chemical kinetics with sufficient level of details. In the present work we use computational fluid dynamics together with three gas phase reaction mechanisms; one detailed mechanism consisting of 81 species and 1401 reactions, and two skeletal mechanisms with 49 and 36 species respectively. Using the detailed mechanism (81 species), the results show a high NO_x reduction at a primary excess air ratio of 0.8, comparable to the NO_x emission reduction level achieved in the corresponding experiment, demonstrating both the validity of the model and the potential of NO_x reduction by staged air combustion