Modeling nitrogen chemistry in the freeboard of biomass-FBC

A recently developed two-step mechanism for modeling the fate of fuel-N from biomass fired combustion devices has been applied in the modeling of the freeboard of a forest residue fired fluidized bubbling bed. With the model the influence of two different air-staging strategies on the NO emissions were studied. Also the description of the release of the fuel-N was addressed by modeling the char-N release in two ways. The predicted NO emissions agreed well with measured ones. Changing the air staging strategy did not change the NO emissions significantly. The reason for this was that most of the nitrogen chemistry occurred in the lower part of the freeboard where the conditions remained almost unchanged.