The NO and N2O formation behavior of six biofuels (spruce wood, beech wood,
alder wood, straw, malt waste, peat) was studied in a formation-rate unit
under conditions relevant to a fluidized-bed combustor and a grate-furnace.
The concentrations of CO2, CO, CH4, other hydrocarbons, NO, N2O, HCN, and
NH3 were measured in the flue gas, shortly after the burning fuel particles
. Most of the fuel nitrogen was released during devolatilization (66-75%).
Relatively high conversions to NO were found. N2O was formed but also rapid
ly destroyed by the reaction: N2O + H --> N-2 + OH. HCN was also formed in
quantities similar to NH3 even during wood combustion. The HCN/NH3 ratios s
eemed to depend on the fuel H/N ratios. The experimental results supported
the hypothesis that the nitrogen of wood and other biofuels also exists in
heterocyclic structures. With the proposed NO and N2O formation mechanism t
he effects of fuel nitrogen content, temperature and oxygen partial pressur
e can be explained. (C) 1999 Elsevier Science Ltd. All rights reserved.