NO and N2O Emissions during Devolatilization and Char Combustion of a Single Biomass Particle under Oxy-fuel Conditions at Fluidized Bed Temperature

Oxy-fuel fluidized bed combustion IS a novel clean-biomass utilization technology. The NO and N2O emissions during oxy-fuel combustion of a single biomass particle at fluidized bed temperature were studied in a flow tube reactor. The method of isothermal thermogravimetric analysis was used to distinguish the devolatilization and char combustion stages of biomass combustion. This work is aimed to study the effects of temperature, CO2 concentration, atmosphere and O-2 concentration, H2O vapor addition, and biomass type on the NO and N2O emissions during oxy-fuel combustion of a single biomass particle at fluidized bed temperature. In oxy-fuel combustion, NO is rapidly formed during the devolatilization stage, while N2O is mainly formed during the char combustion stage. In 30% O-2/70% CO2 at T = 800 degrees C, the conversions of fuel-N to NO and N2O are 11.96% and 18.98%, respectively, The conversion of fuel-N to NO reaches the maximum value at T = 800 degrees C during the devolatilization stage, while it increases with increasing temperature during the char combustion stage. In addition, the conversions of fuel-N to N2O decrease with increasing temperature during the two stages. In oxy-fuel combustion, CO2 suppresses the NO emission and promotes the N2O emission, and H2O vapor addition promotes the NO and N2O reductions. Compared with air combustion, lower conversions of fuel-N to NO and higher conversions of fuel-N to N2O are observed during the two stages in oxy-fuel combustion. During the two stages, the total conversions of fuel-N to NO and N2O are of fuel-N to NO reach the maximum values at (O-2) = 30%, and the conversions of fuel-N to N2O decrease with increasing O-2 concentration. A higher fuel-N content in biomass leads to higher NO and N2O yields but lower conversions of fuel-N to NO and N2O during the two stages. The present results contribute to understanding the NO and N2O emission mechanisms during oxy-fuel fluidized bed combustion.