Influence of oxygen carrier on NOx and N2O emissions in biomass combustion within fluidized beds

Abstract

The Oxygen Carrier Aided Combustion (OCAC) technology has the potential to enhance the combustion efficiency and stability of biomass, while simultaneously facilitating the conversion of NO to N₂. However, current research lacks sufficient investigation into the impact of oxygen carriers on the conventional fuel nitrogen (fuel-N) conversion pathway, particularly in relation to N₂O. This study comprehensively examines the key operating parameters, including ilmenite ore (OC) ratio, O₂ concentration, fluidization velocity, and bed temperature, on NO and N₂O emissions during the OCAC of rice husk in a bubbling fluidized bed reactor. The findings suggest that when OC is used as bed material, the conversion of fuel-N to NO decreases by 8.84 % under a 3 % O₂ concentration at 750 °C, compared to the sand case. This beneficial effect is further enhanced as the temperature increases. Conversely, the conversion of fuel-N to NO increases by 12.15 % and 7.70 % under 6 % and 9 % O₂ concentrations, respectively, compared to the sand case. This suggests a distinct influence mechanism between OCAC and traditional combustion conditions, potentially due to the chemical phases of OC during the redox process. The OCAC operations can lead to an increase in the emission of HCN and N₂O under all tested conditions. The potential conversion pathway of fuel-N under OCAC conditions is summarized.