Theoretical research of the NO and N2O reduction by char in oxy-fuel CFBC: Influence of H2O

Abstract

Oxy-fuel CFBC has lower NO_x emissions compared to air combustion, with the high H₂O content affecting NO and N₂O reduction. This study, using density functional theory and transition state theory, investigates the impact of H₂O on the char model at the electronic level and its subsequent influence on NO and N₂O reduction. Results reveal that H₂O adsorbs onto the active site on char, forming hydroxyl groups and free H atoms. The unstable O atom in –OH group leads to benzene ring rearrangement in the char model, creating additional active sites. NO reduction follows two paths: producing CO(R1) or CO₂(R2). For N₂O reduction(R3), N₂O reduction precedes benzene ring cracking, with CO₂ production providing more active sites. In R1, CO formation limits reactive sites and increases activation energy, while R2 and R3 favor CO₂ formation. Reaction pathways leading to CO₂ formation show lower activation energies and higher pre-exponential factors for N₂ release.