Experimental study on char nitrogen conversion characteristics during char combustion process in pressurized O2/CO2/H2O atmosphere

Pressurized oxy-fuel combustion is an advanced CO₂ capture technology with potential applications in coal-fired power generation. In this study, the conversion behavior of char-nitrogen under pressurized oxy-fuel combustion conditions was investigated using a horizontal furnace across a pressure range of 0.1–1.3 MPa in an O₂/CO₂/H₂O atmosphere. The influences of pressure, gas composition, and residence time on nitrogen conversion were examined, and key factors affecting nitrogen transformation pathways were identified. Results indicated that elevated pressures favored NH₃ formation while inhibiting the formation of NO and NO₂, particularly at pressures above 0.7 MPa. Under pressurized conditions (0.7/1.3 MPa), increasing the O₂/CO₂ ratio further suppressed the conversion of char-N to NO, a contrast to behavior observed at atmospheric pressure. X-ray photoelectron spectroscopy analysis revealed a preferential consumption of nitrogen species, such as pyridinic and pyrrolic nitrogen, with pressurization enhancing the depletion of protonated nitrogen. Furthermore, an increased O₂/CO₂ ratio promoted the conversion of nitrogen oxides and other nitrogenous forms.