Combustion Characteristics, Kinetics, and Molecular Dynamics Insights of Rice Husk Biomass Under Oxy-Fuel Conditions

Rice husk biomass was investigated under O2/CO2 oxy-fuel conditions using Thermogravimetric analysis (TG)-derivative thermogravimetry (DTG)-mass spectrometry (MS) experiments, iso-conversional kinetic analysis, and ReaxFF reactive molecular dynamics simulations. Oxy-fuel combustion significantly enhanced combustion performance compared with air combustion. At 10 °C·min−1, the ignition and burnout temperatures decreased to 235 °C and 435 °C under 70%O2/30%CO2, while the maximum mass loss rate increased more than fivefold and the comprehensive combustion index increased markedly. Online MS analysis showed concentrated CO2 formation and O2 consumption within 280–330 °C, accompanied by markedly suppressed NOx and SO2 emissions. Kinetic analysis revealed high apparent activation energies (525–548 kJ·mol−1) at α ≈ 0.5; these values are conversion-dependent and sensitive to the iso-conversional method employed and therefore reflect relative kinetic trends rather than intrinsic Arrhenius parameters, indicating a transition from chemical control to diffusion–structure-coupled control. Molecular dynamics simulations further confirmed that moderate oxygen enrichment promotes organic backbone cleavage, whereas excessive oxygen leads to a carbon-limited regime. These results provide mechanistic insights into biomass oxy-fuel combustion and its optimization for CO2 capture applications.