Influence of CO2 substitution for N2 on the combustion characteristics and kinetics of oil shale under oxy-fuel conditions

Oxy-fuel combustion is recognized as a near-zero-emission technology and an effective route for large-scale CO₂ capture. Using TGA-DSC-MS, this study performed non-isothermal combustion tests on Fushun and Changji oil shales in two atmospheres—21%O₂/79%N₂ and 21%O₂/79%CO₂—to systematically assess how replacing N₂ with CO₂ alters combustion behavior and kinetic parameters. Across 0–1000 °C, the CO₂-containing atmosphere exhibits weaker momentum diffusion, heat transfer, and mass transport, which elevates ignition and burnout temperatures for both shales, delays the overall combustion process, and diminishes performance. The ignition and burnout stages of both materials are jointly governed by heating rate and CO₂ concentration. Furthermore, the addition of CO₂ causes the decomposition process of carbonates in Changji oil shale to shift from a single weight loss peak to three distinct peaks. Vyazovkin's advanced isoconversional kinetic analysis indicates that, as the combustion reaction progresses, the activation energy of both oil shales first decreases and then increases. In CO₂-enriched atmospheres, higher activation energy is required to complete the combustion process. The significant variation in combustion activation energy with conversion rate under both atmospheres demonstrates that the combustion of organic matter involves multiple parallel or sequential reactions, with the kinetic mechanism dynamically changing.