Combustion Characteristics and Kinetics of Coke in O2/CO2 Atmosphere under Varying Oxygen Concentration

To clarify the effect of oxygen concentration on coke combustion in an O2/CO2 atmosphere, non-isothermal thermogravimetric experiments were conducted at 20%, 40%, and 60% O2 with heating rates of 5, 10, and 20°C·min−1. Combustion characteristic parameters and the flammability, burnout, and comprehensive combustion indices were determined, and the reaction mechanism and kinetic parameters were evaluated by the Z(α) master plot method combined with FWO and KAS model-free methods. Raising the oxygen concentration shifted the TG-DTG and DSC curves toward lower temperatures and increased combustion intensity. At 20 °C·min−1, increasing O2 from 20% to 60% decreased the burnout temperature by 130.02°C and increased the maximum mass loss rate by 76.7%. The optimal combustion performance was obtained at 60% O2 and 5°C·min−1. The Z(α) master plot method revealed a three-stage kinetic mechanism: R3 phase-boundary control, F2/F3 reaction, and D3 three-dimensional diffusion. The FWO method yielded average activation energies of 75.56, 93.29, and 98.62 kJ·mol−1, while the KAS method gave 63.48, 86.00, and 89.27 kJ·mol−1. These values generally decreased with increasing conversion, with the exception of a local increase at α = 0.6 for the 40% O2 atmosphere. The results provide kinetic insight for optimizing oxygen-enriched coke combustion in O2/CO2 recycling systems. Combining the Z(α) master plot method with thermogravimetric analysis, the combustion kinetics mechanism of coke under O2/CO2 conditions is elucidated.Increasing the oxygen concentration significantly improves the combustion performance. The optimal condition is 60% O2 combined with a flow rate of 5°C·min−1.Combustion is stage-controlled by R3 interfacial reaction, F2/F3 reaction and D3 three-dimensional diffusion successively.The activation energy increases with the increase in oxygen concentration and decreases with the increase in conversion rate. Combining the Z(α) master plot method with thermogravimetric analysis, the combustion kinetics mechanism of coke under O2/CO2 conditions is elucidated. Increasing the oxygen concentration significantly improves the combustion performance. The optimal condition is 60% O2 combined with a flow rate of 5°C·min−1. Combustion is stage-controlled by R3 interfacial reaction, F2/F3 reaction and D3 three-dimensional diffusion successively. The activation energy increases with the increase in oxygen concentration and decreases with the increase in conversion rate.