Chemical looping combustion of low-volatile semi-anthracite coal with Co-based metal oxide: Performances, kinetics, and mechanisms

The kinetics of Chemical Looping Combustion (CLC) using Co₃O₄ as an oxygen carrier for low-volatile semi-anthracite coal were studied with the aim of integrating CO₂ capture into the combustion process. The effectiveness of varying temperature regimes (800–950 °C) and oxygen carrier ratios (ϕ = 0.5–2.0) on the CLC process was evaluated. The findings indicate a distinct two-stage combustion sequence: initially, the combustion of volatiles with solid Co₃O₄ occurs between 460 and 650 °C, followed by the combustion of fixed carbon with gas-phase oxygen released from Co₃O₄ between 750 and 950 °C. Moreover, the activation energy for volatile combustion was found to be 82 kJ/mol, while for fixed carbon combustion during the non-isothermal stage, it ranged from 31 to 140 kJ/mol. During the isothermal stage, the activation energy for fixed carbon combustion was approximately 234 kJ/mol, with a reaction rate constant (k₀) of 3.7 × 10⁸ s⁻¹. The kinetics varied from diffusion-controlled reactions at lower temperatures to first-order or phase-boundary-controlled reactions, and then to Avrami-Erofeev modeled kinetics at higher temperatures, influenced by both temperature and oxygen carrier ratios. This pioneering study provides a comprehensive analysis of the multi-stage kinetics of solid fuel CLC, bridging gaps in current knowledge and laying the groundwork for improved design and efficiency of CLC systems for cleaner energy conversion.