Carbothermal interaction between Cu-based oxygen carrier and ash minerals in the chemical-looping gasification of coal and biomass

The carbothermal interaction between Cu-based oxygen carrier and ash minerals in the chemical-looping gasification of coal and biomass were investigated experimentally by considering three factors of reaction temperature, type of ash and ash content. The chemical-looping gasification was simulated by reciprocally switching the redox atmosphere of the fixed bed and the products were characterized by XRD and SEM-EDS and analyzed by thermodynamic calculation. The results show that Fe₂O₃ and Al₂O₃ in the coal ash can easily react with CuO/Cu₂O, forming complexes such as CuAl₂O₄, Cu₂Fe₂O₄ and CuFe₂O₄, which are difficult to reduce. However, CaO can alleviate the sintering of Cu-based oxygen carriers by hindering the formation of Cu-Al and Cu-Si complexes. The increase of reaction temperature promotes the solid-solid reaction of CuO with silicate minerals such as CaSiO₃ and MgSiO₃, producing CaCuSi₂O₆ and CuMgSi₂O₆ and reducing the reactivity of Cu-based oxygen carriers. With the increase of ash content, Ca₂Fe₉O₁₃ generated from Ca²⁺ and Fe³⁺ can react with SiO₂, forming three-phase eutectic CaFeSi₂O₆ with a high-melting point, which co-fuses with Cu-based oxygen carrier and covers the surface of the oxygen carrier, leading to a decrease in the oxygen release performance.