Effect of oxygen decoupling and flow regime on sewage sludge gasification with red mud-based perovskite oxygen...

To realize the resource utilization of municipal sludge and improve the quality of gasification products, the chemical looping gasification (CLG) strategy was proposed to convert high-moisture sludge (HMS) into H₂-rich syngas using a low-cost red mud-based perovskite oxygen carrier (POC), CaMn_0.5Fe_0.5O_3-δ. H₂-TPR analysis showed a high-temperature reduction peak at 651.2 °C and an H₂ uptake of 3.9859 mmol/g, indicating strong reducibility and lattice oxygen mobility associated with Fe/Mn compared to conventional carriers. Under a fuel-to-oxygen-carrier ratio (C/O) of 1.75 at 800 °C in a dual-layer POC reactor, the system achieved 30.5 vol% H₂ and a carbon conversion efficiency (η_C) of 90.8%, outperforming the corresponding fixed-bed configurations. Post reaction XRD and SEM-EDS analyses revealed deeper reduction of the oxygen carrier and enhanced fuel conversion, with the reduced phases such as Fe₃O₄ and MnFe₂O₄ being detected. XPS analysis further showed that the lower-layer POC contained up to 92.65% Mn²⁺ together with partial reduction of Fe³⁺ to Fe²⁺, supporting the active participation of lattice oxygen release and oxygen uncoupling during gas-phase reforming. These results suggest that the staged coupling strategy enhances sludge gasification and syngas upgrading through the combined effects of oxygen-carrier redox activity and improved gas-solid contact. Although the present work demonstrates the feasibility of using red mud-derived POCs for wet sewage sludge gasification, further studies are still needed on quantitative oxygen-decoupling analysis, direct tar/impurity measurement, long-term cyclic stability, and scale-up hydrodynamics.