Enhanced redox performance of cement-modified Fe-based oxygen carrier during biomass chemical looping gasification

In this study, a novel Fe-based OC was synthesized based on cement chemically bonded hematite, containing multiple-component calcium ferrites. Its cyclic performance was evaluated over 10 cycles of BCLG at 850, 900 and 950 °C, respectively, in a batch fluidized-bed reactor. Fresh and used OCs were characterized using TGA, XPS, XRD and SEM/EDS techniques. The best cyclic reactivity was achieved at 950 °C, resulting in an average gasification efficiency of 91.3 % and H2/CO ratio of 2.4 due to superior oxygen diffusivity. At 850 °C, the OC underwent elemental reorganization under repeated limited reduction and complete reoxidation. This structure evolution significantly improved the high-temperature redox reactivity of the used OC (OC850-M10) with the maximum mass loss rate of −4%/min during the TGA tests, compared to −2.6 %/min for fresh OC. For used OCs after 10 cycles at 900 °C (OC900-M10) and 950 °C (OC950-M10), increased oxygen vacancies in OC900-M10 compensated for reactivity loss caused by Fe enrichment, while reactive oxygen accessibility in OC950-M10 was moderately constrained by Fe segregation beyond a critical threshold. Despite the agglomeration after 20 cycles at 950 °C, enhanced overlaying of Fe and inert species further homogenized Fe phases, allowing for the restoration of 98 % of active oxygen after gentle crushing. Moreover, the addition of cement also improved crushing strength (>3 N) over cycling, partially due to the growth of Al2O3 flower-shaped phases in internal voids. These findings suggest that chemical incorporation of cement with hematite prolonged OC longevity.