Abstract: The presence of alkali metals in biomass gasification can readily cause deactivation of oxygen carriers, reduce carbon conversion rate and gasification efficiency, thereby posing significant challenges to the stable operation and engineering application of chemical looping gasification systems. To address this issue, a Ni-based core-shell structured composite oxygen carrier was developed to improve its resistance to alkali-induced deactivation and carbon deposition.Meanwhile, an ex-situ chemical looping gasification configuration process was proposed, aiming to both harness the catalytic role of alkali metals in bond cleavage and gasification, to mitigate their adverse interactions with ash components that may compromise carrier integrity. Furthermore, the effects of different steam-to-biomass mass ratios (1.5, 3.0, 4.5, and 6.0) on gasification performance and oxygen carrier stability were investigated. Experimental results revealed that, the composite carrier exhibited optimal performance under ex-situ operation with S/B ratio of 4.5, at 900 ℃. Over 15 cycles, the gas yield remained stable at 1 887.13 mL/g, while the carbon conversion rate and gasification efficiency were consistently maintained within the ranges of 79%-86% and 113%-122%, respectively. This work proposed and validated an integrated process strategy based on oxygen carrier optimization with coordinated process regulation under coexistence of alkali metals, providing theoretical guidance for the long-term stability and engineering viability of biomass-based chemical looping gasification systems.

Key words: composite oxygen carriers, alkali metal, biomass, chemical looping gasification, mechanism