Chemical looping gasification (CLG) provides an alternative for the conversion and utilization of high-moisture content biomass. However, how to efficiently utilize the self-moisture of biomass with the existence of oxygen carrier (OC) still needs to explore. In this study, digestate, as a high-moisture content biomass waste, was selected as the feedstock. Three experimental conditions, including self-moisture pyrolysis (SMP), self-moisture CLG (SMCLG), and externally injected steam CLG (SCLG), were tested to comparatively investigate the effects of different types of H₂O, the transformation of H₂O during gasification, and the interactions between H₂O and OC. SMCLG showed the best performance, and the highest gasification efficiency reached 81.83% when the self-moisture content was 40%. It indicated OC could absorb H₂O at low temperature and release it at higher temperature, thus facilitating the gasification of pyrolytic char. Based on density functional theory (DFT) calculation, the migration path of H₂O on OC was explained. The adsorption of H₂O was mainly due to the formation of Fe-O bond between Fe and H₂O, and then H₂O dissociates into OH and H on Fe atom. H is transferred to La atom to form La-H bond. This study investigates the effect of OC on the migration and transformation of H₂O in CLG process, which provided a new perspective and development direction for the treatment of high-moisture content biomass.

Chemical looping gasification; self-moisture; Oxygen carrier; DFT