Reaction Characteristics and Kinetics for the Interaction between Biomass and Silico-Ferrite of Calcium and Aluminum (SFCA)-Type Oxygen Carrier in Chemical Looping Gasification

Oxygen carriers (OCs) are the key to developing biomass chemical looping gasification (BCLG), a promising technique for producing syngas from renewable resources. The tested OC pellets mainly contain SFCA-type oxides - khesinite (Ca5Al2Fe173+Mg1.5Si2.5O40) and Ca-Al-Fe-O (Ca5.1Al9.3Fe18.73+Fe0.92+O48) - with a polyhedron-enriched structure containing high oxygen vacancies. Nonisothermal tests coupled with kinetic analysis methods and characterization techniques are conducted to investigate the interaction mechanism between biomass-derived intermediates and SFCA-type OCs during BCLG. The results show that the SFCA-type OCs significantly promote char conversion with a high reaction rate. OCs exhibit a unique reduction pathway during the solid-solid reaction between OCs and char. This redox reaction is controlled by the nucleation mechanism for conversion (alpha) below 0.65, which shifts to the coupled nucleation and diffusion mechanism for higher conversion (alpha >= 0.65). These results are useful for evaluating the possible application of SFCA-type OCs in the BCLG system and optimizing the complex OC structure.