Experiments and modeling of fluidized bed steam-biomass char gasification with a red-mud oxygen carrier at particle scale for chemical looping

Abstract

Chemical Looping Combustion (CLC) of biomass provides a low-cost way for CO2 negative emission. It creates complex multi-component flows including solids of oxygen carrier and fuel, and gasses of steam and/or CO2 as well as other gasification products. Experiments and modeling of steam-gasification of biomass char were investigated using a low-cost red mud as oxygen carrier materials. Effects of temperature, steam concentration, H2 inhibition on chemical reaction kinetics and mass transfer were experimentally investigated and modeled. A self-designed macro-TGA was used to detect its oxidization kinetics under isothermal conditions. The red mud oxygen carrier reduced inhibitory effect of H2 on carbon reaction, thus enhancing char conversion remarkably. With the neglect of the external mass limitation on char conversion, the reaction kinetics during reduction process was calculated by an experimentally-fitted function, expressing the char conversion. Pore structure evolution during the char conversion on kinetics was considered and its function was obtained based on the experimental results. The radial gas profiles under the bed of red mud particles by the solution of interparticle and external mass transfer coupled with the kinetics of char gasification were obtained, revealing the whole process of char conversion in CLC process. A semi-empirical kinetic model, including both of chemical and diffusion processes, provided a good insight of oxidation reaction kinetics, which was proven to be better than the classic models. The experimental data and modeling results got high agreement in both reduction and oxidation reactions.