Experimental and Kinetic Investigations of CO2 Gasification of Fine Chars Separated from a Pilot-Scale Fluidized-Bed Gasifier

The CO2 gasification behaviors of two fine chars separated from a pilot-scale fluidized-bed gasifier were studied in a thermogravimetric analyzer (TGA) within the temperature range of 1000–1300 °C. The physical properties of fine chars were examined by scanning electron microscopy (SEM), N2 adsorption, and X-ray diffraction (XRD). The differences in gasification reactivity and related properties between the fine chars and the corresponding experimental-produced coal chars were also compared. The results show that the fine chars have higher ash content, larger Brunauer–Emmett–Teller (BET) surface area, and better gasification reactivity than the corresponding coal chars. The gasification reactivity of fine chars was promoted by the catalytic alkali and alkaline earth metals (AAEMs) but inhibited by the enrichment of the ash layer in a higher carbon conversion range or the ash melting at a higher temperature. In addition to the AAEMs, the reactivity of different fine chars is mainly influenced by their pore and carbon crystalline structures. The kinetic investigation reveals that the modified random pore model (MRPM) and shifted-modified random pore model (S-MRPM) perform more reasonably than the random pore model (RPM) in some special conditions. Moreover, the reactivity of fine chars increases, and the reaction shifts from chemical reaction control to gas diffusion control as the gasification temperature increases.