Experimental study on the structure and reactivity of char in pressurized O₂/H₂O atmosphere

Pressurized O₂/H₂O combustion is regarded as a promising high-efficiency CCS technology. In this study, char combustion in a pressurized O₂/H₂O atmosphere was performed with a pressurized horizontal tube furnace. The effects of pressure (0.1–1.3 MPa) and H₂O concentration (0–60%) on char conversion, char physicochemical structure and reactivity were investigated by means of XPS, Raman, temperature-programed desorption and TGA tests. The results show that both pressurization and H₂O can promote char conversion and facilitate the formation of carbon‑oxygen bonds on the char surface. Pressure mainly affects the consumption and generation of micropores, while the effect of H₂O on the pore structure has no obvious selectivity. Pressurization reduces the relative content of C–C, while H₂O has the opposite effect. At low pressure (0.1–0.7 MPa) and low H₂O concentration (0–40%), pressurization and H₂O can promote the formation of C(O) on the surface of char. The reactivity of char first decreased and then increased with increasing pressure and increasing H₂O concentration.