Chemical/physical properties of char during devolatilization in inert and reducing conditions

Abstract

The activities of coal chars strongly depend on char chemical/physical properties. In this work, the chars were obtained from rapid pyrolysis of Yuanbaoshan lignite in DTF (1473K, 2×104K/s, in N2), and in FFR under reducing atmosphere similar to that in fuel-rich region of full scale combustion. The chemical structures and physical properties of coal and chars from different extent of devolatilization were examined in order to get a better understanding of char reactivity. 13C-NMR was used to measure the chemical structures quantitatively. N2 adsorption and CO2 adsorption were applied to characterize the physical properties. Results show that pyrolysis is a process of aliphatic compounds release, with a huge number of micropores formed and macropores declined. The chemical structures of mature char are independent of the pyrolysis conditions. The chemical structures of mature chars from both DTF and FFR are remarkably similar, although the proximate and ultimate analyses of them are different. Mature chars show different physical properties, with FFR mature char mainly having micropores and DTF mature char containing both micropores and mesopores. The different reactivity of fully devolatilized chars formed in different pyrolysis conditions mainly depends on physical properties rather than on chemical structures.