Activation and mechanism of chars from partial gasification of lignite at different steam concentrations

The char samples were prepared from the partial gasification of Shengli lignite in a fluidised-bed/fixed-bed reactor, and characterised by BET, Raman, FT-IR, microwave digestion ICP-AES, and TGA. The results indicate that at 800 ℃ and steam atmosphere the decomposition of ether group is made by the inherent char activation, leading to the decrease in the content of short chain or amorphous carbon between aromatic rings to prevent the graphitizing and the enhancement in the degree of defective aromatic structure. With the increasing of steam concentration (10%-25%) the char reactivity is reduced, which is attributed to the weakening of the regeneration of active sites by forming more ether group via the reaction "Ar, R-CO-Ar, R+2H₂O→Ar, R-O-Ar, R+2H₂+CO₂". However, with the continual increasing of steam concentration (25%-40%) the char reactivity is slightly promoted because the content of defective aromatic structure (3-5 rings) is increased due to the enhancement of the reaction (Ar, R-CH=CH₂+H₂O→Ar, R-CO-CH₃+H₂) and the reaction (Ar, R-+H-→Ar, R-H).