不同水蒸气浓度下褐煤气化半焦的活化及机理

以胜利褐煤为原料,利用流化床/固定床石英反应器,进行褐煤气化实验,采用BET、Raman、FT-IR、微波消解ICPAES、TGA等技术表征半焦。结果表明,在800℃水蒸气气氛中,醚基裂解造成芳环间短链或无定形碳含量减少,从而削弱石墨化进程,进而提高芳香结构的缺陷程度,是半焦活化的内在原因。提高水蒸气浓度(10%-25%),半焦的反应性降低,是因为气化过程中半焦的活性位再生能力变弱,而反应(Ar,R-CO-Ar,R+2H_2O→Ar,R-O-Ar,R+2H_2+CO_2)增强,导致醚基含量增加,是半焦活性位再生能力变弱的内在原因。继续提高水蒸气浓度(25%-40%),半焦的反应性略有提高,是因为芳香小环(3-5环)缺陷结构含量增加,而反应(Ar,R-CH=CH_2+H_2O→Ar,R-CO-CH_3+H_2)和反应(Ar,R-+H-→Ar,R-H)增强是芳香小环缺陷结构含量增加的内在原因。

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).