胜利褐煤半焦冷却处理对其微观结构及反应性能的影响

Influence of cooling treatments on char microstructure and reactivity of Shengli brown coal

采用不同的冷却方式对胜利褐煤热解"热"半焦进行冷却处理,考查了冷却方式对半焦微观结构及反应性能的影响。利用特制两段新型石英反应器,在高纯氩气、400、600、800℃的条件下,对褐煤热解30 min制得的"热"焦,分别浸入室温、干冰及液氮环境中得到冷态半焦,然后在15%水蒸气、900℃、10 min的条件下对冷态半焦进行非原位气化反应。为了比较,同样热解条件下制得的"热"半焦不经冷却,通过直接切换反应气氛为15%水蒸气进行原位气化(气化条件与非原位气化相同)。利用TGA、SEM、BET和Raman光谱仪对半焦反应性和微观结构进行表征和分析。结果表明,"热"焦的水蒸气原位气化半焦产率低于冷态半焦的非原位气化。冷却处理对半焦的孔结构影响较大,随着冷却速率的增大,半焦比表面积及总孔容积显著降低,但对半焦的化学结构(芳环体系和含氧官能团)的影响非常小。冷却速率越大,半焦的反应性越低,冷态半焦反应性能降低主要由于冷却对半焦孔结构造成的不可逆转的破坏。

This paper was to examine the changes in structure and reactivity of chars upon to varied cooling approaches for ＂hot＂char derived from Shengli brown coal. The ＂hot＂chars prepared from the pyrolysis of brown coal remained in argon for 30 min in a newly-designed two-stage quartz reactor at 400,600 or 800 ℃,respectively. Subsequently, the ＂hot ＂ chars were used to prepare the ＂cold ＂ char by cooling at room temperature,dry ice and liquid nitrogen. The ＂cold＂chars were then employed to the ex-situ gasification in15% steam atmosphere at 900 ℃ for 10 min. For comparison,the in-situ gasification of ＂hot＂char derived from the same pyrolysis without cooling was conducted by changing the reaction atmosphere from argon to 15% steam（under the same condition as the ex-situ gasification）. Reactivity and physical-chemical structure of chars were characterized by TGA,SEM,BET and Raman spectroscope,respectively. Results showed that the yield of＂hot＂char in-situ gasification was lower than that of the ＂cold＂char ex-situ gasification. Cooling approaches had the obvious influences on the porous structure of subsequent char. The specific surface areas and porous volumes were reduced dramatically with increasing quenching rate,but there was no significant effect on the chemical structure of char（such as aromatic ring systems and O-containing functional groups）. In addition,the reactivity of ＂cold＂chars was decreased with increasing cooling rate. The irreversible destroy of char structure,caused by the cooling treatment,contributed to the decrease of gasification reactivity of chars.