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

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 in 15% 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.