碱金属及灰分对煤焦碳微晶结构及气化反应特性的影响

通过对原煤、酸洗原煤、酸洗后负载NaOH的原煤在750~1050℃热解制得焦样,用X射线衍射技术考察了热解温度、NaOH负载量以及灰分对热解过程中煤焦微晶结构变化的影响,并运用高温高压热天平(PTGA)考察了热解后煤焦的气化反应活性。结果表明碱金属及灰分的存在可以明显减小煤焦的微晶结构参数的变化(堆垛高度Lc、微晶尺寸La、及晶层间距d002),阻碍煤焦的石墨化进程,提高煤焦的气化反应性。随着热解温度的升高,堆垛高度Lc增大显著,而微晶尺寸La和晶层间距d002变化较小。煤焦的气化反应性k0和煤焦微晶结构参数Lc、d002存在如下关系:lnk0=a(Lc/d002)+b;研究还表明用氧化还原循环机理来描述碱金属的催化作用机理是不恰当的,但碱金属Na的存在可以明显降低煤焦的石墨化程度,提高煤的活性,对煤焦的气化起到部分催化作用。

Effects of Alkalimetal and Ash on Crystallite Structure of Coal Char during Pyrolysis and on Gasification Reactivity

The experimental research on pyrolysis of original coal, acid washing deashed coal and alkali metal (NaOH) loaded deashed coal was conducted in tubular furnace for investigating the effects of alkali metal and coal ash on the variation of crystallite structure of chars prepared from above coals, separately, at temperature of 750～1050℃ by using X-Ray diffraction (XRD) technique, and the char gasification reactivity was investigated by pressurized thermogravimeteric analysis system (PTGA). Results show that the existence of alkali metal and ash decreases the crystallite structure parameters of the chars (average stacking height L_c, carbon crystallite site L_a and interplanar spacing d_(002)) prominently, inhibits the progress of char graphitizing and increases the gasification reactivity of the char. L_c increases apparently and L_a, d_(002) change little with the increase of pyrolysis temperature. Char gasification reactivity k_0 has the following linear relationship with L_c: ln k_0=a (L_c/ d_(002)) +b, where a and b are constants related with char species, pyrolysis and gasification conditions. Results also show that it is not suitable to describe the catalysis mechanism of alkali metals Na for char gasification by the mechanism of redox mechanism. But the existence of Na decreases the degree of crystallite and increases the reactivity, which has the catalytic effect on char gasification.