热解过程中煤焦微晶结构变化及其对煤焦气化反应活性的影响

Variation of the crystalline structure of coal char during pyrolysis and its effect on gasification reactivity

利用XRD技术考察了热解温度及升温速率对煤焦微晶结构的影响；使用Shi等的方法计算了煤焦微晶结构参数，获取了950℃～1400℃气化炉下煤焦微晶结构的特征及变化规律；结合热重分析得到了热解温度相关参数影响煤焦气化活性的机理。研究表明，热解温度升高，堆垛高度（Lc）明显增大而微晶尺寸（La）变化不大，说明煤焦基本品格单元主要是进行纵向的接合缩聚，而晶格并没进行明显的内部生长，煤焦的微晶结构随热解温度的提高向有序化发展，但没达到石墨化的程度；慢速热解煤焦的气化反应活性明显低于相同温度下快速热解煤焦，慢速热解中，由于煤焦在高温下停留时间较长，而使煤焦微晶进行结构重整而变得更加有序，芳香单元失去边缘活性位，煤焦气化活性降低。

The effects of pyrolysis temperature and heating rate on crystalline structures of Shenfu char were studied by using X-Ray Diffraction （XRD） technique. Shi et al. ＇s model was adopted to quantitatively process the data of XRD patterns of chars and obtain the crystalline structure parameters of Basic Structure Unit （BSU）. The characteristics and transformation of chars＇ crystalline structure in the temperature range of 950 ℃ 1 400 ℃ were examined . Char gasification reactivity was investigated by using TGA. Under the conditions used in this study, it is found that the average stacking height （ LC ） increases apparently and the carbon crystallite size （ Lo ） of the BSU changes little with the increase of pyrolysis temperature. It means that the coalescence growth of longitudinally adjacent BSUs dominates the growth process of BSUs in the temperature range used. Crystalline structure of chars becomes ordering with the increase of pyrolysis temperature but the graphitization is still not reached. Good correlation is also found between the heating rate and the char gasification reactivity. The chars generated from slow pyrolysis demonstrate a distinct low gasification reactivity as compared with ones from rapid pyrolysis. During slow pyrolysis, relative long resident time at high temperature leads to the further coalescence growth of longitudinally adjacent BSUs and the loss of lateral active sites of aromatic units. Crystalline structure of char reaching unity further would cause the chars less active.