不同煤阶煤中温热解半焦微观结构及形貌研究

Microcrystalline structure and morphology of chars derived from medium-temperature pyrolysis of coals with different metamorphisms

采制胜利褐煤、神木烟煤及太西无烟煤煤样进行终温为750℃的慢速升温（3~15℃/min）及中快速升温（50~750℃/min）热解;借助X射线衍射仪（XRD）和场发射扫描电镜（FESEM）对3种煤样及其热解半焦的微晶结构及微观形貌进行表征,基于XRD谱图解析获得煤样及半焦样的微晶尺寸L_c和L_a并计算石墨化度g.结果表明：随着煤化程度的增加,煤的石墨化度g,微晶堆积高度Lc和径向尺寸L_a增加,层间距d002降低;随着热解升温速度的提高,褐煤热解半焦石墨化度g增加,烟煤则先增加后降低,而无烟煤表现出先大幅度增加后下降、但下降趋势逐渐变缓;煤焦微晶结构参数受升温速率影响的敏感程度不同,3种煤样煤焦微晶层片大小L_a受到中快速升温的影响较大,在慢速升温过程中变化较小.而层片高度L_c受到升温速率影响程度较小,煤焦微晶单元的内部生长受升温速率尤其是快速升温的影响更大;褐煤慢速中温热解有利于获得反应活性高的产物,无烟煤热解有利于制备高石墨化度的炭素材料,而烟煤的可塑性较高,可通过改变升温速率来获得反应性较好或类石墨化等性质不同的产物.

Three coal samples including Shengli lignite,Shenmu bituminous coal and Taixi anthracite,were first prepared and pyrolyzed at slow heating rates（3—15 ℃/min）and mediumfast heating rates（50—750℃/min）respectively.Then the microcrystalline structure and morphology of chars derived from pyrolysis of these coal samples were characterized by means of Xray diffraction（XRD）and field emission scanning electron microscopy（FESEM）.Finally,the degree of graphitization gand the crystallite parameters of coal and chars including Lcand La that indicating the size of aromatic nucleus were acquired based on XRD spectra.Results show that with the increase of coalification,the values of g,L_a and L_c get bigger gradually,while the value of the spacing of aromatic layers d_（002） gets smaller.When the heating rates are enhanced,graphitization degree of lignite chars keeps an upward tendency,but for bituminouscoal and its deriving chars,the gvalue first increases and then declines.The trend of anthracite is similar with that of bituminous coal,but the growth range is more larger than the decreasing one.The crystallite parameters of coal and chars are affected by the heating rates with different sensitivity.L_a of chars is greatly influenced by medium and fast heating rates,but it has less variation in the slow heating process.L_c of chars changes slightly throughout the heating procedure.Microcrystalline unit＇s internal growth is influenced by heating rate,especially fast heating.It can be concluded that by slow heating rate in medium temperature,lignite pyrolysis will produce chars with high reactivity,anthracite pyrolysis will produce carbon materials with high graphitization degree.Due to the high plasticity of bituminous coal,products of high reactivity or graphitization can be obtained by changing the heating rate in pyrolysis.