EVOLUTION OF CHAR CHEMISTRY, CRYSTALLINITY, AND ULTRAFINE STRUCTURE DURING PULVERIZED-COAL COMBUSTION
EVOLUTION OF CHAR CHEMISTRY, CRYSTALLINITY, AND ULTRAFINE STRUCTURE DURING PULVERIZED-COAL COMBUSTION
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DOI：
10.1016/0010-2180(94)00062-w
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发表时间：
1995-01-01
影响因子：
4.4
通讯作者：
HEADLEY, TJ
中科院分区：
文献类型：
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作者：
DAVIS, KA;HURT, RH;HEADLEY, TJ
部分反应的焦炭样品的碳质结构，产生的煤粉直接喷入实验室气流床反应器，其特征在于四种技术，元素分析，二氧化碳蒸气吸附，x射线衍射，和条纹成像，使用高分辨率透射电子显微镜。据观察，早期阶段的非均相氧化进行与后期阶段的碳化，导致优先损失的氢，减少表面积，和发展的结晶秩序。典型的燃烧时间和峰值温度不足以使大多数煤真正（三维）石墨化，而是导致乱层有序区域的增长。这种排序被认为是发生在一个时间尺度上可比的燃烧过程本身，在这里，在100毫秒的顺序，在1800 K的颗粒温度和氧浓度为12摩尔%。这项工作提出的证据表明，在燃尽的后期阶段，这是至关重要的解释和预测飞灰中的未燃碳的焦炭的反应性，显着影响的碳质基质的演变。虽然内表面积和氢含量（芳环聚结的指示）的显着演变发生在早期的焦炭燃烧，这两种现象不起主要作用，在以前的调查中指出的焦炭失活。在本文评价的碳结构的四个指标（H/C比、二氧化碳表面积、X射线衍射的微晶尺寸和HRTEM图像）中，通过HRTEM条纹成像测定的有序材料的体积分数与Illinois #6煤焦的观察到的反应性损失最相关。
The carbonaceous structure of partially reacted char samples, generated by direct injection of pulverized coal into a laboratory entrained flow reactor, was characterized by four techniques, elemental analysis, carbon dioxide vapor adsorption, x-ray diffraction, and fringe-imaging using high-resolution transmission electron microscopy. It is observed that the early stages of heterogeneous oxidation proceed in parallel with the latter stages of carbonization, leading to preferential loss of hydrogen, a reduction in surface area, and the development of crystalline order. Typical combustion times and peak temperatures are insufficient to bring about true (three dimensional) graphitization for most coals, but rather, lead to the growth of regions of turbostratic order. This ordering is seen to occur over a time scale comparable to the combustion process itself-here, on the order of 100 ms at particle temperatures of 1800 K and oxygen concentrations of 12 mol%. This work presents evidence that the reactivity of chars in the latter stages of burnout, which is critically important to the explanation and prediction of unburned carbon in flyash, is significantly impacted by the evolution of the carbonaceous matrix. Although significant evolution of internal surface area and hydrogen content (indicative of aromatic ring coalescence) occurs during early char combustion, these two phenomena do not play a major role in the char deactivation noted in previous investigations. Among the four indicators of carbon structure evaluated herein (H/C ratio, carbon dioxide surface area, crystallite dimensions by x-ray diffraction, and HRTEM images), the volume fraction of ordered material as determined by HRTEM fringe-imaging correlates best with the observed reactivity loss for Illinois #6 coal chars.