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首页> 外文学位 >Structure and combustion reactivity of inertinite-rich and vitrinite-rich South African coal chars: Quantification of the structural factors contributing to reactivity differences.
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Structure and combustion reactivity of inertinite-rich and vitrinite-rich South African coal chars: Quantification of the structural factors contributing to reactivity differences.

机译：富含惰质石和富含镜质石的南非煤焦的结构和燃烧反应性：量化导致反应性差异的结构因素。

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摘要

South Africa has large reserves of Permian-aged, high-ash bituminous coals. Although these coals are of great economic importance, their behavior has not been well studied. This study compares the devolatilization and subsequent combustion behavior of an inertinite-rich (87.7% dmmf) and a vitrinite-rich (91.8% dmmf) South African coal, wet-screened to a narrow particle size distribution of 200 x 400 mesh. Pyrolysis chars were generated under rapid-heating conditions (104--105 °C/s) in a drop-tube reactor to closely resemble chars generated in pulverized combustion conditions. The inertinite-rich coal took 400ms to devolatilize in the drop-tube, compared to only 240ms for the vitrinite-rich sample. The longer residence time in the drop-tube reactor is expected to contribute to reactivity differences. The combustion reactivities of the chars were correlated to a range of chemical, physical, and optical characteristics including the maceral differences and high ash yields. To evaluate the combustion reactivity, isothermal and non-isothermal thermogravimetrical analyses (TGA) were utilized. The vitrinite-rich char had on average 20% higher reaction rates than the inertinite-rich char under the various combustion conditions. To verify these results, temperature programmed oxidation was used and confirmed the higher reactivity of the vitrinite-rich char, where the vitrinite-rich char reached a higher maximum carbon dioxide signal at 590ºC compared to 650ºC for the inertinite-rich char. The char samples were de-ashed with HCl and HF acid which resulted in an increase in combustion reactivity. The maximum reaction rate of the high-ash (36%) inertinite-rich char increased with 80% after de-ashing. This suggested that the ash acted as a barrier, and the removal of ash most likely increased the access to reactive surface area.;The chemical and physical structures of the chars were characterized through a range of different analytical techniques to quantify the factors contributing to reactivity differences. The morphologies of the chars were characterized with SEM and optical microscopy, while quantitative information on the ordered nature of chars was obtained through XRD on de-ashed chars. The inertinite-rich coal experienced limited fluidity during heat-treatment, resulting in slower devolatilization, limited growth in crystallite height (11.8 to 12.6A), only rounding of particle edges, and over 40% of mixed-dense type chars. The vitrinite-char showed more significant structural transformations; producing mostly (80%) extensively swollen crassisphere, tenuisphere, and network-type chars, and XRD showed a large increase in crystallite height (4.3 to 11.7A). Nitrogen adsorption and small-angle X-ray scattering (SAXS) were utilized to compare the nitrogen surface areas and pore size distributions of the two chars. Both chars were mostly mesoporous but the inertinite-rich char had double the average pore size, which also resulted in a larger nitrogen surface area since nitrogen can only access surface areas in larger pores. The BET surface area was 3.9 and 2.7m2/g for the inertinite- and vitrinite-rich chars respectively. SAXS data showed that the vitrinite-rich char had 60% higher frequencies of pores in the micropore range. Helium porosimetry indicated that the inertinite-rich coal and resultant char had higher densities than the vitrinite coal and char; 1.6 and 2.0 g/cm3, compared to 1.3 and 1.9g/cm3 (dry basis). It is difficult to determine the extent to which the above mentioned factors contribute to the combustion reactivity differences. (Abstract shortened by UMI.).
机译：南非有大量的二叠纪年龄，高灰分烟煤。尽管这些煤具有重要的经济意义，但尚未对其行为进行深入研究。这项研究比较了湿筛分至200 x 400目的窄粒度分布的富含惰性钙矿（87.7％dmmf）和富含钙质石（91.8％dmmf）的南非煤的脱挥发分和随后的燃烧行为。在滴管式反应器中，在快速加热条件下（104--105°C / s）产生热解炭，与粉状燃烧条件下产生的炭非常相似。富含惰质岩的煤在滴管中脱挥发分需要400毫秒，而富含镜质岩的样品只有240毫秒。预期在滴管式反应器中更长的停留时间会导致反应性差异。炭的燃烧反应性与一系列化学，物理和光学特性相关，包括宏观差异和高灰分产率。为了评估燃烧反应性，使用了等温和非等温热重分析（TGA）。在各种燃烧条件下，富含镜质煤焦的反应速率平均比富含惰质煤焦的反应速率高20％。为了验证这些结果，使用了程序升温氧化法，并证实了富含镜质炭的炭具有更高的反应性，其中富含镜质炭的炭在590ºC时达到了最高的最大二氧化碳信号，而富含惰质炭的炭则达到了650ºC。炭样品用HCl和HF酸除灰，可提高燃烧反应活性。高灰分（36％）惰质石炭的最大反应速率在脱灰后增加了80％。这表明灰烬起到了屏障的作用，并且灰烬的去除最有可能增加了反应性表面积的获得。炭的化学和物理结构通过一系列不同的分析技术进行了表征，以量化影响反应性的因素差异。通过SEM和光学显微镜对炭的形态进行了表征，同时通过XRD对脱灰后的炭获得了炭有序性质的定量信息。富含惰性矿物的煤在热处理过程中流动性有限，导致脱挥发分较慢，微晶高度（11.8至12.6A）的增长有限，仅颗粒边缘呈圆形，并且混合密实型炭的含量超过40％。镜质炭-炭显示出更显着的结构转变。产生的大部分（80％）的Crassisphere，tenuisphere和网络型炭广泛膨胀，XRD显示微晶高度大幅增加（4.3至11.7A）。利用氮吸附和小角X射线散射（SAXS）来比较两种炭的氮表面积和孔径分布。两种炭都大多是中孔的，但是富含惰质石炭的炭具有平均孔径的两倍，这也导致了较大的氮表面积，因为氮只能进入较大孔的表面积。富含惰质石和镜质体的炭的BET表面积分别为3.9和2.7m2 / g。 SAXS数据表明，富含微晶石的炭在微孔范围内的孔隙频率高60％。氦孔隙率法表明，富含惰质石的煤和生成的炭的密度高于镜质煤和炭。 1.6和2.0 g / cm3，而1.3和1.9g / cm3（干基）。难以确定上述因素对燃烧反应性差异的贡献程度。 （摘要由UMI缩短。）。

著录项

  • 作者

    Louw, Enette.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Engineering Mechanical.;Chemistry Molecular.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 213 p.
  • 总页数 213
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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