Low-temperature pyrolysis offers a potential way of upgrading lignite and producing chars to replace thermal or pulverized coal injection (PCI) coals in combustion or being used as inert components in a blend for coking. In this study, the characteristics of chars from low-temperature pyrolysis of two lignite coals have been investigated. The changes in char morphology and chemical structures were investigated using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The combustion reactivity of chars was analyzed in a thermogravimetric analyer (TGA) using non-isothermal techniques. The results show that chars from low-temperature pyrolysis of lignite coal below 450 °C were more reactive than higher temperature chars. Higher reactivity of low-temperature chars was attributed to the higher concentration of active sites and lower degree of structural order compared to that of high-temperature chars. Indonesian (YN) lignite showed a higher weight loss rate compared to Hulunbeier (HL) coal, which was attributed to a higher concentration of liptinite and vitrinite in YN coal. FTIR analysis indicated that the aliphatic structures and oxygen-containing functional groups decreased with an increasing pyrolysis temperature. The intensity of tightly bound cyclic OH tetramers and OH–ether O hydrogen bonds were higher than other hydrogen bonds in the 3700–3600 cm^–1 region of infrared (IR) spectra. The density of alkyl chains and cross-linking reactions affected the yield of tar. The aromaticity of char increased with an increasing pyrolysis temperature. The abundance of C═O and COOH structures decreased drastically with increasing temperature. A lower concentration of active sites on high-temperature chars resulted in lower combustion reactivity compared to low-temperature chars. The C–O and C═C groups decreased as the temperature increased possibly because of the aromatic condensation. The extent of aromatic substitution decreased up to 650 °C. At temperatures above 650 °C, the degree of aromaticity was strengthened and larger condensed aromatic nuclei were formed. Brunauer–Emmett–Teller (BET) surface area analysis revealed that high-temperature chars have significantly higher surface area compared to chars produced at low temperatures. However, the concentration of active sites was lower in high-temperature chars. Therefore, it can be concluded that diffusion was the main reaction mechanism in high-temperature chars.

中文翻译：

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褐煤低温热解炭的特性

低温热解提供了升级褐煤和生产焦炭的潜在途径，以替代燃烧中的热煤或粉煤注入（PCI）煤，或在焦化混合物中用作惰性组分。在这项研究中，研究了两种褐煤的低温热解焦炭的特性。使用扫描电子显微镜（SEM）和傅里叶变换红外光谱（FTIR）研究了炭的形态和化学结构的变化。使用非等温技术在热重分析仪（TGA）中分析了焦炭的燃烧反应性。结果表明，在低于450°C的条件下褐煤的低温热解炭比高温炭更具活性。与高温炭相比，低温炭的较高反应性归因于较高的活性位点浓度和较低的结构有序度。与呼伦贝尔（HL）煤炭相比，印尼（YN）褐煤显示出更高的失重率，这归因于YN煤中的锂皂石和镜质石浓度更高。FTIR分析表明，脂肪族结构和含氧官能团随着热解温度的升高而降低。在3700–3600 cm处，紧密结合的环状OH四聚体和OH-醚O氢键的强度高于其他氢键 这归因于YN煤中更高含量的锂皂石和镜质石。FTIR分析表明，脂肪族结构和含氧官能团随着热解温度的升高而降低。在3700–3600 cm处，紧密结合的环状OH四聚体和OH-醚O氢键的强度高于其他氢键 这归因于YN煤中更高含量的锂皂石和镜质石。FTIR分析表明，脂肪族结构和含氧官能团随着热解温度的升高而降低。在3700–3600 cm处，紧密结合的环状OH四聚体和OH-醚O氢键的强度高于其他氢键^–1红外（IR）光谱区域。烷基链的密度和交联反应影响焦油的收率。炭的芳香性随热解温度的升高而增加。随着温度的升高，C structuresO和COOH结构的丰度急剧下降。与低温炭相比，活性炭上较低的活性位点浓度导致较低的燃烧反应性。C–O和C═C基团随着温度的升高而降低，这可能是由于芳香族缩合所致。芳族取代的程度降低到650°C。在高于650°C的温度下，芳香度得到增强，并形成了更大的稠合芳香核。Brunauer-Emmett-Teller（BET）的表面积分析表明，与低温下产生的炭相比，高温炭具有明显更高的表面积。但是，活性炭的浓度在高温炭中较低。因此，可以得出结论，扩散是高温炭中的主要反应机理。