Effect of low-temperature pre-oxidation on microstructure and reignition characteristic of water-immersion lignite

IF 3 3区 工程技术 Q2 CHEMISTRY, ANALYTICAL
Wei Zhang, Deming Wang, Haihui Xin, Zhenhai Hou, Chenguang Wang, Zuoming Xu, Zhangfan Qi, Jian Gan
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Abstract

The residual coal is prone to oxidation in different degrees after being immersed-dried in waterlogged goafs, but the reignition characteristics of water-immersion coal by low-temperature pre-oxidation remain unclear. Herein, lignite was pre-oxidized to 40 °C, 80 °C, 120 °C, 160 °C, 200 °C, and 230 °C after 60 days of immersion. Moreover, the microstructure changes of water-immersed lignite after oxidized were investigated using low-temperature nitrogen adsorption and infrared spectroscopy, and its spontaneous combustion characteristics were assessed employing thermogravimetry. The results displayed that the pore volume, specific surface area, and pore diameter increased and then decreased as the pre-oxidation temperature rose. Specifically, lower temperatures (below 80 °C) promoted the formation of micropores and mesopores, as well as the merger and transformation of pores into macropores, which facilitates the diffusion and adsorption of oxygen. However, higher temperature oxidation (> 200 °C) reduced both the number of pores and the content of reducing functional groups (–OH, –CH3, and –CH2). Comparatively, the lignite oxidized at 80 °C maintained a strong chemical reactivity owing to the high relative content of -CH2 and C = O. Furthermore, the pre-oxidation treatment mainly affected the thermal decomposition and gas-phase combustion of the water-immersed coals. Moreover, as the degree of oxidation rose, the characteristic temperatures (T2–T4) and the activation energy first decreased and then increased, while the comprehensive combustion index exhibited an opposite trend. Notably, the critical oxidation temperature of 80 °C is a turning point for the above change. Thus, the pre-oxidation at 80 °C heightens the risk of reignition in water-immersion coal owing to its developed pore structure and abundant active groups. It is imperative to avoid the critical temperature during low-temperature oxidation of water-immersed coals.

Abstract Image

低温预氧化对水浸褐煤微观结构和复燃特性的影响
残留煤炭在浸水干燥后易发生不同程度的氧化,但低温预氧化对浸水煤炭的复燃特性尚不清楚。在本文中,褐煤在浸水 60 天后分别被预氧化至 40 ℃、80 ℃、120 ℃、160 ℃、200 ℃ 和 230 ℃。此外,还利用低温氮吸附和红外光谱法研究了氧化后水浸褐煤的微观结构变化,并利用热重法评估了其自燃特性。结果表明,随着氧化前温度的升高,孔隙体积、比表面积和孔径先增大后减小。具体来说,较低的温度(低于 80 °C)促进了微孔和中孔的形成,以及孔隙向大孔隙的合并和转化,这有利于氧气的扩散和吸附。然而,更高的氧化温度(> 200 °C)会减少孔隙的数量和还原官能团(-OH、-CH3 和 -CH2)的含量。相比之下,在 80 °C 下氧化的褐煤由于 -CH2 和 C = O 的相对含量较高而保持了较强的化学反应活性。此外,预氧化处理主要影响水浸煤的热分解和气相燃烧。此外,随着氧化程度的升高,特征温度(T2-T4)和活化能先降低后升高,而综合燃烧指数则呈现相反的趋势。值得注意的是,80 °C 的临界氧化温度是上述变化的转折点。因此,由于水浸煤的孔隙结构发达,活性基团丰富,80 ℃的预氧化会增加水浸煤的复燃风险。因此,在水浸煤的低温氧化过程中,必须避开临界温度。
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来源期刊
CiteScore
8.50
自引率
9.10%
发文量
577
审稿时长
3.8 months
期刊介绍: Journal of Thermal Analysis and Calorimetry is a fully peer reviewed journal publishing high quality papers covering all aspects of thermal analysis, calorimetry, and experimental thermodynamics. The journal publishes regular and special issues in twelve issues every year. The following types of papers are published: Original Research Papers, Short Communications, Reviews, Modern Instruments, Events and Book reviews. The subjects covered are: thermogravimetry, derivative thermogravimetry, differential thermal analysis, thermodilatometry, differential scanning calorimetry of all types, non-scanning calorimetry of all types, thermometry, evolved gas analysis, thermomechanical analysis, emanation thermal analysis, thermal conductivity, multiple techniques, and miscellaneous thermal methods (including the combination of the thermal method with various instrumental techniques), theory and instrumentation for thermal analysis and calorimetry.
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