Influence of hydrothermal upgrading on physical and chemical structures and moisture readsorption characteristics of a lignite
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摘要: 选取云南昭通褐煤进行了水热提质处理, 依托傅里叶变换红外光谱技术和氮气等温吸附模型分析研究了不同提质温度(150-300 ℃) 下煤样表面含氧官能团和孔隙结构的演化行为, 考察了复吸水特性的变化规律。结果表明, 随着提质温度的不断升高, 主要亲水性含氧官能团(-OH、-COOH、>C=O) 不断减少; 煤样的孔隙结构发生显著改变, 比表面积和总孔容积先增后减, 在250-300 ℃水热条件下有焦油产生; 受理化结构协同影响的复吸水特性得到了有效遏制, 复吸水率随着提质温度的升高不断下降; 对提质褐煤进行储存时, 环境湿度是影响褐煤复吸水的关键因素, 高温水热、低温低湿度储存更能提高褐煤的提质效果。Abstract: Zhaotong lignite from Yunnan province was hydrothermally upgraded at 150-300 ℃, then the changes of surface oxygen-containing groups were analyzed by Fourier transform infrared spectroscopy, and the evolution of pore structure was identified by nitrogen adsorption isotherm. Constant temperature and humidity incubator were used to investigate moisture readsorption characteristics. The results indicate that the main hydrophilic oxygen-containing functional groups (-OH, -COOH, >C=O) decrease and are removed effectively with increase of upgrading temperature. Large changes occur in pore structures of the treated coal, in which the specific surface area and total pore volume increase firstly then decrease with increasing temperature, moreover tar initially generate at 250-300 ℃. Moisture readsorption performance is restrained effectively under the synergy effect of physical and chemical structures, and the moisture readsorption ratio decreases continuously with increase of upgrading temperature. Environment humidity is a key factor affecting moisture readsorption considering storage of the upgraded lignite. Therefore the situation of hydrothermal upgrading at high temperature and storage at low temperature and low humidity could be more advantageous in terms of enhancing efficiency of lignite upgrading.
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图 1 水热改性提质实验装置示意图
Figure 1 Schematic diagram of experimental apparatus for hydrothermal upgrading
图 4 饱和水蒸气压力随温度的变化
Figure 4 Variation of saturated water vapor pressure with temperature
图 7 原煤及提质煤的SEM照片
Figure 7 SEM images of the raw and upgraded lignites
(a): raw coal; (b): SR150; (c): SR200; (d): SR250; (e): SR300
图 8 原煤及提质煤的复吸水过程(RH=80%)
Figure 8 Moisture readsorption of the raw and upgraded lignites (RH=80%)
图 9 不同环境湿度、温度下的复吸水率
Figure 9 Moisture readsorption ratios under different temperature and humidity
表 1 水热提质煤的煤质特性
Table 1 Analysis samples after hydrothermal upgrading
Sample Yield w/% Ultimate analysis wdaf /% Proximate analysis wd% Qnet, d/(MJ·kg-1) Weight ratio (daf) C H N O* S FC V A H/C O/C Raw coal - 57.16 4.93 2.13 33.83 1.95 28.27 47.75 23.98 15.95 0.086 0.592 SR150 90.5 58.24 4.96 2.16 33.14 1.50 30.47 44.99 24.54 16.16 0.085 0.569 SR200 86.2 60.96 5.07 2.24 30.14 1.59 30.71 42.83 26.46 16.76 0.083 0.494 SR250 81.3 63.70 5.06 2.38 27.15 1.71 33.16 39.23 27.61 17.40 0.079 0.426 SR300 73.6 66.74 5.03 2.39 23.90 1.94 34.82 36.22 28.96 18.05 0.075 0.358 O*：by difference；d：dry；daf：dry and ash free；Qnet：net calorific value 
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