提质过程中褐煤表面物理化学结构的调变及其对水分复吸行为的影响

发布时间：2018-04-11 08:39

本文选题：褐煤 + 水分复吸　；参考：《太原理工大学》2016年硕士论文

【摘要】：煤炭作为我国能源消费的基石,长期以来占到能源消费结构的70%左右。随着优质煤资源的日益紧缺,储量丰富的褐煤的大规模开采利用势在必行。但是褐煤水分含量高、热值低、易风化、易自燃等特点严重制约了褐煤的高效清洁利用。褐煤表面含有丰富的含氧官能团,加之疏松多孔的结构使其即使是在干燥提质后也会再次吸收水分。因此,在干燥提质过程中对褐煤物理和化学结构进行调变,是褐煤清洁高效利用的理论基础,具有非常重要的现实意义。本文选取我国典型的褐煤作为研究对象,运用原位傅里叶红外光谱仪对不同提质条件下褐煤基团的变化情况进行了表征,分析了褐煤在干燥提质中各种基团的分解、氧化和转化规律。结合化学滴定法及氮吸附表征结果,考察了不同提质气氛和时间下褐煤物化结构的演变及其对水分复吸特性的影响。研究结果主要包括以下几个方面:(1)提质褐煤的平衡含水量(EMC)随着提质时间的延长及温度的升高而降低。160 oC和200 oC下,氮气气氛中所得提质煤样的EMC明显低于空气氛中所得煤样,但240 oC下,两种气氛下所得煤样的EMC基本相等。(2)CHX基团在提质温度高于200 oC时明显减少,尤其在空气气氛下减少较多。分解活化能的大小顺序为CH2CHCH3,氧化活化能大小顺序为CHCH3CH2。褐煤中羧基的亲水性最强,醛类物质次之,其分别约为酮类物质的9倍和3倍。醌类、酯类和酸酐物质与其平衡含水量之间没有明显关系。(3)提质温度高于160 oC时,N2和水蒸气以及CO2和水蒸气的混合气氛中煤样的失重率大于单一气氛。混合气氛中水蒸气的存在使得褐煤在提质过程中的中孔数量减小,比表面积明显降低,从而使得提质煤的EMC减小。提质煤的在相对湿度95%时水分子填满小于40nm的孔道,EMC与孔体积有良好的线性关系。(4)N2和水蒸气混合气氛下所得提质煤样的COOH含量较N2中得到的煤样有明显增加,但在CO2中,水蒸气的引入对COOH的分解影响不大。N2气氛下,随着干燥提质的进行,OH和C=O含量逐渐减少。在N2和水蒸气混合气氛中,C=O在干燥过程中先减少后增加。(5)相对湿度小于17%时,煤样的水分复吸量主要与含氧官能团的量有关。在17%~75%时,EMC的变化速率较慢,说明水分在褐煤表面形成多层吸附。相对湿度由75%增加到95%时,水分在褐煤孔道中形成毛细凝聚,同时水分在脱附过程中出现滞后现象。
[Abstract]:As the cornerstone of energy consumption in China, coal has accounted for about 70% of the energy consumption structure for a long time.With the increasing shortage of high quality coal resources, it is imperative to exploit lignite with abundant reserves.However, the high moisture content, low calorific value, easy weathering and easy spontaneous combustion of lignite seriously restrict the efficient and clean utilization of lignite.Lignite has abundant oxygen-containing functional groups on the surface, and the porous structure makes it absorb water again even after drying and tempering.Therefore, adjusting the physical and chemical structure of lignite during drying and upgrading is the theoretical basis for the clean and efficient utilization of lignite, which is of great practical significance.In this paper, the typical lignite in China is selected as the research object. The changes of lignite groups under different quality conditions are characterized by in situ Fourier transform infrared spectroscopy (FTIR), and the decomposition of various groups in the drying process of lignite is analyzed.Oxidation and conversion.Combined with the results of chemical titration and nitrogen adsorption, the evolution of the physicochemical structure of lignite and its influence on the water reabsorption characteristics were investigated under different upgrading atmosphere and time.The results include the following aspects: (1) the equilibrium water content of lignite is decreased with the increase of temperature and time. The EMC of extracted coal in nitrogen atmosphere is obviously lower than that in empty atmosphere.However, at 240oC, the EMC of the coal samples obtained in two kinds of atmospheres was basically equal. The EMC group decreased obviously when the quality temperature was higher than 200oC, especially in the air atmosphere.The order of decomposition activation energy is Ch _ 2CHCH _ 3 and the order of oxidation activation energy is CHCH _ 3CH _ 2.The hydrophilicity of carboxyl group was the strongest in lignite, followed by aldehydes, about 9 times and 3 times of ketones, respectively.There is no obvious relationship between quinones, esters and anhydride and their equilibrium water content. 3) the weight loss rate of coal samples in mixed atmosphere of nitrogen and water vapor and CO2 and water vapor is higher than that in single atmosphere when the temperature is higher than 160oC.The presence of water vapor in the mixed atmosphere decreases the number of mesoporous and the specific surface area of lignite in the process of upgrading, thus reducing the EMC of lignite.There is a good linear relationship between the pore volume of extracted coal and the pore volume when the water molecule is filled with water molecule less than 40nm at 95% relative humidity. The COOH content of the extracted coal sample in mixed atmosphere is obviously higher than that of the coal sample in N2, but in CO2, the content of EMC is higher than that of the coal sample in N _ 2, but in CO2, the content of COOH is much higher than that of coal sample in N _ 2.The introduction of water vapor had little effect on the decomposition of COOH in N _ 2 atmosphere, and the content of OH and C _ 2O gradually decreased with the drying and upgrading.In the mixed atmosphere of N2 and water vapor, the moisture reabsorption of coal samples is mainly related to the amount of oxygen functional groups when the relative humidity is less than 17.The change rate of EMC is slow in the range of 17 ~ 75, which indicates that the water is adsorbed on the surface of lignite.When the relative humidity is increased from 75% to 95%, the capillary condensation is formed in the lignite pore channel, and the moisture lags in the desorption process.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TD849.2

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