【作者】 杨卫华；

【导师】 蒋静宇；

【作者基本信息】 中国矿业大学 ， 安全科学与工程， 2020， 硕士

【摘要】 为了系统地研究水分对低阶煤的时变瓦斯动力学特性的影响机制,本研究从三个典型低阶煤矿铁法大兴煤矿、沈北蒲河煤矿、铁法小青煤矿取样,分别编号为TFDX、SBPH、TFXQ,并选取义马新义煤矿的中阶煤样作为对比,编号为YMXY。三个低阶煤样的镜质体反射率（R_o）的范围为0.57～0.70%,对比煤样YMXY的R_o为1.09%。采用工业分析、元素分析以及三种光谱技术分析了四个煤样的化学结构;借助气体吸附法、低场核磁共振（NMR）和小角X射线散射（SAXS）等方法分析了四个煤样的孔隙结构特征;运用蒸汽吸附的方法制备了润湿均匀的含水煤样,采用等温瓦斯吸附/解吸动力学测试装置测试并分析了低阶煤的瓦斯吸附解吸特性;根据三种瓦斯扩散数学模型计算了不同含水率低阶煤样的瓦斯扩散系数,并基于动扩散模型的时变扩散系数分析了水分对低阶煤时变扩散动力学特性的影响机制。本研究主要结论如下:（1）四个煤样微晶单元有序化程度较低,且石墨化程度和芳构化程度普遍较低。其中三个低阶煤样的芳构化程度相对对比煤样YMXY较低,但含氧官能团含量较高。煤的分子结构在一定程度上影响煤体中孔隙的发育,分子结构中的芳香族结构对微孔和中孔的发育在一定程度上产生了抑制的作用,但其中芳香环层的堆积缩合作用却促进了中孔的发育。（2）通过传统的物理吸附法分析得知,三个低阶煤样微孔的比表面积范围为187.736～192.932 m²/g;中孔的孔容为0.017～0.041cm³/g;对比煤样的微孔的比表面积为182.813m²/g,中孔的孔容为0.009cm³/g。NMR实验结果表明三个低阶煤样中的吸附孔较为发育且连通性较好,而对比煤样的渗流孔较为发育且连通性较好。SAXS表明三个低阶煤的中孔较为发育,且煤中存在部分孔径>16nm的封闭孔隙无法用传统的N₂吸附法探测。（3）三个低阶煤样的V_L的范围分别为31.14～35.14m³/t,明显大于YMXY的V_L,其值为28.21m³/t。这主要是由于煤体对瓦斯的吸附能力在很大程度上受孔隙结构的影响,微孔的比表面积和中孔的孔容对低阶煤瓦斯吸附能力起到重要的促进作用。此外,分子结构中的脂肪族结构的含量增强了瓦斯的吸附能力,而芳香族结构则起到了抑制的作用。（4）四个干燥基煤样的极限解吸瓦斯量由大到小的顺序依次为TFDX>SBPH>TFXQ>YMXY。三个低阶煤样由于吸附孔连通性较好,能够使得煤体中的瓦斯在较短的时间内迅速解吸。煤体中水分的增加会使煤体的极限解吸瓦斯量减小,但当增加到一定程度时,其对极限解吸瓦斯量的影响不再明显。（5）动扩散模型计算得到的时变扩散系数能够较为精准地表征低阶颗粒煤甲烷全时扩散量和扩散规律。四个干燥基煤样的初始扩散系数D₀从大到小依次为SBPH>TFDX>TFXQ>YMXY,随着煤中水分的增加,各个煤样的初始扩散系数D₀均降低。煤样的孔隙尺寸越小,D₀受水分影响而下降的幅度就越大。瓦斯在扩散过程中随着孔径的逐渐减小和孔隙网络的复杂程度的增加,时变扩散系数不断衰减。吸附孔连通性越好的煤样,瓦斯的时变扩散系数衰减至0的时间越短。煤体中水分的增加降低了时变扩散系数,减缓了时变扩散系数衰减的速率,同时也缩短了衰减至0的时间。本文共有图45幅,表16个,参考文献134篇。更多还原

【Abstract】 In order to study the influence mechanism of moisture on the time-varying gas dynamic characteristics of low-rank coal systematically,coal samples were taken from three typical low-rank coal mines including Tiefa Daxing Coal Mine,Shenbei Puhe Coal Mine,and Tiefa Xiaoqing Coal Mine,named as TFDX,SBPH and TFXQ.The middle-rank coal sample of Yima Xinyi Coal Mine was selected as the comparison,named as YMXY.The vitrinite reflectance（R_o）of the three low-rank coal samples ranged from 0.57 to 0.70%,and that of YMXY was 1.09%.The chemical structure of the four coal samples was analyzed using proximate analysis,ultimate analysis,and three spectroscopic techniques.The pore structure characteristics of the four coal samples were analyzed by means of gas adsorption,low-field nuclear magnetic resonance（NMR）and small-angle X-ray scattering（SAXS）.The steam-absorbing method was used to make uniformly wetting coal samples.The isothermal gas adsorption/desorption kinetic test device was used to test and analyze the gas adsorption and desorption characteristics of low-rank coal.Based on the three diffusion mathematical models,the gas diffusion coefficients of coal samples with different water contents were calculated,and the mechanism of the influence of moisture on the dynamic of low-rank coal time-varying diffusion was analyzed based on the time-varying diffusion coefficients.The main conclusions of this study are as follows:（1）The order degree of the four coal samples microcrystalline units is low,and the degree of graphitization and aromatization are generally low.Among them,the aromatization degree of three low-rank coal samples is lower than that of the coal sample YMXY,but the content of oxygen-containing functional groups is higher.The molecular structure of coal affects the development of pores in coal to a certain extent.The aromatic structure in the molecular structure inhibits the development of micropores and mesopores to a certain extent,but the accumulation and condensation of the aromatic ring layer promotes the development of mesopores.（2）According to the analysis by traditional physical adsorption methods,the specific surface area of the micropores of the three low-rank coal samples is in the range of 187.736～192.932 m²/g;the pore volume of the mesopores is 0.017～0.041cm³/g;the micropore specific surface area of the comparative coal sample is 182.813 m²/g,and the pore volume of the mesopores is 0.009 cm³/g.NMR experimental results show that the adsorption pores in the three low-rank coal samples are well developed and well connected,while the seepage pores in the comparative coal samples are well developed and well connected.SAXS shows that the mesopores of the three low-rank coals are more developed,and there are some closed pores with a pore diameter>16nm in the coal that cannot be detected by traditional N₂ adsorption methods.（3）The range of V_L of the three low-rank coal samples is 31.14～35.14m³/t,which is obviously larger than that of YMXY,and its value is 28.21m³/t.This is mainly because the adsorption capacity of coal to gas is largely affected by the pore structure and molecular structure.Micropores and mesopores play an important role in promoting the adsorption capacity of low-rank coal gas.The content of aliphatic structure in the molecular structure enhances the gas adsorption capacity,while the aromatic structure plays a role in suppression.（4）The order of limit analytical gas of four dry base coal samples from large to small is TFDX>SBPH>TFXQ>YMXY.The three low-rank coal samples have good connectivity of the adsorption pores,which can make the gas in the coal body desorb quickly in a short time.The increase of moisture in the coal body will reduce the limit desorption gas quantity of the coal body,but when it is increased to a certain extent,its influence on the limit desorption gas quantity is no longer obvious.（5）The time-varying diffusion coefficient calculated by the dynamic diffusion model can accurately characterize the full-time diffusion amount and diffusion law of low-order granular coal methane.The initial diffusion coefficients D₀ of the four dry-base coal samples are SBPH>TFDX>TFXQ>YMXY from large to small.As the moisture in the coal increases,the initial diffusion coefficients D₀ of each coal sample decrease.The smaller the pore size of the coal sample,the greater the decrease in D₀due to moisture.In the process of gas diffusion,as the pore size gradually decreases and the complexity of the pore network increases,the time-varying diffusion coefficient continues to decay.The better the coal sample connectivity,the shorter the time for the time-varying diffusion coefficient of gas to decay to zero.The increase in moisture in the coal reduces the time-varying diffusion coefficient,slows the rate of decay of the time-varying diffusion coefficient,and shortens the time to decay to 0.This article has 45 graphes,16 tables,and 134 references.更多还原