不同煤阶热压型煤的孔隙结构及其力学与渗流特性

Pore structure as well as mechanical and seepage characteristics of hot-pressed coal briquettes with different coal ranks

  • 摘要: 为解决物理相似模拟试验用型煤强度及渗透性与原煤差异较大的问题,探究不同煤阶煤样热压成型后的孔隙结构、力学与渗流特性,揭示煤阶对热压型煤性能的影响机理,采用自主研发的热压型煤成型系统,制备了4种不同煤阶的热压型煤试样,基于高压压汞与低压液氮吸附试验,系统表征并对比了热压型煤与原煤的孔隙结构异同;通过开展单轴压缩与三轴渗流试验,分析了煤阶对热压型煤力学与渗流特性的影响规律;综合获取的关键参数,应用基于欧式距离的相似性度量方法,定量评估了热压型煤与原煤的相似程度。结果表明:在孔隙结构方面,随着煤阶升高热压型煤的最可几孔径先增大后减小,孔隙连通性先增强后减弱;在力学与渗流特性方面,随着煤阶升高,热压型煤的单轴抗压强度及弹性模量逐渐减小,初始渗透率先增大后减小;相似性分析表明,褐煤热压型煤与其原煤的相似度最高,其最可几孔径为原煤的0.8倍,单轴抗压强度达13.04 MPa,弹性模量为其原煤的1.012倍,主应力差峰值为原煤的0.98倍,初始渗透率为其原煤的1.3倍,其余煤阶热压型煤与相应原煤仍存在一定差距。然而,与常规冷压型煤相比,所有煤阶热压型煤的强度皆有所提升,渗透率也均有所减小,且该改性效果随煤阶升高而逐渐减弱,说明煤阶是影响热压型煤性能改善效果的关键因素。

     

    Abstract: To address the problem that the strength and permeability of coal briquettes used in physical similarity simulation tests differ significantly from those of raw coal, this study investigates the pore structure, mechanical and seepage characteristics of coal samples with different ranks after hot-pressing, and reveals the influence mechanism of coal rank on the properties of hot-pressed coal briquettes. Using a self-developed hot-pressed coal briquette forming system, hot-pressed coal briquette specimens of four different coal ranks are prepared. The pore structure characteristics of hot-pressed coal briquettes and raw coal with different coal ranks are comprehensively characterized and compared via high-pressure mercury intrusion and low-pressure nitrogen adsorption tests. Uniaxial compression and triaxial seepage tests are conducted to analyze the influence of coal rank on the mechanical and seepage properties of hot-pressed briquettes. Finally, based on the key parameters obtained, the similarity between hot-pressed coal briquettes and raw coal is quantitatively evaluated using a Euclidean distance-based similarity measurement method. Results indicate that in terms of pore structure, with the increase of coal rank, the most probable pore diameter of hot-pressed coal briquettes first increases and then decreases, and the pore connectivity first enhances and then weakens. In terms of mechanical and seepage properties, uniaxial compressive strength and elastic modulus of hot-pressed coal briquettes decrease gradually with increasing coal rank, while initial permeability first increases and then decreases. Similarity analysis indicates that hot-pressed lignite briquettes exhibit the highest similarity to their raw coal, with the most probable pore diameter being 0.8 times that of raw coal, uniaxial compressive strength of 13.04 MPa, elastic modulus of 1.012 times that of raw coal, peak principal stress difference of 0.98 times that of raw coal, and initial permeability of 1.3 times that of raw coal. Hot-pressed coal briquettes of other coal ranks still show certain gaps compared with their corresponding raw coal. However, compared with conventional cold-pressed briquettes, all hot-pressed briquettes of different coal ranks show increased strength and reduced permeability, and this modification effect gradually weakens with increasing coal rank, indicating that coal rank is a key factor influencing the performance improvement of hot-pressed coal briquettes.

     

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