Development characteristics of coal microfracture and coal petrology control under cyclic high voltage electrical pulse
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摘要: 基于开放式循环高压电脉冲实验平台,针对肥煤、贫煤和无烟煤3种不同变质程度煤样,开展金属丝和含能材料2种能量加载方式下的煤样冲击致裂实验,通过光学显微镜分析循环冲击作用下煤中微裂隙发育的煤级与载荷响应特征,研究微裂隙扩展演化与显微组分之间的关系。结果发现:①增加循环冲击次数,微裂隙密度的增大趋势是非线性的,大致可划分为初期缓慢增加、中期快速增大、后期趋于稳定3个阶段,说明并非循环冲击次数越多致裂效果越好,而是存在一个最佳冲击次数。②金属丝加载方式下煤中微裂隙较含能材料加载下更为发育;整体上,肥煤的微裂隙发育程度高于贫煤,贫煤高于无烟煤,反映循环高压电脉冲在致裂效果上可能具有“双低效应”,即低变质程度煤加载低能量致裂效果可能更好。③微裂隙发育程度在显微组分之间具有差异性和侧重性,镜质组最发育,惰质组次之,壳质组最少,这是镜质组含量大(空间优势)、原位裂隙密度大(位置优势)、脆性较大(力学优势)综合作用的结果。④微裂隙在显微组分中的扩展演化轨迹可归纳为穿越显微组分、局限在显微组分内部、沿显微组分边界发育和形态呈斜列、渐进式张剪性扩展等主要特征。研究结论对进一步揭示循环高压电脉冲煤层致裂微观机制,明确工程实践目标煤层,优化作业工艺参数和提高作业效果具有重要的理论意义。Abstract: Based on the open experimental platform of cycle high voltage electrical pulse generator, the impact cracking experiments of three kinds of coal samples with different metamorphic degrees, namely, fat coal, lean coal and anthracite were carried out under two kinds of energy loading methods: metal wire and energetic material. Then, the characteristics of coal rank and load response of microfracture were analyzed by the polarizing microscope, and the relationship between microfracture evolution and macerals was studied. The results show that the increasing trend between the density of microcracks and the impact times is nonlinear, which can be roughly divided into three stages: slow increase in the initial stage, rapid increase in the middle stage, and stabilization in the later stage in the first place. This means that the cracking effect is not better with more cyclic impacts, and there is an optimal impact number. Second, the microfracture density in coal under wire loading is more developed than that under energetic material loading. In general, the development degree of micro fissures in fat coal is higher than that in lean coal, and that in lean coal is higher than that in anthracite. It shows that the cyclic high-voltage electrical pulse has "double bottom effect" in fracturing effect. Namely, when both low energy loading condition and low rank coal are available, the cracking effect is better. Third, there are some differences and emphases in the development of microfractures among the macerals. Vitrinite is the most developed, followed by inertinite, and exinite is the least developed. This is mainly due to the advantages of vitrinite, such as volume content(space dominance), original fissure density(location advantage) and brittleness(mechanical superiority). Fourth, the microcracks in the macerals can be classified into four main types: through the macerals, confined within the macerals, developing along the boundary of the macerals, showing oblique morphology and progressive tensile shear extension. Finally, these conclusions are of important theoretical significance for further revealing the microscopic mechanism of coal seam fracture induced by cyclic high voltage electric pulse, clarifying the target coal seam in the engineering practice, optimizing the working process parameters and improving the operation results.
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Key words:
- cyclic impact /
- voltage pressure pulse /
- microfracture /
- macerals /
- coal petrology
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表 1 煤岩煤质测试结果及实验条件
Table 1 Coal quality test results and experimental conditions
煤级 编号 加载方式 冲击次数 Rmax/% 显微组分φ/% 工业分析ω/% 镜质组V 惰质组I 壳质组E 水分Mad 灰分Ad 挥发分Vdaf 肥煤 FM1 金属丝 200 1.20 83.87 13.76 2.37 0.86 6.42 35.21 FM2 含能材料 10 1.12 82.38 16.02 1.60 1.03 4.71 29.70 贫煤 PM1 金属丝 60 2.39 89.69 8.74 1.57 1.38 7.35 13.30 PM2 含能材料 60 2.42 90.10 8.87 1.03 1.35 7.48 13.08 无烟煤 WY1 金属丝 150 4.12 92.47 6.48 1.05 3.82 17.84 9.60 WY2 含能材料 125 3.57 90.12 9.32 0.56 3.39 19.21 10.51 -
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