Gas expansion energy of coals with different metamorphic degrees: Evolutionary characteristics and their implications for the outburst prediction
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摘要: 为了提高煤与瓦斯突出(突出)预测的准确性，选取6种不同变质程度的煤样，开展高压压汞实验、等温吸附实验，计算瓦斯膨胀能，分析不同变质程度煤的瓦斯膨胀能演化特征及其与突出预测指标间的关系。结果表明：不同变质程度煤的孔隙结构与吸附性的差异，导致煤体所含的瓦斯膨胀能存在差异。煤的总瓦斯膨胀能与吸附瓦斯膨胀能随瓦斯压力的升高而增大，增加趋势逐渐变缓；相同瓦斯压力下，煤的变质程度越高，总瓦斯膨胀能与吸附瓦斯膨胀能越大。煤的游离瓦斯膨胀能随瓦斯压力升高呈指数增大；相同瓦斯压力下，游离瓦斯膨胀能随单位质量煤体孔隙体积的增加而增大。当Rmax>1.6%，0.74 MPa对应的游离瓦斯膨胀能与初始释放瓦斯膨胀能突出临界指标42.98 mJ/g基本相等，进一步验证了游离瓦斯在突出触发阶段起主要作用，也为突出预测临界压力值采用0.74 MPa的合理性提供了科学依据。当Rmax为0.6%~1.6%时，0.74 MPa对应的游离瓦斯膨胀能小于42.98 mJ/g，夸大了煤体所具备的突出潜能，会加大防突工作量。当Rmax<0.6%，0.74 MPa对应的游离瓦斯膨胀能大于42.98 mJ/g，这会导致低指标突出灾害的发生。因此，在进行煤与瓦斯突出预测和防治时，应充分考虑煤的变质程度对突出的影响，研究可为突出预测提供新的科学依据和方法借鉴。Abstract: To achieve an elevated accuracy in the prediction of coal and gas outbursts, this study conducted mercury injection capillary pressure (MICP) tests and isotherm adsorption experiments on selected six coal samples with different metamorphic degrees. Furthermore, it calculated the gas expansion energy of coals and analyzed the evolutionary characteristics of the gas expansion energy of coals with different metamorphic degrees, as well as their relationships with the prediction indices of coal and gas outbursts. The results of this study are as follows: (1) The differences in the pore structures and adsorptivity of coals with different metamorphic degrees led to different gas expansion energy. (2) The total gas expansion energy and the adsorbed-gas expansion energy increased with gas pressure, with the increasing trend gradually slowing down. Under the same gas pressure, a higher metamorphic degree of coals was associated with higher total gas expansion energy and adsorbed-gas expansion energy. (3) The free-gas expansion energy increased exponentially with gas pressure. Under the same gas pressure, the free-gas expansion energy increased with the pore volume per unit mass of coals. (4) When Rmax > 1.6%, the free-gas expansion energy corresponding to the gas pressure of 0.74 MPa was roughly equivalent to the critical values (42.98 mJ/g) of initially released expansion energy that induced outbursts. This further verifies that free gas plays a major role in the triggering stage of outbursts and also provides a scientific basis for the rationality of using 0.74 MPa as the critical gas pressure value for outburst prediction. When Rmax ranged between 0.6%‒1.6%, the free-gas expansion energy corresponding to the gas pressure of 0.74 MPa was below 42.98 mJ/g, leading to exaggerated outburst potential of coals and increased efforts paid to outburst prevention. When Rmax < 0.6%, the free-gas expansion energy corresponding to 0.74 MPa exceeded 42.98 mJ/g, leading to the occurrence of outbursts under a low index. Therefore, it is necessary to fully consider the influence of coals’ metamorphic degrees on coal and gas outbursts. This study will provide a novel scientific basis and a method reference for the prediction of coal and gas outbursts.
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Key words:
- coal and gas outburst /
- gas expansion energy /
- coal metamorphic degree /
- pore structure /
- gas pressure /
- gas content
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图 1 吸附孔、渗流孔孔隙结构参数变化
Fig. 1 Variations in the structural parameters of adsorption and seepage pores
图 2 不同变质煤的等温吸附曲线
Fig. 2 Isothermal adsorption curves of coals with different metamorphic degrees
图 4 不同变质程度煤的瓦斯膨胀能变化
Fig. 4 Variations in gas expansion energy of coals with different metamorphic degrees
图 5 8 m3/t对应瓦斯膨胀能随煤变质程度的变化
Fig. 5 Gas expansion energy under gas content of 8 m3/t vs. coals’ metamorphic degree
图 6 0.74 MPa对应瓦斯膨胀能随煤阶的变化
Fig. 6 Gas expansion energy under gas pressure of 0.74 MPa vs. coal rank
表 1 煤样基本参数
Table 1 Basic parameters of coal samples
煤种 工业分析w/% Rmax /% 孔隙率/
%孔隙体积 /
(cm3·g−1)Mad Ad Vdaf 褐煤 1.69 6.45 36.33 0.38 7.25 0.057 气煤 2.35 8.15 34.57 0.86 3.42 0.024 肥煤 2.43 9.38 30.45 1.27 3.31 0.022 焦煤 0.61 11.14 18.59 1.60 2.17 0.033 贫煤 1.01 2.12 10.70 2.39 5.00 0.034 无烟煤 1.26 6.31 7.71 3.49 2.89 0.032 注：Mad为空气干燥基水分，Ad为干燥基灰分，Vdaf为干燥无灰基挥发分，Rmax为最大镜质体反射率。 
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表 2 不同变质煤的Langmuir吸附常数
Table 2 Langmuir adsorption constant of coals with different metamorphic degrees
煤样 镜质体反射率Rmax/% Langmuir体积
VL/(cm3·g−1)Langmuir压力
pL/MPa褐煤 0.38 11.02 4.83 气煤 0.86 16.34 4.18 肥煤 1.27 21.63 3.74 焦煤 1.60 26.86 3.96 贫煤 2.39 29.83 4.38 无烟煤 3.49 33.19 5.00
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表 3 0.74 MPa与8 m3/t下不同变质程度煤的瓦斯膨胀能
Table 3 Gas expansion energy of coals with different metamorphic degrees under gas pressure of 0.74 MPa and gas content of 8 m3/t
煤样 Rmax/% 8 m3/t 0.74 MPa W/
(mJ·g−1)W/
42.98W1/
(mJ·g−1)W1/
42.98W2/
(mJ·g−1)W2/
42.98W/
(mJ·g−1)W
/42.98W1/
(mJ·g−1)W1/
42.98W2/
(mJ·g−1)W2/
42.98褐煤 0.38 3 820 88.88 2613.30 60.80 1206.70 28.08 350 8.14 277.59 6.46 72.41 1.68 气煤 0.86 3 270 76.08 2809.66 65.37 460.34 10.71 510 11.87 478.99 11.14 31.01 0.72 肥煤 1.27 2 386 55.51 1935.33 45.03 450.67 10.49 719 16.73 690.27 16.06 28.73 0.67 焦煤 1.60 2 330 54.21 1934.95 45.02 395.05 9.19 850 19.78 807.95 18.80 42.05 0.98 贫煤 2.39 2 330 54.21 1995.19 46.42 334.81 7.79 870 20.24 826.53 19.23 43.47 1.01 无烟煤 3.49 2 380 55.37 2092.55 48.69 287.45 6.69 860 20.01 819.36 19.06 40.64 0.95 注：W/42.98、W1/42.98和W2/42.98分别为总瓦斯膨胀能W、吸附瓦斯膨胀能W1和游离瓦斯膨胀能W2与初始释放瓦斯膨胀能突出临界指标42.98 mJ/g的比值。
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