Study on the air permeability characteristics of coal gangue dump slope gangue particles
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摘要:
煤矸石山斜坡面矸石散体的颗粒偏析现象对其渗透特性有重要影响。为了研究斜坡面的空气渗流特性，基于自主设计的室内渗透率测定装置，结合散体岩土力学理论、通风理论及FLUENT数值模拟，研究了煤矸石山斜坡面不同高度不同深度处矸石散体孔隙率与渗透率的整体分布规律及空气渗流和温度分布特征，并通过现场实测进行验证。结果表明：在研究预设条件下，矸石山斜坡面浅部的孔隙率和渗透率分布特征受到颗粒偏析现象的显著影响，随着高度与深度增大，呈现出非线性负指数衰减规律；随着斜坡面矸石散体的粒径增大，其孔隙率也呈增大趋势，并且其增速逐渐放缓；矸石山顶部覆盖黄土层，导致渗流速度缓慢，氧气质量浓度较低，不利于氧化放热反应的进行，底部孔隙率较大风速过快，积热条件不佳，因此高温区域位于矸石山中上部距坡面2～3 m处，最高可达780 K；风速场在热风压与外界风压的共同影响下，最高风速位于中上部近坡面处，可达0.06 m/s。此外，沿矸石山X方向和Z方向深入，渗流速度与氧气浓度下降速率逐渐减小；整体而言，矸石山斜坡面孔隙率的分布是影响矸石山内部空气渗流特性的一个极为重要的因素。通过对矸石山风速氧气以及温度场的研究，将矸石山大致划分为表层冷却区、聚热易燃区以及内部低温区。研究成果可为我国干燥多风的中西部矿区煤矸石山自燃火区的准确预测和判定提供基础参考。
Abstract:The phenomenon of particle segregation in the gangue aggregate on the slope surface of the coal gangue mountain significantly influences its permeability characteristics. To investigate the air infiltration characteristics of the slope surface, a self-designed indoor permeability measurement device was utilized. By integrating the theories of granular soil mechanics, ventilation, and FLUENT numerical simulation, the overall distribution patterns of porosity and permeability of the gangue aggregate at different heights and depths on the coal gangue slope surface were studied, as well as the characteristics of air infiltration and temperature distribution. These findings were validated through on-site measurements. The results demonstrate that the distribution characteristics of porosity and permeability in the shallow part of the gangue slope surface are significantly affected by the particle segregation phenomenon, exhibiting a nonlinear negative exponential decay pattern as the height and depth increase. As the particle size of the slope surface gangue aggregate increases, its porosity also shows an increasing trend, but the rate of increase gradually slows down. The presence of a loess layer covering the top of the gangue slope hinders fluid flow and results in lower oxygen content, which is unfavorable for exothermic oxidation reactions. Moreover, at the bottom, where the porosity is larger, the wind speed is excessively high, creating unfavorable heat accumulation conditions. Therefore, the high-temperature region is located in the upper part of the gangue slope, 2～3 meters away from the slope surface, reaching temperatures as high as 780 K. Under the combined influence of thermal wind pressure and external wind pressure, the highest wind speed is found in the upper-middle part near the slope surface, reaching up to 0.06 m/s. Furthermore, as we delve deeper into the gangue slope in the X and Z directions, the flow velocity and the rate of decrease in oxygen concentration gradually decrease. Overall, the distribution of porosity on the gangue slope surface is a crucial factor affecting the air infiltration characteristics within the coal gangue mountain. Through the study of wind speed, oxygen concentration, and temperature fields in the gangue slope, this paper roughly categorizes the gangue slope into a surface cooling zone, a heat-gathering flammable zone, and an internal low-temperature zone. The findings from this research can serve as a fundamental reference for accurately predicting and identifying self-ignition fire zones in the arid and windy mining regions of central and western China.
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Keywords:
- coal gangue dump /
- seepage /
- permeability /
- porosity /
- hot air pressure
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图 4 粒径、渗透率和孔隙率的拟合关系
Figure 4. Fitting relationship between particle size, permeability and porosity
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图 6 矸石山内部氧气浓度分布规律
Figure 6. Distribution pattern of oxygen concentration inside the gangue hill
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图 11 矸石山斜坡面测点布置示意
Figure 11. Layout diagram of measuring points on the slope surface of the gangue hill
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图 12 空气渗流速度、渗透率验证效果
Figure 12. Validation effect diagram of air infiltration velocity and permeability
表 1 煤矸石试样的相似级配
Table 1 Similar grading of coal gangue samples
粒径/mm 相似级配/% ＞50 24 30～50 18 10～30 15 5～10 11 ＜5 32 
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表 2 煤矸石压缩试验结果
Table 2 Compression test results of coal gangue
压力/kPa 孔隙比/% 孔隙率/% 压缩系数/MPa−1 0 56.3 36.0 — 200 54.9 35.4 0.070 400 53.6 34.9 0.064 600 52.4 34.4 0.057 800 51.4 33.9 0.052 1000 50.4 33.5 0.047 1200 49.6 33.2 0.043 1400 48.8 32.8 0.042 1600 48.0 32.5 0.036 1800 47.3 32.1 0.035 2000 46.7 31.8 0.033
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表 3 斜坡面不同位置的孔隙率
Table 3 Porosity at different heights of sloped surfaces
高度/m 不同深度下煤矸石散体孔隙率/% 1 m 3 m 5 m 7 m 10 m 16 m 1 37.3 36.2 35.9 35.7 35.6 35.5 3 35.9 32.3 39.0 31 29.4 28.8 5 35.5 35.0 28.1 26.6 25.3 24.0 7 35.3 29.5 26.3 24.4 22.5 26.0 10 35.1 28.6 24.7 22.2 19.7 17.0 16 34.9 27.8 23.0 19.8 16.5 12.9
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表 4 孔隙率和渗透率的计算结果
Table 4 Calculation results of porosity and permeability
粒径/
mm进口压力/
MPa出口压力/
MPa流量/
(10−5·m3·s−1)孔隙率/
%渗透率/
(10−15 m2)0～2.5 0.60 0.10 27.78 7.62 0.10 2.5～5 0.52 0.10 27.78 10.34 0.14 5～7.5 0.45 0.10 27.78 14.31 0.19 7.5～10 0.43 0.10 27.78 16.45 0.21 10～12.5 0.38 0.10 27.78 19.43 0.26 12.5～15 0.37 0.10 27.78 21.58 0.28 15～17.5 0.35 0.10 27.78 22.99 0.32 17.5～20 0.32 0.10 27.78 24.83 0.39 20～22.5 0.30 0.10 27.78 26.03 0.45 22.5～25 0.29 0.10 27.78 26.67 0.49
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表 5 数值模拟参数
Table 5 Numerical simulation parameters
参数 数值 参数 数值 空气密度ρg/(kg·m−3） 1.43 风速v0/(m·s−1) 2 煤矸石密度ρs/(kg·m−3) 2436 氧气体积分数c0/% 21 初始孔隙率e/% 40 大气压Pa/kPa 101.325 初始渗透率k/m2 1.37×10−9 环境温度T/K 293 黄土孔隙率el/% 10 空气动力黏滞系数μ/(kg·m−1·s−1) 1.8×10−5 黄土比热容Cl/(J·kg−1·K−1) 1696 时间步长Δt/s 259200 黄土密度ρl/(kg·m−3） 1600 时步数S 60
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表 6 现场渗流试验参数值
Table 6 On site seepage experimental parameter values
位点 d/m h/m TL/℃ T0/℃ ρ/(kg·m−3) v0/(m·s−1) vm/(m·s−1) θ0/(°) θm/(°) Z/m t/s 5-2 0.8 2.4 29 24.2 1.0260 2.1 3.1 38.9 36.8 15.0 8.2 5-3 1.3 2.0 31.5 24.8 1.0239 1.8 3.1 39.1 37.2 15.0 10.8 8-3 1.3 3.4 35.4 25 1.0232 1.6 3.5 38.7 37.8 14.8 30.4 8-4 1.8 2.9 36.1 25.3 1.0222 1.8 3.5 39 37.9 15.0 39.2 11-5 2.3 4.2 44.8 26.5 1.0215 1.8 3.9 37.9 37.5 15.1 84.5 14-5 2.3 5.8 49.2 28.9 1.0167 1.9 3.7 38.5 37.5 15.0 130.4
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