开采过程中采空区煤自燃与瓦斯复合致灾隐患区域研究

Potential coupled harzard zone of coal spontaneous combustion and gas in goaf under mining condition

矿井开采过程中采空区煤自燃火灾往往诱发瓦斯爆炸的重大灾害事故。为探究矿井开采状态下采空区煤自燃与瓦斯的复合致灾,本文基于数值模拟的手段对煤自燃与瓦斯的复合致灾隐患区域进行判定与分析。使用移动网格的数值方法并利用laplace平滑方法对网格变形进行修正,实现工作面推进状态下采空区逐渐扩大的动态模型。通过对渗流场、浓度场和能量场多物理场耦合求解,建立了工作面推进过程中煤自燃与瓦斯涌出的动态数值模型,得到正常开采状态时采空区孔隙率、氧气体积分数和瓦斯体积分数分布规律。结果表明,瓦斯可爆区域呈斜长条形,进风侧瓦斯可爆区域位于采空区深部,回风侧可爆区域则靠近工作面。基于煤自燃与瓦斯复合致灾理论,对采空区复合致灾隐患区域进行判定,发现煤自燃与瓦斯复合致灾隐患区域主要位于靠近工作面后方15~60 m处的回风侧,而采空区进风侧与深部复合致灾危险性较小。通过定量分析通风量、工作面推进速度和瓦斯涌出衰减速率对复合致灾隐患区域的影响,发现随着通风量增大,氧化带向采空区深部移动,工作面附近瓦斯体积分数降低。在通风速度由0.5 m/s增大至1.2 m/s时,复合致灾隐患区域逐渐扩大,而当继续增大通风量时,隐患区域逐渐缩小。工作面推进速度加快时,瓦斯可爆区域宽度增加,氧化带和瓦斯可爆区间重叠区域扩大。但工作面推进速度增加将有利于降低煤自燃危险性,从而煤自燃和瓦斯复合致灾的危险性减小。煤的瓦斯释放衰减速率增大时,瓦斯体积分数随埋深而增加的增长速度减小,瓦斯可爆区域宽度扩大,从而导致复合致灾隐患区域面积增大。

Coal spontaneous combustion in goaf often induces gas explosion accidents.To explore the coal spontaneous combustion and gas coupled hazard in goaf under mining condition,the zone of coupled potential harzard in goaf is identified and analyzed based on the method of numerical simulation.Based on the moving mesh which is modified by the method of laplace smoothing,the dynamic model of goaf expansion under the advance of the working face is performed.Then,coupling the solution of seepage field,concentration field and energy field,it is developed that a numerical model of coal spontaneous combustion and emission of gas in goaf during the advance of working face.The distribution of volume fraction,oxygen and gas concentration in goaf under mining condition is obtained.The results show that the gas exploitable zone appears as inclined elongated shape,the gas exploitable zone on the inlet side is located in the deep part of the goaf,and the exploitable area on the return air side is close to the working face.According to the theory of coal spontaneous combustion and gas coupled hazard in goaf,the potential dangerous zone of coal spontaneous combustion and gas coupled hazard in goaf is identified.It is found that the potential dangerous zone primarily located between 15 and 60 m from the working face,and the risk of coupled hazard in the air intake side and the deep of the goaf is lower.Moreover,the quantitative relationship between the potential dangerous area and ventilation flux,the advancing speed of the working surface and the attenuation rate of the gas emission is analyzed.It is found that with the increase of the ventilation,the oxidation zone moves to the deep of the goaf,and the concentration of gas near the working surface is reduced.When the ventilation flux increases from 0.5 m/s to 1.2 m/s,the potential dangerous zone expands gradually,but as the ventilation flux continues to increase,it narrows gradually.As the advancing speed of the working surface is increased,the width of the gas exploitable zone is also increased,and the overlap area between the oxidation zone and the gas exploitable zone is expanded.However,the increase of advancing speed of working face will against the coal spontaneous combustion,so the risk of coupled hazard caused by coal spontaneous combustion and gas will be reduced.The width of gas exploitable zone grows with the increase in gas release attenuation rate of coal which leads to the slowly growth of gas concentration with the increase of distance from working face,so the potential dangerous area of coupled hazard increases.