浅埋厚煤层地表漏风对采空区煤自燃影响数值模拟研究

西部矿区浅埋厚煤层通常采用抽出式通风方式,地表漏风不仅使风流紊乱,而且其中的O 2贯穿采空区,与采空区遗煤共同作用使其氧化,从而发生煤自燃,并且产生的CO等有害气体超标,严重影响矿井的正常开采。目前一般采用现场实测、理论分析及实验研究方法对地面漏风引起的采空区内煤自燃的气体浓度场和温度场等进行研究,然而地表裂隙漏风自然发火实验复杂程度较高,理论分析及实验研究方法难以从三维角度认识地表漏风对采空区内煤自燃的影响规律。针对上述问题,根据我国西北矿区埋深浅、煤层厚等特点,建立三维数值计算模型,采用数值模拟与现场实测相结合的方法研究了浅埋厚煤层条件下导气裂隙采空区“三带”分布情况及不同工况下采空区O 2浓度场、CO浓度场、温度场、压力场等的分布规律,并采用ZD5煤矿火灾多参数监测装置进行现场验证。结果表明:采空区内“三带”分布规律和O 2浓度场分布受地表漏风影响明显,采空区顶部O 2容易聚集,改变了采空区内气体流场分布规律,采空区内高体积分数O 2(体积分数为18%~23%)聚集范围为沿采空区走向0~270 m、沿采空区竖直方向3~20 m,特别是在沿采空区走向0~80 m、沿采空区竖直方向3~8 m空间O 2充足、有一定遗煤且热量不容易散失,该区域煤自然发火危险程度较高;采空区内回风隅角压力最小,为-10 Pa,回风口压力最低,进风口压力最大,沿倾向、竖直方向及走向压力均逐渐增大;采空区内温度和CO分布规律类似,在采空区底部受顶部漏风影响很小,主要受工作面进风隅角影响,热量积聚和CO聚集规律与不漏风时基本一致,而从采空区中部开始,温度和CO主要受顶部漏风影响,在中部区域温度和CO均呈现“O”形圈分布,采空区顶部,温度和CO在每个断裂带与采空区交接处达到极大值,并向两侧递减,在最深部的断裂带与采空区交接处出现最大值。

Numerical simulation study on the influence of surface air leakage in shallow thick coal seam on coal spontaneous combustion in goaf

The shallow thick coal seam in the western mine area in China usually adopts the extraction ventilation method.The surface air leakage makes the wind flow disorderly,and the oxygen of the air penetrates the goaf and interacts with the residual coal in goaf to oxidize the coal.Therefore,the coal spontaneous combustion is likely to occur,and the harmful gas such as carbon monoxide exceeds the standard,causing seriously effects on the normal mining of the mine.At present,field measurements,theoretical analysis and experimental research methods are generally used to analyze the gas concentration field and temperature field of coal spontaneous combustion in goaf caused by surface air leakage.However,the spontaneous combustion experiment of surface air leakage is relatively complex.It is difficult to use theoretical analysis and experimental research methods to obtain the influence law of surface air leakage on coal spontaneous combustion in goaf from a three-dimensional perspective.In order to solve the above problems,according to the characteristics of shallow thick coal seam in northwest China,a three-dimensional numerical calculation model is established.Combined numerical simulation and field measurement methods are used to analyze the distribution of"three zones"in the surface air leakage goaf area of shallow thick coal seam.The methods also analyze the distribution law of O 2 concentration field,CO concentration field,temperature field and pressure field in goaf under different working conditions.Moreover,the field validation is carried out by the ZD5 coal mine fire multi-parameter monitoring device.The results show that the distribution of the"three zones"and the O 2 concentration field in goaf are greatly affected by the surface air leakage.It is found that O 2 is easily accumulated at the top of the goaf,which changes the gas flow field distribution in goaf.The concentration range of high volume fraction O 2(volume fraction 18%-23%)in goaf is 0-270 m along the strike direction of the goaf and 3-20 m along the vertical direction of the goaf.In particular,O 2 is sufficient in the range of 0-80 m along the strike direction of the goaf and 3-8 m along the vertical direction of the goaf.In this area,there is a certain amount of residual coal and heat is not easily dissipated,raising the risk of coal spontaneous combustion.The pressure at the corner of return air roadway in goaf is the smallest,-10 Pa,the pressure at the return air roadway outlet is the lowest,and the pressure at the air inlet is the highest.The pressure gradually increases along the inclined direction,the vertical direction and the strike direction.The temperature distribution is similar to the CO distribution in goaf.The goaf floor is little affected by the air leakage from the surface,but largely affected by the corner of the intake air roadway of the working face.The heat accumulation and CO accumulation are basically the same as the situation of no air leakage.From the middle of the goaf,the temperature and CO are mainly affected by the surface air leakage,presenting an"O"ring distribution.At the top of the goaf,the temperature and CO reach maximum values at the junction of each fracture zone and the goaf,then decrease along both sides.The maximum value appears at the junction of the deepest fracture zone and the goaf.