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英文原文Methane moving law with long gas extraction holes in goafYong ZHANG, Xibin ZHANG*,Chunyuan LI, Chuanan LIU, Zufa WANGFaculty of Resources and Safety Engineering, China University of Ming & Technology, Beijing 100083, ChinaAbstractIn order to grasp the methane moving law in goaf and provide a theoretical data for gas extraction holes, the height of caving and fractured zones in the stope has been calculated according to the experiential formula and gas movement law has been observed by field and laboratory experiment. It also gives gas moving characteristics with different position of extraction holes. And it has the best gas extraction result when the final holes are arranged around 30m above the coal seam and 10-20m away from the tailentry in horizontal direction. Besides, the height of final holes should be adjusted to the overburden strata structure. When final holes are near the tailentry, their height should be controlled in the upper of regular caving zone; when they are close to the center of face, their height should be controlled at the bottom of fracture zones. 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of China Academy of Safety Science and Technology, China University of Mining and Technology(Beijing), McGill University and University of Wollongong.Keywords: gas in goaf; gas movement;gas extraction holes; position of extraction holes; expe riment1 IntroductionThe roof strata above the goaf will fracture and form the caving, fracture and bending zones in the vertical direction after mining the coal seam. And there are lots of fractures and cracks in caving and fracture zones, the permeability of the stratum are also high. According to the “O” circle theory of fracture distribution in the stope 1, the gas of goaf will move and gather up along those fractures and cracks. Then it is easier to cause the gas exceeding the limit, which need to take measures to reduce gas content. In order to solve this problem and get the best extraction effect, the layout of holes should be adjusted to the rock structure changes according to the arch structure characteristics of roof stratas movement 2.* Corresponding author. Tel.: +86-15210567715.E-mail address: .1877-7058 2011 Published by Elsevier Ltd.doi:10.1016/eng.2011.11.21793558Yong ZHANG et al. / Procedia Engineering 26 (2011) 357 365Gas in goaf will distribute after holes extraction. Therefore, the relationship between gas moving law and position of gas extraction holes should be studied so that gas in the corner of working face and goaf could be effectively controlled.2 Hydrodynamics equations of gas movementWith the pressure gradient of roadways ventilation, gas penetrates or diffuses to the goaf and then to roadways from the coal seam, and its flow velocity is very low which usually less than 10-5m/s 3. Therefore, the flow of gas and air in goaf belongs to low-speed category, and it hardly has an effect on the roadways ventilation. Despite the pressure gradient is very high, the gas and air flow in the mined-out area and roadways can still be regarded as the incompressible flow 4. Besides, the distribution of rock, fractures and cracks in goaf are irregular. Consequently, the gas movement in the fractured rock of goaf is taken for continuum medium movement in pore medium 5.2.1. Gas Seepage characteristicsGoaf is regarded as porous medium in the research; the source item of fluid momentum loss isdescribed as the following equation 5.In equation 1, Si is the source of momentum equation of the number i (x, y or z ), is the viscosity of molecular, D and C are predefined matrices, |v| is vectors module of velocity, and vJ is the velocity component of the source in x, y or z direction.Generally, the pressure drop is proportional to the velocity in the low laminar flow of porous medium. The porous medium model could be simplified by using Darcy characteristics when the liquid inertial loss is ignored.In equation 2, is the permeability for expressing the space and the function of preventing theviscosity, m2.1.2. Gas diffusion characteristicsThere are two main controlling factors for the gas movement in the goaf. One is the moleculardiffusion caused by the concentration and thermal gradient. Another is viscous flow or mass flow on the action of pressure gradient. According to the Fick characteristics, the following formula is the diffusion equation 4.Yong ZHANG et al. / Procedia Engineering 26 (2011) 357 365In equation 3, Ji is the gas flow caused by the concentration and thermal gradient; DIm is the diffusion coefficient of mixed gas; Xi is the mass fraction of i gas;TiD is the thermal diffusion coefficient; and T is the temperature. When the gas concentration is much higher, equation 7 could be taken place by the diffusion formula of multicomponent.In equation 4, if the gas is i or j, Mi is its molecular weight, Dij is the multicomponent diffusioncoefficient of the No. i gas component in the gas, and Mmix is the molecular weight of mixed gas.1.3. Control equations of gasThe gas emission and movement has close relationship with the air flow condition in gob, and itbelongs to the typical permeation-diffusion process. Because the gas flow in goaf is regarded as the incompressible flow, control equations of flow field can be replaced by the Navier-Stocks equation 6, 7.In formulas, is mixture density, g/m; T is time variable; ui and uj are velocity, m/s; ij is “Kronecker delta”(when i=j, ij =1; if not, ij =0); P is pressure, Pa; ij is shear stress tensor of molecular; Si is the source item of momentum loss to express pore medium; E is the energy in per volume, J; H is total enthalpy in per volume, J/mol; k is the heat transfer coefficient of fluid; T is static temperature, K; ns is the sum of components; Ru is universal constant, and it is 8.3145 J/(molK); if the component is s, Ms is its molecular weight, Ys is its mass concentration; Ds is its mass diffusion coefficient, and hs is its absolute enthalpy value of unit mass.In control equations, equation 5 is the continuum equation of each component, equation 6 is themomentum equation of mixtures, equation 7 is the energy equation of mixtures, and equation 8 is the state equation of ideal gas of mixtures.3. Field observation3.1. Working face situationSynthetic mechanized longwall mining technology and fully caving method for managing mined areas are used in Chengshan mine. The main coal seam is the No.3B coal seam, and its average thickness is 3.0m, average dip angle is 8. And the coal reserves are 600,000t. No.3202 working face of Chengshan mine is 600m along the mining direction and 240m along sloping direction. During drifting the headentry of No.3202 working face, the highest absolute gas emission is even 9.3m 3/min, and it is 41.6m 3/min during mining the working face. Therefore, gas emission is much higher in this coal mine. It is difficult to solve the problem only by ventilation measures. Gas extraction technology is one of the best measures for controlling gas content in the goaf. According to the “O” circle theory of fracture distribution in the stope, gas will move and gather up in the fractures of “O” circle in the goaf. In order to study the range of roof strata and provide the reasonable parameters for gas extraction, the height of roof-falling and fractured zones in the stope is calculated according to the experiential formula 8.In equation 9 and 10, H1 and H2 are the height of roof-falling and fractured zones along the normal direction of the coal seam separately; M is the height of the mining coal seam; K is the broken coefficient of rock in roof-falling zones which is 1.2; and is the dip angle of the coal seam. Then H1 is equal to 15.15m, and H2 is 30.11-40.31m. 3.2. Observation methodSensors are used to monitor and observe gas distribution in goaf and extraction holes respectively. When the working face advances about 80m from the interconnection, the first head of sensors are installed along the tailentry and headentry, which are numbered T1and T4 separately, and it is the first field. Then, the working face goes on advancing 200m and 300m from the interconnection, four sensors are installed along the tailentry and headentry respectively, which they are respectively numbered T2, T3, T5, T6. Sensors of extraction holes are installed in the number 1, 3, 6 holes of the second and third holes field, and they are numbered T2-1, T2-3, T2-6 and T3-1, T3-3, T3-6. Besides, T2-1 and T3-1 are inserted into 120m along the holes; T2-3 and T3-3 are inserted into 80m along the holes; and T2-6 and T3-6 are inserted into 40m along the holes. Figure 1 shows a sketch of the arrangement of gas monitor sensor in No.3202 working face. In figure 1, only the first head of sensors and the second field are indicated.Fig.1 Arrangement of gas monitor sensor in No.3202 working faceYong ZHANG et al. / Procedia Engineering 26 (2011) 357 3653.3. Observation resultsObservation results are shown in figure 2. Gas concentration increases in the goaf with the rising of distance from working face. When the distance from the working face is less than 150m, the change of gas concentration will relatively stable. For example, when the distance from the working face to the observation point is 10m, 50m, 100m and 150m, the average gas concentration is 2.6%, 3.9%, 4.1% and 5.9% separately. But if the distance is more than 150m, gas concentration increases sharply. Gas concentration reaches 10.55% if the distance from the working face is 170m; it is even much more than 16.9% when the distance is far more than 200m. Sensors monitoring result indicates that there exists a huge gas storeroom in the goaf, and the farther the distance from the working face to observation points, the higher the gas concentration gathering up.Fig.2 Changing curve of goaf gas average concentration4. Laboratory experimentWith the influence of construction technology, the monitoring effect of gas distribution near tailentry is much better by using sensors monitoring system in the goaf. But it is difficult to monitor the middle and bottom of the goaf, particularly, it is difficult to know gas distribution well in different holes position. Therefore, the equivalent material simulation is done in the laboratory. The experiment has been done by using integrated simulation table on gas and rock movement which was developed by China University of Mining & Technology, Beijing. The experimental model is shown in figure 3.Fig.3 Integrated simulation table on gas transporting and rock moving4.1. Experimental detailsThe geometry similarity ratio of the model is 1:100, and the integrated simulation table has fourreticular test systems in which there are 320 sampling points. Meanwhile, every sampling point links to a suction pump. Long holes are used to simulate gas extraction in the field, which are also arranged above the tailentry. Besides, the vertical distance above the tailentry is 20cm, 30cm and 40cm respectively, and the horizontal interior distance from the tailentry to holes is 10cm when the vertical distance is 20cm, and it is 10cm, 20cm and 30cm respectively when the vertical distance is 30cm. The extraction flow of holes is 0.4ml/min, the dry bulb temperature is 15.2, the wet bulb temperature is 14.2, the relative humidity is 90, and the velocity pressure of return air is 2.192mm water column.According to the position of extraction holes, there are six testing programs, and experimental results are shown in figure 4. In figure 4, H stands for the horizontal interior distance from the tailentry to gas extraction holes, and V stands for the vertical distance abo ve the tailentry between gas extraction holes and the tailentry.I: The experiment does not use gas extraction in goaf, and its distribution of gas concentration isshown in figure 4(a).II: The experiment uses gas extraction holes in goaf. The vertical distance is 40cm, and holes areparallel with the tailentry. The distribution of gas concentration is shown in figure 4(b).III: The vertical distance above the tailentry is 20cm, and the horizontal interior distance is 10cm. The distribution of gas concentration is shown in figure 4(c).IV: Gas extraction holes are over the tailentry, and the vertical distance is 30cm. The distribution of gas concentration is shown in figure 4(d).V: The vertical distance is 30cm, and the horizontal interior distance is 10cm. The distribution of gas concentration is shown in figure 4(e).VI: The vertical distance is 30cm, and the horizontal interior distance is 20cm. The distribution of gas concentration is shown in figure 4(f).Fig.4 Gas distribution in goaf with different extraction parameters4.2. Experimental resultsWhen the experiment does not use gas extraction in the goaf, the gas concentration is less than 1% near the intake side or even lower, but there is gas of high concentration flowing into the working face near the tailentry side, and the distribution of gas concentration is veined shape in the middle of the goaf. When the experiment is taken II program, the gas concentration reduces integrally in the goaf, but the gas concentration is more than 1% in the upper corner of the tailentry. When the experiment is taken III program, the change of gas concentration is not obvious integrally in the goaf, but the concentration near the tailentry decreases. When the vertical distance above the tailentry is 30cm, the gas concentration all reduces in goaf. When the program is IV, the reduction is obvious near the intake side and gas concentration is less than 0.5%, but it still maybe beyond 1% near the tailentry. When the experiment is taken V program, gas concentration obviously decreases near both intake and tailentry side, but gas concentration is around 1% in the middle of goaf, which is much higher. When the experiment is taken VI program, the whole gas concentration in the goaf reduces obviously; it is around 0.5% in the middle of intake and goaf, but gas gathers up in the upper corner of the woking face.Comparing with all experiments, it is easy to know the follwing views. The position of gas extraction holes has a great effect on gas concentration in the goaf. In the vertical direction above the tailentry, the lower the position of holes, the worse gas extraction results, and gas concentration is limited in return air side of working face. But when the gas extraction holes lay out in high position, gas concentration obviously reduces in return air side. And the extraction result is the best when the vertical distace above the tailentry is 30cm. Besides, if gas is extracted in the top of tailentry, gas concentration will reduce on a large scale. But it is still high in the upper boundary of goaf and it is possible to gas up in the upper corner of working face. With the same vertical distance and same gas extraction volume, holes are moved little distance into working face when the horizontal interior distance over the working face is 10cm and 20cm respectively, while the controlling range changes largely. If holes are too close to the tailentry, though the whole gas concentration reduces obviously in the back of goaf, gas concentration is high near the tailentry, and it is possible to gas up in the upper corner of working face. And if the horizontal interior distance is too far, it is also apt to gas up. In order to reduce the whole gas concentration in the goaf and near the tailentry, and deal with gas in the upper corner of working face, gas extraction holesshould be located over the working face and the reasonable horizontal interior distance from tailentry to holes is 10-20m.Therefore, gas extraction holes should be located above the rock-falling zones and at the bottom of fracture zones as much as possible according to the collapsed state of roof strata. And it is fanshaped for all holes. The height of final holes is different in different position. The height of final holes near the tailentry is about 20m above the regular rock-falling zone; the height of final holes near the middle of goaf is about 30m at the bottom of fracture zone. And the reasonable horizontal interior distance from tailentry to gas extraction holes is 10-20m.5. ConclusionsGas movement in the fractured rock of goaf can be regarded as the incompressible flow in the pore medium, and its moving state is closely related to the airflow. The molecular diffusion and viscous flow (or mass flow) are two main forms of the gas movement in the goaf. And the control equations of flow field can be replaced by the Navier-Stocks equation.Field observation indicates that gas concentration increases in the goaf as the distance from theworking face to observation point rises. When the distance from the back of goaf to the working face is far beyond 150m, its gas concentration is much higher than near the working face. And there exists a huge gas storeroom in the goaf, in which gas has extraction value.In order to reduce the gas concentration in the goaf and the upper corner of working face, gasextraction holes should be loacted according to the collapsed state of roof strata, which is based on the experimental results. Therefore, holes should be arranged to fanshaped pattern as much as possible. The height of final holes near the tailentry is about 20m above the regular rock-falling zone; the height of holes near the middle of goaf is about 30m at the bottom of the fractured zone. And the reasonable horizontal interior distance from tailentry to observation point is 10-20m.AcknowledgementsThis work has been supported by a grant from the Major State Basic Research Development Program of China (973 Program) (No.2011CB201200) and National Natural Science Foundation of China (No.50834005).中文译文采空区瓦斯移动规律与瓦斯抽放孔位置关系张勇，张锡斌，李春园，刘传安，王族发资源与安全工程学院，中国矿业大学，北京100083，中国摘要 为了掌握采空区中的瓦斯移动规律和为瓦斯抽放钻孔提供理论数据，放顶煤和工作面垮落区的高度根据已验证的公式已经计算出来，通过现场和实验室的实验已经观察到了瓦斯的运动规律。它同时也得出了瓦斯运动特征和瓦斯抽放孔不同位置的关系。当最终的抽放孔安排在煤层上方30米和水平偏东10-20米的地方它具有最佳的瓦斯抽放结果。此外，最终抽放孔的高度应该根据覆岩地层结构调整。当最终抽放孔靠近东翼的时候抽放孔的高度应该控制在定期放顶煤上部；当抽放孔靠近工作面中心的时候，抽放孔的高度应该控制在断裂带下部。2011年Elsevier 公司发布。中国科学技术安全学院责任选择和同行评议，中国矿业大学（北京校区），麦吉尔大学，卧龙岗大学。关键词：采空区瓦斯；瓦斯运动规律；瓦斯抽放孔；瓦斯抽放孔位置；实验1简介采空区顶板岩层将破断并将形成放顶煤，煤层采出后在垂直方向上会形成裂隙带和弯曲带。还有很多断裂和裂纹的放顶煤和断裂区，地层渗透率也很高。根据回踩工作面裂隙O型理论分布规律，采空区的瓦斯将会沿着这些裂隙裂缝流动并且聚集。然后，很容易导致瓦斯浓度超标，这就需要采取措施减少瓦斯含量。为了解决这个问题并且得到最佳的抽放效果，应该根据岩石结构的变化调整抽放钻孔的分布根据拱形结构顶板岩层运动的特点。采空区的瓦斯在经过抽放钻孔抽放之后将会重新分布。因此，应该研究瓦斯移动规律和瓦斯抽放钻孔位置之间的关系以使得工作面角落和采空区角落的瓦斯能够被有效的控制。2瓦斯运动的流体动力学方程随着巷道通风的压力梯度，瓦斯从煤层中扩散或渗透到采空区然后再到巷道中，并且它的流速非常的缓慢，平均流速小于10-5m/s。因此，采空区中流动的瓦斯和空气属于低速类别流动，它很难对巷道通风产生影响。虽然压力梯度很高，采空区和巷道中的瓦斯和空气流量仍然被视为不可压缩流体。另外，岩层的分布，采空区中的裂隙和裂缝是不规则的。因此，在采空区裂隙岩体中流动的瓦斯是在空隙介质中的连续介质运动。2.1瓦斯涌出特征 采空区被认为是在研究中被认为是多孔介质；流体动力损失由以下公式求得： 方程式中Si-流体动力损失U-分子粘度D、C-预定义矩阵|v|-速度绝对值Vj-速度的分向量一般情况下，在多孔介质中流动的低流层的压力降于其流速成正比。在液体惯性损失忽略不计的情况下，多孔介质模型可以简化应用于达西特征中。 方程式中： a-渗透性表达的空间和防止粘度的功能 m22.2瓦斯扩散特征采空区中瓦斯的运动有两个主要控制因素，一个是浓度和温度变化引起的分子扩散。另一个是粘性流动或质量流量压力变化的作用。根据菲克特点，得出下面的扩散方程公式。 方程式中：Jj-浓度和温度变化引起的瓦斯流动 Dim-混合气体扩散系数 Xi-瓦斯的质量分数 DiT-热扩散系数 T-温度当气体浓度过高时，就可能发生的方程 7 方程式中：如果瓦斯是i或者j，那么Mj就是它的分子量，Dij是瓦斯中第i号瓦斯组分的扩散系数；Mmix是混合气体的分子量。1.3 瓦斯控制方程采空区瓦斯涌出量与运动已与空气流动状况关系密切，它属于典型的渗透扩散过程。因为在采空区中的气体流量被视为不可压缩流体，流场控制方程可以替换为Navier-Stocks方程。公式中，是混合物的密度，单位是g/m ；T是时间变量；Ui和Uj是速度（m/s）；ij是当i=j时候ij=1；如果i不等于j则ij=0 ；P是压力（Pa）；ij是剪应力分子的张量；Si是流体动力损失；E是单位体积内的能量（J）；H是单位体积内总焓的能量（J/mol）；k是流体的传热系数；T是静态温度（k）；ns是组合成分总和；Ru是通用常数（8.3145 J/(molK)）；如果组分是s，Ms是它的分子量，Ys是它的质量浓度；Ds是它的大量扩散系数，hs是它的焓的绝对值的单位质量。在控制方程中，方程式5是每个组分的连续性方程，方程式6是混合动量方程，方程式7是混合物的能量方程，方程式8是理想气体混合物的状态方程。3现场勘查3.1工作面的状况成山煤矿中使用综合机械化的长臂开采技术，采空区顶板采用完全挎落法管理。主要煤层是三号煤层，平均厚度为3米，倾角平均80。三号煤层储量是600000吨。成山煤矿3202工作面走向长度是600米、倾向长度240米。在测量3202工作面的漂流瓦斯的时候，最高的绝对瓦斯涌出量甚至达到9.3立方米每分钟，但是在开采工作面的过程中他是41.6立方米每分钟。因此，在这个煤矿瓦斯涌出高出很多。所以只通过通风措施是很难解决这个问题的。瓦斯抽放技术是控制采空区瓦斯含量的最佳途径之一。根据回踩工作面裂隙分布的0圈理论，瓦斯将会移动并聚集在采空区中形成0圈的裂缝裂隙中。为了研究顶板岩层的范围，并为瓦斯抽放提供合理的参数，根据公式计算出采场冒顶和裂隙带高度，如下公式： 在公式9和10中，H 1和H2是各个煤层正常方向上冒顶和裂缝的高度；M是开采煤层的高度；K是挎落区岩石的破碎系数，取1.2；是煤层倾角。其中H1是15.15米，H2是30.11到40.31米。3.2 研究方法传感器分别用于监测和观察采空区瓦斯的分布和抽放孔的布置。当工作面从连接向前推进80米的时候，第一个传感器探头装置在工作面运输巷T1和工作面回风巷T4这是第一现场。然后，回采工作面继续向前推进200到300米，分别在运输平巷和回风平巷中装两个探测器T2、T3、T5、T6。抽放钻孔的传感器安装在第二和第三钻孔区域中的1、3、6钻孔中，分别是T2-1, T2-3, T2-6和T3-1, T3-3, T3-6。另外，T2-1, T2-3传感器装在钻孔120米处；T2-3 和T3-3传感器装在钻孔80米处，T2-6 和T3-6传感器装在钻孔40米处。图一显示了3202工作面的瓦斯监测传感器的安排情况。在图一中，只有第一个传感器探头和第二区域有感应显示。图一 No.3202 工作面瓦斯监测传感器的安放图 3.3 观测结果在图二中显示观测结果。随着离工作面距离的增加采空区瓦斯浓度呈现增加趋势。当离工作面距离小于150米的时候，瓦斯浓度的变化相对缓慢且稳定。例如，当观测点离工作面10米、50米、100米、150米的时候，瓦斯平均浓度分别是2.6%、 3.9%、4.1% 和5.9%。但是一旦距离超过150米，瓦斯浓度会急剧增加。距离工作面170米的地方瓦斯浓度可以达到10.55%；如果距离超过200米的时候瓦斯浓度甚至可以达到16.9%。传感器检测表明，在采空区中存在一个庞大大的瓦斯储存室，探测点离工作面越远的位置聚集瓦斯的浓度越高。 到工作面的距离/m4实验室实验由于施工技术的影响，在采空区通过使用传感器监测系统对运输平巷附近的瓦斯分布的监测影响
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