采空區(qū)長距瓦斯抽采通道中瓦斯運移規(guī)律研究外文文獻翻譯、中英文翻譯、外文翻譯
采空區(qū)長距瓦斯抽采通道中瓦斯運移規(guī)律研究外文文獻翻譯、中英文翻譯、外文翻譯,采空區(qū),瓦斯,通道,規(guī)律,研究,外文,文獻,翻譯,中英文
英文原文
Methane moving law with long gas extraction holes in goaf
Yong ZHANG, Xibin ZHANG* , Chunyuan LI, Chuanan LIU, Zufa WANG
Faculty of Resources and Safety Engineering, China University of Ming & Technology, Beijing 100083, China
Abstract：
In 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.
1. Introduction
The 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 strata’s movement [2].Gas 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 movement
With 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 characteristics
Goaf is regarded as porous medium in the research; the source item of fluid momentum loss is described as the following equation [5].
In equation 1, Si is the source of momentum equation of the number i (x, y or z ), μ 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, α is the permeability for expressing the space and the function of preventing the viscosity, m2.
2.2. Gas diffusion characteristics
There are two main controlling factors for the gas movement in the goaf. One is the molecular diffusion 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].
In 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; DiT 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 diffusion coefficient of the No. i gas component in the gas, and Mmix is the molecular weight of mixed gas.
2.3. Control equations of gas
The gas emission and movement has close relationship with the air flow condition in gob, and it belongs 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, ρ is mixture density, g/m; T is time variable; ui and uj are velocity, m/s; δij is “Kronecker delta”(when i=j, δij=1; if not, δij=0); P is pressure, Pa; τij 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/(mol·K); 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 the momentum 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 observation
3.1. Working face situation
Synthetic 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 it’s averagehickness 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 headeof No.3202 working face, the highest absolute gas emission is even 9.3m3/min, and it is 41.6m3/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 θ 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 method
Sensors 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.3.3. Observation results
Observation 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.
4. Laboratory experiment
With 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.
4.1. Experimental details
The geometry similarity ratio of the model is 1:100, and the integrated simulation table has four reticular 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 above 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 is shown in figure 4(a).
II: The experiment uses gas extraction holes in goaf. The vertical distance is 40cm, and holes are parallel 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).
4.2. Experimental results
When 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 holes should 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. Conclusions
Gas 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 the working 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, gas extraction 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.
References
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中文譯文
第一國際論談：礦山安全工程技術(shù)
采空區(qū)長距瓦斯抽采通道中瓦斯運移規(guī)律研究
張勇張錫斌李春元劉傳安王祖發(fā)
資源與安全工程系中國礦業(yè)大學（北京）100083 中國
摘要：為掌握采空區(qū)甲烷運動規(guī)律提供理論數(shù)據(jù)抽取孔，高度及裂隙發(fā)育帶采場，根據(jù)計算的經(jīng)驗公式和氣體運動規(guī)律一直觀察實地和實驗室實驗。它也給氣動特性的不同位置提取孔。它有最好的天然氣開采的結(jié)果時，最后孔設(shè)置在30米以上的煤層和10―20M從尾部的水平方向。此外，最終孔的高度應(yīng)調(diào)整到上覆巖層結(jié)構(gòu)。當最后一洞接近尾部，其高度應(yīng)控制在上經(jīng)常冒落帶；當他們接近的中心，其高度應(yīng)控制在底部斷裂帶。
1 簡介
采空區(qū)上方的頂板巖層破裂形成崩落，斷裂和彎曲區(qū)在垂直方向的煤層開采后。有許多裂縫和裂縫、斷裂帶，滲透率的地層還高。根據(jù)“0”圈斷裂理論分布在采場[ 1]，對采空區(qū)瓦斯將和收集沿裂縫和裂縫。它是容易造成瓦斯超限，需采取措施減少氣體含量。為解決這一問題，獲得最佳提取效果，布局的孔應(yīng)調(diào)整的巖石結(jié)構(gòu)變化根據(jù)拱結(jié)構(gòu)頂板巖層運動特征[2 ]。采空區(qū)瓦斯分布提取后孔。因此，之間的關(guān)系氣動法和位置的提取孔應(yīng)加以研究，使氣體在角落的工作面和采空區(qū)可有效控制。
2 氣體運動的流體力學方程
隨著壓力梯度巷道通風，氣體滲透或擴散到采空區(qū)，然后從煤層，巷道，其流動速度很低，通常小于10-5m / [ 3]。因此，氣體流量和空氣在采空區(qū)屬于低速范疇，它幾乎影響了巷道通風。盡管壓力梯度是很高的，燃氣和空氣流動的采空區(qū)、巷道仍然可以被視為不可壓縮流[ 4]。此外，該分布的巖石裂縫，裂縫和采空區(qū)不規(guī)則。因此，氣體運動在裂隙巖體采空區(qū)視為連續(xù)介質(zhì)運動在孔隙介質(zhì)[ 5]。
2.1氣體滲流特征
采空區(qū)被視為多孔介質(zhì)來研究；源項的流體動力損失描述如下方程[ 5]。
在等式1中，是源動力方程的數(shù)目i（x，y或z），μ是粘度是分子，D和C是預(yù)定義的矩陣，|v|是向量的模速度，與南軍的速度分量的來源，或方向。
一般來說，壓力下降速度成正比的低層流多孔介質(zhì)。多孔介質(zhì)模型可以簡化使用達西特征的液體時，忽略慣性損失。
等式2，α是透氣性表達的空間和功能防止粘度，單位是平方米。
2.2天然氣擴散特征
有兩個個主要控制因素的氣體運動在采空區(qū)。一是分子擴散所造成的濃度和溫度梯度。另一個是粘性流動或流動的壓力梯度的作用。根據(jù)菲克的特點，下面的公式是擴散方程[ 4]。
在方程3中，J1是氣體流動所造成的濃度和溫度梯度；是擴散系數(shù)的混合氣體；i的是質(zhì)量分數(shù)；熱擴散系數(shù)；T是溫度。當氣體濃度較高，方程7可發(fā)生的多組分擴散公式。等式4，氣體是i或j，Mi是其分子量，Dtj是多組分擴散系數(shù)的號我氣體成分的氣體，是分子量的混合氣體。
2.
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