煤矿井下瓦斯涌出控制外文文献翻译、中英文翻译

Control of gas emissions in underground coal mines Klaus Noack*DMT-Gesellschaft fr Forschung und Prfung mbH, Institut fr Bewetterung, Klimatisierung und Staubbekmpfung, Franz-Fischer-Weg 61, Essen, GermanyReceived 2 August 1996; accepted 24 February 1997. Available online 24 November 1998. Abstract A high level of knowledge is now available in the extremely relevant field of underground gas emissions from coal mines. However, there are still tasks seeking improved solutions, such as prediction of gas emissions, choice of the most suitable panel design, extension of predrainage systems, further optimization of postdrainage systems, options for the control of gas emissions during retreat mining operations, and prevention of gas outbursts. Research results on these most important topics are presented and critically evaluated. Methods to predict gas emissions for disturbed and undisturbed longwall faces are presented. Prediction of the worked seam gas emission and the gas emission from headings are also mentioned but not examined in detail. The ventilation requirements are derived from the prediction results and in combination with gas drainage the best distribution of available air currents is planned. The drainage of the gas from the worked coal seam, also referred to as predrainage, can be performed without application of suction only by over or underworking the seam. But in cases where this simple method is not applicable or not effective enough, inseam-boreholes are needed to which suction is applied for a relatively long time. The reason for this is the low permeability of deep coal seams in Europe. The main influences on the efficiency of the different degasing methods are explained. Conventional gas drainage employing cross measure boreholes is still capable of improvement, in terms of drilling and equipment as well as the geometrical borehole parameters and the operation of the overall system. Improved control of gas emissions at the return end of retreating faces can be achieved by installation of gas drainage systems based on drainage roadways or with long and large diameter boreholes. The back-return method can be operated safely only with great difficulty, if at all. Another method is lean-gas drainage from the goaf. The gas outburst situation in Germany is characterized by events predominantly in the form of non-classical outbursts categorized as sudden liberation of significant quantities of gas. Recent research results in this field led to a classification of these phenomena into five categories, for which suitable early detection and prevention measures are mentioned.Author Keywords: gas emission; prediction; pre-degassing; gas drainage; gas outbursts1. Introduction Coal deposits contain mine gas (mostly methane) in quantities which are functions of the degree of coalification and permeability of the overburden rocks. This is the reason why the gas content of coal seams (and rock layers) varies from 0 m3/t in the flame coal and gas-flame coal of the northwestern Ruhr Basin to 25 m3/t in the anthracite of Ibbenbren in Germany.When influenced by mining activities this gas is emitted into the coal mine. For better understanding of this process a distinction has been established between basic and additional gas emissions. Basic gas emission is the gas influx from the worked coal seam, which is the equivalent of a partial influx in a multi-seam deposit and of the total gas influx in a single-seam deposit. Additional gas emission represents gas influx coming from neighbouring coal seams (in the case of a multi-seam deposit) and from associated rock layers. The additional gas emission may be in excess of ten times the basic gas emission. So it is mostly the additional gas emission which determines the measures to control the gas emission. In Germany the gas emission is considered to be under control if the gas concentration of the mine air can be kept permanently at all relevant places under 1% CH4. This value is at an adequate distance to the lower explosion limit of methane-air mixtures, which under normal conditions is 4.4% CH4. In exceptional cases, the permissible limit value can be raised to 1.5% CH4. For historical reasons, different permissible limits sometimes apply in other countries, for example 1.25% CH4 in the United Kingdom and up to 2% CH4 in France. Basically, the options for control of gas emission are as follows:(1) Total avoidance of gas release from the deposit. This is only possible with regard to the additional gas emission and only for mining procedures which do not affect stability; hence permeability of the overlying and underlying strata (e.g., room-and-pillar mining where the pillars are left standing during the development phase).(2) Removal of the gas from the deposit before working. For this purpose, all procedures for pre-degassing, either by vertical or by deflected cross measure boreholes drilled from the surface, or by inseam-holes drilled below ground, are technically suitable provided the natural or induced gas permeability permits pre-degassing.(3) Capture and drainage of the gas during mining operations before it mixes with the air flow. This is a classic procedure developed for capturing the additional gas using drainage boreholes, drainage roadways or drainage chambers.(4) Homogenize and evacuate the gas influx after diluting it with sufficient amount of air. This involves panel design, air supply, air distribution, and the prevention of gas outbursts. The following discussions concentrate on problems which are currently given priority in the European Union (EU) funded research. They also cover a significant portion of the gas emission problems worldwide. Problems from non-EU states (e.g., Australia, the Community of Independent States (CIS), South Africa and the United Stated of America (USA) are also taken into consideration, as far as the authors knowledge permits it. This subject matter is presented in a condensed form under the following headings: prediction of gas emissions; measures taken to control gas emissions; pre-degassing of coal seams; optimization of conventional gas drainage; control of gas emissions for retreating faces; and prevention of gas outbursts.2. Prediction of gas emissions Prediction of firedamp emission has been practized for many years in the German hardcoal industry (Winter, 1958; Schulz, 1959; Noack, 1970 and Noack, 1971; Flgge, 1971; Koppe, 1975) so that several prediction methods are now available. Among these, the following methods are mentioned:(1) the calculation of the amount of gas emission (Koppe, 1976; Noack, 1985), as used to deal with emission from both the worked coal seam and adjacent seams, which are disturbed by earlier mining activities;(2) the calculation of the reduction of gas pressure (Noack and Janas, 1984; Janas, 1985a and Janas, 1985b), as used in undisturbed parts of the deposit; and(3) prediction methods for the worked coal seam gas emission from longwall faces, for the gas emission from headings and for the gas emission from coal seams cut through during drifting. The first two methods provide a prediction of the specific gas emission from a mine working, expressed in cubic metres of gas per ton of saleable coal production. The gas influx to the mine working in cubic metres of gas per unit time, which is a relevant factor for mine planning, can be derived from multiplying the predicted result by the scheduled production volume. Both methods determine the mean gas emission from a coal face area for a nearly constant face advance rate during a sufficiently long period of time (several months). The prediction assumes that the zone from which the gas is emitted is fully developed, in other words the coal face starting phase has been passed. Furthermore, the coal face has to be above a critical length (i.e., longer than 180190 m at 600 m working depth and longer than 220240 m at 1000 m depth). The influx of gas to a coal face area (both into the mine air current and into the gas drainage system) is defined by the following factors: (1) the geometry and size of the zone from which gas is emitted, both in the roof and the floor of the face area, including the number and thickness of gas-bearing strata in that zone; (2) the gas content of the strata; (3) the degree of gas emission, as a function of time- and space-related influences; and (4) the intensity of mining activities. The geometry and size of the zone from which additional gas is emitted are simplified forming a parallelepiped above and below the worked area; its extension normal to the stratification depends on the prediction method. The number and location, type, and thickness of the strata in the zone from which additional gas is emitted can be derived from existing boreholes, staple-shafts, and roadways inclined to the stratification. The gas content of the strata (Paul, 1971; Janas, 1976; Janas and Opahle, 1986) is difficult to determine. There are two alternatives for direct gas content determination available for coal seams (Verlag Glckauf GmbH, 1987). One alternative uses samples of drillings from inseam-boreholes (for developed seams) and the other alternative uses core samples from boreholes inclined to the stratification (for undeveloped seams). Since a suitable method of determining the gas content of rock is not yet available, a double prediction is made with the first prediction neglecting the rock altogether and the second prediction using the assumption of an estimated gas content of the rock strata. The methods for predicting the proportion of gas content emitted are basically divergent. On the one hand the prediction, which is based on the degree of gas emission, assumes that the emitted gas proportion is not a function of the initial gas content but rather of the geometric location of the relevant strata towards the coal face area. The other method, which relies on gas pressure, commences with a fixed residual gas pressure, hence residual gas content. Its value depends on the geometric location of the strata. This means that the emitted proportion of the gas content, representing the balance against the initial gas content, depends on the latter.2.1. Prediction for previously disturbed conditionsThe method to predict the total gas make from longwalling in a previously disturbed zone in shallow to moderately inclined deposits (dip between 0 and 40 gon) is based on the degree of gas emission (Fig. 1). It uses the degree of gas emission curve designated as PFG for the roof (considering an attenuation factor of 0.016) and the curve designated as FGK for the floor.Fig. 1. PFG/FGK method. For practical reasons the upper boundary of the zone from which gas is emitted is assumed to be at h=+165 m, whereas, the lower boundary is at h=59 m. In the absence of empirical data a mean degree of gas emission of 75% in the worked coal seam is assumed. Above the seam, from the h=+0 m level to the h=+20 m level, and below the seam from the h=0 m level to the h=11 m level, the degree of gas emission is assumed to be 100%. For the purpose of prediction, the surrounding rock strata are considered as fictitious coal seams for which reduced gas contents are assumed. The reduction factors are 0.019 (for mudstone), 0.058 (for sandy shale) or 0.096 (for sandstone).2.2. Prediction for previously undisturbed conditions The method to predict the total gas make from longwalling in a previously undisturbed zone is based on the residual gas pressure profiles shown in Fig. 2. There are three zones visible in the roof and two in the floor, which are characterized by varying residual gas pressure gradients. The upper and lower boundaries of the zone from which gas is emitted (hlim and llim, respectively) are defined by the intersection of the residual gas pressure lines and the level of initial gas pressure pu, thus are dependent on the latter.Fig. 2. Gas pressure method: residual gas pressure lines dependent on thickness of the worked coal seam. The breaking points of the residual gas pressure profile for 1 m of worked coal seam thickness (continuous line) are defined by the coordinates in Table 1, whereas the lines are characterized by the residual gas pressure gradients also in Table 1.Table 1. Parameters for the gas pressure methodFull-size table (1K)View Within Article The dotted line on Fig. 2 applies to 1.5 m of worked coal seam thickness and shows that the h1 and h2 ordinate levels relating to the roof increase in linear proportion to the thickness of the worked coal seam, with gradients declining correspondingly. There is no dependence on coal seam thickness in the floor, where the value of l1 remains constant at 33 m. Based on the illustrated residual gas pressure profile, the residual gas pressures are first determined layer by layer in accordance with the mean normal distance of a layer from the worked coal seam and afterwards they are converted to residual gas contents using Langmuirs sorption isotherm. The difference between the initial and residual gas contents finally represents the emitted proportion of the adsorbed gas which is the required value. To this value will then be added the free gas, the proportion of which is found by multiplying the effective porosity of the strata under review by its thickness and gas pressure difference. Empirical values have to be used for the effective porosity of coal and rock for methane. Typical values for the coal are between 1 and 10%, and for the rock they are between 0.3 and 1.3%. The values vary in a wide range and depend on chronostratigraphy. In the absence of empirical values for the proportion of gas emission from the worked coal seam a value of 40% would be assumed.2.3. Comparison of the two methods The gas pressure method may claim the following advantages over the prediction based on the degree of gas emission: There are no rigid delimitations of the upper and lower zones from which gas is emitted. They rather depend on the value of the initial gas pressure and on the type of strata. In the roof the effect of the thickness of the worked coal seam is considered in the profile of residual gas pressure. The prediction takes into account not only the adsorbed gas but also the free gas; this is for both, the coal seams and the surrounding strata. The total gas content rather than the desorbable proportion is used for the prediction.2.4. Other methods The prediction methods for the worked coal seam gas emission in longwalls and for inseam-headings as well as for coal seam cut through operations during drifting with tunneling machines cannot be explained in detail. For further information refer to the following papers: Noack, 1977; Janas and Stamer, 1987; Noack and Janas, 1988; Noack and Opahle, 1992. It should be mentioned that DMT is testing the prediction of gas emission in machine-driven headings on the base of the INERIS method. Fig. 3 shows an excellent conformity between calculated and measured values (Tauzide et al., 1992).Fig. 3. Comparison between calculated and measured values of gas emission.煤矿井下瓦斯涌出控制摘要：一种先进的方法已在与煤矿井下瓦斯涌出极其相关的领域获得。虽然如此，却仍然需要进一步对方法进行改进，如预测瓦斯涌出量，选择最合适的盘区设计，延长预抽放瓦斯系统，进一步优化生产中抽放瓦斯系统，在在后退式开采时控制瓦斯涌出，以及预防瓦斯突出。介绍和批判性的评价这些重要问题的研究成果。介绍已回采和未回采长壁工作面的瓦斯涌出量预测方法。已开采煤层的瓦斯涌出量和巷道瓦斯涌出量的预测方法也被提及但未深入研究。对通风的要求取决于预测结果，制定基于瓦斯抽放的最佳现有风流分配方案。已开采煤层的瓦斯抽放，同预抽放一样，不用使用抽风机，而是通过从上面或下面进入煤层来进行。但有时这种简单的方法不是非常合适或有效，这时将会需要内接缝钻孔，同时会较长时间的使用抽风机，这是由欧洲深煤层的低渗透性决定的。解释影响不同排瓦斯方法效率的主要因素。传统的瓦斯抽放技术，无论从钻眼和设备，以及钻孔的几何参数和操作的整体系统上都有较大的改进空间。通过基于巷道抽放或长而直径大的钻孔抽放的瓦斯抽放系统装置能够达到改善控制后退式开采工作面末端瓦斯涌出的目的。这种方法能在非常困难的情况下安全实施。另一种方法是从采空区倾斜式抽出瓦斯。在德国瓦斯突出以“非典型性”突出为主要形式，即突然释放大量瓦斯。这个领域的最新研究成果将这些现象分为五类，适用于他们的早期检测和预防措施也被提到。关键词：瓦斯涌出 预测 预先脱气 瓦斯抽放 瓦斯突出1 概述煤的沉积物包括瓦斯（主要成分为甲烷），其数量受煤化程度和地表岩层透气性的影响。这就是在德国为何瓦斯在煤层（以及岩层）的含量，从在西北部Ruhr Basin矿中的长焰煤含量为0m3/t到在Ibbenbren矿中的无烟煤含量大于25m3/t的原因。 受采矿活动的影响，瓦斯扩散进矿井。为了更好的理解这个过程，需要区分基本的瓦斯涌出和附加的瓦斯涌出。基本瓦斯涌出是指瓦斯从开采煤层涌出，其等价于在多层沉积物中的部分涌出和在单层沉积物中的全部涌出。附加瓦斯涌出是指相邻煤层（就多层沉积物而言）和连接岩层的瓦斯涌出。附加瓦斯涌出量可能会超过基本瓦斯涌出量的10倍。因此瓦斯涌出的控制措施主要由附加瓦斯涌出量决定。在德国，如果矿井空气中的瓦斯浓度在所有相关地段始终处于1%以下，那么则认为瓦斯涌出量在控制之中。这个值离甲烷空气混合气体的爆炸下限有足够的距离，在正常情况下当达到甲烷空气混合气体的爆炸下限时甲烷的含量为4.4%，在矿井中甲烷浓度的极限值可允许达到1.5%。由于历史的原因，其他的国家有时会使用不同的极限值，如在英国矿井中甲烷允许的极限值为1.25%，在德国则为2%。控制瓦斯涌出的方法基本如下：（1）总体上避免瓦斯从沉积物中释放。这在仅考虑附加瓦斯涌出或采煤过程不影响稳定性时才有可能。（2）在开采之前从沉积物中除去瓦斯。为了这个目的，所有自然的或人为的预先脱气的方法，无论是通过通风，还是从地表打斜交叉测量钻孔，以及从地下打内接缝钻孔，在技术上都是合理的。（3）煤矿生产期间，在瓦斯与空气流混合之前对其进行捕捉和抽放。这是为了使用抽放钻孔，抽放巷道或抽房峒室进行瓦斯捕捉而发展起来的经典方法。（4）用足量的空气将瓦斯流稀释后再将其均质和疏散。这涉及到盘区设计、空气供应、空气分配、以及预防瓦斯突出。接下来的讨论将集中于在欧盟提供基金的研究中现在优先给予考虑的问题。这其中也包括世界上有关瓦斯涌出问题的重要部分。就笔者许可的范围内，来自非欧盟国家（如澳大利亚、独联体、南非、美国）的问题也将被考虑。本文主题的提出是基于对以下几个标题的考虑：瓦斯涌出量预测、考出瓦斯涌出的措施、煤层预先脱气、常规瓦斯抽放技术的优化、后退式开采瓦斯涌出的控制、瓦斯突出的预测。2 瓦斯涌出预测甲烷涌出量预测在德国硬煤工业已经实践了很多年(Winter, 1958; Schulz, 1959; Noack, 1970 and Noack, 1971; Flgge, 1971; Koppe, 1975)。所以现在已经得到了一些预测方法。下面将介绍其中的一些：（1）瓦斯涌出量的估算(Koppe, 1976; Noack, 1985)，就像用于处理已采煤层和邻近煤层的涌出一样，已被先前的采煤活动干扰。（2）瓦斯压力减少量的估算(Noack and Janas, 1984; Janas, 1985a and Janas, 1985b)同样地被应用于沉积物的未开采部分中。（3）长壁工作面的已采煤层的瓦斯涌出预测方法，掘进巷道瓦斯涌出预测方法以及在钻孔时被斜穿的煤层的瓦斯涌出预测方法。前两种方法是预测矿井具体瓦斯涌出量的方法，用平均生产一吨煤涌出的瓦斯立方米数来表示。单位时间内瓦斯涌出的立方米数，可通过预测结果乘以预计产生体积得到，它是制定煤矿计划的一个重要因素。这些方法确定了在相当长的时间内（几个月）以几乎相同的工作面掘进速度工作时采煤工作面的平均瓦斯涌出量。这种预测假定瓦斯涌出的区域已经被全面开拓，也就是说采煤工作面的开始阶段已经过去。此外，采煤工