許廠煤礦180萬噸新井設(shè)計【含CAD圖紙+文檔】
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英文原文
2007 China (Huainan) International Symposium on Coal Gas Control Technology
Gas Drainage in High Efficiency Workings
in German Coal Mines
Dr. Joachim Brandt, DMT GmbH, Germany
Abstract
In the course of increasing production in the workings of German hard coal mining, the part of ventilation techniques as a factor of production has also increasing importance. In view of still increasing production the cooling of the air is critical for the attainable production on the one hand. On the other hand, the increasing gas emissions have to be controlled as well.
This is achieved by fans of high capacity as well as by cross-sections in the underground workings, which are as big as possible, especially in the gateways. Furthermore, increasing cooling power is installed.
The air volumes cannot be enlarged unlimited, yet, and rapidly reach their limit due to national statutory regulations concerning the maximal allowed air velocities.
Besides that, a methane concentration of 1?Vol.-% in the maximum must be maintained in general, which is allowed to be exceeded only with the agreement of the mining authority in defined parts of workings up to a limit of 1,5?Vol. %.
Due to a dense sequence of coal seams in the German hard coal deposits, the firedamp is released during the exploitation not only from the worked seam, but essentially from the seams in the roof and in the floor behind the passage of the longwall. A gas drainage on the base of an efficient technique is necessary, firstly in order to fulfil the safety regulations and secondly to achieve a maximal production in the working.
An investigation, recently finished and executed concerning the improvement of the gas drainage indicated that, by means of rock mechanical calculations and interpretations, an increase in the efficiency of gas drainage boreholes is still possible.
Introduction
The methane emissions in mining operation depend principally on geologic conditions. In rock sequences with a small portion of coal in the roof and the floor, only the released gas quantity from the exploited seam – also defined as basic gas emission?– has to be diluted with the air flow. This methane flow can reduce the exploitation relevantly by an increasing desorbable gas content in the coal. In particular, the coal mass flow quickly exploited with high-capacity production can release very high methane quantities from the accompanying seams. This high methane flow generates an exceeding of the threshold values and leads to switch off of the electrical equipment and to the interruption of production.
In a rock sequence with a high portion of coal in the roof and the floor additional gas from the accompanying seams in the area of gas emissions is released into the air flow behind the passage of the longwall. In the Ruhr Basin this gas flow, also defined as additional gas emission, is normally many times higher than the basic gas emission.
Figure?1 illustrates the loosening of layers caused by longwall mining operation in flat layers. These loosenings can be – according to their degree - flow ways for the released gas from the accompanying seams. The coloured areas mark the degree of loosening with red for intensive, dark blue for light and grey for no loosening.
Figure 1: Example for the loosening of the rocks in the roof and the floor of a longwall operation (view of the left side only; the right side is symmetric)
There can be a high rate of additional gas emissions according to the seam thickness in the area of gas emissions and according to their gas content. Figure 2 shows that the production can decrease dramatically already at low gas contents if there is no gas drainage for the suction of the additional gas emission.
This extreme reduction of saleable output and advance of production requires extreme increasing of the air flow and – furthermore – gas drainage is necessary. Thereby the legal regulations for the German hard coal mining have to be observed, which are the following:
maximum air velocity 6?m/s
maximum methane concentration 1?Vol.-%
exceptional methane concentration 1,5?Vol.-%
minimum negative pressure in the gas drainage 100?hPa
Figure 2: Example for the decline of production in case of (increasing) additional gas emission
Improvement of the gas drainage for maximising the output
After increasing the air flow following the legal regulations, and with the permission by the authorities for maximum methane concentrations of 1,5 Vol.-%, and after commissioning a gas drainage system, the output can be increased to a quantity, which is again profitable (see figure 3).
Normally, the efficiency of the gas drainage system is up to 50% of the total methane flow occurring during exploitation. An additional optimising of the gas drainage above that also increases the face output.
A longwall in seam H of the mine Prosper Haniel serves as an example for optimising gas drainage results (figure?4).
The length of the panel of approx. 960 m was mined with a daily advance of production of approx. 7 m/d in 140 work days although the desorbable gas contents were at approx. 8 m3/t and the gas make from the additional gas emission was 30 m3 on the average per exploited ton. The drained methane quantities were up to approx. 650.000 m3 per week (approx. 65 m3/ min). The gas drainage efficiency reached up to 72%.
The gas drainage boreholes were drilled from both gate ways into the roof and the floor. The distance from one another was 10 m.
Figure?3: Example of increased output by doubling of air flow and installation of a gas drainage system with 50% efficiency.
A gas pipe of 500 mm diameter was available in the loader gate. In the tail gate, a gas pipe of 300 mm width was installed behind the face and extended according to the advance of the exploitation.
The total air flow for the panel was up to 85 m3/s. In the working area methane concentrations of up to 1,5 Vol.-% were locally allowed. Outside the working area towards the air return shaft the limit of 1?%-methane concentration had to be observed.
Principles for gas drainage
A basic draft (figure?5) shows the function of a gas drainage: Gas boreholes are drilled along the goaf shortly behind the longwall. In general, the roof emits the most gas. However, from the floor a considerably additional gas flow can be expected in the case of high gas contents. According to the rock properties, the gas boreholes are tubed at their beginning at a length of 7.5?m to 20 m and the annular space between tube and fractured rocks near to the roadway is sealed with plastic material (adhesive or foam plastic). This technology reduces unwanted leakages. The diameters of these boreholes are 75?mm to 115 mm. Their length depends on the distance of gassy layers (accompanying seams), which have to be drained from the exploited seam. The length varies normally between 30m and 60 m. In particular cases the length can be 100?m and more if there are special rock mechanical conditions.
The incline of the borehole to the roadway axis is between 75 gon and 90 gon. According to the occurring gas volume, the distance between the boreholes can be 10 m to 50 m. The boreholes are connected to the gas pipes by plastic tubes with adequate adapters.
For planning and dimensioning of gas drainage systems, it is necessary to calculate the occurring quantities of gas mixtures in the planned mining operations at an early stage (prediction of gas emissions)
Most important factors concerning the technology of gas drainage
Dimensioning of pipes
Pipes are the most important part of a functional and high-capacity gas drainage system. If they are not dimensioned according to the flow characteristic of the gas quantities to be expected, the success of the gas drainage is put into question. Even high-capacity pumping stations cannot compensate the pressure loss due to pipe cross sections, which are too small. In the range of negative pressure there is only a very small margin of 300 hPa to 400 hPa available for the compensation of pressure consumption (pipe friction, water accumulation, installations, bends of the pipeline).
The normal operating range of the pumps is in general at a negative pressure of 400 hPa to 450 hPa. At the end of the gas collection pipe in the mining area there should be a negative pressure of at least 100 hPa according to the German rules. That means that only approx. 300 hPa to 350 hPa are available for all pressure losses in the gas piping net.
Figure?4: Arrangement of gas boreholes and air supply of a longwall in seam?H, mine Prosper-Haniel.
The context between quantities of gas mixtures, which have to be drained, and pressure losses due to small-dimensioned pipes is illustrated in the following diagram (figure?6):
Figure?5: Basic draft for gas drainage boreholes (schematic diagrams)
A pipe diameter of less than 400 mm is unfavourable. A tolerable pressure loss in the system normally occurs, when there are flow velocities of between 10 m/s and 15 m/s. However, the length of the pipeline has to be taken into consideration (in fig.?6 for 1000?m).
Even at diameters of 300 mm the pressure loss is four times higher compared to a pipe width of 400 mm. The pressure consumption graph rises steeply, when there is a diameter below 300 mm.
The false gas pipe cross section has quickly negative effects on the accessible output of a mining operation due to reduced efficiency of the gas drainage.
High capacity pumps
The pumps to be used should produce negative pressure of up to 500 hPa. Water ring pumps or rotary pumps are suitable here, which are available on the market for any capacity. When planning a pumping station a certain tolerance for capacity modification has to be kept in mind in case the gas quantities increase during the life of the mine.
Figure?6: Pressure consumption depending on pipe diameter
The single capacities of the pumps should be dimensioned according to the minimum and maximum of the gas quantities to be expected (pumps with graduated capacities). A reserve pump is prescribed by law. Water ring pumps have certain advantages compared to rotary pumps if higher negative pressures have to be reached. In case of a pipe system sufficiently dimensioned, the construction types are equivalent.
The drive capacities installed in the gas drainage stations of the German hard coal mines for high gas quantities are 1.5 MW and more, if required. This can cope with volume flows of up to 175 m3/min pure methane, which corresponds to gas mixture quantities of 21000 m3/h at a methane concentration of 50%.
Rock mechanical aspects for the optimisation of the gas drainage
Considering rock mechanical aspects helps to optimise the gas drainage. A preferably precise reproduction of the rock sequence in a rock mechanical computer model offers conclusions for the ideal arrangement and length of gas boreholes. A visual implementation of rock mechanical calculations of the processes of loosening allows insights into the rocks and therefore an idea about the area of gas emissions in the area of loosening of mining operations.
The following figure?7 of a working at the mine Walsum, shows as an example of a single case plastifications – and consequently the occurring flow ways - reaching far into the roof (visible by the light red areas). The dip angle of the rock sequence amounts 20?gon.
Figure?7: Plastifications in the roof and the floor of a working at Walsum mine
By use of this model of rock mechanical reactions, the existing drilling schema was modified (figure?8):
Figure?8: Increase of gas emissions in the case of incline and length modification of the gas boreholes (Walsum mine)
After modifying the bore angle from approx. 80 gon to 90 gon and the bore length from 55 m to 110 m, there was a significantly higher efficiency of the single boreholes (see top graph). As a result, at this working and also in the following working the efficiency of gas drainage could be increased up to more than 70%.
Due to a study of the years 2004 and 2005 led by support of the DMT?GmbH, rock mechanical calculations were made for a high number of workings with various rock sequences of the Carboniferous in the Ruhr Basin. Thereby, processes of rock loosening, which can influence the gas emission, were analysed.
At the same time, occurring rock tensions behind passage of the longwall in the rocks were analysed, which might influence the height and the time of the gas release. This study offers an extensive collection of experiences in this regard, which allow to evaluate future methane flows better and to plan gas drainage systems more reliable.
The following illustration (figure?9) serves as a last example of the complexity of the relations between rock mechanics and gas release.
Here, the processes of loosening (on the left) are compared to the occurring rock tensions (on the right). A sandstone layer of 25 m to 30 m thickness near above the worked seam is remarkable in this example. Compared to the softer kinds of rocks this layer shows only minor plastifications. This fact corresponds to the present mining experiences.
Concerning the rock mechanical comparison to rocks with less solidness, an essentially higher and longer lasting pressure relief of the layers lying above this sandstone occurs.
This means with respect to the gas emissions that the seams lying above the sandstone also underly to a higher and longer lasting pressure relief than it is normally the case for less solid accompanying rocks. For this reason, they emit in total much more methane than one has to expect according to a conventional gas emission.
Figure 9: Plastification and relief of mechanical pressure in the area of looseningof a longwall operation with a thick, hard sandstone layer in the roof
In a single case up to three times higher methane inflows occurred in a seam in a working at the mine Ost than calculated before.
In the meantime the gas drainage system was extended to a capacity of 15.000?m3 gas mixture per hour. Furthermore, a special piping method was developed for the safe suction of the additional gas emission above the sandstone layer. This method guarantees a lifetime of the gas boreholes of more than 12 months.
Additionally, the underground piping net, which has to bridge a length of approx. 12 km from the drainage station at the surface to the exploitation, was extended in a way that two thirds of the pipelines consist of parallel strings with 500 to 600?mm diameter.
Completing Comments
On the whole, increasing gas contents and consequently higher additional gas emissions limit the increase of production.
According to the national laws there must be a high expense for ventilation as well as gas sucking technology to achieve a maximum output. Safety, which is an important factor of production, as well as economical aspects will be maintained.
Additionally, the utilisation of the methane emissions can compensate financial expenses at least partially. However, the gas drainage systems have to be dimensioned optimal. Here, it is important to coordinate the underground gas pipe nets and the above ground gas drainage stations for the gas flows to be expected in the mining operations.
Essen, 04.05.2007
References
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[7]Wang L G,Song Y.A model to risk assessment for mine water-inrush.Journal of Engineering Geology,2001,09(02):158–163.
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中文譯文
2007年中國（淮南）煤層氣控制技術(shù)國際座談會
瓦斯抽放在德國煤礦的高效運作
Joachim Brandt博士
DMT GmbH公司，艾森，德國Essen，2007年4月5日
摘要：在提高德國硬煤開采生產(chǎn)過程中，通風技術(shù)部分作為生產(chǎn)要素的也變得越來越重要。一方面，針對還在增加的生產(chǎn)空氣冷卻十分重要。另一方面,也必須對不斷增加的瓦斯釋放加以控制。
可以通過使用大功率通風機或在井下，尤其是在巷道內(nèi)設(shè)置盡可能大的聯(lián)絡(luò)巷，可以實現(xiàn)這一點。此外，越來越多的制冷設(shè)備也得以安裝。
除此之外，甲烷的濃度必須控制在1?Vol.-%常規(guī)以內(nèi)，常規(guī)規(guī)定甲烷最高濃度可以在采礦專家定義的井下濃度上限1,5?Vol. %。
由于德國的硬煤沉積中煤層沉積致密，瓦斯不僅從廢棄煤層釋放，而且尤其從頂板巖層和長壁工作面后方的兩巷釋放。高效的瓦斯抽采很有必要，首先是為了達到安全規(guī)定，其次是達到生產(chǎn)最大化。
最經(jīng)一項已經(jīng)完成并投入使用的實驗表明，通過巖體力學計算和解釋，提高瓦斯抽放鉆孔的效率仍有可能。
說明
在采礦工程中甲烷排放量主要取決于地質(zhì)條件。在那些頂、底板含有少量煤炭的巖層中，只有那些從已開采煤層且被定義為基本瓦斯排放的瓦斯釋放量才需要用氣流加以稀釋。煤炭中瓦斯含量越高，這種瓦斯氣流就越容易導致開采工作的減緩。特別是，煤炭開采速度越快、量越大，就越容易導致工作面瓦斯的大量釋放。這種高甲烷產(chǎn)生的流量超過閾值并導致關(guān)掉電氣設(shè)備和中斷生產(chǎn)。
在那些頂?shù)装搴写罅棵旱膸r層中，從位于瓦斯卸壓釋放區(qū)的臨近層中釋放的額外瓦斯被四方到工作面后方的廢棄兩巷。在魯爾盆地，這種被稱為額外瓦斯釋放的瓦斯氣流通常比基本瓦斯釋放大好幾倍。
圖1說明了在水平層中因長壁采煤作業(yè)而引起的煤層卸壓。依據(jù)它們的卸壓程度，這種卸壓可以為臨近煤層中的瓦斯釋放提供縫隙。彩色區(qū)域標志著卸壓程度：紅表示強烈，深藍表示輕微，灰表示未卸壓。
根據(jù)瓦斯釋放區(qū)的煤層厚度和瓦斯含量，會有大量的額外瓦斯釋放。圖2表示如果沒有瓦斯抽放來吸收額外瓦斯釋放，采煤作業(yè)能夠迅速的把瓦斯含量降到一個較低值。
這種極端的輸出下降和生產(chǎn)進尺需要急劇的增大風流，并且，瓦斯抽采也是必要的。因此，針對德國硬煤開采的合法規(guī)定必須被遵守，規(guī)定如下：
最大風速： 6m/s
最大甲烷濃度：1?Vol.-%
特殊甲烷濃度：1,5?Vol.-%
瓦斯抽采最低負壓：100?hPa
圖1：長壁采煤作業(yè)的頂?shù)装逍秹旱氖纠ㄖ豢醋筮叄疫厼閷ΨQ）
基于提高產(chǎn)量的瓦斯抽采技術(shù)改進
通過遵循法定的條例來增加風量，經(jīng)過官方允許的最大瓦斯含量（1,5 Vol.-%），并且經(jīng)過調(diào)試瓦斯抽放系統(tǒng)，產(chǎn)量又可以重新達到一個可觀值。（見圖3）
圖2：額外瓦斯釋放量遞增時引起的生產(chǎn)下降。
通常，瓦斯抽放系統(tǒng)的效率是可以抽出煤炭開采過程中50%的瓦斯釋放量。一個經(jīng)優(yōu)化后數(shù)值大于前面數(shù)值的系統(tǒng)也能帶來工作面產(chǎn)量的提高。
Prosper Haniel煤礦的一個位于H煤層的長壁工作面作為優(yōu)化瓦斯抽采系統(tǒng)的結(jié)果的示例（圖4）
該區(qū)段推進長度約960m,在140個工作日內(nèi)日進7m，盡管瓦斯解析量約為8 m3/t且加上額外瓦斯釋放得到的總瓦斯含量為平均每噸30 m3。每周的瓦斯抽放量達到650.000 m3左右（排放速度65 m3/ min左右）。瓦斯抽放時間利用率達到72%。
從工作面兩順槽向頂?shù)装宕虺榉陪@孔，鉆孔間距10m。
一個直徑500mm的瓦斯抽放管可以布置在運輸巷，在軌道巷，在工作面后面布置一個直徑300mm的管子，并依據(jù)開采適時延長。區(qū)段總風流可達85米3/ s。在工作區(qū)域的局部可以允許甲烷濃度達到1、5 Vol. - %。工作面以外的濃度不得高于1%。
圖3：風量加倍且安裝一套效率50%的瓦斯抽采系統(tǒng)后的產(chǎn)量增長示例
圖4：Prosper-Haniel礦一個長壁工作面的瓦斯抽放鉆孔的布置及風量供給
瓦斯抽放的原則
一個基本的草案(圖5)表明瓦斯抽放的機理:緊隨工作面，沿著采空區(qū)打抽放鉆孔。一般來說,頂板釋放大部分瓦斯。然而,若地板含有大量瓦斯，就有可能出現(xiàn)大量的額外瓦斯氣流。根據(jù)巖石特性、氣體鉆井是布置在他們開頭長度為7.5米到20米長。另外，抽放管和鉆空間的環(huán)狀空間由塑料材料(膠或泡沫塑料)充填。該技術(shù)減少不必要的泄漏。這些鉆孔直徑為75毫米到115毫米。它們的長度取決于含瓦斯層(臨近層)的距離，這些瓦斯必須從已經(jīng)形成的縫隙加以抽放。不同的長度通常在30米,60米之間。在特定的情況下, 如果有特殊的巖石力學狀況，長度可以達到100米或更多。
鉆孔與順槽軸間傾角介于75到90幾何角。根據(jù)已測得的瓦斯體積，鉆孔間距可以從10m到50m。用帶有足夠的適配器的塑料管來將鉆孔和瓦斯管道連接起來。
圖5：瓦斯抽放鉆孔基本草稿（原理圖）
對于規(guī)劃與瓦斯抽放系統(tǒng)定型,有一步是必要的,那就是在早期(瓦斯釋放預(yù)測)的計算出區(qū)段回采作業(yè)工作中既得混合氣體的量。
有關(guān)瓦斯抽放技術(shù)的最重要因素
管道尺寸
管道是可用和大容量的瓦斯抽放系統(tǒng)中最重要的部分。如果它們的尺寸不是根據(jù)預(yù)期的瓦斯流量特性來定制，瓦斯抽放就很難成功。即便大容量泵站也不能補償因管道交叉環(huán)節(jié)太小引起的壓力損失。在負壓階段，只有一個非常小范圍的300到400hpa的壓力可用于補償?shù)膲毫ο?管摩擦、積水、設(shè)施、彎曲的管道)。
在泵的正常工作范圍，負壓一般在400到450hpa。根據(jù)德國規(guī)定，在回采區(qū)的瓦斯回收管的末尾應(yīng)該至少有100hpa的負壓。這意味著只有大約300到350hpa的壓力可作用于所有的管道網(wǎng)絡(luò)壓力損失。
下表（圖6）解釋了必須被抽放的混合氣的量和由小尺寸管路引起的壓力損失間的關(guān)系。
圖6:壓力消耗取決于管的直徑
管道直徑小于400毫米是不利的。當流速介于10 m/s和15m/s,一些在允許范圍內(nèi)的壓力損失會經(jīng)常發(fā)生。然而,管道的長度必須被考慮(圖6為1000m)。
即使在直徑300毫米,壓力損失高出管道寬度400毫米時的四倍。當有一個直徑300毫米以下，壓力損耗圖大幅上漲。
瓦斯管路交叉環(huán)節(jié)的無效會很快對因瓦斯抽放效率的降低而引起的回采作業(yè)的產(chǎn)出產(chǎn)生負面影響。
高容量泵
泵的使用將產(chǎn)生達到500hpa的負壓。水環(huán)泵或扶輪泵適合這種能力,可在市場上買到任何容量的。當設(shè)計一個泵站時必須牢記要留有一定的容量變動余地，以防在煤礦服務(wù)年限內(nèi)瓦斯數(shù)量增加。
泵的單個性能需要根據(jù)預(yù)期的瓦斯的最大、最小量加以定型（容量分等級的泵）。依據(jù)規(guī)定留有備用泵。如果有更大的負壓要求，相比扶輪泵，水環(huán)泵有一定的優(yōu)勢。一旦管路系統(tǒng)經(jīng)充分定型，工程類型是等價的。
在德國的硬煤煤礦的瓦斯抽采站，如果需要的話，用以抽采大量瓦斯的驅(qū)動功率可以達到1.5MW或更多。這足以匹配達到175 m3/m
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