Key technologies and equipment for a fully mechanized top-coal caving operation with a large mining height at ultra-thick coal seams

Thick and ultra-thick coal seams are main coal seams for high production rate and high efficiency in Chinese coal mines, which accounts for 44 % of the total minable coal reserve. A fully mechanized top-coal caving mining method is a main underground coal extraction method for ultra-thick coal seams. The coal extraction technologies for coal seams less than 14 m thick were extensively used in China. However, for coal seams with thickness greater than 14 m, there have been no reported cases in the world for underground mechanical extraction with safe performance, high efficiency and high coal recovery ratio. To deal with this case, China Coal Technology ＆ Engineering Group, Datong Coal Mine Group, and other 15 organizations in China launched a fundamental and big project to develop coal mining technologies and equipment for coal seams with thicknesses greater than 14 m. After the completion of the project, a coal extraction method was developed for top-coal caving with a large mining height, as well as a ground control theory for ultra-thick coal seams. In addition, the mining technology for top-coal caving with a large mining height, the ground support technology for roadway in coal seams with a large cross-section, and the prevention and control technology for gas and fire hazards were developed and applied. Furthermore, a hydraulic support with a mining height of 5.2 m, a shearer with high reliability, and auxiliary equipment were developed and manufactured. Practical implication on the technologies and equipment developed was successfully completed at the No. 8105 coal face in the Tashan coal mine, Datong, China. The major achievements of the project are summarized as follows： 1. A top-coal caving method for ultra-thick coal seams is proposed with a cutting height of 5 m and a top-coal caving height of 15 m. A structural mechanical model of overlying strata called cantilever beam-articulated rock beam is established. Based on the model, the load resistance of the hydraulic support with a large mining height for top-coal caving method is determined. With the analysis, the movement characteristics of the top coal and above strata are evaluated during top-coal caving operation at the coal face with a large mining height. Furthermore, there is successful development of comprehensive technologies for preventing and controlling spalling of the coal wall, and the top-coal caving technology with high efficiency and high recovery at the top-coal caving face with a large mining height. This means that the technologies developed have overcome the difficulties in strata control, top-coal caving with high efficiency and high coal recovery, and enabled to achieve a production rate of more than 10 Mtpa at a single top-coal caving face with a large mining height in ultra-thick coal seams; 2. A hydraulic support with 5.2 m supporting height and anti-rockburst capacity, a shearer with high reliability, a scraper conveyor with a large power at the back of face, and a large load and long distance headgate belt conveyor have been successfully developed for a top-coal caving face with large mining height. The study has developed the key technologies for improving the reliability of equipment at the coal face and has overcome the challenges in equipping the top-coal caving face with a large mining height in ultra-thick coal seams; 3. The deformation characteristics of a large cross-section roadway in ultra-thick coal seams are discovered. Based on the findings above, a series of bolt materials with a high yielding strength of 500-830 MPa and a high extension ratio, and cable bolt material with a 1 × 19 structure, large tonnage and high extension ratio are developed. In addition, in order to achieve a safe roadway and a fast face advance, installation equipment for high pre-tension bolt is developed to solve the problems with the support of roadway in coal seams for top-coal caving operation with a large mining height; 4. The characteristics of gas distribution and uneven emission at top-coal caving face with large mining height in ultra-thick coal seams are evaluated. With the application of the technologies of gas drainage in the roof, the difficulties in gas control for high intensive top-coal caving mining operations, known as ＂low gas content, high gas emission＂, are solved. In addition, large flow-rate underground mobile equipment for making nitrogen are developed to solve the problems with fire prevention and safe mining at a top-coal caving face with large mining height and production rate of more than 10 Mtpa. A case study to apply the developed technologies has been conducted at the No. 8105 face, the Tashan coal mine in Datong, China. The case study demonstrates that the three units of equipment, i.e., the support, shearer and scraper conveyor, are rationally equipped. Average equipment usage at the coal face is 92.1%. The coal recovery ratio at the coal face is up to 88.9 %. In 2011, the coal production at the No. 8105 face reached 10.849 Mtpa, exceeding the target of 10 Mtpa for a topcoal caving operation with large mining height performed by Chinese-made mining equipment. The technologies and equipment developed provide a way for extracting ultra-thick coal seams. Currently, the technologies and equipment are used in 13 mining areas in China including Datong, Pingshuo, Shendong and Xinjiang. With the exploitation of coal resources in Western China, there is great potential for the application of the technologies and equipment developed.

Support-surrounding rock relationship and top-coal movement laws in large dip angle fully-mechanized caving face

When mining the fully-mechanized longwall caving face along strike, the unstable equipment, the low top-coal recovery ratio and the difficulty in controlling surrounding rock may occur due to large dip angle. Considering the effects of strike angle on support stability, the ‘‘support-surrounding rock"mechanical models of support topple and support slip were established in this paper. On the basis, the influencing factors of support stability were analyzed and the technical measures of controlling support and surrounding rock stability were put forward. Then the loose particles simulation experiment was conducted to analyze the impacts of caving directions and methods on the top-coal recovery in large dip angle fully-mechanized caving face. Finally, the ‘‘upward sequence and double-openings doublerounds" caving technology was determined. The research results are of great scientific significance and practical values to improve large dip thick seam mining technology.

Study on gob-side entry retaining technique with roadside packing in longwall top-coal caving technology

Pointed out some technical difficulties of gob-side entry retaining with roadside packing in longwall top-coal caving technology (LTCT), and analyzed the function mecha-nism of roadside filling body. Theory analysis shows the mechanical properties of high water material fit for the feature of deformation of gob-side entry retaining in LTCT, and gob-side entry retaining in LTCT face is one of effective ways to increase the recovery ra-tio of mining district.

Three-dimensional experimental study of loose top-coal drawing law for longwall top-coal caving mining technology

Based on the loose medium flow field theory, the loose top-coal drawing law of longwall top-coal caving（LTCC） mining technology is studied by using self-developed three-dimensional（3D） test device. The loose top-coal drawing test with shields and the controlled test without shields are performed in the condition without any boundary effect. Test results show that shields will cause reduction in drawing volume of coal in the LTCC mining. The deflection phenomenon of drawing body is also observed in the controlled test, which is verified that the deflection of drawing body is caused by shield. It is found that the deflection angle decreases with increasing caving height, with the maximum value of atailand the minimum value of 0. In addition, the formula to calculate the drawing volume is proposed subsequently.The deflection of drawing body is numerically simulated using particle flow code PFC3 Dand the proposed formula to calculate drawing volume in LTCC is also verified.

Distribution laws of abutment pressure around fully mechanized top-coal caving face by in-situ measurement

In order to obtain the distribution rules of abutment pressure around the 1151 （3） fully mechanized top-coal caving （FMTC） face of Xieqiao Colliery, the KSE-II-1 type bore-hole stress gauges were installed in the tailentry and headentry to measure the mining-induced stress. The distribution rules of the front and side abutment pressure were demonstrated. The results show that distribution rules of stress are obviously different in the vicinity of the face and entries. The peak value of abutment pressure in the protective coal pillar and face are located commonly in front of the working face along the strike, and they are located at the stress-decreased zone near the face. There is no stress peak value in the lateral coal mass beside the headentry in front of the face on the strike, and the peak value of abutment pressure appears at the rear area of the face. There are stress peak values both in the protective coal pillar and in the lateral coal mass beside the headentry to the dip.

SAFETY PROBLEMS IN FULLY-MECHANIZED TOP-COAL CAVING LONGWALL FACES

The thick-san top-ctal catrig technology has been in use in China for over a decade,and has given rise to siguscant economic efficiendes. Eftorts in reeent years to extend its applica tion to more complex mining conditions, mostly high-gas seams , with or without proneness ofspontaneous combustion. have brought about new safety problems This paper will highlight thefcatures and problems retared with thick-seam top-coal caving systems, compared with conventionai, fully-mecbanized longwall systems , particularly issues retated to methane, spontaneous combustion and dust,and disam the methods and measures to ded with them.

Surface Movement Regularity of Super-Wide Mining Face With Top-Coal Caving

No.4326 super-wide panel of Wangzhuang Coal Mine ( in which the fully-mechanized top-coal caving longwall mining method was used) was monitored for dynamic characteristic of surface movement. The dynamic surface movement in and after mining was predicted by using the Mining Subsidence Prediction System. The results indicate that after mining, the surface above the super-wide panel reaches a state of full subsidence, making the No.309 national highway above the panel be located on the flat bottom of the subsidence basin so that the influence of mining activity in both sides of 4326 panel on the national highway is the smallest.

A low-frequency wideband metamaterial absorber based on a cave-disk resonator and resistive film

A low-frequency wideband, polarization-insensitive and wide-angle metamaterial absorber （MA） is designed, simulated and analyzed. This MA consists of a periodic arrangement of a cave-disk resonator （CDR）, square resistive film （RF）, and metal ground plane （GP） （a 0.8 mm-thick FR-4 dielectric spacer is sandwiched in between the CDR and RF, and another 1.2-mm thick FR-4 dielectric spacer is inserted in between the RF and GP）. The simulated results based on finite integration technology （FIT） indicate that the absorption of the MA is greater than 90% and almost perfectly impedance- matched to the free space in the whole frequency range of 1 GHz–7 GHz. The simulated absorptions under the conditions of different polarization and incident angles indicate that this composite structure absorber is polarization-insensitive and wide-angled. Furthermore, the distribution of the power loss density indicates that the wideband absorptivity is mainly from the composite electromagnetic loss of the CDR and RF. This design provides an effective and feasible way to construct a low-frequency wideband absorber.

Current Situation and Prospect of Top-Coal Caving Technology in China

A great development has been achieved on thick seam longwall top-coal caving technology in China for the recent years, which has raised face output and efficiency and reduced production cost greatly. In this paper, achievements in its production, safety and theoretical research and future tasks are discussed.

Longwall Top-Coal Caving in Thinner Thick-Seam and Research on Light Hydraulic Support

The application of light hydraulic support highlights the advantages of longwall top-coal caving (LTC) in thinner thick-seams (3. 0~ 5. 0 m). Considering the problems in practice, the developing of its new series will promote the mining of LTC with light hydraulic supports. Some relevant technical problems of the caving technology and the future of this series of supports are analyzed in this paper with several new opinions.

Study on Dust-Control WaterInjection in Fully-Mchanized Top-Coal Caving Longwall Faces

Based on the analysis of the top-coal movement, the appropriate position of holes through which dustcoutrol water is injected is confirmed. And a practical test has been carried out, which has achieved good reuslts both in dust control and in the flow rate of water injected into coal.

Numerical and theoretical investigations of the effect of the gangue-coal density ratio on the drawing mechanism in longwall top-coal caving

Discrete element calculations of the top-coal drawing process for diferent gangue-coal density ratios were conducted to investigate the efect of the gangue-coal density ratio on the drawing mechanism in longwall top-coal caving.The efects were analyzed for the drawing body,the top-coal boundary,and the recovery of top coal.The results show that for increasing density ratio,the initial drawing body on the goaf side is farther away from the drawing support and its width and volume gradually increase.The upper part of the sickle-shaped drawing body extends near the initial drawing body with increasing density ratio in the normal cycling stage,and the distance from the drawing body to the initial drawing body is its maximum width.The larger the density ratio,the smaller the height of the top coal above the goaf at the end of the initial drawing process.The height of the top-coal boundary decreases with increasing density ratio,until it reaches a limit.In a normal cycle,due to hysteretic development,the top-coal boundary moves toward the goaf until the density ratio is approximately 2.0,which is consistent with the physical experiment results.Finally,increasing the advance length of the working face is benefcial for increasing the overall recovery of top coal.

Analysis on air-leakage law of goal in condition of ascending mining for top-coal caving

Using the Jisan Coalmine's top-coal caving for the 3down coal seam with ascending mining as the project background, the air-leakage characteristics of the goaf wasanalyzed. Through data fitting of the in situ observation, the models of gas seepage, diffusion and air-leakage in the goaf were established in ascending mining. The ComputationFluid Dynamics software Fluent was used to simulate the air-leakage law of the goaf. Theresults of the numerical simulation provide a basis for the use of the technology of ventilation and fire prevention in the working face of an ascending mining, which ensures thesafety in production in the working face of the top-coal caving for 3_down coal seam in theJisan Coalmine.

Reliability analysis of the velocity matching of coal cutting and caving in fully mechanized top-coal caving face

The matching relationship between coal cutting and caving in fully mechanized top-coal caving face is analyzed in detail from the angle of reliability. The coupling equation of reliability is established correspondingly, and the mathematical equation of the coefficient of velocity matching of coal cutting and caving is obtained, which meets a certain reliability demand for making the working procedure of coal caving not influence coal cutting of coal-cutter. The results show that the relationship between the coefficient of the velocity matching and the reliability of coal cutting and caving system is linear on the whole when R <0.9. It is pointed out that different numerical value should be selected for different coal face according to different demand for reliability.

THE BASIC MECHANICS PROBLEMS AND THE DEVELOPMENT OF LONGWALL TOP-COAL CAVING TECHNIQUE IN CHINA

Since the middle of 1980’s, the longwall top-coal caving technique has beveloped rapidly in China. At present, it is one of the main approaches in the thick coal seam mining. This peper describes some mechanica problems of the caving technique, such as the damage and failure of the top-coal, the strata behaviors in the caving face, and the relation of the support and the surrounding rock. In order to employ the caving technique in a widespred scope, the problems such as the caving technique in the hard coal seam, the moving and running of the loose top-coal,and the upper floating of the gas etc. should be systematically systematically studied.

有限回采空间内贫矿资源无底柱分段崩落法低贫损开采方案研究

做好无底柱分段崩落法的贫损控制对于矿山经济效益及环境保护具有重要意义,但当矿床开采条件复杂、矿石品位较低时,矿石贫损控制难度将会大幅增加,在此条件下如何做好矿石贫损控制一直是崩落法开采方向的重要关注点。金川龙首矿西二采区无底柱分段崩落法采场仅可布置4个分段,回采空间十分有限,不利于矿石的贫损控制,加之西二采区矿石品位较低但经济价值较高,因此在开采过程中需要严格控制矿石贫损。针对西二采区的复杂开采条件及贫损控制需求,提出了一种“首采分段总量控制出矿、中间分段低贫化出矿、最末分段低贫化出矿+辅助进路回收残留矿石”的组合式低贫损回采方案。以西二采区为工程背景,设计并制作了一种高仿真度的物理放矿模型并对该方案展开了试验研究。结果表明:即便是在暂时不考虑回收最末分段残留矿石的情况下,该方案可使西二采区崩落法采场的矿石回收率达到75.6%,而废石混入率仅为6.0%,在确保矿石回收率的基础上显著降低了矿石贫化。该方案在现场应用后,实际的矿石回收指标与试验结果基本接近,表明该方案在西二采区有限回采空间内实现了贫矿资源低成本、高质量回收的总体目标。

大水易淤综放工作面泄水巷煤泥淤积物临界流速研究

高家堡煤矿综放工作面面前淋水,水源主要来自采煤工作面顶板,矿井涌水量达到4000~5000 m^(3)/h。结合开采工作面泄水巷煤泥淤积的特点,利用罗宾诺维奇—莫纳方程和哈根—泊肃叶(Hagen-Poiseuille)等公式,确定了煤泥混合物的流变类型和本构方程;采用大型环管实验法建立了煤—泥—水混合物的流动模型,理论分析了工作面泄水巷煤泥淤积物分别在高低压段和不同剪切速率下的沉降特性;计算得到动水条件下煤泥淤积物发生流动的临界流速为1.1~1.5 m/s,从而得出煤泥淤积物的临界流速。研究煤泥在矿井水流动过程中的淤积机理,可为科学合理的清淤工作提供理论依据。

低渗煤层瓦斯抽采顺层钻孔水力造穴卸压增透效果研究

为了揭示水力造穴参数对钻孔瓦斯抽采效果的影响规律,指导煤层水力造穴增透技术施工参数的合理选择。建立了煤层损伤-应力-渗流耦合模型,分析了不同造穴参数下煤层卸压增透效果,展开了顺层钻孔水力造穴现场工程试验,考察了不同造穴参数下钻孔瓦斯抽采效果,结果表明:采用水力造穴技术形成的孔穴能够有效降低其周围煤体应力,提高煤层渗透率,增加瓦斯钻孔抽采效果;造穴半径越大煤层的卸压程度越大,进而煤层渗透率增幅就越大,但在实际工程中过大的造穴半径会使得孔穴稳定性差,钻孔塌孔堵塞瓦斯涌出通道会使得钻孔瓦斯抽采量有所降低,试验矿井最优造穴半径为0.6 m;造穴间距对它们之间的应力降低区范围有着较大的影响,在一定距离条件下孔穴卸压有着明显的叠加效应,造穴间距越近叠加效应越明显,煤层应力越小,卸压增透效果越好。试验钻孔穴间距由8 m减小到6 m时,单孔平均瓦斯抽采纯量增加389.16%。

低水压掏穴扩孔技术在卸压增透钻孔中的应用

为解决煤矿井下卸压增透钻孔掏穴施工过程中需要配套高压泥浆泵的问题,提出了低水压掏穴扩孔技术。该技术配套开发了双通道掏穴装置、双通道钻杆及双通道送水器等成套技术装备。该技术在朱仙庄煤矿进行现场应用,结果表明,该技术能够在水压2~3 MPa条件下实现卸压增透钻孔“钻进-掏穴”一体化施工,为煤矿煤层卸压增透提供了新的技术方案。

白坪煤业综放工作面火区密闭启封技术应用

结合白坪煤业14204工作面自燃火区及密闭施工实际情况,在进行专项安全风险辨识评估的基础上,利用东部采区现有通风系统,通过局部通风机压风、通风设施构筑等方式,对14204胶带顺槽的8道密闭进行启封,密闭启封期间,巷道内气体浓度、温度均稳定在可控范围。