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 of mechanical principle of floor heave of roadway driving along next goaf in fully mechanized sub-level caving face

Abstract On the basis of analyzing floor strata mechanical circumstance of the roadway, the mechanical model was established. The relative displacement of roadway floor, narrow pillar floor coal mass and floor strata was calculated, the results showed that the high abutment pressure on coal mass beside the roadway was the main reason to lead to relative displacement of floor strata. And the roadway floor heave come mainly from three aspects. Firstly, the roadway floor strata is easily fractured by the stretch stress. Secondly, because the high abutment pressure is greater than the uniaxial compressive strength of floor strata, when the roadway floor strata are fractured, the coal mass floor strata at the same depth will be fractured, and broken rock will fluid into the open roadway. Thirdly, comparing with the coal mass floor, the roadway floor is relative ascending.

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.

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.

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.

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.

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.

浅埋深综放工作面采空区“三带”分布研究

为研究浅埋深综放工作面采空区“三带”分布规律,在串草圪旦煤矿6101综放工作面采空区埋设束管,对采空区“三带”进行了现场实测。实测结果表明:由于煤层埋深浅、地表起伏大、进风侧存在地表漏风,进风侧采空区“三带”明显滞后于回风侧,进回风两侧氧化带宽度分别为87.8 m和61.4 m。利用FLUENT软件对实测条件下该工作面采空区“三带”进行了数值模拟,模拟结果和现场实测结果基本一致。同时模拟了不漏风条件下该工作面采空区“三带”分布,此时采空区散热带、氧化带范围大幅度减小,进风侧采空区氧化带稍大,而工作面中部和回风侧“三带”分布基本一致。

综放架后膏体充填空间实测与顶煤冒放性影响规律研究

针对综合机械化放顶煤开采中的矸石处置问题,提出了一种放顶煤架后膏体充填方法,设计了柳巷煤矿综放工作面采空区空洞现场监测方案,定性分析了5个方面对顶煤冒放性的影响,采用PFC^(2D)数值模拟方法,定量分析了充填高度对顶煤冒放性的影响。研究结果表明:倾向方向上工作面上部端头附近采空区空洞体积最大,走向方向上工作面刚推进到新位置时采空区空洞体积最大,支架顶梁后方空洞体积大于支架尾梁上方;充填高度从0增加至3 m时,顶煤放出率由92.56%降低至86.11%,降低了6.45个百分点,顶煤含矸率由13.94%降低至13.17%,降低了0.77个百分点,相比于顶煤含矸率,充填高度对顶煤放出率影响较大。研究可为类似地质条件综放架后膏体充填开采实现提供理论基础。

综放面采空区漏风规律及防治技术研究

综放工作面采空区漏风易导致遗煤自燃,危及矿井安全。以大南湖一矿1305综放工作面为研究背景,采用数值模拟和现场试验的方法,研究了综放工作面采空区漏风规律,提出了综放工作面端头封堵采空区防漏风技术方案,并在现场进行了试验。结果表明,工作面端头是综放工作面采空区漏风的主要通道,其中进风巷侧端头漏风率达19%;风流在采空区内渗透深度约160 m;工作面端头封堵后,风流在采空区内渗透深度缩减至100 m左右;1305综放工作面端头封堵后,采空区漏风率降低17个百分点。

复杂不规则采空区围岩冒落持续监测及周期性冒落特征分析

复杂不规则采空区因其形成条件的特殊性和工程环境的复杂性,在形成初期常表现为剧烈且无规律的阵发性冒落,对采空区安全治理极为不利。以河北某铁矿因下部民采空区与生产区域采场相互贯穿形成的复杂不规则冒落空区为工程背景,结合三维激光扫描技术、现场调查结果和开拓、采准工程现状等,提出了联合监听冒落岩块撞击声响与监测拱脚变形的采空区冒落持续监测方法,得到拱脚变形破坏引起采空区批量冒落的周期性冒落特征。冒落岩块撞击声响监听结果显示,空区发生阵发性冒落的持续时间约5个月,经短暂稳定阶段后进入周期性冒落阶段。结合拱脚变形监测结果,可知该空区周期性冒落阶段周期为15~30 d,空区围岩批量冒落滞后拱脚变形破坏的时间为3~8 d,可见空区拱脚变形破坏可作为空区围岩进入批量冒落的前兆,提出监测2次空区边界扩展差hk来预测空区围岩批量冒落的发生时机。研究结果对于同类型空区冒落监测和安全治理具有一定的借鉴意义。

注氮条件下大采高综放工作面采空区自燃“三带”的分布规律

为解决大采高综放工作面因采高大、回采率低、开采扰动强等造成采空区遗煤自燃危险性增大的问题,以宁夏某煤矿大采高综放工作面为研究对象,应用渗透率演变方程和气体流动模型,分析注氮前后氧浓度时空演化规律及采空区自燃“三带”分布特征。结果表明:采空区氧浓度在注氮条件下呈现出中部大,两侧小的倒“U”型分布;在氧浓度划分下,氧化带范围呈现出先增大后减小的半月形,最大宽度由未注氮时的100 m缩小到50 m;在风速划分下,氧化带较未注氮时整体向工作面方向前移了15 m左右,有效降低了自燃危险区范围。