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.

Theoretical description of drawing body shape in an inclined seam with longwall top coal caving mining

Understanding the characteristics of drawing body shape is essential for optimization of drawing parameters in longwall top coal caving mining.In this study,both physical experiments and theoretical analysis are employed to investigate these characteristics and derive a theoretical equation for the drawing body shape along the working face in an inclined seam.By analyzing the initial positions of drawn marked particles,the characteristics of the drawing body shape for different seam dip angles are obtained.It is shown that the drawing body of the top coal exhibits a shape-difference and volume-symmetry characteristic,on taking a vertical line through the center of support opening as the axis of symmetry,the shapes of the drawing body on the two sides of this axis are clearly different,but their volumes are equal.By establishing theoretical models of the drawing body in the initial drawing stage and the normal drawing stage,a theoretical equation for the drawing body in an inclined seam is proposed,which can accurately describe the characteristics of the drawing body shape.The shape characteristics and volume symmetry of the drawing body are further analyzed by comparing the results of theoretical calculations and numerical simulations.It is shown that one side of the drawing body is divided into two parts by an inflection point,with the lower part being a variation development area.This variation development area increases gradually with increasing seam dip angle,resulting in an asymmetry of the drawing body shape.However,the volume symmetry coefficient fluctuates around 1 for all values of the seam dip angle variation,and the volumes of the drawing body on the two sides are more or less equal as the variation development volume is more or less equal to the cut volume.Both theoretical calculations and numerical simulations confirm that the drawing body of the top coal exhibits the shape-difference and volume-symmetry characteristic.

Drawing mechanisms for top coal in longwall top coal caving(LTCC):A review of two decades of literature

This review details the state of the art in research on top coal drawing mechanisms in Longwall top coal caving(LTCC)by examining the relevant literature over the last two decades.It startswith an introduction of the brief history and basic procedures of LTCC.The framework of research on the drawing mechanism,basic concepts,and some theoretical models of LTCC are detailed in sect.research framework of top coal drawingmechanism.The authors note that theTop coal drawbody(TCD),Top coal boundary(TCB)and Top coal recovery ratio(TCRR)are key factors in the drawingmechanism.TheBody-boundary-ratio(BBR)research system has been the classic framework for research over the last 20 years.The modified Bergmark-Roos model,which considers the effects of the supporting rear canopy,flowing velocity of top coal,and its shape factor,is optimal for characterizing the TCD.A 3Dmodel to describe the TCB that considers the thicknesses of the coal seam and roof strata is reviewed.In sect.physical testing and numerical simulation,the physical tests and numerical simulations in the literature are classified for ease of bibliographical review,and classic conclusions regarding the drawing mechanism of top coal are presented and discussedwith elaborate illustrations and descriptions.The deflection of the TCDis noted,and is caused by the shape of the rear canopy.The inclined coal seam always induces a largerTCD,and a deflection in theTCDhas also been observed in it.The effects of the drawing sequence and drawing interval on the TCRR are reviewed,where a long drawing interval is found to lead to significant loss of top coal.Its flowing behavior and velocity distribution are also presented.Sect.practical applications of drawingmechanisms forLTCCmines 4 summarizes over 10 cases where the TCRRof LTCCmines improved due to the guidance of the drawing mechanism.The final section provides a summary of the work here and some open questions.Prospective investigations are highlighted to give researchers guidance on promising issues in future research on LTCC.

Numerical investigation on the caving mechanism with different standard deviations of top coal block size in LTCC

The size distribution of the broken top coal blocks is an important factor,affecting the recovery ratio and the efficiency of drawing top coal in longwall top coal caving(LTCC)mining panel.The standard deviation of top coal block size(dt)is one of the main parameters to reflect the size distribution of top coal.To find the effect of dt on the caving mechanism,this study simulates experiments with 9 different dt by using discrete element software PFC.The dt is divided into two stages:uniform distribution stage(UDS)whose dt is less than 0.1(Schemes 1–5),and nonuniform distribution stage(NDS)whose dt is more than 0.1(Schemes 6–9).This research mainly investigates the variation of recovery ratio,drawing body shape,boundary of top coal,and contact force between particles in the two stages,respectively.The results showed that with the increasing dt,the recovery ratio of the panel increases first and then decreases in UDS.It is the largest in Scheme 3,which mainly increases the drawing volume at the side of starting drawing end.However,the recovery ratio decreases first and then increases quickly in NDS,and it is the largest in Scheme 9,where the drawing volume at the side of finishing drawing end are relatively higher.In UDS,the major size of top coal is basically medium,while in NDS,the size varies from medium to small,and then to large,with a distinct difference in shape and volume of the drawing body.When the major size of top coal is medium and small,the cross-section width of the initial boundary of top coal at each height is relatively small.Conversely,when the top coal size is large,the initial boundary of top coal has a larger opening range,the rotating angle of lower boundary is relatively small in the normal drawing stage,which is conducive to the development of drawing body and reduces the residual top coal,and the maximum particle velocity and the particles movement angle are both larger.This study lays a foundation for the prediction of recovery ratio,and suggests that the uniform top coal is more manageable and has a larger recovery ratio.

Characteristics of Gas Emission at Super-Length Fully-Mechanized Top Coal Caving Face

Characteristics of gas emission at the K8206 working face in the Third mine of the Yangquan Coal Group were investigated. The effects of strata movement,advancing velocity of working face,production capacity of working face and gas extraction capability of strike high-level entry on gas emission at K8206 working face were analyzed. A regression equation,reflecting the relationship between relative gas emission rate and the production capacity of work-ing faces,was established. Another regression equation showing the relationship between the gas emission rate from adjacent layers when the working face was advancing for one metre and advancing velocity was derived. It can be con-cluded that,1) the amount of gas emitted at the K8206 working face is far greater than that of ordinary top coal caving faces with a dip length of 180-190 m; 2) the dynamic process of gas emission from adjacent layers during the initial mining stage is controlled by the movement of key strata; 3) the amount of gas emitted that needs to be forced out by air is greatly affected by the capability of gas extraction; 4) when the advancing velocity is between 3.5-5.5 m/d or when the output is up to 8-12 kt/d,the gas emission from adjacent layers is almost constant.

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.

Caving thickness effects of surrounding rocks macro stress shell evolving characteristics

In order to explore the influence of different caving thicknesses on the MSS distributionand evolving characteristics of surrounding rocks in unsymmetrical disposal andfully mechanized top-coal caving (FMTC),based on unsymmetrical disposal characteristics,the analyses of numerical simulation,material simulation and in-situ observation weresynthetically applied according to the geological and technical conditions of the 1151(3)working face in Xieqiao Mine.The results show that the stress peak value of the MSS-baseand the ratio of MSS-body height to caving thickness are nonlinear and inverselyproportional to the caving thickness.The MSS-base width,the MSS-body height,theMSS-base distance to working face wall and the rise distance of MSS-base beside coalpillar are nonlinear and directly proportional to the caving thickness.The characteristics ofMSS distribution and its evolving rules of surrounding rocks and the integrated cavingthickness effects are obtained.The investigations will provide lots of theoretic referencesto the surrounding rocks' stability control of the working face and roadway,roadway layout,gas extraction and exploitation,and efficiency of caving,etc.

特厚煤层综放开采合理放煤工艺参数研究

针对不连沟煤矿特厚煤层综放开采放煤工艺参数确定的合理性问题,通过实测特厚煤层单轮顺序放煤时单个支架的连续放煤时间,在倾向方向基于“大、中、小、微”放煤理念确定了“大”放煤、“中”放煤、“小”放煤、“微”放煤的循环内位置和放煤间距;在走向方向通过布置多点位移计测试了不同顶煤高度、不同循环时的顶煤运移轨迹曲线,得出在倾斜方向的顶煤移动轨迹曲线方程,确定不同放煤步距时的工艺损失。研究结果表明:单放煤口充分放煤时,工作面倾向方向影响距离6~12架,倾向单架放煤影响半径平均7.6 m;循环内两端“大”放煤、中间“中”放煤、其余“小”放煤和“微”放煤交替;本架放煤在垂高12.3 m层位的走向影响距离平均4.9 m,在垂高8.3 m层位的走向影响距离平均3.8 m,拟合确定了不同放煤步距的顶煤走向运移方程,理论得出循环步距0.8 m比1.6 m减少煤炭损失694 t。研究结果为指导不连沟煤矿特厚煤层综放开采合理放煤和提高资源回收率提供依据。

我国综放开采40年及展望

我国应用和创新发展综放开采技术40 a来,取得了巨大成功和重大科技创新,实现了厚煤层一次采全高和高产高效低成本开采,综放开采技术已经成为我国开采厚煤层的主要方法,也是我国在世界煤炭开采行业的标志性技术。在综放开采技术发展过程中,先后试验了高位放煤、中位放煤、低位放煤,最终形成了我国的低位放煤综放开采技术。支架结构形式从早期的四柱支架发展到今天四柱与两柱并存的局面,对于智能开采工作面两柱支架更具优势。我国的综放开采技术可以分为2个阶段。在前20 a的探索和推广应用阶段,针对我国煤层条件,充分发挥了综放开采的技术优势,形成了高产高效综放开采模式、“三软”厚煤层综放开采模式、“两硬”厚煤层综放开采模式、急倾斜厚煤层综放开采模式等。在最近20 a的技术创新和输出阶段,我国创造性地开发了特厚煤层大采高综放开采技术、急倾斜厚煤层综放开采技术等,在智能化开采与智能放煤技术等方面取得了突破性进展,实现了综放开采技术从引进到输出的飞跃式发展。我国已经形成了一批专注综放开采技术研究的科技队伍,无论是综放开采的理论成果,还是技术成果都遥遥领先于世界其他国家。综放开采技术的进一步发展需要集中到综放工作面的全面智能化开采、智能放煤技术开发,提高工作面端头顶煤采出率技术,开发基于采动岩层运动的保水开采、绿色开采和减灾开采等技术,建立覆岩运动的统一场理论,研究综放开采低碳技术路径。

水平分段综放开采顶煤放出体理论计算模型

水平分段综放开采是急倾斜特厚煤层的主要开采方法之一。水平分段综放开采工作面相对较短,导致顶、底板边壁对放煤规律的影响较大。基于BBR理论,采用Bergmark-Roos (B-R)模型分析了存在倾斜边壁影响时的顶煤运移规律及放出体形态变化机理;建立了水平分段综放开采受顶、底板侧边壁影响的放出体理论计算模型,推导了包含轴倾角参数的放出体边界方程;通过颗粒流离散元数值分析得出了轴倾角参数与边界条件的定量关系,采用物理相似实验数据对理论模型进行了验证,提出了不同煤层倾角范围内的合理分段高度及放煤方式优化建议。研究结果表明:倾斜边壁的存在使得散体顶煤受到更大的横向应力,从而改变了顶煤颗粒运移加速度的方向;近边壁处放煤口两侧散体顶煤递补潜力的差异,导致其运移加速度的大小不同;顶煤加速度大小和方向的改变导致放出体轴线方向偏离重力方向。受倾斜边壁影响,放出体形态在轴线两侧呈现非对称性,与近底板侧相比,近顶板侧放出体受边界影响的程度更大;放出体轴倾角β随着煤层倾角的增大呈线性增大关系。随着不放煤段长度的增大,近顶、底板侧放出体的轴倾角均逐渐趋近于90°。物理模拟试验结果验证了理论模型的准确性;采用“底板单轮、中部多轮”、端头逆序放煤方式可有效利用放出体形态特征,减少近顶、底板侧残煤损失。

特厚煤层综放开采多口同时放煤三维实验研究

为提高特厚煤层综放工作面顶煤回收率及放煤效率,重点研究了多口同时放煤的放煤方式。根据塔山煤矿8222工作面实际情况,进行了多口同时放煤三维相似模拟实验。结果表明:首次放煤时,单口放煤放出体大致呈下窄上宽的漏斗状,多口同时放煤放出体呈现中部宽、两端窄的特点,放煤量呈现单口>双口>三口的现象。首次放煤时,开口数目越多煤岩分界线的斜率越大,对顶煤的扰动范围越大,煤岩分界线的最低点越高,损失的低位顶煤越多,且煤岩分界线最低点基本在该组支架的中心位置;放煤结束后,三口组放出更多支架上方及前方的中低位顶煤,放煤量总体呈现三口>双口>单口的现象。

浅埋煤层不同工作面重复扰动下大巷煤柱稳定性研究

以赵家梁煤矿3-1煤层大巷煤柱回收为研究背景,通过物理相似模拟及现场监测,研究浅埋煤层不同工作面采动影响下覆岩垮落特征以及重复扰动下大巷煤柱应力演化规律。结果表明:3101工作面回采后,1^(#)大巷煤柱应力峰值5.09 MPa,应力集中系数为1.62;3102工作面回采后,2^(#)大巷煤柱应力峰值5.7 MPa,应力集中系数为1.54;大巷煤柱回收工作面回采后,1^(#)和2^(#)大巷煤柱垂直应力分布由单峰型分布转为马鞍型分布,1^(#)大巷煤柱应力峰值7.4 MPa,应力集中系数为1.87,2^(#)大巷煤柱应力峰值8.46 MPa,应力集中系数为2.1。现场实测数据与物理相似模拟试验所得数据相符,研究结果可为大巷煤柱回收工作面的安全生产提供参考依据。

保德煤矿智能综放工作面建设关键技术研究

针对现有智能综放工作面建设的研究成果缺乏某个综放工作面系统化建设实施研究的问题,以国家能源集团神东煤炭集团有限责任公司保德煤矿81309智能综放工作面为研究背景,在液压支架电液控制系统及综采自动化系统配置的基础上,详细介绍了设备升级改造、有限透明开采模型构建、智能放煤工艺决策、煤矸识别方法优化、多模式融合集成控制等关键技术。①对采煤机电控系统进行国产化升级改造,加装惯导系统,配套光纤复合电缆/5G通信,实现采煤机姿态及控制数据高效稳定传输。采用迈步自移设备列车系统并配套管缆伸缩装置,实现设备列车拉移由1~2人完成。②对智能规划中心数据源中的地质模型进行迭代修正,经过一系列换算和多源异构数据融合,形成有限透明开采地质模型。③针对81309工作面一刀一放2轮顺序放煤方式,构建了10个智能综放回采阶段并设计了对应的采煤机、综放液压支架、前后刮板输送机的动作和时间,实现了中部跟机自动化采放、三角煤区域自动开采。④采用振动煤矸识别与视频煤矸识别相结合的方式,建成智能综放煤矸识别系统。⑤以SAM型综采自动化控制系统为枢纽,通过整合液压支架电液控制、视频监控、采煤机电控、三机泵站集控,构建出智能化集中控制系统,初步建成基于透明开采的“采−支−识−放−运”各环节自适应的综放开采工作面。调试结果表明,81309综放工作面中部实现单班自动控制割煤4刀,液压支架实现自动跟机拉架、联动收伸护帮/伸缩梁、自主推溜等功能,智能化集中控制系统可一键启停生产系统,对设备运行数据进行实时监控。

特厚高放顶煤开采注氮煤自燃危险抑制特性研究

针对特厚高放顶煤回采工作面采空区遗煤量大、漏风严重等问题,通过程序升温氧化实验和热释放测试实验,对未注氮与注氮条件下的煤体氧化自燃过程气体产物、氧气消耗和热释放特性进行分析;利用数值模拟软件,对不同注氮位置条件下注氮对采空区煤自燃危险区域的抑制性进行分析;并进行注氮方案优化。结果表明:注氮时能抑制煤体氧化自燃反应进程,各气体产物出现的温度点延缓25~30℃,耗氧速率、放热量大幅度降低,未注氮时的放热量是注氮时放热量的5.67倍;不同位置注氮时采空区煤自燃危险区域差异收缩,注氮口2、3、4、5即进风一侧分别距工作面60、80、100、120 m位置注氮时危险区域抑制面积依次占比为12.28%、32.71%、39.71%、44.09%,采空区温度抑制变化主要集中在注氮口附近区域;注氮口2、3联合注氮优化方案能有效抑制47.25%的采空区煤自燃危险区域。

王家岭煤矿12309工作面顶煤破碎特征及运移规律研究

为掌握12309工作面顶煤破碎特征及运移规律,采用理论分析+现场观测分析进行顶煤破碎特征的分析,根据顶煤破坏规律分析得出顶煤受力特征,基于现场测试得出顶煤破碎块度及冒落特征;通过数值模拟进行顶煤运移规律的分析,并在工作面回采期间进行顶煤活动规律的监测。结果表明,顶煤冒落块度基本在40 cm×30 cm×30 cm内,顶煤一般在支架顶梁后方及时垮落;顶煤放出7次后即进入稳定周期,顶煤的运移主要出现在超前工作面10~30 m内,工作面走向上顶煤运移可划分为4个区域。

大水易淤综放工作面泄水巷煤泥淤积物沉降特性分析

针对高家堡煤矿开采工作面面前淋水问题,分析其主要水源来自采煤工作面顶板,矿井涌水量4000~5000 m 3/h,结合开采工作面泄水巷煤泥淤积的特点,通过COMSOL数值模拟方式,模拟了不同流速条件下煤泥混合物的沉降情况,包括煤泥淤积物动态流动特征模拟、不同初始流速下煤泥颗粒沉降情况模拟、不同初始流速对煤泥混合物速度分布影响、不同初始流速对煤泥混合物稳定性影响。通过分析不同初始入口流速下管道出口附近截面煤泥颗粒体积分数分布,确定煤泥混合物的不淤临界流速为1.2~1.4 m/s,分析了煤泥混合物流动过程中的淤积机理,从而得到煤泥淤积物的沉降特性,为科学合理的清淤工作提供理论依据。

急倾斜水平分段放顶煤开采应力分布规律及冲击地压防治

为了揭示急倾斜煤层水平分段放顶煤开采应力场分布特征及冲击地压显现规律,以王家山煤矿东一采区为工程背景;理论分析了急倾斜水平分段开采冲击地压显现特征,数值模拟分析了急倾斜煤层水平分段开采应力场演化规律;揭示了急倾斜煤层水平分段开采矿震动载扰动诱发底煤冲击地压显现的规律。结果表明:随着开采分段数增加,工作面采动应力持续增大,顶板巷应力集中程度高于底板巷,最大主应力由原水平方向分布转为沿垂直煤层倾向分布,导致顶板巷周围煤体水平应力集中程度高;工作面煤体水平应力场倾向方向呈现先增大再减小的趋势,且顶板侧水平应力明显高于底板侧水平应力,应力峰值与开采深度呈线性正相关关系,顶板巷冲击危险性明显较高。根据冲击地压发生规律,针对性制定了急倾斜水平分段开采冲击地压防治方案并进行了防治实践,监测表明防冲效果显著。

厚煤层放顶煤开采放煤高度的模拟分析

厚煤层进行放顶煤开采是主要的开采方式,在开采过程中,存在放煤高度的最大值及最小值。采用离散元分析的形式对不同放煤高度的应力变化及回收率变化分析,结果表明,在放煤高度最大为6 m时,工作面的最大应力集中系数及剧烈影响范围最大,且此时的回收率最高。

影响顶煤放出主要因素的工艺实践与分析

为解决放顶采煤方式在综采工作面开采的实际应用中存在的产量低、煤炭质量低以及回采率低的问题,以苇湖梁煤矿6#煤层所属工作面为研究对象开展研究,在对其地质、煤层等条件和放顶采煤工艺参数应用现状分析的基础上,重点对不同放煤方式、放煤步距条件以及水平分段高度对顶煤放出的影响进行对比分析,为后续改进放顶开采方式的工艺参数奠定基础。