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.

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.

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.

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.

Mating model on production capacity for the system of cutting coal and drawing top-coal in FMMSC

Being a safe and highly-efficient mining method, fully mechanized mining with sublevel caving （FMMSC） was extensively employed in Chinese coal mines with thick seam. In order to make drawing top-coal furthest to parallel work with shearer cutting coal, decrease failure ratio of rear scraper conveyor and increase safe production capacity of equipments, based on production technology, set up the mating model of safe production capacity of equipments for the system of drawing top-coal and shearer cutting coal in coal face with sublevel caving. It is mean capability of drawing top-coal adapted to the capability of shearer cutting coal in a working circle in the coal face that was deduced. The type selection of equipment of rear scraper conveyor can be tackled with this mating model. The model was applied in FMMSC in Yangcun Coal Mine, Yima Coal Group of China. With the mating light-equipments, the coal output in coal face attained 1.05 Mt in 2004. It gained better technical-economic benefit.

Improving recovery in sublevel top coal caving mining by using partially reverse drawing technique

The sublevel top coal caving(SLTCC)mining technology is extensively employed in steeply inclined thick coal seams.Because of the typical characteristics of the short coal face in this mining method,a signifi-cant portion of the top coal is lost at the face end.For reducing the coal loss,the partially reverse drawing technique(PRDT)is proposed as a novel top coal drawing technique.Meanwhile,based on the Bergmark-Roos model(B-R model),a theoretical method for calculating the recovery ratio of top coal based on the top coal boundary equation and residual top coal amount is proposed.The mechanism of PRDT to reduce top coal loss at the face end is revealed by comparing with single-round sequential drawing technique(SSDT).Physical experiments and in-site observation data were used to verify the theoretical model.The results show that PRDT can effectively reduce the amount of residual coal near the roof by optimizing the shape characteristics of top coal boundary.Suggestions for improve recovery ratio in Wudong Coal Mine were given based on its face parameters.

综放工作面围岩控制与智能化放煤技术现状及展望

分析了厚及特厚煤层智能化综放工作面围岩控制技术与智能化放顶煤技术发展现状及存在的问题,从巷道围岩高效支护、工作面超前支护、坚硬特厚顶煤冒放性、液压支架位姿监测及智能化放顶煤5个方面提出了工程实际需求。针对综放工作面实现安全、高效、智能化开采存在的技术难题与工程需求,对综放工作面围岩控制技术、智能化放煤技术进行了研究:构建了坚硬特厚煤层顶煤悬臂梁力学模型,研发了提高顶煤冒放性及放出率关键技术,实现了坚硬特厚煤层超大采高综放开采;研发了单元式超前液压支架顶梁可旋转自复位装置,实现了液压支架顶梁根据巷道顶板倾斜角度自动旋转支护,有效提高了单元式超前液压支架对巷道顶底板的适应性;提出了采用巷道支护液压支架替代传统锚网支护结构的思路,具有支护效率高、成本低、节省工作面超前支护等优点;开发了基于立柱与尾梁千斤顶行程的综放液压支架支护姿态监测装置与算法,提高了液压支架支护姿态解算效率与精度;提出了基于透明地质模型、煤量监测装置与煤矸识别装置融合的智能放煤控制方法,可有效解决多夹矸层特厚顶煤智能化放煤技术难题。提出智能地质保障技术、机器视觉精准测量与智能感知技术、综放工作面设备智能精准自适应控制技术、综放工作面数字孪生技术等是智能化综放开采技术与装备的发展趋势。

混合煤矸放落态势特征研究

传统的基于图像检测技术的放顶煤过程中煤流动态特性研究多侧重于某一特定阶段的图像分析,未结合全阶段的动态特性进行综合分析;现有研究较少将放顶煤过程中上覆岩层的松散区变化与放煤过程中的煤矸分离和煤流特性相结合,缺乏对放煤过程的全局性系统分析。针对上述问题,对放顶煤过程中的煤流动态特性、煤矸分离效果及上覆岩层松散区凹陷变化进行了系统研究。首先,提出了一种基于双光流网络的放顶煤过程动态分析方法。实验结果表明:不同放煤方案下,放煤速度不随放煤形式和规律的变化而改变,平均检测准确率随着放煤口数量的增多而提高,尤其在不同放煤步距阶段呈明显线性增长;顶煤放出率与平均检测准确率呈正相关关系,验证了该方法在放顶煤过程监测中的有效性。其次,利用OpenCV技术对上覆岩层松散区凹陷面积进行实验分析。结果表明,初始放煤阶段松散区凹陷面积急剧增长,随后随时间推移逐渐趋于稳定;通过凹陷面积的动态变化趋势,可有效判断顶煤的放出过程,实现透明化放煤监测。最后,结合称重实验数据,分析了放煤量、放出率与含矸率之间的关系。结果表明,初始放煤阶段纯煤放出量最大,周期放煤阶段纯煤放出量趋于稳定,含矸率则随着放煤口数量的增多而减少。该结果进一步揭示了放煤方式对煤矸分离和顶煤放出率的影响。

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。

大倾角综放工作面顶煤损失分布特征及放煤步距优化

为提高唐山矿0291综放工作面的顶煤回收率,针对生产过程中的端头、架间、初采等7个方面的顶煤损失问题,理论计算了顶煤损失量,分析了工作面顶煤损失分布特征,将步距间损失作为优化对象,选用PFC2D软件对放煤步距进行优化,按照“见矸即停”原则,比较不同放煤步距的顶煤放出量,模拟结果表明:顶煤放出量随着支架的推移呈现明显的波动性,“一刀一放”的放煤量在80~560块之间,“二刀一放”的放煤量在50~680块之间,“三刀一放”的放煤量在100~1100块之间,从放出总量来看,放煤效率最高的是“一刀一放”,其顶煤放出总量为3832块,因此放煤步距优化为“一刀一放”时,可有效降低放煤步距间损失。

近距离特厚煤层综放开采可行性及合理放煤工艺研究

目前针对近距离煤层厚度变化范围较大、煤层厚度超出正常开采高度的工作面的合理放煤工艺参数研究较少。以内蒙古平庄煤业(集团)有限责任公司西露天煤矿011N1^(-1)工作面为研究对象,开展了近距离特厚煤层综放开采可行性及合理放煤工艺研究。首先,通过理论分析计算出近距离特厚煤层上方021N2工作面开采后底板最大破坏深度为3.88 m,小于011N1^(-1)工作面与021N2工作面之间的距离,表明对下煤层011N1^(-1)工作面进行综放开采是可行的。然后,结合理论分析与现场实测,采用模糊数学方法量化了煤体单轴抗压强度、煤层埋深、煤层厚度、煤体裂隙发育程度、顶板级别及煤层夹矸厚度对顶煤冒放性的影响,基于隶属度函数评定011N1^(-1)工作面顶煤冒放性为中等水平。最后,基于PFC 2D离散元颗粒流软件建立了放煤数值模型,分析了不同采放比和放煤方式对顶煤采出率的影响,发现当煤层厚度超过正常开采高度时,将工作面采放比定为1∶4.5可有效适应煤层厚度变化,此时对顶煤采出率的影响较小,且采用三轮放煤工艺可有效提高顶煤采出率。现场放煤效果表明,优化放煤工艺后,随着煤层厚度的增大,增大采放比能够较好地适应地质条件变化,显著提高工作面顶煤采出量。

综放工作面液压支架安全回撤平台研究与应用

针对综放工作面液压支架回撤速度慢、转向过程液压支架底板下陷和易侧倾倒架等控制难题,综合采用现场调研、数值模拟和理论分析方法,开发了综放工作面液压支架安全回撤平台,分析了该回撤平台的主要结构和运行流程,模拟研究了液压支架和回撤平台作用过程中的应力和位移特征,并在水峪煤业典型综放面进行了现场工业性试验,综合应用效果良好,对类似综放面液压支架安全回撤提供一定参考。

基于工艺引擎的规划放煤控制系统

目前对综放智能化的研究主要聚焦于感知方面,对放煤过程智能化的研究较少,自动放煤控制技术存在自适应性不足、效率较低、放煤质量难以把控等问题。为了提升放煤过程的智能化水平与运行效率,设计了一种基于工艺引擎的规划放煤控制系统。该系统由放煤管控单元和窗口决策单元组成:规划放煤管控单元通过异步递进的放煤调度策略、柔性切换技术及规划放煤工艺编辑引擎,实现采煤机位置弱关联的自动顺序放煤及工艺在线编辑,通过关联后部刮板输送机负载,动态调整工艺启停,保障刮板输送机安全作业;窗口决策单元通过PID控制算法动态调节尾梁角度,实现放煤窗口反馈控制,采用遗传算法优化BP神经网络对放煤窗口大小进行智能决策,以适应不同工况,提高放煤质量。现场应用结果表明:基于异步递进的放煤调度策略与柔性切换技术提升了单刀自动运行效率,无需再手动接管;每一班组自动化运行刀数提升了33.3%;系统关联的后部刮板输送机负载、泵站等设备可动态调整工艺启停,每班后部刮板输送机平均停止次数下降了61.1%,可保障作业安全;工艺编辑引擎能适应多种场景下的应用,工艺调整用时大幅度降低;后部动作与前部动作相互叠加,使得单刀平均用时缩短了9.3%,提升了开采效率;倾角传感关联控制与规划放煤窗口智能决策将每日发热量提升了10.3%,改善了放煤质量。

特厚弱胶结顶板煤层综放开采覆岩破坏特征与强矿压机理

针对新疆准东二矿1101工作面,通过分析现场矿压和微震数据,研究了综放工作面矿压显现规律以及顶板破坏特征和矿压显现之间的关系。研究结果表明:(1)准东二矿特厚煤层弱胶结顶板1101首采工作面基本顶初次来压步距为43.37 m,关键层初次来压步距为81 m,基本顶和关键层交替破断形成大小周期来压,大周期来压步距为30~40 m,小周期来压步距为18~22 m。(2)截止到工作面推进至270 m,小能量微震事件主要发生在顶煤中,大能量微震事件主要发生在关键层及以上岩层,微震能量大小呈现周期性变化,顶板裂隙发育高度为距离煤层顶板258 m左右。(3)压架事故发生在基本顶和关键层周期来压阶段,压架事故往往伴随大能量微震事件的发生。(4)综放工作面顶板形成“组合悬臂梁-铰接岩块”平衡结构,组合悬臂梁断裂形成小周期来压,关键层断裂同时压断下方悬臂梁形成大周期来压,然而弱胶结顶板使得关键层破断后不易形成稳定的铰接结构,破断岩块发生滑落失稳,对工作面造成冲击动载荷,造成压架事故的发生。在此基础上,提出了提高液压支架初撑力至31.4 MPa,控制工作面推进速度在5 m/d左右的防治措施。

低位综放工作面提高顶煤回采率的放煤方式优化

针对古城煤矿低位综放工作面顶煤回采率低的问题,以S1306低位综放工作面为背景,分析了现有放煤方式。首先,通过建立不同放煤方式与放煤口长度的PFC数值计算模型,分析了不同放煤口长度以及相同放煤口长度、不同放煤方式下顶煤回采率;其次,提出了双口间隔动态放煤方式,对比分析了单口顺序放煤、双口顺序放煤以及双口间隔动态放煤的顶煤回采率;最后,研究了不同采放比对3种放煤方式顶煤回采率的影响。研究表明:低位综放工作面顶煤回采率随着放煤口长度的增大而逐渐减小;放煤口长度一定时,单口顺序放煤顶煤回采率大于双口顺序放煤的顶煤回采率;双口间隔动态放煤顶煤回采率相较于单口顺序放煤提高了约8.44%,放煤时间节省了46%,且放煤均衡性优于单口顺序放煤与双口顺序放煤;双口间隔动态放煤和单口顺序放煤的顶煤回采率均随着采放比的增大而增大,当采放比小于1∶1时,双口间隔动态放煤顶煤回采率大于单口顺序放煤方式,当采放比大于1∶1时,两者之间差距明显减小,但双口间隔动态放煤的时间大大缩短。因此,双口间隔动态放煤方式结合了低位综放工作面条件下单口放煤方式顶煤回采率高和双口放煤方式放煤时间短的优势。

放顶煤开采顶板控制参数优化研究

针对某矿的放顶煤工艺存在顶板管理及回采率较低的问题,通过分析巷道和破碎顶的顶板管理及回采率低的原因,提出了对采煤工艺的优化设计,具体优化了放煤步距及采放比,并进行实际应用。结果表明,将放煤步距设为1.13 m、采放比设为1.08,使用一采一放的放煤工艺后,工作面的回采率达到92.1%,保证了煤炭资源的高效开采。

急倾斜极软厚煤层走向长壁综放开采技术研究

以峰峰集团山西大远煤业1201急倾斜工作面为背景,系统研究了急倾斜厚煤层走向长壁综放开采的基本问题,指出支架的合理设计是该类煤层成功开采的首要条件,支架设计要充分考虑急倾斜厚煤层综放开采的顶板活动规律,以工作面上部顶板的冲击载荷确定支架的工作阻力。同时急倾斜支架要有足够的抗侧向挤压能力,结合工作面采放工艺确定侧护板的抗挤压能力。急倾斜厚煤层综放开采的顶煤放出体与煤岩分界面具有明显的不对称性。结合顶煤放出规律、支架稳定性等综合确定采放工艺,提出"下行动态分段、段内上行放煤"的采放工艺,适用于急倾斜厚煤层走向长壁综放开采,可最大限度地减少采放过程中对支架的不利影响,并可获得较高的顶煤采出率。工作面安装前需对软弱底板进行加固。

煤层条件对顶煤可放性的影响研究

根据现场观测、相似材料模型试验和数值分析结果，研究了影响放顶煤开采顶煤可放性的煤层条件，提出了各种条件的临界值、影响规律和次序，得出了预测各种煤层顶煤可放性的综合表达式和分类方案。