New technological partition for “three zones” spontaneous coal combustion in goaf

On detailed analysis basis of spontaneous coal combustion for the three zones in mine goaf,we use O2 and CO concentrations to divide the three zones of the coal combustion.Through our experiment,we selected a typical working face and focused on the changes in gas concentrations.In order to overcome establishment limitations of actual layout location and underground conditions in a mine goaf,we based our observations on the three zones,combined them with numerical simulation,described the distribution and the changes in O2 and CO concentrations during the coal spontaneous combustion in the goaf,which provided us with an understanding of the distribution of coal spontaneous combustion in the three zones in the form of maps.Essentially,our study summarizes the changes of O2and CO concentrations in the entire goaf and shows them to be in agreement with our observations at the scene.The study shows that it is feasible to divide the three zones,given our comprehensive targets of O2,CO and our numerical simulation.This method avoids the limitation of dividing the three zones with a single target and the likely errors of observations at the scene.In addition,the method offers a basis for optimizing measures of fre-fghting with important and practical effects.

CFD simulation of spontaneous coal combustion in irregular patterns of goaf with multiple points of leaking air

Based on the non-linear air leakage seepage equation for an anisotropic porous medium, on the seepage diffusion equation of multicomponent gas and on the seepage synthetic heat transfer equation of a porous medium, the numerical model for field flow problems of irregular patterns of a goaf with multiple points of leaking air is established and simultaneously solved by the upwind mode finite element method (G3 computer program). According to the complexity of irregular patterns of a goaf with multiple points of leaking air, the flow pattern in a large area of such a goaf and the variation in gases of methane, oxygen and CO and in temperature are theoretically described. In the calculation, the goaf is regarded as a caving anisotropic medium and the coupling effect of methane effusion on spontaneous combustion is considered. The simulation results agree well with practical experience. In addition, the spontaneous combustion process is also simulated, indicating that 1) the spontaneous combustion often takes place near the area where fresh air leaks in and 2) the fire sources can be classified into static and dynamic zones. Therefore, in practical fire preventing and extinguishing, we should clearly distinguish the upstream air leaking points from the downstream ones in order to take proper measures for leakage stopping.

Study on numerical simulation of spontaneous combustion prevention mechanism by nitrogen injection in goaf

Based on heterogeneous and porous medium seepage of air leakage-diffusion equation, as well as, gas and porous medium synthesis heat transferring equation, a spontaneous combustion non-steady numerical model of nitrogen injection goaf was established, which can be solved by upwind finite element numerical simulation method si- multaneously. Taking the working face for example; air leakage seepage, nitrogen flow and gas distribution can be described in visual display in nitrogen injection goaf and the oxygen （O2）, carbon monoxide （CO） concentration and temperature distribution, as well as, their change were described in theory during the coal left behind combustion in goaf, which above reveals the complex mechanics course （mechanism） of seepage, diffusion and oxidation heat releasing during coal spontaneous combustion and its restraining. During the calculation, the effect factors of gas springing out and working face advancing were considered fully, and the spontaneous combustion course under different amount of nitrogen injection was simulated. The conclusions were obtained that under nitrogen injection condition, the high spontaneous combustion temperature area lean to the inlet air, but the shape becomes narrower, with the amount of nitrogen rising, the spontaneous combustion period becomes longer till to it does not happen. Meanwhile the nitrogen injection accelerates gas springing out in goaf. The result that turns out in theory simulation fits to practical nitrogen injection.

Research on ＂three zone＂ classification of spontaneous combustion and its numerical simulation in gob of mines under the sea

According to the classification standard of spontaneous combustion ＂three zone＂ in gob and the analysis of aerodynamics and energy equation of relax loose coal body, the paper used the method of computer simulation analysis to get the air distribution. The paper also determined the three zone area of H2103 fully mechanized caving face in Beizao Mine.

Risk assessment of gas control and spontaneous combustion of coal under gas drainage of an upper tunnel

The adjustment of the gas drainage rate has an immediate impact on air leakage in gob,thus resulting in the change of self-heating of coal.While regulating the gas drainage parameters,the risk of spontaneous combustion of coal should be considered.The risk assessment of gas control and spontaneous combustion of coal under gas drainage in a tunnel was investigated at different gas drainage rates.The distributions of the air volume along the working face,the gas management effects and the width of the oxidation zone were subjected to risk analysis.As the simulation results showed,with increasing gas drainage rate,although the safety of gas dilution by ventilation was assured,the intensifying air leakage caused the oxidation zone to move into the deeper gob and led to an increase in the width of the oxidation zone.A risk assessment method was proposed to determine a suitable gas drainage rate for the upper tunnel.The correctness of the risk assessment and the validity of the numerical modelling were confirmed by the field measurements.

A new forecast model for the carbon-monoxide concentration in the upper corner of mining face

The CO gas in the upper comer along with the work of mining face in different coal-seam of Lingwu coal-field has deeply affected judgment for the degree of the coal spontaneous combustion and safety work. For this issue, a new calculation and forecast model of the carbon monoxide concentration in the upper comer of mining face was deduced for analyzing and calculating the date from the lab and test-in-place, during this course using the knowledge of heat transfer, fluid dynamics, and mathematics. The model took into account the characteristics of the coal spontaneous combustion, coal mining conditions, and other correlate factors, so the CO concentration of the upper comer safe under the normal condition, and it is in danger when the coal reached spontaneous combustion, which can be calculated accurately with the model and compared with the measured concentration with a tolerance of less than 12%.

岩块尺度对采空区煤自燃区域的影响研究

为探究综放采空区岩块尺度对煤自然发火的影响,采用Fluent软件数值模拟不同直径岩块条件下采空区的煤自燃规律,分析采空区氧浓度场和风速场,分别以氧气体积分数和风速为指标,确定采空区氧化带面积并以二场叠加场作为采空区煤自燃危险区划分标准,研究煤自燃危险区域与岩块直径的关系。研究结果表明:当岩块直径由0增加到10 m时,以氧气体积分数为指标,氧化带宽度变小,面积由5563.84 m^(2)减至2602.69 m^(2);以风速为指标,氧化带面积由3376.60 m^(2)减至1262.95 m^(2);将2种指标确定的氧化带进行叠加得到煤自燃危险区,随着岩块直径的增加,其面积由1854.04 m^(2)减至552.91 m^(2),煤自燃危险区最大宽度由20.40 m缩减至9.06 m。研究结果可为采空区煤自燃发火区域的确定提供参考。

不同通风方式下“110工法”采空区自燃“三带”数值模拟研究

为探究不同通风方式下“110工法”采空区自燃“三带”分布特征,以顾北矿1532(1)工作面“两进一回”通风方式为工程背景,基于风流控制方程、浓度组分方程和能量方程等,利用Fluent数值模拟方法建立煤自然发火多物理场耦合数值模型、工作面实时动态推进模型,模拟了3种通风方式下“110工法”采空区自燃“三带”分布特征。结果表明:随着工作面不断推进,在通风方式1(机巷侧和沿空留巷进风,回风巷回风)和通风方式2(机巷侧和回风巷进风,沿空留巷回风)条件下,采空区氧化自燃带均匀分布在运输巷侧、工作面中部和留巷侧,其氧气体积分数分布形状相差不大,采空区温度首先升高,开采约50 d后,最高温度出现在运输巷侧深部,且该位置温度不随工作面继续推进而升高;在通风方式3(沿空留巷和回风巷进风,机巷侧回风)条件下,采空区留巷侧氧化自燃带变宽2~4倍,工作面中部和运输巷侧明显变窄,采空区运输巷侧氧气体积分数较低,留巷侧氧气体积分数较高,漏风量明显增大。采空区高温位置主要出现在1532(1)工作面始采线留巷侧,且当工作面开采50 d后,此处采空区温度最高。综上所述并结合现场实际情况,对氧化自燃带宽度及位置进行分析,最终确定通风方式3更有利于防止煤自燃的发生,对矿井煤自燃的预防提供了理论指导。

覆岩离层注浆采空区自燃“三带”分布规律

覆岩离层注浆技术通过压实采空区内的破碎岩体,改变了采空区的流场特性和自燃“三带”的分布情况。为了探讨屯兰矿22301综采工作面离层注浆件下采空区遗煤自燃风险范围,基于实测和数值模拟相结合的方法,对该工作面采空区内存在的自燃“三带”进行准确划分;并提出了注浆钻孔的空隙率三维数学模型,评估不同注浆钻孔位置对采空区流场的影响。结果表明:修正后的空隙率三维数学模型能更好地反映注浆后采空区的气体流场,其模拟结果与现场实测结果的残差精度提高22%;相比于未注浆情况,离层注浆后采空区受到压实作用,有效抑制采空区自然发火的危险性,并导致工作面漏风风流向上汇聚,使采空区垮落带较高位置的氧气体积分数增加;注浆钻孔的布置参数对采空区流场将产生影响,其影响关联度依次为钻孔间距、钻孔排数、钻孔影响半径。

密闭采空区不同惰化置换方案效果仿真

针对密闭采空区瓦斯抽采过程中在负压作用下外界O_(2)通过裂隙进入采空区易引发煤自燃的问题,常采用抽采的同时注惰性气体以置换抽出的瓦斯的方案,此法可平衡气压、防止外界空气进入采空区,达到防治煤自燃的目的。采用数值模拟的方法研究置换过程中相关物理参数流场变化规律,并提出了自由混合置换法、正压置换法、负压置换法、正压-负压置换法4种方案;以O_(2)最大体积分数低于2%为置换达标标准,对比了4种方案下耗费总时长、消耗氮量、通风机运转时间、累计注氮时长等置换成本评价指标,找出可用于置换方案决策的方法,并给出不同地质条件下密闭采空区适用方案。

朱集西煤矿自燃“三带”分布及注氮参数研究

为了研究朱集西煤矿11503综采工作面采空区自燃“三带”分布规律,在进、回风巷侧埋设束管对采空区内部氧气浓度变化规律进行现场实测,并采用数值模拟的方法研究不同注氮流量下自燃“三带”分布变化规律,确定合理的注氮流量。研究表明:增加注氮流量,采空区氧化带的分布范围和宽度会减小,当注氮流量增加至900 m^(3)/h以上时对减小氧化带宽度效果甚微,据此确定了合理的注氮流量900 m^(3)/h;通过计算得到11503工作面安全通风量为222 m^(3)/min。研究结果为该工作面的后续防灭火工作提供参考。

基于PFC-CFD的采空区自燃“三带”预测

采空区遗煤自燃是导致煤矿火灾的主要原因之一,且多数发生于采空区自燃“三带”的氧化带中。为更准确地预测划分采空区自燃“三带”、预防矿井火灾,提出了PFC-CFD采空区流场演化模型。首先利用PFC颗粒流模拟软件模拟采空区覆岩的垮落和空隙率分布,然后使用UDF函数将PFC模拟得到的空隙率分布数据导入CFD中,通过建立采空区物理模型对采空区内的氧气流场进行模拟预测,最终得到采空区自燃“三带”范围。现场实测表明,基于PFC-CFD的采空区自燃“三带”预测结果更接近现场实际,优于单一CFD方法的预测结果,表明利用空隙率动态演化分析采空区流场变化,进而预测遗煤自燃危险区域的方法是可靠的,对预防采空区自然发火具有一定理论指导和实际应用意义。

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。

大倾角工作面采空区均压-注氮联合防火数值模拟研究

以峻德煤矿93172大倾角外部漏风工作面为例,研究大倾角外部漏风采空区均压参数合理性以及对注氮防火的影响。采用Fluent数值模拟方法对采空区进行流场分析,充分考虑位压的影响,合理设置工作面和采空区进回风口及漏风口压力边界参数;建立了“L”形大倾角采空区冒落分布模型,进行采空区“恰当均压”,“欠均压”,“过均压”数值模拟,探究不同均压工况的采空区自燃三带分布,同时探讨了采空区均压注氮的合理参数选择。结果表明:“恰当均压”的采空区自然氧化带宽度最短;注氮防火应在“恰当均压”条件下进行,否则将会极大降低采空区惰化效果,徒增注氮量。研究结果对现场科学制定均压-注氮联合防火措施提供理论指导,同时压力边界参数设置方法为大倾角工作面采空区均压-注氮联合防火相关数值模拟研究提供科学参考。

浅埋近距离煤层群开采过程中上覆采空区自燃危险区预测研究

为揭示浅埋深近距离煤层群开采过程中地表裂隙发育对上覆采空区遗煤自燃的影响规律及影响范围,以苏家沟煤矿为研究背景,建立采空区流场流动及低温氧化的数学模型和三维几何模型。采用FLUENT模拟软件模拟了下煤层工作面推进过程中上覆采空区的氧气分布情况,得到了浅埋近距离煤层上覆采空区基于裂隙动态发育的氧气场和风流场的分布规律。依据采空区自燃危险区域判定理论,对上部煤层采空区内的自然发火危险区域进行预测。结果表明:连通地表与采空区的裂隙数量随工作面的推进而增加,上覆采空区氧化升温区域主要集中在滞后工作面0~20 m范围内,采空区深部的氧化带分布在新、老裂隙附近,在进风侧靠近地表且在回风侧靠近裂隙底端;当工作面推进120 m,即产生3条贯通型裂缝时,采空区自燃危险性最大,结合风流场云图确定上煤层底板自燃危险区距工作面水平距离为97.5 m,是煤矿开采过程中的重点防护区域。

高位钻孔抽采对采空区自燃“三带”的影响研究

以甘肃某矿北1103工作面为背景,采用数值模拟、现场观测等方法研究高位钻孔抽采对采空区自燃“三带”的影响。结果表明:采空区内部漏风路径与钻孔至工作面的距离呈正相关关系,采空区氧化带、窒息带所处区域随漏风路径的增加向采空区深部扩大;随着钻孔抽采流量的增加,采空区氧化带范围随之增加,但钻孔与工作面的瓦斯浓度呈降低趋势;随着抽采负压的增大,氧化带、散热带的边界线在进风侧向采空区深部移动,在回风侧向工作面方向移动。

贵州某矿采空区标志性气体优选及自燃“三带”划分

为解决贵州某矿采空区自然发火早期精准预测预报的难题,以该矿12501工作面采空区为研究对象,利用程序升温实验重点分析煤样在升温氧化过程中CO、CO_(2)、C_(2)H_(4)、C_(2)H_(6)等气体的变化规律,通过数值模拟及现场实测对采空区自燃“三带”进行了划分。结果表明:CO、C_(2)H_(4)、C_(2)H_(2)可作为自然发火标志气体,C_(2)H_(4)/C_(2)H_(6)可作为判别煤自然发火进程的辅助指标;散热带平均宽度约18 m,氧化带平均宽度约53 m,氧化带以外为窒息带;当采煤工作面的推进速度大于0.53 m/d时,采空区无自然发火危险;当工作面连续超过114 d时,推进速度均小于0.53 m/d,采空区将有自然发火危险。研究结果为贵州某矿煤层自燃预报提供了理论依据及数据参考,对防治煤层自燃具有重要意义。

再生顶板条件下煤自燃危险区域空间分布特征

为避免煤层开采过程中再生顶板遗煤自燃,明确其内部流场特性,探究煤自燃危险区域动态特征,以山东某矿再生顶板遗煤自燃特性分析为例,采用数值模拟方法,对比分析采空区及再生顶板在不同风量下的漏风特征,并结合再生顶板结构特性,基于氧气质量分数与漏风速度复合指标,采取投影叠加判定新方法,确定煤自燃危险区域范围。研究结果表明:采空区深度小于60 m时,氧气质量分数逐渐减小,60 m后氧气质量分数不再受风量影响;而再生顶板氧气质量分数分布具有非对称性,在回风巷尾端会形成一个“三角形”中空区域。采空区在倾向上20~40 m范围内发生漏风回流,而再生顶板漏风速度分布呈“U”型对称分布。采空区煤自燃危险区域变化特征与氧化带相类似,而再生顶板煤自燃危险区域范围主要分布在靠近进风巷中部及回风巷前中部内侧区域,且随风量的增加,危险区域面积逐渐增大并逐渐向尾部延伸。

一面四巷瓦斯抽采对采空区遗煤自燃影响数值模拟研究

为研究高瓦斯易自燃煤层不同瓦斯治理条件下采空区自燃“三带”及温度场分布变化规律,结合某高瓦斯易自燃工作面的实际条件,构建了“一面四巷”采空区自然发火物理模型,将程序升温试验得到的煤样氧化耗氧参数和放热参数应用到数值模拟中,分别研究了不同供风量、低抽流量及高抽流量对采空区自燃“三带”及温度场分布的影响,定量分析了氧化带最大宽度、氧化带面积和采空区最高温度点等参数随供风量、低抽流量及高抽流量的变化规律。结果表明:在模拟测试范围内,提高供风量、低抽流量及高抽流量均会造成采空区漏风量增多,不利于采空区遗煤自燃防治;最高温度点变化不明显(仅在1 K范围内变化),高抽流量变化对采空区氧化带宽度和面积及最高温度的影响大于供风量和低抽流量;氧化带最大宽度随供风量增大而增加,采空区最高温度和氧化带面积随供风量增加而减小,供风量从1600 m^(3)/min增加到1900 m^(3)/min时,氧化带最大宽度增加了2 m(74~76 m),最高温度降低了0.1 K(315.38~315.28 K),氧化带面积减小了180.08 m^(2)(8669.49~8489.41 m^(2));氧化带最大宽度随低抽流量增大而增加,采空区最高温度和氧化带面积均随抽采流量增大而增加,低抽流量从200 m^(3)/min增加到300 m^(3)/min时,氧化带最大宽度增加了2 m(75~77 m),最高温度升高了0.152 K(315.340~315.492 K),氧化带面积扩大了51.56 m^(2)(8553.79~8605.35 m^(2))。高抽流量从80 m^(3)/min增加到240 m^(3)/min时,氧化带最大宽度保持在75 m,最高温度升高了0.76 K(315.13~315.89 K)。

基于“三带”分析的采空区遗煤自燃气体分布规律及自燃危险研究

采空区漏风导致遗煤自燃是煤矿最严重的灾害之一,为提高把控采空区漏风遗煤自燃的能力,本文以神东某煤矿31103工作面为研究对象,分析了工作面开采后覆岩“三带”分布特征,探究了采空区覆岩孔隙率分布规律,基于密闭漏风条件下采空区氧浓度分布数值模拟结果对自燃影响性进行研究,并结合31103工作面实际情况分析采空区自燃发火危险性。研究结果表明:当密闭漏风量在5.3 m^(3)/min时,随着密闭位置的增大,漏风源对采空区氧气分布及自燃“三带”分布的影响作用逐渐增强,漏风源形成的高氧区扩大了遗煤的自燃危险性。该研究成果可为类似漏风条件下采空区遗煤自燃的针对性防治提供理论参考。