Method for prevention and control of spontaneous combustion of coal seam and its application in mining field

Spontaneous combustion of coal seam has been and continues to be a big problem in coal mines. It could pose great threat to the safety of the whole mine and all miners, especially when it occurs in or nearby coal mines. Besides, environment of area surrounded mines during combustion can be threatened where large amount of toxic gases including CO_2, CO, SO_2 and H_2S can be leased by fire in mine. Hence, it is important and significant for scholars to study the controlling and preventing of the coal seam fire. In this paper, the complicated reasons for the occurrence and development of spontaneous combustion in coal seam are analysed and different models under various air leakage situations are built as well. Based on the model and approximately calculation, the difficulty of fire extinguishment in coal seam is pointed out as the difficulty and poor effect to remove the large amount of heat released. Detailed measurements about backfilling and case analyses are also provided on the basis of the recent ten years' practice of controlling spontaneous combustion in coal seams in China. A technical fire prevention and control method has been concluded as five steps including detection, prevention, sealing, injection and pressure adjustment. However, various backfill materials require different application and environmental factors, so in this paper, analyses and discussion about the effect and engineering application of prevention of spontaneous combustion are provided according to different backfilling technologies and methods. Once the aforementioned fire prevention can be widely applied and regulated in mines, green mining will be achievable concerning mine fire prevention and control.

Statistical analysis to establish an ignition scenario based on extrinsic and intrinsic variables of coal seams that affect spontaneous combustion

Spontaneous combustion of coal seams in open pit mines is a problem that occurs in coal mines around the world.Theories have been developed that express several factors which generate self-heating in the coal and favor combustion.The synergy of these factors contributes to the increase in the temperature of oxidation reactions,facilitating the culmination of the activation energy of the system,in which the ignition develops and the reaction is spontaneous.Currently,the incidence of each variable’s susceptibility to coal combustion is unknown,so in this work a methodology was developed to determine statistically which of the variables has the greatest contribution in the phenomenon.Descriptive statistics,atypical values detection,principal component determination,cluster analysis,and logistic regression were used to determine how many indicator variables are necessary to describe susceptibility to coal combustion.For the analysis,21,000 data from different seams of two open-pit coal mines in endwalls and abandoned pits were processed with consideration given to extrinsic and intrinsic factors.Seam temperature,atmospheric pressure,wind speed,oxygen,methane,height,ash,volatile matter,heat power,vitrinite,liptinite and the Hardgrove Index are the most influential variables in the phenomenon.

A study of fire propagation in coal seam with numerical simulation of heat transfer and chemical reaction rate in mining field

Spontaneous combustion of coal is a problem that affects the mining operation and generates environ-mental,economic,social and geotechnical impacts.This phenomenon has been divided into two pro-cesses:ignition and propagation.Fire propagation develops in coal seams because of a set of factors such as direction and wind speed,fracturing and temperature.In this work,heat transfer and chemical kinetics are studied from conservation equations of energy and species,respectively,using the software COMSOL Multiphysics to simulate the propagation of fires in coal seams.Two possible scenarios were analyzed that usually occur in the walls of the coal seams,such as fire focus and fire complete screens.It was found that the propagation kinetics of the fire changes depending on the temperature,the fractur-ing of rock mass and the area of fire influence.For temperature values lower than 300℃,there is con-sumption around 250 cm^3/h,values around 700℃,the consumption is 1500 cm^3/h,and for fires of 1200℃ have values of 3000 cm^3/h.Depending on the speed of propagation can vary from 4 to 17cm/day,considering on the level and fracturing of the final wall of the open pit.

Study on partition of spontaneous combustion danger zone and prediction of self-ignition in coalmine based on numeric simulation

By solving steady model of air flow diffusion and chemical reaction in loose coal, distribution of oxygen concentration and flow velocity magnitude were obtained. Compared the simulating results with critic value as well as duration of spontaneous combustion from large-scale spontaneous combustion experiment, 'three zones' of spontaneous combustion were partitioned and mining conditions to avoid spontaneous combustion were obtained. The above method was employed to partition 'three zones' in gob of fully mechanized top-coal caving long wall face and got fairly good result. Calculation of the above method is much smaller than simulating the whole process of coal spontaneous combustion, but the prediction precision can satisfy the demand of predicting and extinguishing spontaneous combustion in mining.

Disasters of gas-coal spontaneous combustion in goaf of steeply inclined extra-thick coal seams

In light of the escalating global energy imperatives,mining of challenging-to-access resources,such as steeply inclined extra-thick coal seams(SIEC),has emerged as one of the future trends within the domain of energy advancement.However,there is a risk of gas and coal spontaneous combustion coupling disasters(GCC)within the goaf of SIEC due to the complex goaf structure engendered by the unique mining methodologies of SIEC.To ensure that SIEC is mined safely and efficiently,this study conducts research on the GCC within the goaf of SIEC using field observation,theoretical analysis,and numerical modeling.The results demonstrate that the dip angle,the structural dimensions in terms of width-to-length ratio,and compressive strength of the overlying rock are the key factors contributing to the goaf instability of SIEC.The gangue was asymmetrically filled,primarily accumulating within the central and lower portions of the goaf,and the filling height increased proportionally with the advancing caving height,the expansion coefficient,and the thickness of the surrounding rock formation.The GCC occurs in the goaf of SIEC,with an air-return side range of 41 m and an air-intake side range of 14 m,at the intersection area of the“<”-shaped oxygen concentration distribution(coal spontaneous combustion)and the“>”-shaped gas concentration distribution(gas explosion).The optimal nitrogen flow rate is 1000 m3/h with an injection port situated 25 m away from the working face for the highest nitrogen diffusion efficacy and lowest risk of gas explosion,coal spontaneous combustion,and GCC.It has significant engineering applications for ensuring the safe mining of SIEC threatened by the GCC.

Presenting an engineering classification system for coal spontaneous combustion potential

The phenomenon of coal spontaneous combustion is one of the common hazards in coal mines and also one of the important reasons for the loss of coal in piles and mines. Based on previous researches, different types of coals have different spontaneous combustion characteristics. For coal loss prevention, a measure is necessary for prediction of coal spontaneous combustion. In this study, a new engineering classification system called ＂Coal Spontaneous Combustion Potential Index （CSCPI）＂ is presented based on the Fuzzy Delphi Analytic Hierarchy Process （FDAHP） approach. CSCPI classifies coals based on their spontaneous combustion capability. After recognition of the roles of the effective parameters influencing the initiation of a spontaneous combustion, a series of intrinsic, geological, and mining characteristics of coal seams are investigated. Then, the main stages of the implementation of the FDAHP method are studied and the weight of each parameter involved is calculated. A classification list of each parameter is formed, the CSCPI system is described, and the engineering classifying system is subsequently presented. In the CSCPI system, each coal seam can be rated by a number from 0 to 100; a higher number implies a greater ease for the coal spontaneous combustion capability. Based on the CSCPI system, the propensity of spontaneous combustion of coal can be classified into three potential levels： low, medium, and high. Finally, using the events of coal spontaneous combustion occurring in one of the Iranian coal mines, Eastern Alborz Coal Mines, an initial validation of the mentioned systematic approach is conducted. Comparison of the results obtained in this study illustrate a relatively good agreement.

Experiment Research of Application of FMCCT in Complex-Condition Coal Seams

The fully-mechanized caving coal technique (FMCCT) is a great technique progress of mining method in thick coal seams in China, and it has succeeded in some suitable condition mines. This paper introduces some technical measures and achieved outcomes in gas and fire precaution and support selection for the use of the fully-mechanized caving coal technique in the complex-condition coal seams based on the practice of Weijiadi Coal Mine, in which the technique is used in the gently inclined extremelythick soft coal seam with the dangers of coal and gas outburst and spontaneous combustion.

Comparative Experimental Analysis on Coal Spontaneous Combustion

The goal of this study was to investigate coal quality features and their relationship to coal spontaneous combustion characteristics in multi-seam coal mines to better predict when coal spontaneous combustion is likely to occur.To that end,coal samples of various particle sizes were obtained from five coal seams(Nos.6,8,9,12 and 20)in the Shuangyashan City Xin’an Coal Mine.The samples were then respectively heated using a temperature programming system to observe and compare similarities and differences in the sponta-neous combustion process of different particle sizes in response to rising temperature.The experimental results show,that in all five coal seams,the concentration of CO,C_(2)H_(4),and C_(2)H_(6) increased with a certain degree of regularity as a function of rising temperature.However,of these three gasses,only CO and C_(2)H_(4) can be used as indicators to predict coal mine spontaneous combustion.The critical temperature for samples from all five coal seams ranged from 50–85℃,while the dry cracking temperature of coal seams 8 and 12(80–100℃)were lower than those of 6,9,and 20(100–120℃).Furthermore,the production rate of CO,C_(2)H_(4),and C_(2)H_(6) is related to both coal particle size and temperature.The smaller the particle size,the faster the production rate;and the higher the temperature,the more gas that gets produced.All five coal seems are mainly com-posed of long flame coal.However,they differ in that the No.12 coal seam contains weak cohesive coal;the No.8 coal seam contains lean and gas coal;and the Nos.6,9,and 20 coal seams contain a certain amount of anthracite.During the programmed coal heating,the CO,C_(2)H_(4),and C_(2)H_(6) release trend for the coal seams was No.12>No.8>Nos.6,9,and 20.These results demonstrate that the presence of weak cohesive coal and anthracite highly influence the concentration of CO,C_(2)H_(4),and C_(2)H_(6) released during coal spontaneous combustion.

深部开采高温热液侵蚀煤自燃特性

深部开采过程中,矿井水温度显著高于浅部煤层,高温热液侵蚀作用影响着煤体物化特征,进而对其自然发火特性产生影响。为研究深部开采热液侵蚀作用下的煤自然发火特性及其影响机制,通过低场核磁共振、分子动力学模拟、力学测试及C600微量热实验,分析了热液侵蚀作用对煤体孔隙度、孔径分布、力学强度、氧化热特征参数的影响规律,并结合相关性分析,定量描述了各个参数间的相关度。研究结果表明:热液侵蚀煤体受热应力和溶胀作用的双重影响,内部孔隙结构发生显著变化,热液温度与煤体总孔隙度之间存在显著正相关关系,相关系数为0.97;随着热液温度的升高,煤体总孔隙度由0.24%增长至1.35%,微孔占比由69%以上降至60%以下,中孔、大孔占比增大;煤体孔隙大小显著影响着氧气的扩散系数,随着煤体孔隙宽度的线性增加,氧气扩散系数呈指数增加;受高温热液侵蚀作用影响,煤体孔隙发育以及部分有机质的溶解显著降低了煤体的力学强度,从原煤到80℃热液侵蚀煤体,其抗压强度均值由23 MPa降低至11.6 MPa,降低了50%;相较于原煤,热液侵蚀煤体的放热强度更高,放热量更大,TH40、TH50、TH60、TH70、TH80放热量分别增加了12.61%、16.63%、17.32%、19.36%和25.02%,热液温度与煤氧化放热量间相关系数为0.92。高温热液侵蚀作用显著影响着煤的孔隙度及氧化过程,随着热液温度升高,煤体孔隙度增大,力学强度减弱,氧化过程耗氧量及氧化速率加快,放热量增加。高温热液侵蚀煤具有更高的自燃危险性,且热液温度越高,风险越大。

深部采空区煤自燃早期预测预报方法研究

目的煤矿深部开采中出现的“三高一扰动”特点,导致深部采空区煤自燃危险区域出现判定困难和煤自燃早期预测预报理论依据不足等问题。方法在分析深部高应力条件下,煤氧化气体衍生规律的基础上,计算不同轴向应力下煤体的格雷哈姆系数和链烷比,结果结果表明:不同承压状态下,煤样氧化自燃过程中CO,CO_(2)气体的生成量随温度升高而增加;相同温度条件下,随着轴向应力增加,CO和CO_(2)气体的生成量先增加后减小。相同温度条件下,随着轴向应力增大,格雷哈姆系数先增大后减小,R1在9 MPa时达到极大值,R2在6 MPa时达到极大值,R3在9 MPa时达到极大值;相同轴向应力条件下,随着煤样室内温度升高,格雷哈姆系数基本呈线性变化。相同温度条件下,随着轴向应力增加,煤样的链烷比逐渐增大;不同承压状态下链烷比随着温度升高而升高。结论研究结果可为深部煤自燃早期预测预报提供理论依据。

矿井火灾智能监测预警技术近20年研究进展及展望

为加强矿井火灾智能监测预警系统建设,提出了矿井火灾智能监测预警技术研究思路,从矿井火灾智能感知技术及装备、预测技术及模型、智能预警系统及平台3方面综述了矿井火灾智能监测预警技术研究进展。首先,总结了内外因火灾信息监测技术及装备,归纳了基于图像视频识别的识别流程,阐述了多源信息融合在火灾监测过程中的应用情况。其次,介绍了矿井火灾的预测技术及模型,包括支持向量机、人工神经网络、随机森林算法等机器学习算法。然后,阐述了矿井火灾预警系统及平台:在总结矿井煤自燃和外因火灾分级预警技术的基础上,介绍了矿井火灾预警系统平台的感知层、网络层、服务融合层以及应用层方面的进展内容;归纳了预警系统各层的内涵及应用框架;搭建了矿井火灾智能监测预警系统。最后,展望了我国矿井火灾智能监测预警技术的未来发展趋势,具体包括:在矿井火灾信息智能感知技术方面,提出加强传感技术及装备研发;在矿井火灾智能预测技术方面,提出加强隐蔽火源的位置探寻方法研究,构建火灾灾害透明化模型;在矿井火灾智能预警系统建设方面,提出将大数据融入智能判识,查明矿井火灾风险源及隐蔽火源位置的预报,实现特殊条件下煤自燃的预警。在矿井火灾智能判识与防控技术联动方面,提出利用大型语言模型在智能判识的基础上实现对矿井火灾的自适应防控。

易自燃厚煤层综采工作面CO溯源数值分析

甘肃某矿厚煤层2804综放工作面,回采期间的上隅角CO浓度长期保持150×10^(-6)左右,严重威胁井下人员安全。实验揭示了不同温度和O_(2)浓度下CO生成规律,建立了采空区CO生成运移的热-固-流-化多场耦合模型,定量分析了地温、工作面风量及回采速度对采空区CO生成-运移规律的影响。结果表明,当温度超过40℃时,煤的氧化反应速率开始增加,且随O_(2)浓度增大,煤的氧化反应越剧烈,生成的CO越多;回采过程中工作面上隅角CO浓度呈现递增趋势,生成速率先增大后减小,且随着地温、风量增大而增大;综合分析认为2804工作面上隅角CO主要来源于采空区内部浮煤氧化。

残煤复采区巷道掘进凝胶堵漏防灭火技术研究

采空区中遗留煤炭自燃现象直接影响着煤矿的安全高效开采,而采用堵漏材料封闭漏风通道是解决采空区煤自燃问题的有效方法。以运河煤矿F1301复采工作面为工程背景,针对在采空区中掘进巷道时遗留松散煤体的自燃隐患问题,制定了松散煤体凝胶堵漏防灭火技术实施方案,采用COMSOL数值模拟方法研究了不同注胶时间与压力下的凝胶扩散规律,并进行了工程应用。结果表明:注胶时间和压力与凝胶扩散范围成正比,综合考虑注胶效果与成本,选取10 MPa、140~160 min为最佳的注胶压力与时间,注胶钻孔间距设置为5 m;实施凝胶堵漏防灭火方案后,巷道两侧观测钻孔监测数据显示,标志气体CO体积分数稳定于24×10^(-6)以下,凝胶堵漏防灭火效果良好,有效消除了采空区遗留煤炭自然发火隐患。

采空区煤自燃高温点识别与探测技术研究与展望

我国因采煤活动造成的采空区总量大、范围广,针对采空区煤自燃高温点的有效识别与探测是煤矿安全生产的重要保障。从采空区煤自燃发生过程、高温点的形成运移特点概述了采空区高温点的生成演化特性,为采空区煤自燃高温点的有效识别与探测提供基础理论支撑。围绕地下直探技术、地表及空天探测技术的基本原理、研究进展以及现场实际应用效果,从可靠性、稳定性等方面进行多元比较,剖析现有煤自燃高温点识别探测技术的适用性。针对探测中存在的实际难点,拓展分析了矿井声波温度信息探测、基于量子技术的热源探测、毫米雷达波探测技术等新兴技术的研究现状和应用潜力,进一步推动采空区隐蔽火源精细化探测技术发展创新。通过对现有技术的综合性研判及新兴技术的前瞻性思考,展望了煤自燃隐蔽火源探测技术的未来发展趋势,结合当前物探技术和多元信息融合理论的发展趋势,提出了采空区高温点动态运移智能可视化系统构想,从“空-天-地-孔”的综合化分时分区多维探测模式应用、“特征获取-场景仿真规划-动态决策”逐级时空演化数字孪生模型两方面阐述了矿井开采全生命周期平台建设的现实意义。通过该构想的逐步实施,为实现采空区隐蔽火源的高效识别预测和矿井智能化建设提供新的决策思路。

火成岩侵蚀对煤自燃特性及其结构的影响

为探究火成岩侵蚀对煤自燃特性及结构的影响规律,以陕西、辽宁区域两煤矿同工作面原生煤及火成岩侵蚀煤为研究对象,采用程序升温试验、红外光谱分析、低温氮气吸附和压汞实验,分别从宏观和微观角度对煤的氧化特性、自燃极限参数、活性官能团含量以及孔隙结构特征进行分析。结果表明:火成岩侵蚀增大煤的自燃风险,会提升煤体内部的气体流通性,火成岩侵蚀煤体具有更高的氧化活性;此外,火成岩侵蚀改变煤层赋存条件,增大煤层开采难度,提高采空区内漏风强度,延长采空区“氧化升温带”遗煤的氧化时间,从外部影响因素层面提升煤炭的自燃风险;火成岩侵蚀改变煤自身结构和煤自燃外部环境因素,加剧了侵蚀煤层的自燃风险。

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。

近距离煤层群联合开采火区“三位一体”治理技术

针对近距离煤层群开采期间的自然发火防治难题,以新维煤矿2110、3108工作面断层区域火点处置为例,通过实验研究与现场实践相结合的手段,开展隐蔽火点的探测与综合治理技术研究。3号煤层自然发火模拟实验结果表明:CO、C_(2)H_(4)体积分数与煤温呈二次函数关系,可用于煤层自然发火预测预报;氧气体积分数的降低可以有效抑制煤自燃氧化进程,氧气体积分数为7%时最为明显,因此将其设为3号煤层自然发火的临界氧气体积分数。通过自燃隐患分析结合钻孔探查划定了3110轨道巷以西长80 m、宽10 m的F9断层区域为自然发火隐患区域,并提出以注浆降温为先导,以注胶堵漏为核心,以注氮阻爆为手段的液-胶-气“三位一体”的火区治理思路,累计向隐患区域注浆180 t、注胶504 m^(3),2110工作面采空区注氮流量保持在810 m^(3)/h,实现了火区的有效治理,保障了2个工作面的顺利启封与安全回采。

矿井煤自燃灾害监测预警技术及发展趋势

以降低矿井火灾的发生率为目标,梳理了矿井煤自燃灾害现有监测预警技术的发展现状,总结了现有技术的局限性和不足,指出未来发展应注重先进监测技术的应用、预测技术准确性的提升、预警系统和智能化管理的发展等。针对矿井煤自燃灾害隐蔽性、持续性、扩散性和难以控制的特点,提出矿井煤自燃灾害监测预警技术未来发展方向:提升煤自然发火临界值确定方法的综合性,利用新兴设备和先进技术完善煤自然发火临界值的确定方法;针对矿井煤自燃复杂环境,可通过研究声波探测等新型先进技术手段,提高矿井煤自燃监测参数的全面性和精细化;推动矿井煤自燃监测预警技术的创新性和决策的智能化,利用数字孪生技术提供精准的模拟与预测能力、优化防控方案、提供培训和应急管理以及数据分析和决策支持等方面的帮助;聚焦矿井自燃灾害全面感知、精准预测与防控智能一体化建设,加强对矿井自燃灾害数据分析、灾前主动预警、灾后事故治理、火区自动封闭等技术的研究。

特厚煤层重复采动作用下采空区自燃“三带”位移变化

为探究特厚煤层重复采动下采空区煤自燃“三带”的分布特征,基于束管监测系统,在铜川下石节煤矿222工作面进行现场实测,确定其自燃“三带”的分布规律。借助Fluent软件分别模拟重复采动及单一采动时采空区内氧气浓度的动态分布规律,发现重复采动采空区内实测结果与数值模拟结果基本一致。与单一采动模拟结果对比,重复采动导致采空区内部的散热带和氧化带出现缩短趋势;在进风侧散热带前移6.8%,氧化带前移7.0%;回风侧散热带前移14.3%,氧化带前移11.3%。研究成果能够为重复采动作用下采空区煤自燃危险区域防治提供依据。

新型阻燃泡沫在煤矿防自燃和灭火中的应用研究

煤炭自燃和火灾导致大量的煤炭资源损失和人员伤亡,但目前使用的常用灭火材料如水、普通泡沫等难以长期有效抑制煤自燃且无法快速灭火,因此,研发了一种新型阻燃泡沫。通过正交试验确定了阻燃泡沫的最佳成分配比,从自由基、官能团和CO生成速率3个方面考察了其阻燃性能,从煤在灭火过程中温度降低的速率和时间来考察其灭火性能。结果表明,新型阻燃泡沫在抑制自由基生成和煤氧化复合反应方面优于水和普通泡沫;低温阶段主要依靠水蒸发冷却、隔离煤与氧接触等物理抑制方法,高温阶段主要依靠Mg Cl2抑制煤氧化复合反应;与水和普通泡沫相比,阻燃泡沫可以快速扑灭煤火,防止闷烧。工程实践结果表明,使用新型阻燃泡沫后能明显降低煤体温度。