Application of Roadway Spray Material to Fire Prevention in Goaf Excavation

In order to reduce the risk of spontaneous combustion in goaf during goaf excavation process, polymer modified cement mortar spraying material was used to spray and seal the roadway surface. The experimental application was carried out in the upper channel 2304 of a mine in Henan Province. The test results showed that polymer modified cement mortar spraying material could effectively support the roadway and greatly reduce the deformation rate of the roadway. The best spraying thickness is 5 mm. Through the monitoring of tunnel air leakage, it is concluded that the polymer modified cement mortar spraying material can reduce the tunnel air leakage and play a better sealing effect.

Research on the feasibility of storage and estimation model of storage capacity of CO_(2)in fissures of coal mine old goaf

The concept of the carbon cycle in the old goaf of a coal mine based on CO_(2)utilization and storage was put forward adhering to the principle of low-carbon development,utilization of space resources in old goafs,and associated gas resources development.Firstly,the evolution characteristics of overburden fissures in the goaf of the case was studied using a two-dimensional physical similarity simulation test,the sealing performance of the caprocks after stabilization was analyzed,and the fissures were counted and classi-fied.Then,the process of gaseous CO_(2)injection in the connected fissure was simulated by Ansys Fluent software,and the migration law and distribution characteristics of CO_(2)under the condition of gaseous CO_(2)injection were analyzed.Finally,the estimation models of free CO_(2)storage capacity in the old goaf were constructed considering the proportion of connected fissure and the effectiveness of CO_(2)injection.The CO_(2)storage capacity in the old goaf of the case coal mine was estimated.The results showed that a caprock group of“hard-thickness low-permeability hard-thickness”was formed after the caprock-fissures system in the goaf of the case tended to be stable vertically.The connected fissure,occlude cracks,and micro-fractures in the goaf accounted for 85.5%,8.5%,and 6%of the total fissures,respectively.Gaseous CO_(2)first migrated to the bottom of the connected fissure after CO_(2)was injected into the goaf,then spread horizontally along the bottom of the connected fissure after reaching the bottom,and finally spread longitudinally after filling the bottom of the entire connected fissure.The theoretical and effective storage capacities of free CO_(2)at normal temperature and pressure in the old goaf of the case were 9757 and 7477 t,respectively.The effective storage capacity of free CO_(2)at normal temperature and pressure in the old goaf after all minefield mined was 193404 t.The research can provide some reference for the coal mining industry to help the goal of“carbon peaking and carbon neutrality”.

Algorithm for cavity flow in a new-born goaf and experimental verification

Prevention and control measures of spontaneous combustion of coal and gas accumulation in a goaf require an accurate description of its gas flow state.However,the commonly used fluid dynamics in porous media is not suitable for the new-born goaf with fracture cavity combination,multi-scale,and large blocks.In this study,we propose a cavity flow algorithm to accurately describe the gas flow state in the new-born goaf.The genetic algorithm(GA)is used to randomly generate the binary matrix of a goaf caving shape.The difference between the gas flow state calculated by the lattice Boltzmann method(LBM)and the measured data at the boundary or internal measuring points of the real goaf is taken as the GA fitness value,and the real goaf caving shape and the gas flow state are quickly addressed by GA.The experimental model of new-born goaf is established,and the laser Doppler anemometry(LDA)experiment is carried out.The results show that the Jaccard similarity coefficient between the reconstructed caving shape and the real caving shape is 0.7473,the mean square error between the calculated wind speed and the LDA-measured value is 0.0244,and the R2 coefficient is 0.8986,which verify the feasibility of the algorithm.

Effect of periodic wide atmospheric pressure change on CO emission in closed goaf

Atmospheric pressure fuctuation is one of the most important factors afecting the climate environment and gas emission in the fre area.To obtain the infuence rule of the surface atmospheric pressure change on the gas sampling and abnormal emission in the mine closed goaf,the No.1 coal mine in Dananhu was taken as the research object.Using Fourier transform and Fisher harmonic analysis and other statistical methods,the infuence of the periodic variation of atmospheric pressure on the gas leakage and outfow in the closed goaf was studied.The results showed that there were three atmospheric pressure periods of 15.2 d,1 d and 182.2 d,and the probability was greater than 95%.The time period with the highest number of atmospheric pressure peaks was 7:00–8:00,which accounted for 20.2%of total occurrence number in a day.And the time periods with the highest number of atmospheric pressure trough were 2:00,15:00 and 16:00,accounting for 27.4%.The peak-to-trough transition time was mainly concentrated around 6 h,and the diurnal variation curve of atmospheric pressure was mainly bimodal.The atmospheric pressure change rate was mostly concentrated in 10–50 Pa/h.It was determined that the distance that the gas sampling pipe was pre-laid into the inner side of the closed wall should be greater than 44.4 m,and the CO concentration and atmospheric pressure in the closed goaf were both periodic and negative with atmospheric pressure.The research results have important guiding signifcance for the monitoring,early warning and environmental protection of the goaf.

孔庄煤矿7436工作面CO_(2)惰化技术参数优化

为对孔庄煤矿7436工作面二氧化碳惰化技术参数进行优化,介绍了矿井二氧化碳灌注工艺,建立了二氧化碳惰化采空区指标体系,确认了7436工作面惰化参数。使用Fluent数值模拟方法建立采空区物理模型,研究了不同注气口深度、不同注气量情况下采空区惰化效果以及上隅角二氧化碳体积分数,通过对比其惰化效果,得出最佳惰化技术参数。研究结果表明:当注气量增加到一定程度后,惰化采空区的效果便会减弱,而注气口深度对氧化带宽度的影响无显著规律,因此可得出注气量为影响惰化效果的主要因素。通过对比不同工况下的采空区氧化带宽度,综合考虑安全等因素,确定7436工作面当注气口深度为30 m,注气量为750 m^(3)/h时为最佳注惰参数。

基于CFD的采空区三维流场分析及注氮参数优化研究

注氮是煤矿采空区发生自然发火征兆时常用的抑制措施,因其效果显著、安全可靠等特点被广泛应用于采空区灭火实践。注氮位置选取、注氮量的多少等直接影响注氮的效果及成本;采用数值模拟及现场实测相结合的方法,对注氮防灭火参数进行优化。以试验工作面为原型建立仿真物理模型,通过现场实测数据验证模型的有效性。在开展数值模拟试验的过程中,通过研究不同注氮位置、不同注氮流量等对采空区“三带”的影响,找到最优注氮参数,并进行了现场实测验证。研究结果表明,注氮口在进风侧距离工作面50 m处、注氮流量1 000 m~3/h时,注氮效果良好且成本最低。

孤岛工作面采空区防火通风技术研究

孤岛工作面采空区防火通风工作高质量落实,对降低火灾事故的发生风险,保障生产安全,有着重要的意义。由于采空区的环境复杂,给防火通风带来很大挑战,需引入新技术和新手段,构建完善的防火通风系统,实现有效的防护。现针对采空区防火通风建设相关问题,展开具体的论述,提出防火通风的策略。

煤矿采空区灌浆装备研发与应用

灌浆装备作为煤矿采空区防灭火工作的重要手段,应该向规范化、集成化、智能化的方向发展。为解决在现有地面灌浆系统传统装备使用过程中发现的不足,在分析了现有设备缺陷的基础上,神东煤炭集团形成了灌浆装备设计目标,提出了装备关键技术性能,设计研发了一套具有可靠性、灵活性、实用性、先进性的多功能地面移动灌浆装备,提炼了装备关键创新点,总结了装备研发价值,并将该装备在神东煤炭集团上湾煤矿进行现场应用。结果表明,该装备大幅度提高了神东公司防灭火注浆工程施工效率,应用效果良好,对煤矿采空区防灭火技术及装备的发展具有促进意义。

红树梁煤矿浅埋煤层防灭火技术探索与应用

矿井火灾是煤炭开采过程中的主要灾害之一,会对煤矿的安全生产构成严重威胁。为保障红树梁煤矿开采工作的顺利进行,基于矿区自身的煤层性质及赋存条件,对浅埋深煤层自然发火的防治技术展开探索。在分析注氮、喷洒阻化剂、采后灌浆、均压等防灭火措施的基础上,配合日常火情预测预报系统以及合理的采煤工艺和通风系统,提出了适合该矿区的经济高效的综合防灭火技术。实践表明,该技术可以有效确保工作面安全顺利回采,提升矿井的安全生产水平,具有一定的应用价值。

近距离煤层群开采复合采空区火区综合治理技术实践

针对近距离煤层开采形成的上下煤层复合采空区火区治理难题,以唐山沟煤矿83101工作面复合采空区火区为例,采取漏风封堵、均压控风和注浆注氮降温等技术对火区进行治理。启封前,采用注氮惰化及注浆封堵协同技术,在控制异常区域温度和CO气体扩散的同时,降低氧气体积分数,抑制遗煤氧化;启封后,采用均压控风技术,并对高温区域进行强化注浆降温,有效阻断遗煤氧化自燃的蔓延,减少有害气体扩散。现场结果表明,83101复合采空区火区启封前后未发生火区复燃现象,实现了工作面在慢采条件下的安全复采。该实践成果可为近距离煤层开采火区启封及工作面安全复采提供有力支撑。

复杂地质工作面采空区综合防灭火技术研究

为了探索复杂地质条件下综采工作面采空区防灭火技术,通过现场布置束管测点方式研究了采空区遗煤自燃“三带”的分布规律,并在此基础上结合地质条件,研究实施了下隅角密闭、挂风障、降低供风量和采空区注氮等综合防灭火措施。结果表明:工作面采取综合防火措施后可缩小氧化带范围,使得采空区遗煤及时进入到窒息带内,消除了遗煤自然发火环境;在工作面过断层等地质复杂地段,喷射阻化剂后采空区内各测点CO浓度不断降低,当断层进入到采空区内60 m后,CO浓度均处于安全指标值以下。

台阶型煤体孤岛开采自然发火防治技术应用

金桥煤矿1306工作面四面临空,孤岛布置,分层开采,上分层存在遗留煤柱,形成了特殊的“台阶型”构造。针对1306工作面漏风通道多,自然发火风险较大的实际,分正常回采、回撤2个阶段制定针对性防灭火措施。回采期间采取了沿空喷涂、采空区注氮、停采线及采空区压注凝胶、遗煤喷洒阻化剂等措施,回撤期间重点采取了架后压注凝胶措施。通过对安全监控系统、采空区微漏风监测系统及人工检测数据进行耦合性分析,对1306工作面防灭火效果进行验证,得出1306工作面防灭火措施落实得当,肯定了台阶型煤体孤岛开采自然发火防治技术的成效。该技术能够为后续不规则工作面防灭火工作提供技术支撑,对类似开采条件的矿井有一定的借鉴作用。

大气压变化对采空区压力参数影响的研究

季节的更替会导致气温的骤变,影响地表气压的变化,地表气温昼夜温差大,气压变化明显,而井下气温、气压基本处于恒定状态,因此会造成两者之间压差急剧变化。矿井采空区密闭受地面大气压变化的影响,常常会出现呼吸性供氧,造成密闭内气体向外溢出,引起瓦斯超限事故;或者空气进入密闭后与密闭内的遗煤相互作用自燃后造成密闭内发生火灾,故采空区内的气压与地表大气压力息息相关。以大水头煤矿东107工作面密闭采空区为研究对象,通过1 d时间内的地表大气压、温度的变化与采空区密闭内的气压变化、采空区密闭内外的差压变化进行分析研究,得出采空区密闭内外差压变化的时间规律,可为采空区的抽采及防灭火方案的制定提供应用支撑。

采空区均压防灭火技术在滕东煤矿的应用

为了解决采空区漏风造成遗煤自燃的难题,提出了一种煤矿井下调整采空区两端压差的方法,对滕东煤矿通风系统现状进行分析。以均压防灭火机理为依据,设计滕东煤矿均压防灭火工艺方案,利用连通管将各封闭空间互相连接,以此维持封闭空间的压力,保持采空区两端压力平衡,达到防止向采空区漏风供氧的目的。通过在滕东煤矿的井下现场试验,均压防灭火技术能够使密闭内外压力差降到0~20 Pa,使采空区密闭内外压力达到均衡,阻止气体的逸出,有效防止向采空区漏风供氧,从而防止采空区遗煤发生自燃,在滕东煤矿取得较好的防治效果。

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。

Identifcation of large-scale goaf instability in underground mine using particle swarm optimization and support vector machine

An approach which combines particle swarm optimization and support vector machine(PSO–SVM)is proposed to forecast large-scale goaf instability(LSGI).Firstly,influencing factors of goaf safety are analyzed,and following parameters were selected as evaluation indexes in the LSGI:uniaxial compressive strength(UCS)of rock,elastic modulus(E)of rock,rock quality designation(RQD),area ration of pillar(Sp),the ratio of width to height of the pillar(w/h),depth of ore body(H),volume of goaf(V),dip of ore body(a)and area of goaf(Sg).Then LSGI forecasting model by PSO-SVM was established according to the influencing factors.The performance of hybrid model(PSO+SVM=PSO–SVM)has been compared with the grid search method of support vector machine(GSM–SVM)model.The actual data of 40 goafs are applied to research the forecasting ability of the proposed method,and two cases of underground mine are also validated by the proposed model.The results indicated that the heuristic algorithm of PSO can speed up the SVM parameter optimization search,and the predictive ability of the PSO–SVM model with the RBF kernel function is acceptable and robust,which might hold a high potential to become a useful tool in goaf risky prediction research.

Hydraulic support crushed mechanism for the shallow seam mining face under the roadway pillars of room mining goaf

While the fully-mechanized longwall mining technology was employed in a shallow seam under a room mining goaf and overlained by thin bedrock and thick loose sands, the roadway pillars in the abandoned room mining goaf were in a stress-concentrated state, which may cause abnormal roof weighting, violent ground pressure behaviours, even roof fall and hydraulic support crushed(HSC) accidents. In this case,longwall mining safety and efficiency were seriously challenged. Based on the HSC accidents occurred during the longwall mining of 3-1-2 seam, which locates under the intersection zone of roadway pillars in the room mining goaf of 3-1-1 seam, this paper employed ground rock mechanics to analyse the overlying strata structure movement rules and presented the main influence factors and determination methods for the hydraulic support working resistance. The FLAC3 D software was used to simulate the overlying strata stress and plastic zone distribution characteristics. Field observation was implemented to contrastively analyse the hydraulic support working resistance distribution rules under the roadway pillars in strike direction, normal room mining goaf, roadway pillars in dip direction and intersection zone of roadway pillars. The results indicate that the key strata break along with rotations and reactions of the coal pillars deliver a larger concentrated load to the hydraulic support under intersection zone of roadway pillars than other conditions. The ‘‘overburden strata-key strata-roadway pillars-immediate roof" integrated load has exceeded the yield load that leads to HSC accidents. Findings in HSC mechanism provide a reasonable basis for shallow seam mining, and have important significance for the implementation of safe and efficient mining.

Mapping coalmine goaf using transient electromagnetic method and high density resistivity method in Ordos City, China

The research about subsurface characteristics by using transient electromagnetic method（TEM） and high density resistivity method（HDRM） were already conducted in Ordos. The objective of this research is to detect coalmine goaf areas based on rock resistivity. The data processing using wavelet transform, three point smoothing, RES2 DINV and Maxwell processing software to obtain 2D resistivity structure. The results showed that the layers with maximum resistivity values（30e33 U m on Line 1, 30e31 U m on Line 2, 32e40 U m on Line3） are founded at station 1e7, and 14e20 on Line 1,13e18 on Line 2, and 8e13 and 16e20 on Line 3 which is predicted as goaf layer, and the minimum resistivity values（20e26 U m of TEM, 45e75 U m of HDRM） at the other layers. This resistivity difference was caused by the geology and characteristics of the study area which is located close by the cleugh with rich coal, so the goaf area distinguishable with aquifer layer and coal seam. The results were also significant accidents and serious destruction of ecological environment.

Ultimately exposed roof area prediction of bauxite deposit goaf based on macro joint damage

The ultimately exposed roof area(UERA)of goaf is crucial to the safety and economics of underground mining.The prediction models do not consider the mechanical weakness of rock mass and ignore the influence of the joint damage factor,causing a large predicted exposure area with a high roof falling risk.This work adopted joint damage factor to derive a new UERA prediction model.The relationships between the UERA(S)and the span ratio(m),the density(k)and the diameter of fracture(d)were analysed by the new prediction model.The results showed that the exposed area S and the span ratio m have a U-shaped curve relationship.The S decreases with the increase of m and then increases when m is beyond 2.The exposed roof area S is in an inversely proportional power-law relationship with the fracture surface density k,and the curvature of the S-k relationship curve decreases when d=0.5 and k>7,and S is close to 0.There is a negative correlation between S and the fracture surface diameter d,the curvature of the S-d curve decreases with the increase of d and k,and the variation rate increases first and then decreases with the increase of d;when k=0.5 and d>9,S is close to 0.The predicted values of the UERA prediction model are 119.3,112.8,and 114.6 m2 with different joint damage parameters,which are slightly smaller than the actual critical exposure area of a roof(S=120 m2).The case study shows that the alternative prediction model is reasonable and acceptable and provides new theoretical support for the underground mining safety of sedimentary bauxite ore.

Numerical simulation to determine the gas explosion risk in longwall goaf areas:A case study of Xutuan Colliery

Underground gassy longwall mining goafs may suffer potential gas explosions during the mining process because of the irregularity of gas emissions in the goaf and poor ventilation of the working face,which are risks difficult to control.In this work,the 3235 working face of the Xutuan Colliery in Suzhou City,China,was researched as a case study.The effects of air quantity and gas emission on the three-dimensional distribution of oxygen and methane concentration in the longwall goaf were studied.Based on the revised Coward’s triangle and linear coupling region formula,the coupled methane-oxygen explosive hazard zones(CEHZs)were drawn.Furthermore,a simple practical index was proposed to quantitatively determine the gas explosion risk in the longwall goaf.The results showed that the CEHZs mainly focus on the intake side where the risk of gas explosion is greatest.The CEHZ is reduced with increasing air quantity.Moreover,the higher the gas emission,the larger the CEHZ,which moves towards the intake side at low goaf heights and shifts to the deeper parts of the goaf at high heights.In addition,the risk of gas explosion is reduced as air quantities increase,but when gas emissions increase to a higher level(greater than 50 m3/min),the volume of the CEHZ does not decrease with the increase of air quantity,and the risk of gas explosion no longer shows a linear downward trend.This study is of significance as it seeks to reduce gas explosion accidents and improve mine production safety.