放顶煤开采初期放煤口附近煤体瓦斯压力分布规律研究.pdf

放顶煤开采初期放煤口附近煤体瓦斯 压力分布规律研究 夏永军 1 ,唐 娟 1 ,孟贤正 1 ,2 ,程国强 3 1. 煤炭科学研究总院重庆研究院,重庆400037; 2.安徽理工大学,安徽 淮南232001; 3.山东科技大学,山东 青岛266510 摘 要放顶煤工作面前方煤体瓦斯运移主要是沿煤层层面向已采空间的渗流,在综放工作面循环 向前推进时,煤体瓦斯渗流场结构发生变化。为进一步探索综放工作面前方煤体瓦斯压力的分布变化 规律,有效地进行瓦斯综合治理,运用ANSYS10. 0的瞬态分析模块进行了综放工作面附近煤体瓦斯压力 模拟分析。研究表明,综放工作面在推进过程中前方应力降低区瓦斯压力变化梯度大,在应力增高区瓦 斯压力较高,压力梯度变化小;初放期在工作面前方附近首轮循环放顶煤形成的瓦斯压力梯度比第2轮 循环形成的瓦斯压力梯度大。 关键词综放工作面;放顶煤;瓦斯压力;垮落;压力梯度 中图分类号TD712 . 52 文献标识码A 文章编号1008 - 4495200901 - 0004 - 03 收稿日期2007 - 12 - 21;2008 - 08 - 10修订 基金项目国家重点基础研究发展计划 973 计划项目 2005CB221504 作者简介夏永军 1976 , 男,重庆万州人,硕士,工程师, 从事煤矿瓦斯防治研究工作。E- mail cqxiayongjun 。 放顶煤开采以大大减少巷道工程量,缩短采煤 准备工期,采煤工效高等显著特点,在我国已经得到 广泛的应用。另一方面,放顶煤开采过程中又存在 瓦斯涌出量大幅度增加,瓦斯涌出不均衡,上隅角瓦 斯超限几率大等问题。尤其在回采过程中由于顶煤 厚度较大,与一般综采相比,整个采场顶板活动范围 较大,随之对煤体瓦斯流动产生明显影响,采场附近 瓦斯活动剧烈。因此,必须掌握综放工作面采场煤 体瓦斯活动规律,进而采取有效的瓦斯防治措施,实 现 综 放 工 作 面 的 安 全 高 效 开 采。笔 者 利 用 ANSYS10. 0的瞬态分析模块对综放工作面煤体瓦斯 压力分布规律进行了模拟分析。 1 煤层中瓦斯流动的基本方程 瓦斯在煤层中的赋存和运移情况极其复杂,为 了建立煤层瓦斯流动的连续方程,作如下基本假 设 [1] 1 瓦斯在煤层中渗流符合达西定律 qx -Kx 9 9x qy -Ky 9 9y qz -Kz 9 9z 1 式中qx,qy,qz分别为瓦斯渗流速度分量;Kx,Ky,Kz 分别为煤层瓦斯渗透系数分量;为势,计算公式为 z p ρg 2 其中p为瓦斯压力;ρ为瓦斯密度;z为位置势,即由 于瓦斯重力而引起的势。 对于煤层中瓦斯而言,密度ρ很小,重力产生的 势可以忽略不计,因此式2可写为 p ρg 3 所以 qx - Kx ρg 9p 9x qy - Ky ρg 9p 9y qz - Kz ρg 9p 9z 4 2 煤层中吸附瓦斯量满足朗格缪尔方程 煤层中瓦斯由两部分组成,一部分是处在吸附 状态下,而另一部分是以游离形式赋存的。 结合朗格 缪尔公式,单位体积煤中吸附瓦斯质量为 WC abp 1 bpρ 5 式中WC为单位体积煤中吸附瓦斯质量,kgΠm 3 ;a为 煤的最大吸附瓦斯含量,m 3Π m 3 ;b为煤的吸附常数, MPa - 1 ;p为煤层瓦斯压力,MPa ;ρ为单位体积所含 瓦斯质量,kgΠm 3 。 煤中游离瓦斯由以下公式给出 WCBn p p0 ρ6 4 2009年2月 矿业安全与环保 第36卷第1期 式中WCB为单位体积煤中游离瓦斯质量,kgΠm 3 ;p0 为标准大气压,p0 0. 101 3 MPa ;n为孔隙率, 。 单位体积煤层中瓦斯总质量W为 WWCBWCn p p0 ρ abp 1 bpρ 7 通常吸附瓦斯占80 ～90 ,而游离瓦斯仅占 10 ～20 。 3 瓦斯为理想气体,流动过程为等温过程 有如下瓦斯状态方程 ρ p RT 8 式中T为温度,K;R为瓦斯气体常数。 在以上假设基础上,可建立煤层瓦斯流动的连 续方程 9 9x Kx 9p 2 9x 9 9y Ky 9p 2 9y 9 9z Kz 9p 2 9z 2n p0 - ab 2ρ p 1 bp 2 abρ 1 bp 9p 2 9t 9 令 p 2 P, Sp 2n p0 - ab 2ρ p 1 bp 2 abρ 1 bp 10 因此 9 9x Kx 9P 9x 9 9y Ky 9P 9y 9 9z Kz 9P 9z Sp 9P 9t 11 式11即为瓦斯渗流的基本方程。 热传导方程为 9 9x Kx 9T 9x 9 9y Ky 9T 9y 9 9z Kz 9T 9z ρc 9T 9t 12 式12在形式上与瓦斯渗流的基本方程完全一 样。 因此可以用分析热传导的方法或程序分析瓦斯 渗流。 2 瓦斯渗流参数 根据文献[1 - 2] ,计算中取p1 2 MPa ,p0为标 准大气压,取p0 0. 1 MPa。 瓦斯含量参数ρ 1. 4 tΠm 3 ,a 31. 48 m 3Π t ,b 0. 101 4 MPa - 1 ,n 011。 周世宁院士在计算瓦斯在实际煤层中的流动 时,煤层透气性系数随时间和空间的变化采用下式 表示 [3] λλ0 1 - ρe- n′t x m′ 13 式中ρ,n′ 为待定常数;m′ 为指数,取决于矿山压力 和煤质结构。 采用式13计算煤与瓦斯突出时应力降低区煤 体的透气性系数,取m′ - 1 ,由于时间较短,所以 忽略时间效应,即取ρ 0 ,则有 λ λ0 x0 x x位于应力降低区 λ0 x位于弹性区 14 式中x0为煤体应力降低区的特征尺寸;x为煤壁到 应力降低区的距离;λ0为煤层原始透气性系数,取 λ00. 39 m2Π MPa 2 d 。 3 计算模型及参数 考虑在顶煤初放期进行计算。采用平面应变模 型,单元大小为2 m1. 25 m ,模型走向长50 m ,倾向 长150 m ,煤层高度为10 m。模型在下伏岩层施加y 方向的位移约束,在两侧施加x方向的位移约束,埋 深400 m ,在模型上部施加10 MPa的应力。模型内 施加2 MPa的瓦斯压力,采空区及巷道内瓦斯压力 为0. 1 MPa。 模拟综放工作面采高2. 5 m ,采放比1∶3。 模型中模拟开挖利用单元生死来实现,支架使用杆 单元实现,模拟直接顶随放随垮落。模拟采用的岩 石参数及尺寸见表1。 表1 计算采用的岩体力学参数及尺寸 项目 密度 ρ Πkg Πm3 弹性模量 EΠGPa 泊松比 μ 黏聚力 cΠMPa 摩擦角 φ Π 抗拉强度 σTΠMPa 高度Π m 上覆岩层2 53010.850.1472.45402.0130 老顶2 87333.40.2353.2421.2910 直接顶2 46019.50.22.75381.845 煤层1 3805.30.321.25320.15 直接底2 46019.50.22.75381.845 老底2 580250.1592.5423.610 下伏岩层2 53010.850.1472.45402.0130 4 数值计算结果分析 巷道开挖后,出现了自由面,引起局部区域的应 力松弛,使煤层内的瓦斯向自由面侧流动。提取了 距底板5 m ,距工作面25 m位置处的瓦斯压力数据, 其变化情况见图1。 图1 巷道开挖后瓦斯压力变化图 5 2009年2月 矿业安全与环保 第36卷第1期 由图1可以看出,巷道开挖后引起瓦斯流动,使 瓦斯压力降低,其影响范围为距进风巷8 m左右,距 离进风巷大于8 m的地方瓦斯压力恢复为原始状态 下的2 MPa。 顶煤垮落后也产生了自由面,大量瓦斯向采空 区侧流动,提取了顶煤第1循环垮落和顶煤第2循 环垮落后的瓦斯压力数据变化情况。2次数据取距 底板5 m距进风巷72 m位置处,瓦斯压力变化见 图23。 图2 顶煤第1次垮落后瓦斯压力变化图 图3 顶煤第2次垮落后瓦斯压力变化图 由图2可以看出,顶煤第1次垮落后,在工作面 前方2 m范围,煤体瓦斯压力值较低,约为0. 1 MPa , 然后瓦斯压力梯度陡增,压力增高。在距离工作面 2～5 m的煤体,存在明显的瓦斯压力梯度,超过5 m 的范围,瓦斯压力梯度变化趋于平缓。由图3可以 看出,顶煤第2次垮落后,近工作面瓦斯压力低值区 域变宽,在距离工作面4. 5 m范围,瓦斯压力值为 0. 1 MPa ,之后瓦斯压力梯度陡增,压力增高,与顶煤 第1次垮落过程相比,瓦斯压力梯度的范围明显变 窄,仅为1 m左右。 由顶煤两次垮落过程瓦斯压力分布图可以得 知工作面前方卸压区瓦斯压力变化梯度大,在应力 增高区瓦斯压力较高,但是压力梯度变化小;初放期 在工作面前方附近首轮循环放顶煤形成的瓦斯压力 梯度比第2轮循环形成的瓦斯压力梯度大。 5 结论 探索了采高2. 5 m、 采放比1∶3时,原始煤体瓦 斯压力2 MPa条件下,综放工作面顶煤初次垮落过 程煤体瓦斯渗流演化和发展规律,经过理论及数值 分析,得出如下结论 1 顶煤垮落后产生了自由面,距煤壁5 m范围 内瓦斯压力急剧下降,近煤壁范围出现瓦斯压力等 值特性,且数值较低。 2 工作面前方应力降低区瓦斯压力变化梯度 大,在应力增高区瓦斯压力较高,但是压力梯度变化 小;初放期在工作面前方附近首轮循环放顶煤形成的 瓦斯压力梯度比第2轮循环形成的瓦斯压力梯度大。 3 在顶煤放落之前,应加强工作面前方煤体瓦 斯抽排工作,使应力增高区往煤体深部转移,防止近 工作面区域煤体产生较大瓦斯压力梯度,有利于工 作面安全回采放顶。 参考文献 [1]胡千庭.煤与瓦斯突出的力学作用机理及应用研究[D]. 北京中国矿业大学,2007. [2]李树刚.综放开采围岩活动及瓦斯运移[M].徐州中 国矿业大学出版社, 2000. [3]周世宁,林柏泉.煤层瓦斯赋存及流动规律[M].北京 煤炭工业出版社, 1998. 责任编辑吴自立 上接第3页 [3]张辛亥,徐精彩,邓军,等.煤的耗氧速度及其影响因素恒温 实验研究[J ].西安科技大学学报,2001 , 223 243 - 246. [4]邓军,徐精彩,李莉,等.煤的粒度与耗氧速度关系的实 验研究[J ].西安交通大学学报, 1999 ,3312 106 - 107. [5]徐精彩,许满贵,文虎,等.煤氧复合速率变化规律研究 [J ].煤炭转化,2000 , 233 65 - 66. [6]何启林,王德明.煤的氧化和热解反应的动力学研究 [J ].北京科技大学学报,2006 ,281 2 - 4. [7]戴广龙.煤低温氧化及自燃特性的综合实验研究[D]. 徐州中国矿业大学, 2005. [8]叶振兴.煤的低温氧化实验及对模拟试验数值模拟研究 [D].淮南安徽理工大学, 2005. [9]胡荣祖,史启祯.热分析动力学[M].北京科学出版社, 2001. [10] H. WANG, B. Z. DLUG OG ORSKI, E. M. KENNEDY. K i2 netic Modeling of Low - Temperature Oxidation of Coal [J ]. Combustion and Flame ,2002 ,131452 - 469. [11]夏少武.活化能及其计算[M].北京高等教育出版社, 1993. 责任编辑卫 蓉 6 2009年2月 矿业安全与环保 第36卷第1期 Vol.36 No.1 2009MINING SAFETY the activation energy E and the pre - exponential factor A at different temperature stage were also calcu2 lated by slope and intercept. In particular , the relation between activation energy E and temperature T and reaction velocity and the ation of negative activation energy for Chaili gas coal were explained according to T olman’s definition on acti2 vation energy E. Studyon Distribution Regularity of Coal - body G as Pressure near Coal Draw - point in Early Stage of Caving Mining4 - The gas migration in coal body infront of the fully mechanized cavingface mainly seepages along the coal seam surface to the mined - out space. When a fully mechanized caving face is cyclically ad2 vanced forward , the structure of the seepage fieldof coal body gas changed. Simu2 lation analysis was made on the gas pressure near the fully mechanized cavingface by using ANSYS10.0 transient analysis module in order to further probe into the variation regularity of gas pressure distribution in the coal body infront of the fully mechanized caving face and effectively control the gas. Study indicated that the varying gradient of gas pressure in the stress - lowering zone in front of the fully mechanized caving face is large , but in the stress - increasing zone , the gas pres2 sure is relatively high and the varying gradient of gas pressure is small ; the gradi2 ent of gas pressure ed in the first coal - caving cycle in front of the face is larger than that in the second coal - caving cycle. Simulative Study on G as Pressure Distribution Based on Lattice Boltzmann 7 - A new dynamic model for the simulation of two - dimensional gas pressure in fissured coal was established based on Lattice Boltzmann LBM , and simulation study was made on the spatial distribution and time evolvement of gas pressure , the simulation results indicated that the gas pressure distribution is relat2 ed to the exposure time and the position of coal wall ; the longer the exposure time of coal wall , the smaller the gas pressure gradient at the coal wall and the larger the variation range of gas pressure in gas flow fluid. The spatial gas pressure was in a quadratic curve distribution. The simulation results are consistent with the theoretical analysis and experimental results. This showed that LBM is a new cal2 culation for studying gas migration regularity in coal seam. Simulation and Analysison Breathingof G ob10 - Based on the establishment of three - dimensional spontaneous combustion prediction model for the gobof fully - mechanized caving face , numerical simulation on the breathing of the gob of fully - mechanized caving face of high - gassy coal seam was conducted by using nu2 merical simulation software under gas drainage condition ,“Three - zones”of spontaneous combustion of coal were divided according to the simulated results , and the dangerous zone and degree of spontaneous combustion of float coal in the gob of thisface were also analyzed , which can be used to guide the prevention and control work of spontaneous combustion of float coal in the gob of the face with similar conditions. Comparative Study on Surface Subsidence Prediction Based on BP - ANN M odel 17 - Based on comprehensive analysis of the factors influencing surface subsid2 ence , a prediction model for surface subsidence was established by different meth2 ods of back propagation artificial neural network BP - ANN . A large amount of data obtained at observation stations in a mining field was used for training and perance test of BP - ANN models , and comparison and analysison these mod2 els were made. The results indicated that it is much more reasonable to use BP - ANN model to predict the mining subsidence. The limited artificial factors during the prediction , simplified the complexproblems and made the solution more reasonable and creditable. So , it has a certain application value. uation of Mine Ventilation System Based on Gray Cluster Analysis and Fuzzy Comprehensive uation26 - Based on extensive investigation and analysis of main factors influencing the running of mine ventilation system , a comprehensive uation index systemfor mine ventilation systemwas constructed by utilizing the principle and of multi - objective decision - marking theory. And a com2 prehensive uation model for mine ventilation system was established by using the gray cluster analysis in gray theory and the fuzzy comprehensive uation , this thus quantitatively solved the uation grade of the ventilation effect of mine ventilation system. In this paper , uation was made by taking Tangs2 hangou Coal Mine as an example , and the uation results were consistent with the actual survey. Application of Isotopic Technique in Identification of Mine Water Inrush Source 32 - The application of isotopic technique can get critical data which can’t be obtained by conventional , this thus plays an important role for the analysis of supply source of underground water , the linkage between each water - bearing beds, the age and the mixing proportion of underground water and so on. The study results showed that the application of this technique can accurately and rap2 idly determine the isotopic characteristics of underground water and identify the main source of mine water inrush. The application of this technique can provide scientific basis for the working - out of effective mine water prevention and control s. Study of Coal Mine Emergency Rescue Ination Management System Based on NET Plat35 - The traditional coalmine emergency rescue ination system based on CΠS structure has some disadvantages such as miscellaneous program2 ming , connatural hidden trouble and low efficiency , so a of system design and realization based on BΠS structure was put forward. This system runs on Mi2 crosoft. NET plat which uses SQL Server 2003 as database server and ASP. NET environment for programming. It uses ADO. NET, the subassemblyof ASP. NETto access the database. which makes the system reliable , efficient , conve2 nient and easy to maintain. The practice showed that the system is helpful and universal. Application of Matter - Element M odel in uation and Prediction of Seam Roof Stability38 - In this paper , a stability identification and prediction model for coal seam roof was established and the mater - element correlative function for the stability uation of coal seam roof and the calculation for mater - ele2 ment correlative degree were given according to some factors influencing the stabil2 ity classification of coal seam roof and by applying the matter - elements model in order to accurately predict the stability of coal seam roof. The classification stan2 dard suitable for prolongable theory for stability grade of coal seam roof was also established , which employed the complex weight of inds and made full use of the ination obtained by the subjective objective favoritism. The application re2 sults indicated that this model is suitable for the identification and uation of coal seam roof stability. Study on Construction of Early Warning System of Floor Water Inrush in Mine W orking Face58 - Starting from correlative concepts about floor water inrush in the working face and based on the analysis of various factors influencing mine wa2 ter inrush , this paper described the function and significance of constructing early warning system of floor water inrush. By taking the early warning theory as the guide and according to the actual requirements for mine water hazard prevention and control , an early warning system of floor water inrush was constructed , this paper put forward the logic structure and overall framework of this system and ana2 lyzed the function of its main composing layers. So it provided a new scheme for building the early warning system of floor water inrush.