A general solution and approximation for the diffusion of gas in a spherical coal sample

The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relationship was theoretically derived, what are the assumptions and applicable conditions and how large the error will be. In this paper, the analytical solutions of gas concentration and fractional gas loss for the diffusion of gas in a spherical coal sample were given with detailed mathematical derivations based on the diffusion equation. The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken. The results indicate that the square root relationship of gas release is the first term of the approximation, and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a spherical coal sample.

Experimental study on the type change of liquid flow in broken coal samples

A test system of the permeability of broken coal samples mainly consists of a CMT5305 electronic universal test machine, crushed rock compaction containing cylinder and a self-designed seepage circuit, which is composed of a gear pump, a reversing valve, a relief valve and other components. By using the steady penetration method, the permeability and non-Darcy flow β factor of broken coal samples under five different porosity levels were measured, the grain diameters of the coal samples were selected as 2.5-5 mm, 5-10 mm, 10-15 mm, 15-20 mm, 20-25 mm and 2.5-25 ram, respectively. After measuring the permeability under each porosity, the overfall pressure of the relief valve continuously increased until the coal sample was broken down. In this way, the flow type of liquid inside the broken coal samples changed from seepage to pipe flow. The correlation between breakdown pressure gradient （BPG） and porosity was analyzed, and the BPG was compared with the pressure gradient when seepage instability occurred. The results show that, ①the non-Darcy flow β factor was negative before broken coal samples with six kinds of diameters were broken down; ②the BPG of coal samples with a grain size of 2.5-25 mm was lower than that of the others; ③ the BPG of coal samples with a single diameter under the same porosity increased as the grain size increased; ④ the BPG could be fitted by an exponential function with porosity, and the exponent decreased as the grain size increased for coal samples with a single diameter; ⑤ the BPG was slightly less than the seepage instability pressure gradient. The change in liquid flow type from seepage to pipe flow could be regarded as the performance of the seepage instability.

Gas diffusion in a cylindrical coal sample – A general solution,approximation and error analyses

The analytical mathematical solutions of gas concentration and fractional gas loss for the diffusion of gas in a cylindrical coal sample were given with detailed mathematical derivations by assuming that the diffusion of gas through the coal matrix is concentration gradient-driven and obeys the Fick’s Second Law of Diffusion.The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken.The results indicate that the square root relationship of gas release in the early stage of desorption,which is widely used to provide a simple and fast estimation of the lost gas,is the first term of the approximation,and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a cylindrical coal sample.

Thermo-chemical conversion of coal samples under high temperature

Exhaustion of profitable coal resources makes for need of innovation including underground coal gasification(UCG).One of the most important problems of UCG is evaluation of the combustion area in underground coal seams.Physicochemical parameters of coal,in a whole,and coal mineral substance are changed under heating and combusting.Thermo-chemical conversion of coal mineral components has an effect on magnetic characteristics of coal seam and can be used for real-time control of combusting area.To this guessing check laboratory experiments have been made as an activity of the Far Eastern Federal University.Our investigation based on a theoretical analysis and laboratory simulation tests.Typical results of the laboratory experiments are presented below.Under heating coal thermo-chemical magnetization is forming.Coal's magnetic parameters varieties from anti-ferromagnetiсto ferromagnetic.Anti-ferromagnetic pyrite and siderite presented into coal mass is transformed into magnetic hematite and magnetite under heating.Therefore,geomagnetic is expected to be a useful geophysical tool to for evaluation of combustion volume and its migration for underground coal gasification.

Calcium and Lead Levels in the Biological Samples and Their Effect on the Biochemical Parameters of Indoor and Outdoor Workers of Five Zonal Areas of Coal Mining Field

Workers of the Lakhra coal mining Sindh Pakistan were affected by a multi-factorial exposure of heavy metals. The prevalence of lead (Pb) exposures in work-related symptoms among workers of indoor and outdoor mining of Lakhra coal mining was evaluated in detail. The biological samples (scalp hair and blood) of 270 workers of Lakhra coal mining {official and control subjects} (indoor and outdoor) 18 to 55 years age group and 70 referent subjects of same age-groups were examined. The biological samples (blood and scalp hair) of workers of Lakhra coal mining and referent subjects were analyzed for calcium (Ca) and lead (Pb). Flame atomic absorption spectrometry was applied for the determination of the Ca in digested samples of studied subjects by the microwave oven whereas, the Pb contents were measured by electrothermal atomic absorption spectrometry. The validity of the methodology was checked by using the certified human hair material (BCR 397) and lyophilized human blood (Clincheck). The results indicated the higher contents of Pb in biological samples of indoor and outdoor mining workers than referents. However, the levels of Ca were found to be lower in indoor and outdoor mining workers than those of referents. It can be concluded that immediate action should be taken by recommended authorities to improve the ventilation and hygiene practices inside the industries, mines, and other workplaces.

bStudy on constitutive relationship of coal based on conventional triaxial compression test

Constitutive relationship of coal under triaxial compression must be determined during solving the theoretical calculation and numerical simulation about coal body failure. This paper carried out conventional triaxial compression test on No.3 coal of Baodian Colliery using MTS815.03 servo-controlled rock mechanical test system. The results indicate that the failure process of coal can be divided into 5 stages： densification stage, apparent linear elastic deformation stage, accelerated inelastic deformation stage, fracture and developing stage and plasticity flow stage. Combined with the test results, the constitutive relationship model of coal can be simplified as the four segments of straight line model of elastic-plastic hardening-plastic softening-residual perfectly plastic. Through fitting calculation of test data, the segmented constitutive equation of coal can be obtained.

Porosity Analysis Based on CT Images of Coal Under Uniaxial Loading

According to the character of CT image, surface porosity and voxel porosity are defined from pixel and voxel scale respectively. Digital Terrain Model (DTM) method is applied to calculate the surface porosity, and the method of voxel porosity is also presented based on Industrial CT grey image. With proposed methods, CT images of coal under differ-ent uniaxial loading are analyzed, and the relation curves between two kinds of porosity and stress separately are shown. All of these porosities reflect inner damage of coal. The surface porosity shows the pore with pixel scale, and voxel porosity denotes the pore inner pixel. The voxel porosity reflects the character of CT image better.

Floor dust erosion during early stages of coal dust explosion development

An ignition of methane and air can generate enough air flow to raise mixtures of combustible coal and rock dust.The expanding high temperature combustion products ignite the suspended dust mixture and will continue to propagate following the available combustible fuel supply.If the concentration of the dispersed rock dust is sufficient,the flame will stop propagating.Large-scale explosion tests were conducted within the National Institute for Occupational Safety and Health(NIOSH)Lake Lynn Experimental Mine(LLEM)to measure the dynamic pressure history and the post-explosion dust scour depth.The aim of this effort is to provide quantitative data on depth of dust removal during the early stages of explosion development and its relationship to the depth of floor dust collected for assessing the incombustible content most likely to participate in the combustion process.This experimental work on dust removal on is not only important for coal mine safety but also for industrial dust explosions.

Study on combustion kinetics of the blend melt with coal and waste plastic

The combustiondynamic experiments of blend-melt samples of blending pulverized coal and waste plastic are carried out in different proportions at different combustion temperatures.The experiment shows that all of correlation coefficients for fitting straight lines of curve F(a)-1/T of the blend-melt samples are above 0.95,which indicates that the combustion of samples conforms to the rules of first order reaction.The experiment also shows that the activation energy is the lowest and the combustion becomes easier with the mix proportion of 20%-25% at 200 ℃.

全自动煤炭采制样系统的设计研究

钢铁企业的入厂煤炭具有品种繁多、煤质差异大、检测项目多的特点,其质量检验重点关注如何在煤炭的采样、制样和化验环节避免样品污染和黏附。通过对破碎、缩分设备的优化,设计了一种全自动煤炭采制样系统。结果表明:该系统实现了在线粒度分析、全水分检测、一般分析试验煤样和存查煤样的封装标识,是目前钢铁企业煤炭采制样系统进料品种复杂、自动化程度较高的设计方案之一。

煤层瓦斯含量测定技术及装备研究进展

瓦斯含量是煤与瓦斯突出危险预测、煤层瓦斯资源量估算、矿井瓦斯治理工程设计的重要参数。围绕如何在大区域准确快速测定煤层瓦斯含量,依托国家科技重大专项、国家自然科学基金和煤炭企业联合基金等项目科技攻关,在取样、测试方面取得了一定进展。主要表现在如下4个方面:①煤层瓦斯含量测定取样经历了孔口接样、岩心管定点取样、压力引射定点取样和密闭取样4个阶段,密闭取样装备保压能力达到11.5 MPa,煤心直径达到38 mm;②针对不同煤层地质条件,发展形成了顺煤层定向长钻孔密闭取样、底板穿层钻孔密闭取样和顶(底)板梳状定向长钻孔密闭取样3种取样技术;③在河南焦作和山西晋城矿区硬煤层中,顺层定向长钻孔取样深度达到516 m,密闭取样法测得煤层瓦斯含量较常规取样法分别平均提高了0.44倍和1.04倍。在安徽淮南矿区碎软煤层中,穿层钻孔密闭取样深度达到209 m,测得煤层瓦斯含量较常规取样法平均提高了0.26倍;在安徽淮北矿区碎软煤层中,顶(底)板梳状钻孔密闭取样深度达到484 m,测得煤层瓦斯含量较常规取样法平均提高了0.19倍,密闭取样法在煤层瓦斯含量测定精度、探测范围上优于常规取样法;④在瓦斯含量测试方面,除了传统解吸法测试,发展了系列煤矿井下瓦斯含量快速测试装备,可实现最快30 min内测得煤层瓦斯含量,一般用于百米孔内的瓦斯含量测试。提出了煤层瓦斯含量测定密闭取样装备需向小型化、轻量化的方向发展,并能实现随钻密闭取样。在测试上,应根据实际情况确定合理的解吸终止限,并将测试装备和密闭取样装备进一步结合,以实现深孔瓦斯含量快速准确测定。密闭取样技术已成为煤层瓦斯含量大区域精准勘查、预测的主要手段,是煤炭安全高效开采的重要技术保障。

“双曲线”型煤样承载力学特性试验研究

煤炭地下气化结束后,两气化炉间形成类“双曲线”形煤柱,支撑覆岩,保障气化区域安全稳定。为研究类“双曲线”形煤柱承载力学特性,基于声发射监测系统和XTDIC三维全场应变测量系统,开展了不同侧向拱高(h=0,3,7,10,13,17 mm)的6组“双曲线”形煤样单轴压缩试验,分析了h对煤样峰值载荷、变形破坏及声发射特征的影响,揭示了其承载破坏机制。结果表明:①“双曲线”形煤样可分为矩形结构(主要承载体)和侧向拱结构,其承载破坏机制与其受力形式、侧向拱结构有关;随着h增大,煤样承载能力降低,与h=0煤样相比,峰值载荷分别降低了7.66%,13.56%,26.83%,35.28%,62.75%。②随着h增大,煤样整体受力形式由以受压为主向受压–受弯曲转变,中部区域产生应力集中而形成薄弱区,对应的水平位移场向中部迁移,最终汇集于中部边缘处;而垂直位移场由水平条带状向倾斜条带状转变,最终集中于煤样侧向拱结构上端。③在轴向载荷作用下,煤样侧向拱结构对其矩形结构中部区域产生等效作用力,加之煤样非均质性影响,加剧了薄弱区损伤程度,该作用随着h增大而增强,煤样承受载荷未超过其抗拉强度即产生剪切破坏,其破坏模式由拉–剪混合破坏向剪切破坏转变,均伴随着不同程度的剥落和局部弹射破坏。④煤样声发射累计计数–时间曲线演化可分为3种类型,当h为0和3 mm时,分为“上凸”式增长、相对快速增长、快速增长、“突变”式增长4个阶段,其演化特征与常规煤岩试样一致;当h为7 mm和10 mm时,分为相对快速增长、快速增长、“突变”式增长3个阶段;当h为13 mm和17 mm时,分为快速增长和“突变”式增长2个阶段;峰后阶段均呈“突变”式增长,而峰前阶段增长形式不一致是由煤样裂纹稳定扩展和中部区域持续损伤共同导致的。

松软破碎煤体取制样与剪切试验系统研制及应用

研究松软破碎煤体力学性质对巷道支护和煤与瓦斯突出预测等工作具有重要意义,但当前缺乏有效的松软破碎煤体取样、制样及力学特性分析装置。为此,研发了一套松软破碎煤体取制样与剪切试验系统,主要由取样装置、制样装置和力学特性参数测试系统组成,各部分具有以下主要功能与特点:①取样装置中的单动三管取芯器包含脑袋总成、外管总成及内管总成3部分,内外管间设置稳定环,保证内外管同心,内管总成腔体内部设置衬管用于储存煤心,取芯钻进时内管不随外管旋转;当钻取的煤心充满衬管后,退出取芯器,拆卸取出衬管,将煤心连同衬管一并取出并进行封装。取样装置灵活、轻便、易拆装携带。②制样装置包含脱模仪、切割机、冰箱、热风枪4部分,脱膜仪用于脱去煤心外层衬管,切割机、冰箱和热风枪用于对煤心进行切割、冷冻和热缩;制作标准煤心试件分为打孔润湿、冷冻切割和热缩脱模3个步骤,采用端头局部冷冻切割、脱模与热缩均匀同步等技术,实现多种标准尺寸试件制备,制样方法完善、成功率高。③力学特性参数测试系统包含主体结构、伺服油源控制装置和软件系统3部分,能实现限制性及非限制性直剪试验功能,主要用于开展松软破碎煤体标准试件不同法向应力下直剪试验、不同围压下三轴压缩试验。整体设计结构简单、操作方便。研究利用单动三管取芯器获取松软破碎煤体,利用脱模仪等制样装置将其制备成标准试件,进而在力学特性参数测试系统上分别开展松软破碎煤体标准试件在0.04、0.05、0.06、0.07、0.08、0.09 MPa法向应力下的直剪试验和0.2、0.3、0.4 MPa围压下的三轴压缩试验,并求得两种试验条件下松软破碎煤体的黏聚力和内摩擦角等抗剪强度参数,其中直剪试验求得的黏聚力和内摩擦角为0.125 kPa和37.2°,三轴压缩试验求得的黏聚力和内摩擦角为0.121 kPa和36.4°。结果表明,该套系统具有较好的实用性和可靠性,为研究松软破碎煤体力学特性提供了较好的试验平台和方法。

准东高铁煤中伴生矿物对水煤浆成浆性能影响

准东黑山矿区将军庙二矿的准东高铁煤储量丰富,是优质动力煤产区,以该煤样为原料煤,考察煤中主要伴生矿物对水煤浆性能影响。用煤炭浮沉分离方法获得不同矿物含量、种类和分布规律的不同密度等级煤样,并对煤样进行成浆性影响评价。经能谱仪(EDS)、X射线衍射仪(XRD)和X射线荧光仪(XRF)确定煤样中元素含量及矿物组成。最后利用SPSS软件计算不同矿物元素含量与成浆性能相关性。发现准东高铁煤密度主要集中于1.40~1.50 g/cm^(3),占整体的55.88%,而密度>1.50 g/cm^(3)煤样约占4.88%;黄铁矿、硫酸铁、高岭土和石英石含量随煤样密度增大而增加,密度>1.50 g/cm^(3)煤样中伴生矿物含量高,Al、Si、S和Fe元素含量均达到最大,其中Fe元素质量分数从<0.5%增至5.97%;水煤浆样品黏度和稳定性也随制备煤样密度增加而下降,使用密度<1.40 g/cm^(3)的ZD1煤样制备的水煤浆黏度960 mPa·s,析水率1.37%,而采用密度>1.50 g/cm^(3)煤样制备的浆体样品整体过于稀薄,成浆黏度降至320 mPa·s,析水率达9.09%;相关性分析显示,煤中伴生Na、Mg和Ca元素在各个密度等级煤样中分布相对均匀,与成浆性能无明显相关性,而Al、Si、S和Fe元素的含量与成浆黏度和稳定性分别呈现显著和极其显著的负相关,即黄铁矿、硫酸铁、高岭土和石英石质量分数越高,水煤浆黏度、稳定性下降趋势越显著。

不同含水状态下煤样蠕变实验研究

通过保持结构完整性浸水装置、X射线衍射仪及电液伺服加载煤岩体三轴蠕变渗流实验平台,实验得到上湾煤矿煤样的饱水曲线、不同含水状态下微观组分变化及蠕变特征。实验结果表明:煤样含水率与浸水时间呈负指数函数关系,含水率变化可分为加速增长、减速增长及稳定3个阶段;1次饱和过程中,随着含水率增加,煤样石英含量几乎保持不变,而高岭石等黏土矿物含量在这一过程中减少较多;干湿循环过程中,煤样石英含量衰减与循环次数成正比;随着含水率及干湿循环次数增加,煤样进入稳态蠕变及加速蠕变所需轴向荷载降低。

基于煤样残余瓦斯压力的煤层瓦斯压力推算方法研究与应用

煤矿瓦斯灾害防治亟需一种操作简单、测定准确、适用性强的煤层瓦斯压力确定方法。首先,从理论上对煤样残余瓦斯压力影响因素进行了分析;然后,实验研究了煤样残余瓦斯压力与煤样初始瓦斯压力的关联性,并提出了基于煤样残余瓦斯压力的煤层瓦斯压力推算方法;最后,进行了工程应用。研究结果显示:煤样残余瓦斯压力主要受控于煤层瓦斯压力、煤样粒度、瓦斯解吸时间和煤质特性,煤样残余瓦斯压力和煤样初始瓦斯压力呈线性关系,采用煤样残余瓦斯压力推算的煤层瓦斯压力相对可靠。

煤质检测的质量控制研究

煤质检测是评估煤炭性能的重要组成部分,在本次研究中,详细阐述了煤炭检测工作内容,包括样本制样、挥发分检测、全硫检测等,并针对煤质检测质量控制方案展开研究,包括制样环节质量控制、化验过程质量控制、精密度控制方案等。最后文章对煤质检测质量控制的支持保障策略展开研究,包括人员培训方案、实验设备选择要求等。

含水率影响下煤样拉伸与压缩力学特性试验

为揭示含水率对煤样拉伸与压缩力学特性的影响,选取韩家洼煤业公司22号煤层煤样,开展不同含水率和围压下煤样的巴西圆盘劈裂试验、单轴压缩试验以及三轴压缩试验,探究含水煤样的力学变化特征。结果表明:煤样的强度、弹性模量随含水率增加呈指数函数降低,煤样达到饱和状态时,其强度下降了48.3%,弹性模量下降了37.6%;随着含水率的增加,煤样的塑性增强,试样容易破碎;三轴压缩下,围压升高煤样破坏的峰值有所提升,煤样的强度提高,但不同围压状况下含水煤样的强度明显低于干燥试样;含水率对于煤样的内摩擦角影响较小,但对煤样的黏结力有显著影响。

动态加载下饱水煤样力学特性及能量耗散规律

为探究饱水煤样在动态加载下的力学特性和能量变化特征,采用直径50 mm的分离式霍普金森杆装置(SHPB)对饱水和自然状态2种煤样开展冲击加载试验,分析含水状态对煤样的动态强度、应变、损伤和能量传递效率的影响。结果表明:在应变率14.25~59.57 s^(-1)内,水体对煤样动态强度具有双重作用,表现为低应变率弱化和高应变率强化;相同冲击载荷下,自然、饱水煤的变形差异显著,最大应变相差38.46%;煤样含水状态显著影响能量传递效率,其中自然和饱水煤样的能耗密度均与入射能呈线性增长关系,且自然煤能量反射率大于饱水煤能量反射率,自然煤透射率小于饱水煤透射率,耗散率二者近似相等。

煤样制备13mm混合缩分机性能判定

混合、缩分是煤样制备过程中不可或缺的环节,混合缩分机的应用很大程度上降低了制样程序的繁琐操作及劳动强度。根据GB/T 19494.3-2004《煤炭机械化采样第3部分:精密度测定和偏倚试验》对13 mm混合缩分机进行灰分精密度判定以及灰分偏倚判定。统计分析所有试验数据,证明该13 mm混合缩分机的缩分精密度满足GB/T 474-2008《煤样的制备方法》中规定的相关要求,缩分不存在偏倚。