Methods to determine the mine gas explosibility – An overview

Mine gas explosions present a serious safety threat in the worldwide mining industry. Since the beginning of mining, many coal miners have been killed due to the explosions. Accordingly, on a regular basis, mine operators should get air samples from the underground atmosphere. At the same time, monitoring and tracking the explosibility of the air sample should be done as a timely matter to avoid any potential explosions. All these works can provide very important information to assist the mine operators to well understand the mine atmospheric status and its trends. In additional, when facing the coal spontaneous combustion, mine fire events, or other chemical reactions related mine accidents, determination of explosibility is a definitely significant work for the safety of miners and mine rescue personnel especially when planning and implementing any mine rescue strategies. For many years, mining engineers and researchers have developed a number of methods for assessing the explosibility of the air–gas-mixture. Their research results provide a baseline for judgments of the mine gas explosibility and in determining the extent of change. In this paper, main popular and typical methods used in mining industry to determine the mine gas explosibility are introduced and reviewed. Case demonstrations for each method are also shown and can be used to instruct readers to understand how to apply them. Finally, a brief discussion about the current methods is presented and some preliminary suggestions are also listed for the further improvements in the future research.     

“Vybuchovy trojuhelnik”: A software tool for evaluation of explosibility of coal mine atmosphere

Rescue operations during mine fires or methane explosions are highly dangerous for rescue workers. The knowledge of the composition of the coal mine atmosphere and the calculations of its explosibility may help to increase the safety of the rescuers. In the Czech Republic, a system called “Mine Gas Laboratory” (DPL) has been used for these purposes. The DPL allows measurement of the composition of the mine atmosphere and transmits the data necessary for evaluation to the surface. Up to now the explosibility evaluation of the coal mine atmosphere has depended either on the rescuers’ experience or on software code calculation. The code called “Vybuchovy trojuhelnik” (explosion triangle) is a graphical computing system intended for fast assessment of explosibility of fuel–air mixture. This article introduces the code and describes two simple methods of explosibility evaluation. The first method is “explosion triangle analysis”—a graphical method based on empirical graphs transformed into equations. The second method uses thermodynamic calculation based on chemical balance dynamics and Gibbs and Helmholtz energy. According to the requirements of the Czech Bureau of Mining (CBU) and Central Mine Rescue Service (HBZS), the code solves the problems of explosion triangle for both standard and non-standard coal mine atmosphere compositions. Unfortunately, the atmosphere composition must be introduced manually due to the unknown format of the data transmitted from the old DPL model. On 1 September 2005, a project started to develop a new system for on-line monitoring and atmosphere explosibility evaluation. The system should be able to measure CO₂, O₂, CH₄, H₂ and CO concentrations as well as the wind speed, temperature and humidity. The “Vybuchovy trojuhelnik” code will be used as a basis for explosibility evaluation, and an on-line connection with the new model of DPL will be established.     

多元可燃气体爆炸极限理论预测模型研究*

为准确掌握和预测多元可燃气体的爆炸极限,开展2种多元可燃气体爆炸极限的理论预测模型研究。第1种模型针对“多种可燃气体+多种惰性气体”在空气中或氧气中混合,基于求解可燃气体绝热火焰温度的总比热特性方法以及化学平衡反应中的贫燃料(富氧)反应,提出该多元可燃气体的爆炸下限预测模型;第2种模型针对“可燃气体+惰性气体+氧气”混合,基于热平衡方程及混合气体的各组分浓度、淬灭电势及燃烧潜热,提出该多元可燃气体的爆炸极限预测模型。结果表明:在预测多元可燃气体的爆炸极限时,第1种模型具有较广泛的应用性,且表现出较高的准确度;第2种模型具有使用简单的特点,且扩展了LCR（勒夏特列原理）的应用范围。     

多元可燃性混合气体临界氧浓度的测定

可燃性气体(蒸气)的临界氧浓度目前只限于对单元气体混合物的研究,且影响因素较少提及。通过实验测定了人工煤气、液化石油气的爆炸极限和临界氧浓度,对可燃性气体(蒸气)临界氧浓度的影响因素进行了研究,所测定的数据为煤气、液化石油气的安全防爆工作提供了依据。     

中国煤矿安全技术进展

本文综述了我国在防治矿井瓦斯,矿井火灾和煤矿粉尘三个方面的技术概况。反映了为适应煤炭生产技术的发展,我国在这三方面的技术进展及所取得的效果。矿井瓦斯防治技术方面,主要介绍了矿井瓦斯涌出量的确定,瓦斯抽放工艺及装备,煤与瓦斯突出预测预报和综合防止煤与瓦斯突出技术的情况及成果。矿井火灾防治技术方面,着重介绍了矿井火灾预测预报技术,尤其是煤炭自燃发火早期预测预报技术以及煤矿自然发火防治技术中在灌浆代用材料,惰气防灭火等方面的发展及现状。煤矿粉尘防治技术方面,扼要介绍控制粉尘危险的基本途径,以防尘为中心包括降尘、除尘和防止煤尘爆炸及爆炸传播技术的一整套治理煤矿粉尘的工艺及装备,简要介绍了瓦斯煤尘爆炸的实验能力。通过本文的介绍,可以对我国在防治煤矿安全生产中主要自然灾害的技术对策和取得的成果有一个较全面的了解。     

Effect of self-inhibition at a flame propagation in rich gaseous mixtures of combustible–air–diluent

An analysis of published experimental data characterizing the influence of diluents of various chemical nature (both halogenated and chemically inert) on upper flammability limits of flammable gases in air (methane and hydrogen have been considered as examples) has been done. Dependences of critical oxygen concentration and critical fuel equivalence ratio _cr for mixtures combustible–air–diluent at upper flammability limits on diluent concentration were determined. The obtained data were interpreted on the basis of the concept of self-inhibition at combustion of rich mixtures of organic combustibles in air. A method for evaluation of relative effectiveness of various inhibitors and for determination of availability of self-inhibitive properties of a combustible gas has been proposed.     

基于分段拟合的煤自燃指标气体优选研究*

为更加精确地得出煤自燃的临界温度并找出煤自燃各个阶段最优的指标气体,以此提高煤层自燃预测预报的准确性,选取西北某矿2号煤和3号煤典型煤样开展程序升温-气相色谱实验,采用分段直线拟合的方法,得出煤自燃过程中的耗氧速率突变点温度和氧化产物生成量激增点温度,在此基础上采用灰色关联度分析法对煤干裂温度之后的指标气体进行优选。结果表明:2号煤和3号煤的自燃临界温度分别为73.0 ℃和72.1 ℃,干裂温度分别为112.6 ℃和109.8 ℃;CO适用于2种煤样全温度下的预测预报;φ(C2H4)/φ(C2H6)和C2H4是2号煤干裂温度之后较优的预测预报指标气体;φ(C2H4)/φ(C2H6),C2H4和C2H6是3号煤干裂温度之后较优的预测预报指标气体。     

基于熵值法和支持向量机的煤矿应急救援能力评价模型

为增强煤矿应急救援能力,提高评价的精度,弥补单一评价方法的缺陷,构建了基于熵值法和支持向量机的煤矿应急救援能力评价模型。根据各评价指标数据所提供的信息量,运用熵值法设定指标权重,进一步将指标权重定量化、客观化;同时鉴于煤矿应急救援能力评价数据难收集、影响因素复杂多变的状况,结合具有处理非线性、小样本数据问题的支持向量机进行评价,保证了评价结果的准确性。实证分析表明,该模型的评价结果与煤矿实际应急救援能力非常接近,可用于实际的煤矿应急救援能力评价。     

Gas explosions caused by gasification of condensed phase combustibles

For reasonable explanation about recent accidental gas explosions caused by condensed phase combustibles occurred in Japan, the processes of such gas explosions have been investigated. When the combustible is of condensed phase at its initial state, gasification is necessary to form a flammable mixture causing a gas explosion. The process of gasification characterizes such a gas explosion. When the combustible is RDF (refuse derived fuel), the temperature was inferred to spontaneously increase. Also, the flammable gas should be generated within a confined high temperature region in the pile and come through a low temperature layer without combustion. The growth of a flammable layer after gasoline is spread over floor is analytically evaluated. The flame propagation through the flammable layer established over the floor enhances the pressure enough to break the structure of the office. Long-term heating is inferred to cause ignition of dried garbage, and the mechanism of flammable gas generation would be similar to that in the case of the RDF explosion. For prevention of losses at accidental explosions caused by gasification of condensed phase combustibles, understanding of the phenomena is the most important.     

混合气体爆炸性MFC图形分析

判断混合气体爆炸性常用 3种方法 ,即科瓦德爆炸三角形法、美国矿业局采用的爆炸三角形计算法和最小助燃氧浓度法 ,然而如何准确、快速、形象地得到分析结果在防灾救灾中是十分关键的。笔者的重点是提供一个图形分析方法解决上述问题。VC ++是方法的基本理论依据 ,用一个实例来验证方法的有效性。总之 ,研究表明 :图形分析法可提高安全管理效率。     

Flammability of methane,propane, and hydrogen gases

This paper reports the results of flammability studies for methane, propane, hydrogen, and deuterium gases in air conducted by the Pittsburgh Research Laboratory. Knowledge of the explosion hazards of these gases is important to the coal mining industry and to other industries that produce or use flammable gases. The experimental research was conducted in 20 L and 120 L closed explosion chambers under both quiescent and turbulent conditions, using both electric spark and pyrotechnic ignition sources. The data reported here generally confirm the data of previous investigators, but they are more comprehensive than those reported previously. The results illustrate the complications associated with buoyancy, turbulence, selective diffusion, and ignitor strength versus chamber size. Although the lower flammable limits (LFLs) are well defined for methane (CH₄) and propane (C₃H₈), the LFLs for hydrogen (H₂) and its heavier isotope deuterium (D₂) are much more dependent on the limit criterion chosen. A similar behavior is observed for the upper flammable limit of propane. The data presented include lower and upper flammable limits, maximum pressures, and maximum rates of pressure rise. The rates of pressure rise, even when normalized by the cube root of the chamber volume (V^1/3), are shown to be sensitive to chamber size.     

Process of accidental explosions at a refuse derived fuel storage

Accidental gas explosions occurred at a refuse-derived-fuel (RDF) storage in Japan, and two fire fighters on duty were dead. The flammable gases, which caused the gas explosions generated during a RDF fire. It means that gas explosions could occur in the use of solid fuels under certain conditions. This study has been conducted for exploring the process to gas explosions in the RDF storage. The temperature at a part of the RDF pile in the storage was inferred to spontaneously increase, and the prediction of the temperature increase was attempted on the basis of the Frank-Kamenetskii theory. It was shown that the critical temperature of RDF for spontaneous temperature rise depends on the size of the pile. Larger the pile, lower the critical temperature. The possibility of accumulation of flammable gas in the space of the RDF storage is discussed. It is indicated that the spread rate of thermal wave is slow and a high temperature region likely established. After the RDF pile ignites, the oxygen concentration near the burning site becomes low and the flammable species components in the generated gas increases. Those species pass through surrounding low temperature region and come out into the space over the RDF pile without combustion. An explosion would occur when a fresh air comes into the storage, mixes with the flammable gas coming out from the pile to form a flammable mixture, and then the flammable mixture ignites. The most effective means to prevent accidental explosions is to avoid spontaneous ignition by cooling the heated RDF. If spontaneous ignition occurs, elimination of flammable gases from the storage should be strongly recommended.     

受限空间煤尘爆炸毒害气体传播伤害研究

为减少煤矿煤尘爆炸后毒气对人的危害,为煤矿防爆、抑爆和安全评价,以及事故应急救援等提供理论依据,研究了煤尘爆炸后毒气的传播伤害规律。基于质量守恒定律与空气动力学理论,建立煤尘爆炸后风流作用下的毒害气体在受限空间内的数学传播模型,得到巷道内毒气传播的弥散系数,计算出沿爆炸传播方向毒气浓度随距离变化的关系,划分伤害三区并推导出相应的伤害范围计算公式。研究表明:毒气传播的峰值点随风流方向移动,其峰值点浓度逐渐变小。     

混合气体爆炸性现场测试实验研究

为测定现场可燃混合气体的爆炸性,对比分析了国内外实验室爆炸极限的测定装置及爆炸性判定方法,设计研制了混合气体爆炸性现场测试装置。装置实现了爆炸性环境现场的自动采样、超高温点火、高速压力和温度测定及爆炸性自行判定。开展了丙烷、乙烯和液化石油气等典型可燃气体爆炸性实验,提出了基于压力和火焰温度变化相结合的气体爆炸性判定指标,改变了传统目测判定方式。研究结果表明:20 L球和1 L爆炸腔以爆炸压力提升来判定,比管式法测定的爆炸极限范围窄,以压力提升量5%~10%判定较适宜;1 L爆炸腔以爆炸过程温度提升量来判定,爆炸极限范围比以爆炸压力提升量判定宽,与目测观察的管式测定法相比,略宽于管式测定法和大部分文献数据。     

基于非分散红外技术的煤矿井下有害气体定量探测方法研究

煤矿井下有害气体的浓度监测对煤矿生产安全预警至关重要。介绍了一种基于非分散红外光谱技术能够同时定量探测煤矿井下一氧化碳、甲烷等有害气体的方法。入射红外光经过高速旋转的滤光轮,得到各种待测气体相应滤波通道的调制光信号,经怀特池中待测气体吸收后得到各种气体的吸光度。通过非线性最小二乘拟合吸收光与被测气体浓度,得到测量系统的浓度定标曲线,一氧化碳、甲烷和二氧化碳三者定标拟合相关系数分别为0.9992、0.9996和0.9998。分析了系统的测量精度,通过比较样气标准浓度与实测浓度大小,发现所有被测气体的这两组数据的相关性均大于0.998,测量误差均小于5%。实验结果表明,采用非分散红外光谱技术可以实现煤矿井下多组分有害气体的同步精确探测,为扩展煤矿安全预警技术手段提供了参考。     

FA型高炉煤气管道火焰捕器研制

研制满足高炉煤气管道阻火的火焰捕器.内径88 mm、199 mm和305 mm组合爆炸管道模拟实验结果表明,FA型火焰捕器的阻火性能良好,满足高炉煤气管道阻火的技术要求,各项技术性能指标达到了设计要求.     

市政污水检查井可燃气体组分及分布影响因素研究

为研究市政污水管网内主要可燃气体成分与分布,以实现其燃爆灾害的精准防控,本文采用现场检测的方法采集污水检查井内甲烷、氢气等5种可燃气体以及总的可燃气体浓度,统计分析污水管网各可燃气体的浓度范围,研究检查井深度和季节对甲烷浓度分布的影响。研究结果表明:污水检查井内甲烷浓度占比较大,一氧化碳、硫化氢、氢气和氨气所占比例较小;沿检查井深度方向,甲烷分布规律不尽相同,大部分检查井内甲烷随着与井口距离的增大呈逐渐增大变化趋势;季节对甲烷浓度变化影响较大,夏秋两季甲烷浓度较高,春季次之,冬季未检出甲烷。     

密闭液封堵条件下的瓦斯解吸规律实验研究

瓦斯严重威胁着煤矿的安全生产,煤层瓦斯解吸规律与矿井瓦斯灾害关系非常密切。本文首先提出了密闭液封堵条件下的瓦斯解吸实验原理,制定了相应的实验方案;然后,开展了密闭液封堵条件下的煤芯瓦斯解吸规律实验;最后,进行了密闭液封堵煤芯瓦斯的现场取芯试验。研究结果显示,与自由状态下解吸相比,密闭条件下的瓦斯解吸量呈现不同程度的降低,效果显著;在取芯过程中,密闭液能够包裹煤芯,该测定技术所获得的煤芯瓦斯解吸量与残存量之和,比普通煤芯取样法平均提高了9%。因此,利用该技术所测得的煤层瓦斯含量,其可靠性与准确率更高。     

煤体初始瓦斯涌出规律预测煤巷突出危险性研究*

为提高煤巷突出危险性预测的准确性,基于摩尔库伦准则,建立煤巷突出平衡方程,探究煤巷突出发生条件;通过COMSOL Multiphysics模拟软件探究钻孔瓦斯涌出量和瓦斯压力的关系;利用ZTL20/1000-Z型矿用隔爆型连续流量法煤层巷道突出预测装置,以薛湖煤矿二煤层为试验对象,进行煤巷突出危险性预测试验研究。结果表明:钻孔瓦斯涌出量与瓦斯压力呈线性关系,钻孔初始瓦斯流量可以作为预测煤巷突出危险性的敏感指标;最大流量峰面积、钻屑量和钻孔瓦斯涌出初速度变化趋势基本相同,且最大流量峰面积取值范围较广;最大流量峰面积突出临界值取值为59.30 (L·m2)/min。     

改进BP算法在煤与瓦斯突出预测中的应用

为了正确预测煤与瓦斯突出的趋势与危险性 ,基于反向BP神经网络 ,笔者提出了一种改进的BP网络模型 :为了加快BP网络的收敛速度 ,增强其跳出局部极小点的能力 ,采用了自适应变步长法和改进模拟退火法 (SA法 )相结合的方法。实际应用表明 ,该模型收敛速度快 ,准确性高 ,具有较高的可靠性和实用性 ,是一种十分有效的煤与瓦斯突出危险性预测方法。