Study of the features of outburst caused by rock cross-cut coal uncovering and the law of gas dilatation energy release

To study the law of gas dilatation energy release of rock cross-cut coal uncovering face, according to the analysis of the physical parameters distribution features of coal and rock mass in front of crosscut face,the equations of elastic potential of coal and gas dilatation energy theory were set up to process a contrast calculation of the sizes of two kinds of energy. The results show that gas dilatation energy is the uppermost energy source causing outburst occurrence. Furthermore, the mathematical model of spherical flow field gas dilatation energy release was established and MATLAB software was applied to make a numerical calculation analysis on the law of gas dilatation energy release. The results indicate that the gas dilatation energy is closely related to gas parameters and its energy index does reflect the possibility of coal seam outburst.

Energy-limiting factor for coal and gas outburst occurrence in intact coal seam

This research reviewed the mechanics and gas desorption properties of intact coal,and tested the crushing work ratios of different intact coals,and then,studied the stress conditions for the failure or crushing of intact coal and the gas demand for the pulverization of intact coal particles.When a real-life outburst case is examined,the required minimum stress for intact coal outburst is estimated.The study concludes that the crushing work ratios of three intact coal samples vary from 294.3732 to 945.8048 J/m^(2).For the real-life case,more than 2300 MJ of transport work is needed,and 10062.09,7046.57 and 5895.47 m^(3) of gas is required when the gas pressure is 1,2 and 3 MPa,respectively.The crushing work exceeds the transport work and even reaches 13.96 times of the transport work.How to provide such an enormous crushing work is an energy-limiting factor for the outburst in intact coal.The strain energy is needed for the crushing work,and the required minimum stress is over 54.35 MPa,even reaching 300.44 MPa.These minimum stresses far exceed the in-situ vertical and horizontal stresses that can be provided at the 300–700 m mining depth range.

Comparing potentials for gas outburst in a Chinese anthracite and an Australian bituminous coal mine

Gas outbursts in underground mining occur under conditions of high gas desorption rate and gas content,combined with high stress regime, low coal strength and high Young's modulus. This combination of gas and stress factors occurs more often in deep mining. Hence, as the depth of mining increases, the potential for outburst increases. This study proposes a conceptual model to evaluate outburst potential in terms of an outburst indicator. The model was used to evaluate the potential for gas outburst in two mines, by comparing numerical simulations of gas flow behavior under typical stress regimes in an Australian gassy mine extracting a medium-volatile bituminous coal, and a Chinese gassy coal mine in Qinshui Basin(Shanxi province) extracting anthracite coal. We coupled the stress simulation program(FLAC3D) with the gas simulation program(SIMED II) to compute the stress and gas pressure and gas content distribution following development of a roadway into the targeted coal seams. The data from gas content and stress distribution were then used to quantify the intensity of energy release in the event of an outburst.

Experimental research into the effect of gas pressure,particle size and nozzle area on initial gas-release energy during gas desorption

Coal and gas outburst is a violent disaster driven by released energy from gas desorption.The initial expansion energy of released gas(IEERG)is a new method to predict coal and gas outburst.In this paper,an instrument for IEERG measurement was developed.Compared with previous setups,the new one which is equipped with three convergent nozzles and quick-release mechanism gets improved in data acquisition and gas sealing and releasing performance.To comprehensively know the effect of gas pressure,particle size,and nozzle area on IEERG,a series of experiments were carried out with this new setup.The variable control test results indicated that the gas pressure-IEERG curves remain the linear trend and the particle size-IEERG curves maintain the negative exponential trend for nozzle areas at 1.13,2.26,and3.39 mm2,respectively.The increase in nozzle area leads to deceases in value of IEERG and absolute value of slope of fitting curves in each test.In addition,the orthogonal experiment showed that the influence of gas pressure,nozzle area,and particle size on IEERG decreases in turn.Only gas pressure had a marked impact on IEERG.This work offers great importance in improving the accuracy of prediction of coal and gas outburst.

Micro shape of coal particle and crushing energy

A large amount of energy is consumed in a coal and gas outburst since a mass of coal is pulverized and ejected, accompanying a great quantity of gas emitted, resulting in a major mining hazard in underground coal mining around the world. Understanding how potential energy stored in gassy coal seams dissipates in the process of outbursting may possibly be a key to clarify the mechanisms responsible for coal and gas outburst. The present study was aimed to evaluate energy for crushing coal to various size fractions in coal and gas outbursts through theoretical and experimental investigation into the shape of fine coal particles and their equivalent diameter. Theoretical analysis indicates that the shape of a particle has a significant impact both on its equivalent diameter and hence on its outer surface area.Microscopic observations demonstrate the particle fraction with diameters less than 0.075 mm, produced from crushing coal samples, mostly takes on a spherical or ellipsoidal shape, and experimental data also show this part of particles consists of 30%–50% surface area newly generated from crushing operation,though these fine coal accounts for only less than ten percentages by weight. Further, analysis of experimental data indicates that the total surface area of this particle size fraction varies exponentially with input crushing energy, and the specific area energy is not a constant but probably in association with physical properties and textures of material.

Fractal characteristics of surface crack evolution in the process of gas-containing coal extrusion

In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camera and then the images were processed by sketch. Based on the above description, the paper studied the fractal dimension values from different positions of coal surface as well as their changing laws with time. The results show that there is a growing parabola trend of crack dimension value in the process of coal extrusion. Accordingly, we drew the conclusion that extruded coal crack evolution is a process of fractal dimension value increase. On the basis of fractal dimension values taken from different parts of coal masses, a fractal dimension of the contour map was drawn. Thus, it is clear that the contour map involves different crack fractal dimension values from different positions. To be specific, where there are complicated force and violent movement in coal mass, there are higher fractal dimension values, i.e., the further the middle of observation surface is from the exit of coal mass, and the lower the fractal dimension value is. In line with fractal geometry and energy theory of coal and gas outburst, this study presents the relation between fractal dimension and energy in the process of extruding. In conclusion, the evolution of crack fractal dimension value can signify that of energy, which has laid a solid foundation for the quantification research on the mechanism of gas-containing coal extrusion.

单位等量解吸焓对煤与瓦斯突出综合作用假说的补充

基于平顶山五矿中阶原生煤和构造煤的系列等温吸附实验数据计算温度-压力-吸附方程(TPAE)参数。通过TPAE方程计算结果证实,吸附是可以自发进行的放热反应,解吸是无法自发进行的吸热反应;热力学计算证明当吸附量增加,其单位等量解吸焓却按幂函数关系下降;原生煤单位等量解吸焓是构造煤单位等量解吸焓的2.2倍;煤靠吸收环境能量进行瓦斯解吸、降低温度、升高压力;而瓦斯压力升高和温度降低都有利于其余煤增加吸附以达到新的瓦斯气液平衡;煤吸附量持续增加带来的直接后果是其单位等量解吸焓的持续下降;环境能量输入与瓦斯内能蓄积转移显示互为诱因、互相强化,直至新一波的环境能量输入,诱发吸附瓦斯解吸达到足够高的压差梯度发生瓦斯突出;瓦斯突出是按准备、启动、发展和终止的先后次序发生;准备与启动的分段节点是有无工程活动,启动与发展的分段节点是圈闭瓦斯的煤壁是否被突破,发展与终止的分段节点是构造煤的吸附量是否接近于0。

孟津矿钻屑瓦斯解吸指标临界值研究

为了消除石门揭煤过程中煤与瓦斯突出危险性,孟津矿采用钻屑瓦斯解吸指标Δh2进行预测。通过煤与瓦斯突出能量方程及实验室测定的钻屑解吸强度和瓦斯压力的关系确定出孟津矿瓦斯突出压力临界值,进而推导出钻屑瓦斯解吸指标的临界值Δh2=200 Pa,结果表明:该临界值适合孟津矿,保证了煤矿安全生产。

基于能量方程的含瓦斯煤岩动力灾害分类

为了有效辨识深部含瓦斯煤岩动力灾害,基于能量方程,依据发生动力灾害的能量源将含瓦斯煤岩动力灾害分为三大类:瓦斯主导型、地应力主导型和冲击诱导型。又进一步将瓦斯主导型分为瓦斯突出型、冲击-突出型;地应力主导型分为压出型和冲击-压出型;冲击诱导型分为冲击诱导突出和冲击诱导压出型。对含瓦斯煤岩进行科学分类不仅有利于深入理解动力灾害发生、发展过程,而且对深部煤岩动力灾害的有效防治有指导性。

低瓦斯条件下煤与瓦斯突出过程的能量分析

瓦斯突出是世界上的重大灾害,是国内外煤矿安全开采的重大科学和技术难题。近年来,特重大瓦斯突出事故在低瓦斯矿井接连发生。为了探究发生低瓦斯突出的合理性和产生机理,构建了以煤层埋深,瓦斯压力以及煤体坚固性系数为变量的突出过程能量方程。通过计算,一方面验证了低瓦斯条件下突出现象的存在性和合理性,在突出源区低瓦斯条件下,异常地应力以及煤体坚固性系数起着主导作用;另一方面,对于极破碎的构造煤来说,一旦达到一定开采深度,就会发生低瓦斯突出现象,此时瓦斯压力0.74 MPa就不能作为判定是否发生突出的依据。

义安矿二_1煤层区域预测指标临界值研究

为了消除煤与瓦斯突出的危险性,依据《防治煤与瓦斯突出规定》选取煤层瓦斯含量和煤层瓦斯压力作为义安矿二1煤层区域预测指标。通过构建煤与瓦斯突出能量方程并结合实验室研究,确定了瓦斯压力和瓦斯含量的临界值,并对其临界值0.60MPa和8m3/t进行了验证。结果表明:该临界值适合义安矿,保证了煤矿安全生产。