Analysis of pulverized tectonic coal gas expansion energy in underground mines and its influence on the environment

2019 ◽  
Vol 27 (2) ◽  
pp. 1508-1520 ◽  
Author(s):  
Zhenyang Wang ◽  
Yuanping Cheng ◽  
Liang Wang ◽  
Chenghao Wang ◽  
Yang Lei ◽  
...  
Keyword(s):  
Underground Mines ◽  
Coal Gas ◽  
Tectonic Coal ◽  
Expansion Energy ◽  
Gas Expansion

scholarly journals An explanation of large-scale coal and gas outbursts in underground coal mines: the effect of low-permeability zones on abnormally abundant gas

2014 ◽  
Vol 14 (8) ◽  
pp. 2125-2132 ◽  
Author(s):  
F. H. An ◽  
Y. P. Cheng
Keyword(s):  
High Pressure ◽  
Coal Seam ◽  
Large Scale ◽  
Underground Mines ◽  
Low Permeability ◽  
Gas Distribution ◽  
Coal Gas ◽  
Annular Zone ◽  
Wall Deformation ◽  
Coal And Gas Outbursts

Abstract. Large-scale coal and gas outbursts pose a risk of fatal disasters in underground mines. Large-scale outbursts (outburst of coal and rock greater than 500 t) in recent years in China indicate that there is abundant gas in areas of outbursts containing large amounts of potential energy. The adequate sealing properties of the roof and floor of a coal seam are required for local abundant gas around the site of an outburst, but an annular low-permeability zone in a coal seam, which prevents the loss by gas migration through the coal seam itself, is also required. The distribution of coal gas with this annular zone of low permeability is described, and it is proposed that the annular zone of low permeability creates conditions for confining the coal gas. The effect of this low-permeability zone on the gas distribution is analyzed after allowing for simplifications in the model. The results show that the permeability and length of the low-permeability zone have a great impact on the gas distribution, and the permeability is required to be several orders of magnitude less than that of normal coal and enough length is also in demand. A steep gradient of gas pressure in the low-permeability zone and the high-pressure gas in the abundant zone of gas can promote coal mass failure and coal wall deformation, thereby accelerating the coal and gas outburst. The high-pressure gas in abundant zone of gas will lead to a large-scale outburst if an outburst occurs.

scholarly journals Shear deformation of fold structures in coal measure strata and coal-gas outbursts: Constraint and mechanism

2017 ◽  
Vol 36 (2) ◽  
pp. 185-203 ◽  
Author(s):  
Tianrang Jia ◽  
Zhendong Feng ◽  
Guoying Wei ◽  
Yiwen Ju
Keyword(s):  
Mechanical Properties ◽  
Stress Concentration ◽  
Power Source ◽  
Coal Bed ◽  
Rock Layer ◽  
Distribution Law ◽  
Coal Gas ◽  
Material Basis ◽  
Fold Structure ◽  
Tectonic Coal

The coal measure strata formed in the late Paleozoic era underwent tectonic movements on several occasions, leading to the development of a range of fold structures in the strata as a result of highly interlayered gliding and shearing deformation. In addition, brittle ductile tectonic coals were widely distributed in the reservoir, constituting one of the primary causes of coal-gas outbursts in Chinese mines. This indicates a strong connection between shear deformation and such outbursts. In this study, structural geology, gas geology, and rock mechanics are all taken into consideration to investigate the controlling effects of the fold structure formation process on coal thickness and tectonic coal formation. Numerical simulation, based on the stress test data, was deployed to identify the stress distribution law adjacent to fold structures under the modern stress field. Additionally, the mechanical mechanism underpinning coal-gas outbursts near the fold structure was determined by making a comparison with the distribution law relating to such outbursts. The results demonstrate that the formation and evolution of the fold structure not only form the material basis of outbursts but also control their power source. During the fold formation process, interbed sliding and shearing between strong and weak rock strata were caused by differences in the mechanical properties of the coal bed and rock layer, resulting not only in a change to the local thickness of the coal seam but also in its deformation and structural alteration. Interbed shearing and local stress concentration, caused by the coal gangue, led to coal damage and the development of layered tectonic coal of consistent thickness, simultaneously improving its ability to adsorb gas and providing the material basis for coal-gas outbursts. This reduced the seam’s capacity to resist such events. The conditions for these outbursts are created by the sudden desorption of excess gas as a result of formation pressure release during coal mining and the widespread distribution of tectonic coal. Under the modern tectonic stress field, the stress distribution characteristic is controlled by the fold structure shape; and because of the aforementioned differences in the mechanical properties of the coal bed and rock layer, the interlayer deformation is asynchronous. This causes shear stress concentration within a specific range of the anticline’s two wings. This concentration zone happens to be exactly aligned with that of coal-gas outbursts, meaning that shear stress concentration is considered to be both the power source for and main cause of the region’s outbursts.

scholarly journals An explanation of large-scale coal and gas outbursts in underground coal mines: the effect of low-permeability zones on abnormally abundant gas

2013 ◽  
Vol 1 (5) ◽  
pp. 4751-4775 ◽  
Author(s):  
F. H. An ◽  
Y. P. Cheng
Keyword(s):  
Coal Seam ◽  
Large Scale ◽  
Gas Pressure ◽  
Underground Mines ◽  
Low Permeability ◽  
Gas Distribution ◽  
Coal Gas ◽  
Annular Zone ◽  
Wall Deformation ◽  
Coal And Gas Outbursts

Abstract. Large-scale coal and gas outbursts post a risk of fatal disasters in underground mines. Large-scale outbursts (outburst of coal and rock greater than 500 t) in recent years in China indicate that there is abundant gas in areas of outbursts containing large amounts of potential energy. The adequate sealing properties of the roof and floor of a coal seam are required for local abundant gas around the site of an outburst, but an annular low-permeability zone in a coal seam, which prevents the loss by gas migration through the coal seam itself, is also required. The distribution of coal gas with this annular zone of low permeability is described, and it is proposed that the annular zone of low permeability creates conditions for confining the coal gas. The effect of this low-permeability zone on the gas distribution is analyzed after allowing for simplifications in the model. The results show that the permeability and length of the low-permeability zone have a great impact on the gas distribution. A steep gradient of gas pressure in the low-permeability zone and the high gas pressure in the abundant zone of gas can promote coal mass failure and coal wall deformation, thereby accelerating the coal and gas outburst. The high pressure gas in abundant zone of gas will lead to a large-scale outburst if an outburst occurs.

scholarly journals Dynamic Characterization during Gas Initial Desorption of Coal Particles and Its Influence on the Initiation of Coal and Gas Outbursts

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1101
Author(s):  
Chaojie Wang ◽  
Xiaowei Li ◽  
Changhang Xu ◽  
Yujia Chen ◽  
Zexiang Tang ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Dynamic Effect ◽  
Coal Mass ◽  
Gas Pressure ◽  
Coal Surface ◽  
Dynamic Characterization ◽  
Coal Particles ◽  
Expansion Energy ◽  
Gas Expansion ◽  
Two Peaks

The law of gas initial desorption from coals is greatly important for understanding the occurrence mechanism and predicting coal and gas outburst (hereinafter referred to as ‘outburst’). However, dynamic characterization of gas initial desorption remains to be investigated. In this study, by monitoring the gas pressure and temperature of tectonically deformed (TD) coal and primary-undeformed (PU) coal, we established the evolution laws of gas key parameters during the initial desorption. The results indicate that the gas pressure drop rate, mass flow rate, initial desorption rate, and gas velocity increase with increasing gas pressure, with stronger gas dynamic effect, generating a high pressure gradient on the coal surface. Under the same gas pressure, the pressure gradient formed on the TD coal surface is greater than that formed on the surface of the PU coal, resulting in easily initiating an outburst in the TD coal. Moreover, the increased gas pressure increases temperature change rates (falling rate and rising rate) of coal mass. The minimum and final stable temperatures in the TD coal are generally lower compared to the PU coal. The releasing process of gas expansion energy can be divided into two stages exhibiting two peaks which increase as gas pressure increases. The two peak values for the TD coal both are about 2–3 times of those of the PU coal. In addition, the total gas expansion energy released by TD coal is far greater than that released by PU coal. The two peaks and the total values of gas expansion energy also prove that the damage of gas pressure to coal mass increases with the increased pressure, more likely producing pulverized coals and more prone to initiate an outburst.

scholarly journals Experimental Investigation on the Release Rule of the Gas Expansion Potential of Loaded Water-Filled Soft Coal

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Hengjie Qin ◽  
Jianping Wei ◽  
Donghao Li ◽  
Sen Li
Keyword(s):  
Water Content ◽  
Minimum Energy ◽  
Gas Pressure ◽  
Coal And Gas Outburst ◽  
Energy Evolution ◽  
Experimental Conditions ◽  
Gas Outburst ◽  
Minimum Energy Consumption ◽  
Expansion Energy ◽  
Gas Expansion

The aim of this study was to explore the evolution and release rule of internal energy storage in the process of coal and gas outburst and to further reveal the mechanism of coal and gas outburst from the perspective of energy. In this paper, the experiment of gas expansion energy release of coal samples under different adsorption pressures and with different moisture contents was carried out with the self-developed experimental device for release of gas-bearing coal expansion energy under load, and the energy of the whole outburst process was divided into three parts: the total expansion energy of gas, the energy consumed by destroying and throwing out coal body and the energy released inefficiently. On the basis of reasonable assumption, the energy evolution calculation model of each part was constructed with mathematical method. By analyzing the changes and distribution rules of three parts of energy under different experimental conditions, this paper explored the controlling effects of gas pressure, water content, and other variables on the energy evolution rules in the process of coal and gas outburst. Experimental and theoretical studies showed that in the gas-dominated coal and gas outburst process, the destruction of coal body was in the form of stratification; under each experimental condition, there existed a critical gas pressure value for the occurrence of coal and gas outburst, and there was a sudden change of energy evolution near this value; the existence of water made the critical pressure and the minimum energy consumption of coal and gas outburst increase obviously; under the experimental conditions, there was a linear relationship between the critical gas pressure and water content and a positive exponential relationship between the minimum energy consumption and water content.

scholarly journals Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Jie Cao ◽  
Qianting Hu ◽  
Yanan Gao ◽  
Minghui Li ◽  
Dongling Sun
Keyword(s):  
Diffusion Coefficient ◽  
Coal Seam ◽  
Volumetric Strain ◽  
Gas Pressure ◽  
Coal Seams ◽  
Distribution Law ◽  
Free Gas ◽  
Working Face ◽  
Expansion Energy ◽  
Gas Expansion

Due to the insufficient understanding of the outburst mechanism, the coal and gas outburst disasters in China are more serious. Gas expansion energy is the main source of energy that causes outburst. In order to explore the distribution law of gas expansion energy in outburst coal seams, a gas-solid coupling equation of outburst coal seams was established. The distribution law of coal stress field, deformation field, gas flow field, and gas expansion energy were simulated and analyzed by using COMSOL Multiphysics. The results showed that from the excavation face to the deep part of coal seam, the stress presented unloading zone, stress concentration zone, and original stress zone. The volumetric strain and permeability reached the minimum, while the gas pressure reached the maximum at the peak value of vertical stress. As time goes on, the gas pressure in the fracture near the working face gradually decreased and was less than the pressure in coal matrix. The total gas expansion energy consists of free gas and desorption gas expansion energy. Affected by the excavation, free gas expansion energy maintained a constant value in the original coal seam and gradually decreased in the area close to the working face. The expansion energy provided by desorption gas was zero in the original coal seam. And it first increased and then decreased rapidly near the working face. Compared with stress and coal seam thickness, gas pressure and initial diffusion coefficient had significant influence on gas expansion energy of coal seam. When the diffusion coefficient was greater than 1e-9 m2/s, the gas expansion energy of the coal seam near the working face was significantly higher than that of the original coal seam, which had the risk of inducing outburst.

Expansion energy of coal gas for the initiation of coal and gas outbursts

Fuel ◽  
2019 ◽  
Vol 235 ◽  
pp. 551-557 ◽  
Author(s):  
Fenghua An ◽  
Yu Yuan ◽  
Xiangjun Chen ◽  
Zhiqiang Li ◽  
Liyang Li
Keyword(s):  
Coal Gas ◽  
Expansion Energy ◽  
Coal And Gas Outbursts

scholarly journals Laboratory Study Phenomenon of Coal and Gas Outburst Based on a Mid-scale Simulation System

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Baisheng Nie ◽  
Yankun Ma ◽  
Shoutao Hu ◽  
Junqing Meng
Keyword(s):  
Internal Energy ◽  
Propagation Velocity ◽  
Strain Energy ◽  
Simulation System ◽  
Gas Pressure ◽  
Coal And Gas Outburst ◽  
Gas Outburst ◽  
Coal Particles ◽  
Expansion Energy ◽  
Gas Expansion

Abstract Outburst simulation experiments facilitate understanding coal and gas outburst in underground mining. With the help of the mid-scale simulation system, a model based on similitude principle, coal seam sandwiched by roof and floor, was constructed to conduct an outburst experiment. It had a three-dimensional size of 1500 mm × 600 mm × 1000 mm with 0.5 MPa gas pressure. The experimental procedures include specimen preparation, moulding, sealing, gas charging and adsorption, and completion. The outburst process was investigated by analyzing the gas pressure variation, temperature variation, outburst propagation velocity, particle size of outburst coal and energy transformation. During the experiment, each gas charging was accompanied with gas pressure or temperature fluctuation because of coal behavior of gas adsorption-desorption. The outburst propagation velocity was 17.2 m/s, obtained by a mass-weighted calculation of velocities of outburst coal. The small-size coal particles have a higher desorption rate and tend to participate in outburst process. According to energy conservation law, the energy forms of the outburst included elastic strain energy (Ee), gas expansion energy (Ep), internal energy of coal (ΔU), breakage work (W1), throwing out work (W2) and gas-flow loss energy (ΔE), and each was calculated respectively. Gas potential energy, including gas expansion energy and internal energy of coal, registered a larger percent and was far greater than the strain energy. And it can be the main factor influencing the occurrence of low-threshold outburst. The experimental system provides a feasible way to study the initiation and evolution of coal and gas outbursts.

scholarly journals Experimental Research on Coal and Gas Delay Outburst and AE Characteristics under Conditions of Geostress and Gas Pressure Disturbance

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Geng Jiabo ◽  
Liu Jiangtong ◽  
Li Xiaoshuang ◽  
Nie Wen ◽  
Zhang Dongming ◽  
...  
Keyword(s):  
Simulation System ◽  
Gas Pressure ◽  
Distinctive Features ◽  
Gas Accumulation ◽  
Low Intensity ◽  
Preparation Stage ◽  
Expansion Energy ◽  
Gas Expansion ◽  
Ae Signals ◽  
Dominant Parameter

Adopting yellow mud as barrier layer materials, coal and gas delay outburst experiments under conditions of geostress and gas accumulation disturbance were carried out by using self-developed simulation system, to find out roles of geostress and gas pressure played in the process of the delay outburst and ways to predict it, through analysis of variations of gas pressure, and AE characteristics during the process. The results show that after the geostress increased by 0.11 MPa from 1.80 MPa, an outburst occurs, while in gas accumulation situations, the gas pressure increase of 0.27 MPa from 0.67 MPa induces an outburst; hence, geostress is one of the dominant factors impacting an outburst occurrence. The lasting time of the outburst triggering under geostress disturbance is shorter than that under gas accumulation disturbance, while the duration of the outburst development under gas accumulation conditions is longer than that under geostress conditions. Coal seam breakage by geostress is the precondition for an outburst risk, and gas expansion energy is the dominant parameter influencing the duration of the outburst development. The AE signals show distinctive features in different stages of the outburst under geostress disturbance. At the preparation stage of the outburst, the AE signals increase sharply but have a low intensity and then drop to a lower balance level. At the triggering stage, the AE signals become active and increasing until up to the peak where the outburst occurs, and the intensity is highest.

Sign in / Sign up

Export Citation Format

Share Document