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 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 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.

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.

scholarly journals The effects of magnetic field strength on the properties of wind generated from hot accretion flow

2018 ◽  
Vol 615 ◽  
pp. A35 ◽  
Author(s):  
De-Fu Bu ◽  
Amin Mosallanezhad
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Pressure Gradient ◽  
Magnetic Field Strength ◽  
Magnetic Pressure ◽  
Gas Pressure ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Black Hole Accretion ◽  
The Magnetic Field

Context. Observations indicate that wind can be generated in hot accretion flow. Wind generated from weakly magnetized accretion flow has been studied. However, the properties of wind generated from strongly magnetized hot accretion flow have not been studied. Aims. In this paper, we study the properties of wind generated from both weakly and strongly magnetized accretion flow. We focus on how the magnetic field strength affects the wind properties. Methods. We solve steady-state two-dimensional magnetohydrodynamic equations of black hole accretion in the presence of a largescale magnetic field. We assume self-similarity in radial direction. The magnetic field is assumed to be evenly symmetric with the equatorial plane. Results. We find that wind exists in both weakly and strongly magnetized accretion flows. When the magnetic field is weak (magnetic pressure is more than two orders of magnitude smaller than gas pressure), wind is driven by gas pressure gradient and centrifugal forces. When the magnetic field is strong (magnetic pressure is slightly smaller than gas pressure), wind is driven by gas pressure gradient and magnetic pressure gradient forces. The power of wind in the strongly magnetized case is just slightly larger than that in the weakly magnetized case. The power of wind lies in a range PW ~ 10−4–10−3 Ṁinc2, with Ṁin and c being mass inflow rate and speed of light, respectively. The possible role of wind in active galactic nuclei feedback is briefly discussed.

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 The Mass and Size Distribution of Planetesimals Formed by the Streaming Instability. II. The Effect of the Radial Gas Pressure Gradient

2019 ◽  
Vol 883 (2) ◽  
pp. 192 ◽  
Author(s):  
Charles P. Abod ◽  
Jacob B. Simon ◽  
Rixin Li ◽  
Philip J. Armitage ◽  
Andrew N. Youdin ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Size Distribution ◽  
Gas Pressure ◽  
Streaming Instability

On the role and the origin of the gas pressure gradient in the discharge of fine solids from hoppers

2003 ◽  
Vol 58 (23-24) ◽  
pp. 5269-5278 ◽  
Author(s):  
Diego Barletta ◽  
Giorgio Donsı̀ ◽  
Giovanna Ferrari ◽  
Massimo Poletto
Keyword(s):  
Pressure Gradient ◽  
Gas Pressure

scholarly journals A 200 pc Ring of Molecular Gas and an Outburst in the Galaxy M82

1987 ◽  
Vol 115 ◽  
pp. 614-620
Author(s):  
N. Nakai ◽  
M. Hayashi ◽  
T. Hasegawa ◽  
Y. Sofue ◽  
T. Handa ◽  
...  
Keyword(s):  
Star Formation ◽  
Central Region ◽  
Intensity Distribution ◽  
Energy Supply ◽  
Galactic Plane ◽  
Ring Structure ◽  
Molecular Gas ◽  
The Galaxy ◽  
Expansion Energy ◽  
Two Peaks

The CO (J=1-0) emission in M82 has been mapped with the Nobeyama 45-m telescope. The CO intensity distribution in the central region is resolved into two peaks. An axisymmetric model reveals a ring structure of molecular gas at a distance of 80-400 pc (centered near 200 pc) from the nucleus. This “200-pc ring” corresponds to just the region of a star formation burst. The molecular gas in M82 is also expanding out of the galactic plane with a velocity of 100-500 km s−1. The expansion energy of (0.1-1.4) x 1056 erg can be explained by the energy supply of supernovae in the central region.

scholarly journals Mechanical Behavior and Permeability Evolution of Coal under Different Mining-Induced Stress Conditions and Gas Pressures

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2677
Author(s):  
Zetian Zhang ◽  
Ru Zhang ◽  
Zhiguo Cao ◽  
Mingzhong Gao ◽  
Yong Zhang ◽  
...  
Keyword(s):  
Triaxial Compression ◽  
Volumetric Strain ◽  
Coal Mass ◽  
Gas Pressure ◽  
Stress Conditions ◽  
Permeability Evolution ◽  
Compression Tests ◽  
Induced Stress ◽  
Conventional Triaxial Compression ◽  
Gas Pressures

The gas permeability and mechanical properties of coal, which are seriously influenced by mining-induced stress evolution and gas pressure conditions, are key issues in coal mining and enhanced coalbed methane recovery. To obtain a comprehensive understanding of the effects of mining-induced stress conditions and gas pressures on the mechanical behavior and permeability evolution of coal, a series of mining-induced stress unloading experiments at different gas pressures were conducted. The test results are compared with the results of conventional triaxial compression tests also conducted at different gas pressures, and the different mechanisms between these two methods were theoretically analyzed. The test results show that under the same mining-induced stress conditions, the strength of the coal mass decreases with increasing gas pressure, while the absolute deformation of the coal mass increases. Under real mining-induced stress conditions, the volumetric strain of the coal mass remains negative, which means that the volume of the coal mass continues to increase. The volumetric strain corresponding to the peak stress of the coal mass increases with gas pressure in the same mining layout simulation. However, in conventional triaxial compression tests, the coal mass volume continues to decrease and in a compressional state, and there is no obvious deformation stage that occurs during the mining-induced stress unloading tests. The theoretical and experimental analyses show that mining-induced stress unloading and gas pressure changes greatly impact the deformation, failure mechanism and permeability enhancement of coal.

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