scholarly journals Characteristics of gas pressure change during the freezing process of gas-containing coal

2022 ◽  
pp. 014459872110731
Author(s):  
Jun Liu ◽  
Yanzhao Wei ◽  
Wei Wang ◽  
Luwei Zhang ◽  
Jinqi Wu
Keyword(s):  
Coal Sample ◽  
Gas Adsorption ◽  
Gas Pressure ◽  
Shanxi Province ◽  
Freezing Process ◽  
Rapid Decline ◽  
Freezing Response ◽  
Response Characteristics ◽  
Soft Coal ◽  
Sample Tank

To investigate the characteristics of gas pressure changes during the freezing of gas-containing composite coal, an experimental device for determining the freezing response characteristics of gas-containing coal was independently designed. Coal samples with different firmness coefficients from the No. 3 coal seam in Yuxi Coal Mine in Jincheng, Shanxi Province, were selected to determine the different freezing response characteristics. The gas pressure evolved under different temperatures (-10 °C-15 °C-20 °C-25 °C-30 °C) and different adsorption equilibrium pressures (1.0 MPa, 1.5 MPa, 2.0 MPa). The research results reveal that, during the freezing process of the gas-containing coal sample, the gas pressure in the coal sample tank changed as a monotonously decreasing function and underwent three stages: rapid decline, decline, and slow decline. The relationship between the gas pressure of the coal sample tank and the freezing time is described by a power function. Low temperatures promoted gas adsorption. As the freezing temperature decreased, the decrease of gas pressure in the coal sample tank became faster. During the freezing process, the adsorption capacity of soft coal was larger, and the gas pressure of soft coal was lower.

Experimental Investigation of the Influence of the Adsorption Gas on the Permeability Characteristics of the Coal Containing Gas

2012 ◽  
Vol 616-618 ◽  
pp. 190-196
Author(s):  
Deng Ke Wang ◽  
Jian Ping Wei ◽  
Le Wei ◽  
Heng Jie Qin
Keyword(s):  
Coal Sample ◽  
Gas Adsorption ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Experimental System ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Permeability Characteristics ◽  
Gas Seepage ◽  
Loading Case

A large number of laboratory experiments on the gas seepage characteristics by the self-developed gas-bearing coal triaxial compression experimental system and conducts the comparative analysis of the similarities and differences of the permeability among CO2, CH4 and N2. The results show that given the condition of constant gas pressure, the permeability of the coal sample decreases with the increase of the confining pressure; under the constant confining pressure, the permeability of the coal sample decreases with the increase of the gas pressure; gases of different adsorbabilities have different permeabilities. The stronger the gas adsorption is, the worse its permeability will be; in the axial loading case, the permeabilities of different gases all reduce firstly and increase afterward, showing the generally V-shaped variation law. The results are of certain theoretical values on the in-depth understanding of the migration law of the gas in coal seams.

scholarly journals Experimental study on the influence of aerated gas pressure and confining pressure on low-rank coal gas adsorption process

2021 ◽  
pp. 014459872110310
Author(s):  
Ming Yang ◽  
Gaini Jia ◽  
Jianliang Gao ◽  
Jiajia Liu ◽  
Xuebo Zhang ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Coal Sample ◽  
Adsorption Process ◽  
Gas Adsorption ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Pressure Point ◽  
Adsorbed Gas ◽  
Confining Pressures ◽  
Total Adsorption

To deeply study the variation characteristics of the gas content in the process of gas adsorption for coal samples under different gas pressures and confining pressures, low-field nuclear magnetic resonance technology was used to carry out experimental research on the gas adsorption of coal. The relationship between the T2 spectrum amplitude integral and the gas quantity was analyzed. The results show the following: (1) When the samples were inflated for 11 h at each gas pressure point (0.31, 0.74, 1.11, and 1.46 MPa), after ∼5 h of adsorption, the amount of adsorbed gas exceeded 85.0% of the total adsorption capacity; additionally, as the adsorption time increased, the amount of adsorbed gas gradually tended to stabilize. When the gas pressure was >1 MPa, the amount of adsorbed gas exceeded 90.0% of the total adsorption capacity; Higher the pressure of aerated gas, greater the gas pressure gradient or concentration gradient on the surface of the coal sample and the greater the driving force for gas molecules to seep or diffuse into the coal sample. (2) When the samples were inflated for 11 h at each confining pressure point (3, 4, 5, and 7 MPa), the adsorbed gas increased by ∼85.0% of the total adsorbed gas in the first 5 h. When the pressure was <5 MPa, the amount of adsorbed gas exceeded 85.0% of the total amount of adsorption; that is, the increase in adsorbed gas was the largest at ∼5 h in the adsorption process for the columnar coal sample under different confining pressures, and the increase was ∼5.0% from 7–11 h. When the large pores in the coal sample closed, the amount of gas that seeped into the deep part of the coal sample within the same aeration time was reduced.

scholarly journals Effect of Gas on Burst Proneness and Energy Dissipation of Loaded Coal: An Experimental Study Using a Novel Gas-Solid Coupling Loading Apparatus

2021 ◽  
Vol 2021 ◽  
pp. 1-21
Author(s):  
Zuguang Wang ◽  
Huamin Li ◽  
Shen Wang ◽  
Baobin Gao ◽  
Wen Wang
Keyword(s):  
Elastic Modulus ◽  
Energy Dissipation ◽  
Rock Burst ◽  
Coal Sample ◽  
Gas Adsorption ◽  
Gas Pressure ◽  
Uniaxial Loading ◽  
Gas Outburst ◽  
Coal Rock ◽  
Dynamic Disaster

Deep coal mining is seriously affected by a combined dynamic disaster of rock burst and coal and gas outburst, but the influence mechanism of gas on this combined dynamic disaster is still not very clear, which is significantly different from the single type disasters. In this study, to explore the effect of gas on the coal-rock burst, a novel gas-solid coupling loading apparatus is designed to realize gas adsorption of coal sample with burst proneness and provide uniaxial loading environment under different gas pressure. A series of uniaxial compression tests of gas-containing coal with different gas pressure is carried out, and the energy dissipation process is monitored by an acoustic emission (AE) system. Results show that the macroscopic volume strain of the coal sample increases as gas adsorption and gas pressure increase under constant uniaxial loading pressure. Gas has the ability to expand the pores and natural fractures in coal sample by mechanical and physicochemical effects, which leads to a degradation in microstructure integrity of coal sample. With the increase of gas pressure, both the macrouniaxial compression strength (UCS) and elastic modulus show a downward trend; the UCS and elastic modulus of coal samples with 2 MPa gas pressure reduce by 58.78% and 48.82%, respectively, compared to those of the original coal samples. The main reason is that gas changes the pore-fissure structure and the mesoscopic stress environment inside the coal sample. Owing to the gas, the accumulated elastic energy of the gas-containing coal samples before failure reduces significantly, whereas the energy dissipated during loading increases, and the energy release process in the postpeak stage is smoother, indicating the participation of gas weakens the burst proneness of the coal sample. This study is of important scientific value for revealing the mechanism of combined dynamic disaster and the critical occurrence conditions of coal-rock burst and coal and gas outburst.

Research of Coal Pores and Integrity Evaluation Method Based on Fractal Theory

2014 ◽  
Vol 670-671 ◽  
pp. 258-262 ◽  
Author(s):  
Ji Li ◽  
Xin Wu
Keyword(s):  
Fractal Dimension ◽  
Coal Sample ◽  
Evaluation Method ◽  
Structural Integrity ◽  
Gas Adsorption ◽  
Fractal Theory ◽  
Physical And Mechanical Properties ◽  
Box Dimension ◽  
Sem Images ◽  
Sem Image

Coal is a natural porous media, its porosity and structural integrity influenced the gas adsorption and desorption characteristics greatly, as well as physical and mechanical properties of coal. Scanning electron microscopy (SEM) is applied to acquire SEM image of four kinds of coal samples at different zoom levels, and the box dimension can be worked out based on the pore preprocessing of SEM images. Then, the numerical value of box dimension is used to describe the development degree of the four kinds of coal sample and four development degrees’ sequence. At last, the intrinsic relevance between fractal dimension and other parameters is analyzed through mathematic method. The results show as follows: coal sample has self-similarity characteristic; the fractal dimension is related to both the total number of pores and porosity degree; the data of the coal pore, analyzed through fractal dimension, are consistent with that through traditional method; what’s more, fractal dimension has more advantages in describing accuracy and simplicity.

scholarly journals Permeability Enhancement Properties of High-Pressure Abrasive Water Jet Flushing and Its Application in a Soft Coal Seam

2021 ◽  
Vol 9 ◽  
Author(s):  
Xinzhe Zhang ◽  
Piotr Wiśniewski ◽  
Sławomir Dykas ◽  
Guojie Zhang
Keyword(s):  
High Pressure ◽  
Coal Seam ◽  
Water Jet ◽  
Gas Pressure ◽  
Theory And Practice ◽  
Abrasive Water Jet ◽  
Gas Drainage ◽  
Permeability Enhancement ◽  
Soft Coal ◽  
Soft Coal Seam

High-pressure abrasive water jet flushing (HPAWJF) is an effective method used to improve coal seam permeability. In this study, based on the theories of gas flow and coal deformation, a coupled gas-rock model is established to investigate realistic failure processes by introducing equations for the evolution of mesoscopic element damage along with coal mass deformation. Numerical simulation of the failure and pressure relief processes is carried out under different coal seam permeability and flushing length conditions. Distributions of the seepage and gas pressure fields of the realistic failure process are analyzed. The effects of flushing permeability enhancement in a soft coal seam on the gas drainage from boreholes are revealed by conducting a field experiment. Conclusions can be extracted that the gas pressure of the slotted soft coal seam is reduced and that the gas drainage volume is three times higher than that of a conventional borehole. Field tests demonstrate that the gas drainage effect of the soft coal seam is significantly improved and that tunneling speed is nearly doubled. The results obtained from this study can provide guidance to gas drainage in soft coal seams regarding the theory and practice application of the HPAWJF method.

scholarly journals Guiding Effect of Soft Tectonic Coal on Coal and Gas Outburst and its Experimental Study

2021 ◽  
Author(s):  
Qingyi Tu ◽  
Sheng Xue ◽  
Yuanping Cheng ◽  
Wei Zhang ◽  
Gaofeng Shi ◽  
...  
Keyword(s):  
Physical Simulation ◽  
Local Existence ◽  
Coal Pillar ◽  
Gas Pressure ◽  
Coal And Gas Outburst ◽  
Control Group ◽  
Long Distance ◽  
Gas Outburst ◽  
Soft Coal ◽  
Tectonic Coal

Abstract Soft tectonic coal commonly exists in coal and gas outburst zones. The physical simulation experiment was carried out to reproduce the influences of soft coal area on the outburst, and the guiding action mechanism of soft tectonic coal on the outburst was investigated. This study concludes that the amount of outburst coal in the experiments of group with local existence of soft coal area are relatively lower. The outburst coal amount (3.8035 kg) and relative outburst intensity (21.02%) in the GR5# experiment were both lower than that in the GN6# experiment of control group. However, the outburst coal in the experiments of group with local existence of soft coal area could be commonly migrated to a long distance, the maximum throwing distances in the three experiments were all over 16.73 m, reaching as high as 20.10 m. Under the gas pressure of 0.30 MPa in the group with local existence of soft coal area, the outburst coal amount (2.7355 kg) was smaller than the amount (2.803 kg) of pulverized coal filled, and the 2.0 cm coal pillar experiences failure only nearby the outburst mouth. As the gas pressure increases, the failure degree of the coal pillar becomes higher and higher until complete failure. The outburst development sequence is changed due to the existence of the soft tectonic soft area. Once the sealing conditions are destructed, the outburst firstly develops in the soft tectonic coal area. Nevertheless, sufficient energy is supplied to transport the coal mass in the soft tectonic coal area to a farther distance, while the residual outburst energy can just result in the outburst of a small quantity of coal masses in the normal area. This research will be of great scientific significance for explaining the soft tectonic coal-induced change of outburst starting and development sequence.

scholarly journals Experimental Analysis of Pore Structure and Fractal Characteristics of Soft and Hard Coals With Same Coalification

2021 ◽  
Author(s):  
Barkat Ullah ◽  
Yuanping Cheng ◽  
Liang Wang ◽  
Weihua Yang ◽  
Izhar Mithal Jiskani ◽  
...  
Keyword(s):  
Pore Structure ◽  
Adsorption Capacity ◽  
Gas Adsorption ◽  
Hysteresis Loops ◽  
Control Measures ◽  
Practical Significance ◽  
Coal Bed ◽  
Hard Coal ◽  
Pore Surface ◽  
Soft Coal

Abstract Accurate and quantitative investigation of the physical structure and fractal geometry of coal has important theoretical and practical significance for coal bed methane and the prevention of dynamic disasters such as coal and gas outbursts. This study investigates the pore structure and fractural characteristics of soft and hard coals using nitrogen and carbon dioxide (N2/CO2) adsorption. Coal samples from Pingdingshan Mine in Henan province of China were collected and pulverized to the required size (0.2-0.25mm). N2/CO2 adsorption tests were performed to evaluate the pore size distribution (PSD), specific surface area (SSA), and pore volume (PV). The pore structure was characterized based on fractural theory. The results unveiled that the strength of coal has a significant influence on pore structure and fracture dimensions. The obvious N2-adsorption isotherms of the coals were verified as Type IV (A) and Type II. The shape of the hysteresis loops indicates the presence of slit-shaped pores. There are significant differences in SSA and PV between both coals. The soft coal showed larger SSA and PV than hard coal that shows consistency with adsorption capacity. The fractal dimensions of soft coal are respectively larger than that of hard coal. The greater the value of D1 (complexity of pore surface) of soft coal is, the larger the pore surface roughness and gas adsorption capacity is. The results enable us to conclude that the characterization of pores and fractures of soft and hard coals is different, tending to different adsorption/desorption characteristics and outburst sensitivity. In this regard, results provide a reference for formulating corresponding coal and gas outburst prevention and control measures.

The mechanism of gas pressure and temperature dependent surface flashover in compressed gas involving gas adsorption

2021 ◽  
Vol 539 ◽  
pp. 148107
Author(s):  
Zhen Li ◽  
Shengtao Li ◽  
Haoming Xu ◽  
Guanghao Qu ◽  
Huan Niu ◽  
...  
Keyword(s):  
Gas Adsorption ◽  
Gas Pressure ◽  
Temperature Dependent ◽  
Surface Flashover ◽  
Compressed Gas

scholarly journals Study on the Effect of Soft and Hard Coal Pore Structure on Gas Adsorption Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xun Zhao ◽  
Tao Feng ◽  
Ping Wang ◽  
Ze Liao
Keyword(s):  
Pore Structure ◽  
Adsorption Capacity ◽  
Residence Time ◽  
Coalbed Methane ◽  
Gas Adsorption ◽  
Nitrogen Adsorption ◽  
Hard Coal ◽  
Research Results ◽  
Adsorption Characteristics ◽  
Soft Coal

In order to grasp the effect of soft and hard coal pore structure on gas adsorption characteristics, based on fractal geometry theory, low-temperature nitrogen adsorption and constant temperature adsorption test methods are used to test the pore structure characteristics of soft coal and its influence on gas adsorption characteristics. We used box dimension algorithm to measure the fractal dimension and distribution of coal sample microstructure. The research results show that the initial nitrogen adsorption capacity of soft coal is greater than that of hard coal, and the adsorption hysteresis loop of soft coal is more obvious than that of hard coal. And the adsorption curve rises faster in the high relative pressure section. The specific surface area and pore volume of soft coal are larger than those of hard coal. The number of pores is much larger than that of hard coal. In particular, the superposition of the adsorption force field in the micropores and the diffusion in the mesopores enhance the adsorption potential of soft coal. Introducing the concept of adsorption residence time, it is concluded that more adsorption sites on the surface of soft coal make the adsorption and residence time of gas on the surface of soft coal longer. Fractal characteristics of the soft coal surface are more obvious. The saturated adsorption capacity of soft coal and the rate of reaching saturation adsorption are both greater than those of hard coal. The research results of this manuscript will provide a theoretical basis for in-depth analysis of the adsorption/desorption mechanism of coalbed methane in soft coal seams and the formulation of practical coalbed methane control measures.

scholarly journals Study on Mechanical Failure and PermeabilityCharacteristicsof Porous Gas-Bearing Coal under Triaxial Stress

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Xue-bo Zhang ◽  
Wen-yuan Wang ◽  
Ming Yang ◽  
Hang-hang Cai ◽  
Jia-jia Liu ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Elastic Modulus ◽  
Coal Sample ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Peak Strength ◽  
Triaxial Stress ◽  
Peak Strain ◽  
Permeability Characteristics ◽  
Gas Bearing

To explore the mechanical failure and permeability characteristics of porous gas-bearing coal under triaxial stress, the triaxial compression experiment was carried out for porous and conventional gas-bearing coal samples based on the triaxial creep-seepage experiment system and sound emission signal acquisition system. Acoustic emission testing was carried out at the same time of loading failure. The experimental results showed that (1) under fixed gas pressure but changing confining pressure, the porous gas-bearing coal sample had higher peak strength and elastic modulus but lower peak strain; under changing gas pressure but fixed confining pressure, the porous gas-bearing coal sample had lower peak strength and peak strain but higher elastic modulus. When either confining pressure or gas pressure was changed, the mechanical properties of the two kinds of gas-bearing coal samples showed a good consistency, but the mechanical parameters differed greatly, with the peak strength, peak strain, and elastic modulus of porous coal samples are reduced by 1/4, 2/3, and 3/4, respectively. (2) When either the confining pressure or gas pressure was changed, the permeability of the porous gas-bearing coal sample was larger than that of the conventional gas-bearing coal sample. However, the change rules of permeability characteristics of the two were basically the same, except that there was a large difference in permeability value that the porous gas-bearing coal sample increases nearly twice as much as that of the conventional gas-bearing coal sample. (3) In the whole stress-strain process, the acoustic emission characteristics of the porous gas-bearing coal sample differed significantly from those of the conventional gas-bearing coal sample. The maximum ringdown count of the porous gas-bearing coal sample can be reduced by one-third at most, the maximum energy can be reduced by nearly half at most, and the maximum amplitude changes little with only 1–3 dB reduction. The research results have important guiding significance for the prediction of failure and instability of coal tunnel and the development of relevant protective techniques.

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