Relationship between wave speed variation and microstructure of coal under wet conditions

Wang, Gang; Li, Jinzhou; Liu, Zhiyuan; Qin, Xiangjie; Yan, Song

doi:10.1016/j.ijrmms.2019.104203

Cited by 22 publications

(5 citation statements)

References 32 publications

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“…Many software has been used to simulate the evolution of the flow field, such as ANSYSFLUENT, FEFLOW, and FLOTHERM. Among them, ANSYSFLUENT is one of the most commonly used in coal mining face worldwide as it has a good modelling foundation, advanced numerical methods, and powerful preprocessing functions with simulation results much closer to the actual situation on the site [28][29][30][31][32] . Therefore, it was selected to numerically simulate and analyze the spatial distribution and diffusion of outflow hydrogen sulphide gas with air ventilation under the disturbance of two operations: coal cutting with shearers and coal caving with supports with the west wing fully mechanized caving face of +575 level #45 coal seam of the Wudong Coal Mine as the simulation prototype.…”

Section: Numerical Simulation Of the Distribution Of Outflow Hydrogen Sulphide Due To Mining In Steeply Inclined And Extremely Thick Coalmentioning

confidence: 99%

Prevention and Control of Hydrogen Sulphide Accidents in Mining Extremely Thick Coal Seam: A Case Study in Wudong Coal Mine

Xuchao

Wang

et al. 2021

Geofluids

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Hydrogen sulphide is a toxic gas often present in coal seams and seriously threatens the lives and health of underground workers in coal mines. In this study, we theoretically modelled hydrogen sulphide generation in extremely thick underground coal mines with the +575 level #45 coal seam of Wudong Coal Mine as an example and obtained the on-site hydrogen sulphide emission pattern and spatial distribution features by combining field measurements and computational fluid dynamics simulation. The results showed that hydrogen sulphide mainly exists in the coal porous system in an adsorbed state. Because hydrogen sulphide has a molecular weight greater than the average molecular weight of air molecules, its concentration decreases with the increase of altitude to the bottom plate. When mining the upper stratified coal stratum, it diffuses widely in the working space; while when mining the lower coal stratum, it mainly concentrates at the bottom of the working face. Based on these analyses, on-site treatments were carried out using mixtures with different concentrations of sodium carbonate and sodium bicarbonate. In addition, different combinations of catalysts as well as type A and type B wetting agents were also tested. Eventually, a neutral KXL-I absorbent was developed, and the process of preinjecting absorbent and spraying absorbent was designed. The results showed that the newly developed KXL-I absorbent has high hydrogen sulphide absorption ability and is suitable for use as an absorbent in Wudong Coal Mine; preinjecting and spraying the absorbent can effectively prevent hydrogen sulphide disasters in the +575 level #45 coal seam in Wudong Coal Mine with the optimal final concentration of 0.9% and the absorption rate of 87% at the shearer of 66.6% at the support. Overall, our study provides valuable information for the prevention and control of hydrogen sulphide disasters in coal mines.

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Section: Numerical Simulation Of the Distribution Of Outflow Hydrogen Sulphide Due To Mining In Steeply Inclined And Extremely Thick Coalmentioning

confidence: 99%

Prevention and Control of Hydrogen Sulphide Accidents in Mining Extremely Thick Coal Seam: A Case Study in Wudong Coal Mine

Xuchao

Wang

et al. 2021

Geofluids

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“…By emphatically investigating the changes of heat and energy during methane adsorption/desorption with different coal ranks, Ye et al found that the adsorption capacity of the low- and medium-rank coals is more readily affected by temperature. Wang et al ,, not only conducted a critical research on the microscopic pore structure properties of coal and the gas flow characteristics in coal but also proposed the fluid–solid conjugate heat transfer model using ANSYS software and 3D reconstruction technology and successfully addressed the current challenges in identifying the seepage and deformation characteristics of coal at high temperatures. In reality, at a higher temperature, the thermal kinetics of methane gas molecules is more intense, and the gas kinetic viscosity is increased.…”

Section: Introductionmentioning

confidence: 99%

Modeling of Gas Desorption and Diffusion Kinetics in a Coal Seam Combined with a Free Gas Density Gradient Concept

Qin

Yang

et al. 2022

Energy Fuels

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Gas diffusion in a coal seam plays an essential role in the efficient and effective exploitation of underground coalbed methane (CBM). Based on the concept of free gas density gradient-driven flow, in this work, we formulated and validated a theoretical model to quantify gas desorption and diffusion kinetics in a coal seam at different temperatures. Once the governing equations are formulated and non-dimensionalized, they are numerically solved with the finite difference method and then validated with the experimental measurements on gas desorption at different temperatures. The mechanism of temperature affecting gas diffusion kinetics was elaborately explored. Also, the advantages of the proposed free gas density gradient model (FGDGM) compared to the traditional unipore diffusion model (UDM) were well evaluated and discussed. It is found that the FGDGM simulations are basically consistent with the experimental data, but the UDM prediction deviates significantly from the experimental measurements at different temperatures. By introducing a new dimensionless temperature variable and performing sensitivity analysis, the dimensionless gas desorption is found to increase with temperature, while the incremental gas desorption varies across the entire temperature range. With the temperature increasing from 293 to 313 K, both the gas desorption increment and gas yield enhancement are found to be the largest. In addition, there exists a linear relationship between diffusivity and temperature because a high temperature increases the gas molecules’ activity and accelerates the pore expansion. It is clearly found that temperature has a considerable contribution to the gas diffusion kinetics in a coal seam, and appropriately boosting the coal temperature to enhance CBM recovery is feasible and valuable.

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“…Hydraulic fracturing is an efficient technique for reservoir stimulation to enhance coalbed methane (CBM) recovery or improve water injection into coal seams. − In fractured coal seams, artificial fractures with different scales are produced to improve fluid migration. − In addition, during underground coal mining, a lot of fractures induced by mining are created ahead of the coal mining working face. , Regardless of the disruption by fracturing or mining, the coal seams contain multiscale pore–fractures, including primary pores, microfractures, and artificial fractures, which provide channels for fluid migration …”

Section: Introductionmentioning

confidence: 99%

Evaluation of Compressibility of Multiscale Pore–Fractures in Fractured Low-Rank Coals by Low-Field Nuclear Magnetic Resonance

et al. 2021

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Evaluation of stress sensitivity of multiscale pores in coal seams stimulated by hydraulic fracturing or that disturbed by underground mining is significant to coalbed methane recovery and gas disaster control. In this work, two types of low-rank coals are selected to investigate the stress sensitivity of pore−fractures with different scales by the low-field nuclear magnetic resonance (LF-NMR) method. The compressibility changes of multiscale pores in intact coal cores and coal cores with self-supported and proppant-supported fractures under different loading paths are analyzed. The results show that the volume of pores decreases with the increasing confining stress, except some specific cases caused by water migration across pores with different scales. In the loading−unloading process, an "unloading memory effect" is observed. After three cycles of loading−unloading, the pore volume cannot recover to the initial value. The pore compressibility is not a constant but decreases with the increasing confining stress. Besides, the pore compressibility is also scale-dependent, and the compressibility of fractures can be 10 times greater than that of the micropores. The existence of the artificial fracture can obviously increase the compressibility of the coal, while the introduction of the proppants can significantly reduce the fracture compressibility. During the loading−unloading process, there exists a 2−30% loss of the compressibility, even when the confining stress decreases to the initial value. The compressibility measured by LF-NMR has a value and variation trend similar to that measured by the permeability−stress method, indicating that LF-NMR is an effective method for the compressibility tests of coal.

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Relationship between wave speed variation and microstructure of coal under wet conditions

Cited by 22 publications

References 32 publications

Prevention and Control of Hydrogen Sulphide Accidents in Mining Extremely Thick Coal Seam: A Case Study in Wudong Coal Mine

Prevention and Control of Hydrogen Sulphide Accidents in Mining Extremely Thick Coal Seam: A Case Study in Wudong Coal Mine

Modeling of Gas Desorption and Diffusion Kinetics in a Coal Seam Combined with a Free Gas Density Gradient Concept

Evaluation of Compressibility of Multiscale Pore–Fractures in Fractured Low-Rank Coals by Low-Field Nuclear Magnetic Resonance

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