Relationship Between Micropore Structure of Different Coal Ranks and Methane Diffusion

Li, Yidong; Pan, Jienan; Cheng, Nannan; Wang, Zhenzhi; Zhang, Lei; Liu, Weiqing

doi:10.1007/s11053-022-10108-w

Cited by 10 publications

(8 citation statements)

References 36 publications

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“…20 Li et al investigated the diffusion characteristics of methane in coal micropore structures by extensive adsorption resolution experiments and fractal theory and concluded that the transport of methane in curved pores showed a significant decrease. 4 relationships between the adsorption density and the methane pressure and temperature. 21 It can be concluded that the adsorption energy parameter is often introduced in the MD study of coal micropores to investigate the gas adsorption state, while the energy change of the adsorbed molecules in the process from the free state to the adsorbed state is very complicated, and it is often more difficult to express the adsorption process after the introduction of potential energy provided by irregular surfaces (e.g., the surface of the coal pore).…”

Section: Introductionmentioning

confidence: 99%

“…In coal seams, 80–90% of the gas is adsorbed on the inner surface of the coal pore structure. − Coal is a complex porous material, in which the specific surface area and pore volume of the nanopores account for 97 and 68% of the total amounts, respectively. − Therefore, coal nanopores are the primary pores that adsorb gas. , However, owing to the limited measurement accuracy of research tools, research progress on coal nanopores is very slow. In recent years, benefiting from the progress in science and technology, molecular simulation methods such as molecular mechanics, molecular dynamics (MD), and density functional theory (DFT) have been widely used in microscopic model construction and dynamics calculations. − Accordingly, the nanopore structure of coal has received considerable attention. ,− Many researchers have studied the adsorption of methane and other gases onto coal nanopores using molecular simulation methods.…”

Section: Introductionmentioning

confidence: 99%

“…The results showed that methane molecules preferentially occupy strong surface sites with high adsorption potential energy and the adsorption process increased the surface free energy of the coal . Li et al investigated the diffusion characteristics of methane in coal micropore structures by extensive adsorption resolution experiments and fractal theory and concluded that the transport of methane in curved pores showed a significant decrease . Zhu et al used MD simulations to establish an equation of state for adsorbed methane and studied the relationships between the adsorption density and the methane pressure and temperature …”

Section: Introductionmentioning

confidence: 99%

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Modeling Methane Adsorption Distance Using Carbon Nanotubes and Bituminous Coal Pore Models

Zha,

Lin,

Liu

et al. 2024

Energy Fuels

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To simplify the analysis of the adsorption of methane by coal, single-walled carbon nanotubes (SWCNTs), slit graphene lamellae, and bituminous coal pore models were constructed, and the adsorption of methane molecules in the three models was studied using molecular dynamics and density functional theory. The results show that methane molecules cannot be adsorbed within carbon nanotubes with a pore size of 0.5 nm. In carbon nanotubes with a pore size of 1 nm, adsorbed methane is influenced by the inner wall of the SWCNTs to induce dipoles and to interact with nearby methane molecules. In large-pore-size carbon nanotubes and graphene sheets, methane molecules adsorb and accumulate on the wall surface to form adsorption rings, the thickness of which gradually increases with the pore size under the effect of curvature, ranging from 0.455 to 0.521 nm. This criterion for adsorption was applied to the pore model of bituminous coal, and 52 adsorbed methane states were determined. Furthermore, the Brunauer–Emmett–Teller equation was used to fit the methane isothermal adsorption curve of the bituminous coal pore model, and the adsorption quantity of methane in a single molecular layer was 54, confirming that the adsorption criterion of 0.521 nm is reasonable.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modeling Methane Adsorption Distance Using Carbon Nanotubes and Bituminous Coal Pore Models

Zha,

Lin,

Liu

et al. 2024

Energy Fuels

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“…Researchers − characterized the pore structure of coal by mercury injection, low-temperature nitrogen, and CO 2 adsorption, and so on. Combined with the gas isothermal desorption experiment, it is concluded that the diffusion coefficient of methane is closely related to the specific surface area and pore volume of coal pores. , In addition, gas diffusion in coal is also affected by other factors, such as pressure, temperature, and moisture content. − …”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Properties of Gas Diffusion in Various Rank Coals under Positive Pressure

et al. 2023

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A kind of closed mining and nonventilation working face is proposed, which provides a possibility for eliminating coal mine accidents and extracting high-purity gas. During mining, a confined space above normal pressure is formed in the face. Geological conditions cause significant differences in the physicochemical properties of coal and affect the occurrence and migration of gas in coal seams. The pore structures of five coal samples were obtained by mercury injection and low-temperature nitrogen adsorption. The self-made positive pressure desorption experimental device was used to conduct isothermal desorption experiments under different environmental pressures. An extended Langmuir model was proposed to carry out regression analysis on the curve of positive pressure desorption with time. The effect of coal pore structure on gas diffusion properties was discussed. The results indicate that the development degree of micropores in coal determines the amount of gas adsorption. With the increase of coal rank, both the ultimate desorption quantity and desorption rate first decrease and then increase. The positive pressure enhances the concentration of methane outside the coal and inhibits methane diffusion. With an increase of positive pressure, the desorption capacity of the high-rank ZG was significantly inhibited, and the desorption limit and initial desorption rate decreased by 15.80–44.54 and 16.92–47.93%, respectively. The diffusion coefficient of the middle-rank XS has the greatest decrease rate of 1.56–18.05%. The pore structure of coal is the essential reason that affects methane diffusion.

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“…According to previous studies, gas diffusion in the coal matrix was found to be influenced by several factors. Pore parameters, as important parameters to characterize coal reservoirs, can affect gas diffusion to different degrees, where an increase in parameters such as porosity, pore volume, and specific surface area can lead to an increase in the diffusion coefficient. − Diffusion can be classified as Knudsen diffusion, Fick diffusion, and transition diffusion according to the relationship between pore size and Knudsen number, and the type of diffusion gradually changes from Fick diffusion to transition diffusion as the pore size increases with pressure reduction. , In addition, metamorphism as an important indicator to characterize the degree of coal evolution has an obvious controlling effect on the diffusion coefficient, which generally shows an asymmetric U-shaped trend of decreasing and then increasing with the increase of metamorphism. , The particle size of the sample also affects the diffusion coefficient, which is found to increase and then decrease with increasing pressure for large samples of 1–3 mm, while the diffusion coefficient for small samples of 0.2–0.25 mm shows an opposite trend . Although pressure is also an important factor that influences the diffusion coefficient, there is no unified recognition until now; some scholars believe that the diffusion coefficient is positively correlated with pressure, while others believe that the diffusion coefficient is negatively correlated with pressure. ,, Gas property is also an essential factor affecting the diffusion coefficient, and the diffusion coefficients of different gases in coal seams vary greatly, and generally, the diffusion coefficients of CO 2 are 1–2 orders of magnitude higher than those of N 2 and CH 4 . , Although the role of different factors on the diffusion coefficient has been discussed in previous studies, the laws of diffusion transport in different scales and the mechanism of influence are less studied; therefore, this paper focuses on the variation law of diffusion coefficient in different scales for an intensive study.…”

Section: Introductionmentioning

confidence: 99%

Gas Diffusion Characteristics and Size Effect in Coal Particles with Different Degrees of Metamorphism

Zhai

Song

et al. 2023

Energy Fuels

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Coalbed methane (CBM) is a green unconventional energy source where the gas diffusion efficiency in coal directly limits the production capacity. Therefore, different gas adsorption experiments were used to determine the diffusion characteristics of coal samples with varying degrees of metamorphism. The influence law based on the gas type, pore structure, and coal sample size on the gas diffusion coefficient was analyzed, and the synergistic control effect of various factors on diffusion was discussed. The results show that when the particle size is the same, the diffusion coefficient of different gases shows the change rule of CO2 > N2 > CH4, and the diffusion coefficient of different samples is positively correlated with the degree of pore development. When the particle size is different, the diffusion coefficient is negatively correlated with the pore development degree and positively correlated with the sample particle size. The effective diffusion coefficient is consistent with the diffusion coefficient when the particle size of the sample is the same, and the effective diffusion coefficient is opposite to the diffusion coefficient when the particle size decreases. The analysis reveals that the diffusion coefficients of different gas are limited by the diameter of gas molecular dynamics, and the diffusion coefficient is reduced with the decrease in the diameter of the gas molecular dynamics. The change of diffusion coefficient caused by particle size change is positively correlated with the change of diffusion cross section caused by size effect. The difference between the effective diffusion coefficient and the diffusion coefficient mainly comes from whether the effective diffusion path is calculated. Therefore, when the particle size is constant, the effective diffusion coefficient can replace the diffusion coefficient to characterize the diffusion behavior. When the particle size is different, it is more appropriate to use the diffusion coefficient to characterize the gas diffusion behavior. The significance of the research findings in revealing gas transport in the coal matrix and coalbed methane formation is substantial.

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Relationship Between Micropore Structure of Different Coal Ranks and Methane Diffusion

Cited by 10 publications

References 36 publications

Modeling Methane Adsorption Distance Using Carbon Nanotubes and Bituminous Coal Pore Models

Modeling Methane Adsorption Distance Using Carbon Nanotubes and Bituminous Coal Pore Models

Experimental Study on the Properties of Gas Diffusion in Various Rank Coals under Positive Pressure

Gas Diffusion Characteristics and Size Effect in Coal Particles with Different Degrees of Metamorphism

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