New insights into the CH4 adsorption capacity of coal based on microscopic pore properties

Hu, Biao; Cheng, Yuanping; He, Xuhua; Wang, Zhenyang; Jiang, Zhaonan; Li, Wei; Wang, Liang

doi:10.1016/j.fuel.2019.116675

Cited by 94 publications

(83 citation statements)

References 57 publications

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“…Through low-temperature N 2 adsorption (LTAN) and lowpressure CO 2 adsorption (LPCA) experiments, Hu et al (2020) and found that super micropore structures smaller than 2 nm accounted for the majority of the total pore specific surface, while methane adsorption capacity increased with the increase of micropore PV and micropore SSA, concluding that super micropore structures smaller than 2 nm were the dominant factor affecting methane adsorption capacity. The production of CBM mainly goes through the processes of drainage depressurization-desorption-diffusion-seepage (Lin et al, 2016;Gao et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

Ren

Weng

et al. 2022

Front. Earth Sci.

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Pore is the main adsorption and desorption space of coalbed methane (CBM). Pore size configuration and connectivity affect the adsorption/desorption hysteresis effect. Using tectonically deformed coal (TDC) and original structure coal of medium- and high-rank coal as the research objects, through the N2/CO2 adsorption experiment to analyze the pore size distribution and connectivity of different scales. We investigate the control mechanism of heterogeneous evolution in the key pore scales against adsorption/desorption hysteresis characteristics during coal metamorphism and deformation by combining the CH4 isothermal adsorption/desorption experiment under 30°C equilibrium moisture. The findings indicate that the super micropores (<2 nm) are mainly combination ink bottle-shaped pores and have worse connectivity as the degree of metamorphism and deformation increases. The super micropores occupy the vast majority of pore volume and specific surface area; its pore size distribution curve change presents an “M” bimodal type and is mainly concentrated in two pore segments of 0.45–0.70 nm and 0.70–0.90 nm. The effect of ductile deformation exerts a significantly greater effect on super micropores than brittle deformation. The exhibited adsorption–desorption characteristics are the result of the combined effect of the unique pore structure of the TDCs and different moisture contents. The presence of a large number of super micropores is the most important factor influencing the degree of gas desorption hysteresis. The “ink-bottle effect” is the primary cause of gas desorption hysteresis. For CBM development, some novel methods to increase desorption and diffusion rate at the super micropores scale should be considered.

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Section: Introductionmentioning

confidence: 99%

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

Ren

Weng

et al. 2022

Front. Earth Sci.

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“…According to the dynamic diameter of methane, methane molecules can only be adsorbed on the inner surface of micropores (0.38-0.76 nm) due to the limited pore space. For larger micropores, methane can not only be adsorbed on the inner surface of the micropores, but also can be filled into the pore volume [39]. Figure 9 shows that the correlations of the maximum adsorption capacity with the pore volume of 0.38-2 nm micropores and 0.38-0.76 nm micropores are both high.…”

Section: Effect Of Pore Volume On Methane Adsorptionmentioning

confidence: 98%

Effects of Pore Structure of Different Rank Coals on Methane Adsorption Heat

Wang

Zeng

et al. 2021

Processes

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Adsorption thermodynamic characteristics are an important part of the methane adsorption mechanism, and are useful for understanding the energy transmission mechanism of coalbed methane (CBM) migration in coal reservoirs. To study the effect of coal pore characteristics on methane adsorption heat, five different types of rank coals were used for low-pressure nitrogen, low-pressure carbon dioxide, and methane adsorption experiments. Pore structure and adsorption parameters, including maximum adsorption capacity and adsorption heat, were obtained for five coal samples, and their relationships were investigated. The results show that the low-pressure nitrogen adsorption method can measure pores within 1.7–300 nm, while the low-pressure carbon dioxide adsorption method can measure micropores within 0.38–1.14 nm. For the five coal samples, comprehensive pore structure parameters were obtained by combining the results of the low-pressure nitrogen and carbon dioxide adsorption experiments. The comprehensive results show that micropores contribute the most to the specific surface area of anthracite, lean coal, fat coal, and lignite, while mesopores contribute the most to the specific surface area of coking coal. Mesopores contribute the most to the pore volume of the five coal samples. The maximum adsorption capacity has a significant positive correlation with the specific surface area and pore volume of micropores less than 2 nm, indicating that methane is mainly adsorbed on the surface of micropores, and can also fill the micropores. The adsorption heat has a significant positive correlation with the specific surface area and pore volume of micropores within 0.38–0.76 nm, indicating that micropores in this range play a major role in determining the methane adsorption heat.

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“…The specific surface area of pore under 2 nm is much more than that of pore between 2 and 10 nm. Due to the most CH 4 adsorbed in pores under 2 nm in the form of micropore filling, 30 the development degree of micropore below 2 nm will determine the gas adsorption capacity of coal samples.…”

Section: The Pore Morphology Of the Coal Samplesmentioning

confidence: 99%

“…The gas adsorption/desorption process of natural moisture coal samples and dried coal samples at 30°C were recorded. Studies suggest that the methane‐coal sorption obey Langmuir's law, 30,31 and thus, the Langmuir equation can be used to calculate the amount of methane adsorbed by coal:

Q = \frac{italicabP}{1 + b P}

where P is the gas pressure, MPa; Q is the gas amount per mass of coal sample, m 3 /t; a is the Langmuir volume, which represents the maximum gas adsorption capacity of coal, m 3 /t; b represents the reciprocal of the Langmuir pressure, MPa −1 .…”

Section: The Coal Deformation Characteristics Induced By Methane Adsorption/desorptionmentioning

confidence: 99%

Effects of pore morphology and moisture on CBM‐related sorption‐induced coal deformation: An experimental investigation

Chu

Liu

Wang

et al. 2021

Energy Science & Engineering

Self Cite

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Coalbed methane (CBM) is an important resource of energy. For CBM recovery, sorption‐induced coal deformation can cause significant reservoir permeability change. Moisture content and coal pore morphology affect the gas adsorption capacity and can alter the coal deformation of the coal seam. Therefore, it is crucial to establish a coal gas moisture‐coupled model for CBM production prediction. However, there are currently insufficient data available for quantitative analyses. In this paper, a series of typical sorption‐induced strain experiments were carried out during methane adsorption and desorption on coal samples with different metamorphic degrees and moisture content. The pore morphology and adsorption capacity of coals were measured to analyze the reason for different deformation of coals with various pore structures and moisture. Results show that the adsorption capacity and deformation is corresponding to the specific surface area of micropore, which first decreases and then increases with coal ranks. The deformation and adsorption gas content of dried coals is greater than that of natural moisture coals, which means that moisture can reduce the sorption capacity of coals, resulting in the decrease of gas adsorption‐induced coal deformation. There is also residual deformation of coal samples after gas desorption caused by the residual adsorbed gas in coals. This paper quantitatively investigates the effects of pore characteristics and moisture on coal deformation and the internal mechanism. This work will provide essential information for building out a fully cross‐coupled model of coal gas‐moisture relationships for CBM production prediction.

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New insights into the CH4 adsorption capacity of coal based on microscopic pore properties

Cited by 94 publications

References 57 publications

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

The Influence Mechanism of Pore Structure of Tectonically Deformed Coal on the Adsorption and Desorption Hysteresis

Effects of Pore Structure of Different Rank Coals on Methane Adsorption Heat

Effects of pore morphology and moisture on CBM‐related sorption‐induced coal deformation: An experimental investigation

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