Influence of matrix size and pore damage path on the size dependence of gas adsorption capacity of coal

et al. 2022

Energy Fuels

The fundamental understanding of the coal–gas interaction is important for improving coalbed methane (CBM) extraction efficiency. However, the sorption and strain kinetics of gas adsorption–desorption on coal still need to be further explored due to the unclear mechanism. In this paper, a series of isotherm sorption experiments monitoring sorption and strain versus time are performed. The results show that sorption and strain kinetics exhibit three-stage evolution behavior controlled by coal pore structure and interface sorption sites. Different gases, pressures, and sorption processes have significant effects on kinetic behavior. Moreover, the apparent strain obtained from a combination of sorption-induced deformation and gas-loading compression is anisotropic and asynchronous. For the apparent strain, the sorption-induced deformation is the main controlling factor, followed by gas-loading compression. The relationship between sorption and strain is approximately linear, but it is also affected by gas, pressure, and the sorption process. This fundamental exploration of the coal–gas interaction has implications for efficient CBM extraction.

Section: Resultsmentioning

confidence: 99%

Kinetic Behavior of Sorption and Strain during Coal–Gas Interaction

Min

et al. 2022

Energy Fuels

“…The saturation pressure ( P 0 ) of the nitrogen at 77 K was measured by the instrument using a P 0 cell. Nevertheless, due to the large size of the N 2 molecule, this method may not be suitable for pores with a width of less than 2 nm (Zhao et al 2021a). N 2 can form a welldefined monolayer on the surface of the adsorbent because of its eternal quadrupole moment (Vishal et al 2019).…”

Section: Lpga-n 2 /Co 2 Adsorption Experimentsmentioning

confidence: 99%

Experimental analysis of pore structure and fractal characteristics of soft and hard coals with same coalification

Ullah

Cheng

et al. 2022

Int J Coal Sci Technol

Self Cite

Accurate and quantitative investigation of the physical structure and fractal geometry of coal has important theoretical and practical significance for coal bed methane (CBM) development and the prevention of dynamic disasters such as coal and gas outbursts. This study investigates the pore structure and fractal 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 (0.20–0.25 mm). N2/CO2 adsorption tests were performed to evaluate the specific surface area (SSA), pore size distribution (PSD), and pore volume (PV) using Braunuer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and Density Functional Theory (DFT). The pore structure was characterized based on the theory of fractal dimensions. The results unveiled that the strength of coal has a significant influence on pore structure and fractal dimensions. There are significant differences in SSA and PV between both coals. The BJH-PV and BET-SSA obtained by N2-adsorption for soft coal are 0.029–0.032 cm3/g and 3.523–4.783 m2/g. While the values of PV and SSA obtained by CO2-adsorption are 0.037–0.039 cm3/g and 106.016–111.870 m2/g. Soft coal shows greater SSA and PV than hard coal, which is consistent with the adsorption capacity ($${V}_{\mathrm{L}}$$ V L ). The fractal dimensions of soft and hard coal are respectively different. The Ding coal exhibits larger D1 and smaller D2, and the reverse for the Wu coal seam is observed. 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 fractal dimensions of soft and hard coals is different, tending to different adsorption/desorption characteristics. In this regard, the results provide a reference for formulating corresponding coal and gas outburst prevention and control measures.

“…It is worth noting that the particle size ranges of corresponding to the inflection points are 0.25-1 mm. Combined with the concept of critical particle size proposed by Airey [44] and research and analysis of critical particle size by scholars, Zhao et al [37] measured the critical particle size ranges of coal samples which 13 Geofluids 14 Geofluids were 0.375-0.75 mm. Liu Y. and Liu M. [45] believed that the critical particle size was 0.75 mm.…”

Section: Relationship Between Pore Volumes and Fractalmentioning

confidence: 99%

“…Jiang [36] studied the fractal dimension characteristics of coal samples under different particle size conditions and found that the decrease of particle size leads to the sharp increase in the adsorption/desorption rate of coal samples. Zhao et al [37] analyzed the boundary point of fracture and matrix by fractal dimensions and proposed the size ranges of matrix.…”

Section: Introductionmentioning

confidence: 99%

Effect of Fragmentation on Pore Structures and Fractal Characteristics of Intact Coal and Deformed Coal Based on Experiments

et al. 2022

Geofluids

Coal mining has to develop to deeper strata with the increasing demand for coal, which leads to frequent coal and gas outburst disasters. Especially, when there is a deformed coal in the coal seam, the outburst disasters are easier and more intense. Coal and gas outburst disasters can be promoted by the fragmentation. In order to clearly explain the reasons for the impact of fragmentation on deformed coal and gas outburst, mercury intrusion porosimetry, low-temperature liquid N2 adsorption test, and scanning electron microscope were carried out in this paper. The differences in pore characteristics of intact coal and deformed coal under different particle size conditions were analyzed from pore shapes, pore size distributions, and fractal dimensions. The damage paths of fragmentation on various kinds of pores in intact coal are as follows: macropores, mesopores, minipores, and micropores, and those on various kinds of pores in deformed coal are as follows: macropores, micropores, mesopores, and minipores. According to the fractal dimension theory and experimental results, the calculative results of fractal dimensions show that the fragmentation and tectonism reduce the surface roughness and structural complexity of macropores and mesopores and increase those of minipores and micropores in deformed coal. Finally, combined with the coupling effect of fragmentation and tectonism on pores, the reason of deformed coal with high crushing degree in fields of outburst was explained. The research provides the basis for the prevention of coal and gas outburst.