Gas Adsorption Capacity of Coal Frozen with Liquid Nitrogen and Variations in the Proportions of the Organic Functional Groups on the Coal after Freezing

Qin, Lei; Wang, Ping; Li, Shugang; Lin, Haiqing; Zhao, Pengxiang; Ma, Chao; Yang, Erhao

doi:10.1021/acs.energyfuels.0c04035

Cited by 34 publications

(17 citation statements)

References 38 publications

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“…After 3 h of ultrasonic treatment, several long fractures along the bedding plane were generated, the secondary branch fractures perpendicular to the bedding plane were also developed, and an interwoven fracture network was gradually formed on the end face. The interwoven and penetrating pore-fracture network will contribute to gas diffusion and seepage …”

Section: Resultsmentioning

confidence: 99%

Changes of Coal Molecular and Pore Structure under Ultrasonic Stimulation

Sun

et al. 2021

Energy Fuels

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In view of the limitation of the conventional coal seam fracturing method, an ultrasonic stimulation method was proposed. Utilizing the combined effects of ultrasonic cavitation, mechanical vibration, and thermal conditions, the coal will form a network of intertwined cracks, and the gas will desorb and flow more easily. Current research on the changes of coal molecular and pore structure under ultrasonic stimulation is not in-depth. In this paper, the coal samples were treated by ultrasonic stimulation at 30 kHz frequency, and the changes of temperature, molecular structure, and pore structure of different scales were captured by combining a temperature acquisition unit, an infrared spectrometer, a stereoscopic microscope, a low-field nuclear magnetic resonance apparatus, and a three-dimensional X-ray microscope. The main conclusions are as follows: The temperature rise of coal during ultrasonic stimulation can be divided into three stages, namely, rapid rise, slow rise, and fluctuating rise. Also, the maximum temperature within 1 h can reach 263.9 °C. The oxygencontaining functional groups were decomposed and removed under ultrasonic stimulation, thus reducing the methane adsorption capacity of coal. The main fractures parallel to the bedding direction and the secondary branch fractures perpendicular to the bedding direction were produced. Furthermore, the primary and secondary fractures were penetrated, and the surface porosity increased to 3.93% after 3 h of treatment. Ultrasonic stimulation had little effect on the micropores and transition pores, but it increased the mesopores, macropores, and fractures. The effective porosity and free fluid proportion increased significantly with the increase in ultrasonic processing time by 43.86 and 31.30%, respectively. After ultrasonic stimulation, the scanned pore-fracture network model was highly connected and showed an ordered network and cross-linking, thus providing space for gas desorption and seepage.

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Section: Resultsmentioning

confidence: 99%

Changes of Coal Molecular and Pore Structure under Ultrasonic Stimulation

Sun

et al. 2021

Energy Fuels

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“…Finally, the valve between the sample cell and the manifold was opened, and methane was injected into the cell. The methane adsorbability of coal can be calculated using the Helmholtz equilibrium equation …”

Section: Methodsmentioning

confidence: 99%

Microwave-Induced Microstructure Evolution of Coal and Its Effects on the Methane Adsorption Characteristic

Shi

et al. 2021

Energy Fuels

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Coalbed methane (CBM) reservoirs usually require stimulation to enhance the permeability. Characterized by the transformation of electromagnetic energy into thermal energy, microwave heating may be a promising CBM stimulation approach. In this work, the microstructure evolution of coal affected by microwave heating was investigated by Fourier transform infrared spectroscopy (FTIR), low-temperature nitrogen adsorption (LT-N2GA), and scanning electron microscopy (SEM). In addition, the methane adsorption property of coal was evaluated using a high-pressure adsorption instrument. The results indicate that microwave heating would cause the pyrolysis of ether groups, oxygen-containing groups, and aliphatic hydrocarbon in coal. After microwave treatment, the volume and connectivity between mesopores and micropores increase. The decrease in the methane adsorbability of coal may be attributed to the reduction of the methane adsorption site induced by microwave heating. The outcome of this study implies that microwave heating can be used to promote CBM recovery.

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“…These features result in an increase in mine gas emission quantity. Gas release limits mine efficient mining [6][7][8][9]. The problem of high gas accumulation in the return airway corner caused by high gas emission from goaf during coal seam mining has not been fully solved [10,11].…”

Section: Introductionmentioning

confidence: 99%

The Law of Fracture Evolution of Overlying Strata and Gas Emission in Goaf under the Influence of Mining

Cheng

Yu³

et al. 2021

Geofluids

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Mining is associated with poor safety due to pressure relief gas emission from the goaf during the production period. The aim of this study was to explore a case study of the Wangjialing coal mine 12322 working face in Shanxi, China, through physical simulation and field observation. The mine is characterized by overlying strata fracture in goaf during the process of working face mining. A mathematical model of gas source emission from the working face and gas migration and the finite element COMSOL software were used to simulate the law of gas migration in the region with overlying strata fissures under the influence of mining. The simulation results were used to explore the law of distribution of pressure relief gas in goaf. Rational parameters of the high-level directional long borehole for the pressure relief gas extraction in goaf were designed based on experimental results. The results showed that the development of the region with overlying strata fissures is affected by mining. In addition, the “trapezoid platform structure” is formed after fracture areas are connected. The maximum height of the stope caving zone was between 26.8 m and 28.1 m, and the maximum height of the fracture zone was approximately 110 m. The gas concentration exhibited a saddle-shaped distribution on the cut surface of the direction of the strike. Furthermore, the gas concentration showed an overall upward trend from the intake airflow roadway to the return airflow roadway and gradually decreased after reaching the maximum. In the vertical direction, gas concentration increased with the increase in the layer, and the position of the highest point of gas concentration gradually shifted to the direction of the intake airflow roadway. Construction parameters of the high directional long borehole were designed through simulation results. After steady extraction and stable extraction, the maximum gas concentration in the upper corner of the working face was 0.49%, and the maximum gas concentration in return airflow was 0.34%. The findings of this study provide information on the law of fracture evolution of overlying strata and gas migration in goaf under the influence of mining. These findings provide a basis for reducing gas overlimit in the working face or return airway corner, thus improving the safety production capacity of the coal mine.

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Gas Adsorption Capacity of Coal Frozen with Liquid Nitrogen and Variations in the Proportions of the Organic Functional Groups on the Coal after Freezing

Cited by 34 publications

References 38 publications

Changes of Coal Molecular and Pore Structure under Ultrasonic Stimulation

Changes of Coal Molecular and Pore Structure under Ultrasonic Stimulation

Microwave-Induced Microstructure Evolution of Coal and Its Effects on the Methane Adsorption Characteristic

The Law of Fracture Evolution of Overlying Strata and Gas Emission in Goaf under the Influence of Mining

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