The application of cyclical microwave modification for accelerating the extraction of coalbed methane (CBM) from anthracite is limited. In this study, the apparent permeability of anthracite samples before and after each microwave treatment (three in total) for 120 s was measured by a self-built permeability-testing platform. Microcomputed tomography (micro-CT) technology and image-processing technology were employed to analyze the 3D micron-scale pore structures, especially the quantitative characterization of connected pores and throats. After modification, the average apparent permeability increased from 0.6 to 5.8 × 10 –3 μm 2 . The generation, expansion, and connection of micron-scale pores and fractures became more obvious with each treatment. The total porosity increased from 3.5 to 6.2%, the connected porosity increased from 0.9 to 4.8%, and the porosity of isolated pores decreased from 2.5 to 1.4% after three cycles. The number, volume, and surface area of the connected pores as well as the number, radius, and surface area of the throats were significantly increased. In addition, the release of alkyl side chains from the anthracite surface reduced the capacity of the anthracite to adsorb CH 4 and the decomposition of minerals promoted the development and connectivity of pores. As a result, the gas seepage channels have been greatly improved. This work provides a basis for micron-scale pore characterization after cyclical microwave modification and contributes to CBM extraction.
The application of electrochemical modification for accelerating methane extraction in lean coal seams is limited due to the lack of experimental and theoretical research studies. Therefore, electrochemical modification with different electric potential gradient values was selected to modify lean coals in this study; meanwhile, the amount of methane adsorption and the methane desorption ratio were tested and analyzed. The results showed that the maximum amount of methane adsorption in coal samples decreased after electrochemical modification and the decrease in methane adsorption increased with an increase in electric potential gradient. The methane desorption ratio increased from 83.20% up to 87.84 and 86.90% at the anode and cathode zone, respectively, after electrochemical modification using a 4 V/cm electric potential gradient. A higher electric potential gradient performs better in the electrochemical modification. The mechanism of electrochemical modification using different electric potential gradients was revealed based on the measurements of Fourier transform infrared spectroscopy and liquid nitrogen adsorption. It is due to an increase in acid groups in coal molecular structure and the change of the specific surface area of coal after modification. The results obtained from this work contribute to the methane extraction via the electrochemical method in lean coal seams.
To better understand the methane adsorption behavior after microwave exposure, the importance of quantitatively characterizing the effect of cyclical microwave exposure on the molecular structures of coals cannot be overemphasized, with implications for enhancing coalbed methane (CBM) extraction. Thus, cyclical microwave exposure experiments of three different metamorphic coals were conducted, and the methane adsorption capacity before and after each microwave exposure (10 in total) for 120 s was evaluated. Fourier transform infrared spectroscopy analysis and peak fitting technology were applied to quantitatively characterize the changes in the structural parameters of coal molecules. The results showed that after modification, the structural parameters like aromatic carbon fraction (f a–F), aromaticity (I 1 and I 2), degree of condensation (DOC 1 and DOC 2), and the maturity of organic matter (“C”) gradually increased with increasing exposure times, while the length of the aliphatic chain or its branching degree (CH 2/CH 3) and the hydrocarbon generating capacity (“A”) showed a decreasing trend. The Langmuir volume (V L) of three different rank coal samples decreased from 29.2, 32.8, and 40.4 mL/g to 25.7, 29.3, and 35.7 mL/g, respectively; the Langmuir pressure (P L) increased from 0.588, 0.844, and 0.942 MPa to 0.626, 1.007, and 1.139 MPa, respectively. The modification mechanism was investigated by analyzing the relationship between the methane adsorption behaviors and molecular structures in coals. The release of alkane side chains and the oxidation of oxygen-containing functional groups caused by microwave exposure decreased the number of methane adsorption sites. As a result, the methane adsorption capability decreased. In addition, the decomposition of minerals affects methane adsorption behaviors in coals. This work provides a basis for microwave modification of coal as well as in situ enhancement of CBM extraction using microwave exposure.
Accelerating the drainage of water in coal reservoirs can significantly improve the extraction efficiency of coalbed methane (CBM). The movement of water with different pH values in anthracite was tested and analyzed. The results showed that the electro-osmotic flow velocity increased first and then slightly decreased with the increase of time up to 120 h. The electro-osmotic flow was markedly strengthened under a strong acid (pH 2) or strong alkaline (pH 13) environment, and the direction of electro-osmosis was reversed at a pH of 3−4. The changes in zeta potential, surface groups, and minerals in anthracite were tested to analyze the mechanism of electroosmotic characteristics. The results obtained from this work will provide a basis for the process of drainage and depressurization during the CBM extraction.
A quantitative characterization of methane (CH 4 ) adsorption on coal with different pressures and temperatures, and a better understanding of the mechanism of the interaction energy and coal swelling is of great significance for the commercial extraction of coal bed methane (CBM). Therefore, CH 4 adsorption isotherms of anthracite with temperatures ranging from 273 to 323 K have been simulated and tested. When the pressure increased up to 20 MPa, both the simulated and experimental results showed that CH 4 adsorption conforms to the Langmuir model. The interaction energies between anthracite and CH 4 markedly increased at first and then slightly decreased with increasing pressure. When the temperature increased to 323 K, CH 4 maximum adsorption decreased exponentially, the interaction energies between anthracite and CH 4 become more positive and anthracite swelling decreased. The radial distribution function (RDF) results showed that CH 4 is strongly adsorbed by the sites of the carbon atoms, followed by hydrogen and nitrogen atoms of anthracite. The results of this study can provide details of the correlation among methane adsorption, interaction energies, and anthracite swelling, and also contribute to the evaluation and extraction of CBM.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.