CO₂ adsorption of anthracite with different moisture contents and its implications for geological storage

Authors

ZHANG Jinchao, School of Resources and Earth Sciences, China University of Mining and Technology, Xuzhou 221116, Chin; Key Laboratory of Coal Methane Resources and Reservoir Formation Process of the Ministry of Education, China University of Mining and Technology, Xuzhou 221008, ChinaFollow
SANG Shuxun, School of Resources and Earth Sciences, China University of Mining and Technology, Xuzhou 221116, China; Key Laboratory of Coal Methane Resources and Reservoir Formation Process of the Ministry of Education, China University of Mining and Technology, Xuzhou 221008, China; Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China; Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou 221008, ChinaFollow
HAN Sijie, Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221008, China; Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology, Xuzhou 221008, China
ZHANG Fengbi, Department of Natural Resources, Zhongshan District, Liupanshui City, Guizhou Province, Liupanshui 553000, China
XU Ang, School of Resources and Earth Sciences, China University of Mining and Technology, Xuzhou 221116, Chin; Key Laboratory of Coal Methane Resources and Reservoir Formation Process of the Ministry of Education, China University of Mining and Technology, Xuzhou 221008, China
LIU Qishan, China Petroleum Pipeline Engineering Corporation, Langfang 065000, China

Abstract

CO₂ geological storage in deep coal seams is regarded as an important pathway to achieve “2030 carbon peak and 2060 carbon neutrality goals”. The moisture content in coal seams plays a significant role in the CO₂ storage capacity mainly based on CO₂ adsorption. In this study, the anthracite from the Qinshui Basin was collected to conduct high-pressure CO₂ adsorption isothermal experiments under dry, moisture-equilibrated and moisture-saturated conditions at 45℃. The CO₂ excess adsorption curve was corrected by the reduction of CO₂ dissolution. The adsorption capacity and adsorption heat were calculated using the modified D-R adsorption model. On the bases of the comparison of three CO₂ absolute adsorption curves at different moisture conditions, the microscopic mechanism of moisture saturation enhancing the adsorption capacity was explained. The results show that (1) the CO₂ adsorption capacity of dry, moisture-equilibrated and moisture-saturated coal samples are 56.72 cm³/g, 45.19 cm³/g and 48.36 cm³/g, and their adsorption heat are 29.42 kJ/mol, 26.23 kJ/mol and 27.24 kJ/mol, respectively. (2) With the CO₂ density less than 0.16 g/cm³ (6.48 MPa), the absolute adsorption capacity of anthracite in descending order is dry coal, moisture-saturated coal, and moisture-equilibrated coal, but when the CO₂ is in a supercritical state, the order changes to dry coal, moisture-equilibrated coal, and moisture-saturated coal. (3) The preferential occupation of high-energy adsorption sites by water molecules is the main reason for the reduction of the CO₂ adsorption capacity of moisture-equilibrated coal samples. The interaction between the coal-H₂O system and CO₂ is stronger than that between coal and CO₂ under the competitive adsorption of CO₂ and H₂O, resulting in the higher adsorption capacity of moisture-saturated coal samples being higher than that of dry coal samples in the supercritical stage of CO₂. (4) Adsorption storage is the main form of CO₂ geological storage in coal. In deep coal reservoirs, moisture saturation plays a more obvious role in increasing the adsorption capacity of supercritical CO₂. High-pressure water injection into deep coal seams is an effective way to improve CO₂ storage capacity and the permeability of coal seams.

Keywords

moisture saturation, anthracite, adsorption capacity, CO2 geological storage, Qinshui Basin

DOI

10.12363/issn.1001-1986.21.12.0758

Recommended Citation

ZHANG Jinchao, SANG Shuxun, HAN Sijie, et al. (2022) "CO₂ adsorption of anthracite with different moisture contents and its implications for geological storage," Coal Geology & Exploration: Vol. 50: Iss. 9, Article 12.
DOI: 10.12363/issn.1001-1986.21.12.0758
Available at: https://cge.researchcommons.org/journal/vol50/iss9/12

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