Hydrogen adsorption characteristics of coal rock and its geological significance

Abstract

Hydrogen, as an important clean energy source that can be used as an alternative to fossil energy, can reduce global greenhouse gas emissions. However, the large-scale hydrogen industry requires large reservoirs to store hydrogen, and the use of underground reservoirs to store large amounts of hydrogen has become a new topic. In this paper, 11 coal samples with different metamorphic degrees of Carboniferous-Permian in Ordos Basin, Qinshui Basin and Ningwu Basin of China were investigated. Based on the specific surface area and total pore volume, the amount of hydrogen adsorbed by coal rock was evaluated by hydrogen isothermal adsorption experiment and Langmuir model. The mechanism of hydrogen adsorption by coal rock was discussed in combination with coal quality, organic geochemistry, mineral and pore structure characteristics. The results show that the Langmuir model is suitable for the calculation and evaluation of the potential of simulating the hydrogen adsorption of coal rock. Coal rock with different metamorphic degrees has high hydrogen adsorption capacity, and the higher the metamorphic degree, the higher the organic matter abundance and the more developed micropores, the higher the hydrogen adsorption capacity. Hydrogen in coal rock is mainly physically adsorbed on the surface of coal rock by van der Waals force. With the increase of coal rock metamorphic degree, the more micropores formed by organic matter, the more pore volume and total specific surface area provided by organic matter, which increases the amount of hydrogen adsorption, and the higher pore connectivity can improve the efficiency of hydrogen entering pores and being adsorbed. The amount of hydrogen adsorbed by coal rock will increase with the increase of pressure, but due to the reasons such as intermolecular repulsion, the adsorption rate will decrease, and the hydrogen storage will reach saturation. The development of deep coal seams in China provides a good foundation for hydrogen storage in coal seams. However, due to chemical reactions, competitive adsorption and other problems, hydrogen will be lost and lost in coal-rock reservoirs. The use of high pressure for hydrogen storage or acquisition of hydrogen will cause irreversible damage to the structure of coal-rock reservoirs, which has adverse effects on the use of coal-rock reservoirs for one or more storage of hydrogen. Deep coal seams with high metamorphic degree have certain potential as hydrogen storage horizons but further research is still needed to overcome some key problems such as hydrogen loss and reservoir damage.

Keywords

• deep coal rock
• hydrogen adsorption
• hydrogen storage potential
• hydrogen consumption
• hydrogen storage mechanisms