Overview and Outlook on Utilization Technologies of Low-Concentration Coal Mine Methane

Abstract

Coal mine methane (CMM) with the worldwide reserves of 2.6 × 1014 m3 is one of the important unconventional natural gases. However, most of the low-concentration coal mine methane (LC-CMM, cCH4 < 30 vol %) is not utilized and directly emitted to the atmosphere, producing up to about 28 billion m3 CH4 emissions annually and causing a serious greenhouse effect and energy loss. Evidently, resource utilization of LC-CMM is of vital significance to achieve energy transition and carbon neutrality. Herein, we review the recent advances of LC-CMM utilization technologies in terms of low-concentration drainage gas (1 vol % < cCH4 < 30 vol %) and ventilation air methane (VAM, cCH4 < 0.75 vol %). Especially, the great progresses of LC-CMM utilization in China are extensively introduced. A large amount of the low-concentration drainage gas with cCH4 > 6 vol % has been utilized in China due to the wide application of specially designed internal combustion engines (ICEs) and safe pipeline transport technologies. To avoid the shortages of low efficiency and high pollution of ICEs, solid oxide fuel cells (SOFCs) fueled by LC-CMM were recently proposed and modified for improving safety, efficiency, and stability. Also, methane enrichment such as pressure swing adsorption (PSA) and direct burning are key technologies to improve the utilization ratio of the drainage gas with cCH4 < 6 vol %. The modifications to improve the safety and efficiency of the PSA process and the new metal fiber combustion have been developed and applied in China. Furthermore, the recent advances of VAM utilization technologies are introduced. A thermal flow reverse reactor (TFRR) for VAM utilization has been applied in some coal mines. VAM enrichment and a catalytic flow reverse reactor (CFRR) create opportunities to efficiently use VAM with much lower CH4 concentration. Finally, the technical and economic challenges as well as the coping strategies of LC-CMM utilization are described. It is believed that LC-CMM with all various CH4 concentrations can be effectively and cleanly utilized in the near future, contributing to the new energy structure establishment and environment protection.

Hydrogen Production from Coal Industry Methane

“…11). Low-concentration methane-air mixtures (VAM) are also used to generate electricity or, more often, are simply burned with the release of carbon dioxide into the atmosphere [20,[25][26][27]. For example, during coal mining in China, Shanxi Province, a number of projects (TUNLAN, MALAN, DUERPING) are being implemented to minimise coal industry methane (CMM, VAM) emissions and their optimal utilisation [28].…”

Evolution of methane permeability and fracture structure of coal: implications for methane extraction in deep coal seams

“…Ignoring the compression storage of uid in the coal samples, the relationship for this condition can be obtained as eqn (2).…”

“…Gas accidents mainly include gas explosions, coal and gas outbursts, gas combustion and gas asphyxiation. [1][2][3] With the increasing emphasis on gas disasters and the advances in gas control technology, some achievements have been made in gas disaster prevention, but coal mine gas accidents continue to happen. Methane is an efficient and clean energy with a caloric value of 35.9 MJ m −3 , equal to the caloric value of 1.2 kg of standard coal.…”

Enrichment of Low-Quality Methane by Various Combinations of Vacuum and Temperature Swing Adsorption Processes

“…As part of CMM, coal mine drainage gas typically contains 30–95% CH 4 in Australia, whereas many coal mines in China and Russia come across poor drainage gas having less than 30% CH 4 and even as low as 3% CH 4 due to various geological conditions. , Although the extracted CMM has been partly used for onsite heat and fuel sources, a huge volume of poor drainage gas (>20 billion m 3 /year of extracted CMM) in China has been, however, directly discharged into the atmosphere, which contributes to global warming, wasting an enormous amount of energy source. Low CMM concentrations have given rise to the low utilization of CMM, mainly due to the difficulty in upgrading CH 4 effectively and economically with a high explosion risk . Therefore, it is important to develop feasible technologies for low-quality CMM to be utilized in a safe manner, consequently reducing CMM emissions and saving the energy source, providing technology options for mine operators to implement.…”

“…Currently, many countries such as the United States, Australia, and Germany do not permit the use of low-concentration (<25% CH 4 ) drainage gas. The same was the case in China until safe pipeline transport technologies were developed . Thus, this paper aims to provide mine operators with various enrichment technology options using various combinations of VSA and TSA processes, focusing on poor drainage gas with methane concentrations ranging from 3 to 9% to enrich up to more than 9% CH 4 in the final product.…”