Post-outburst coal pulverization: Experimental insights with representative accident samples

ABSTRACT

Coal and gas outburst accidents pose a serious threat to safe coal mining. Coal pulverization and transportation are integral to outbursts, aiding in understanding outbursts process and holding great potential for elucidating outburst mechanisms. However, the lack of on-site coal sample makes it challenging to assess coal pulverization characteristics during outbursts. We collected coal samples from the forefront of five outburst sites in typical tectonic areas over the past decade. Three coal powders and coal blocks underwent particle size, low-pressure N₂/CO₂ adsorption and adsorption/desorption experiments to characterize their coal-gas properties. The impact of coal pulverization on coal transportation and outburst initiation was evaluated based on energy conservation principles. The results indicate that the particle size range of coal blocks is 0.27 μm to 2.6 mm, with over 50% consisting of particles smaller than 50 μm. The formation of micron-sized outburst coal powder is associated with tectonic movements. Pulverization increases micropore and some mesopore pore volume, and specific surface area initially increases and then decreases with decreasing particle size. The ultimate adsorption capacity of outburst coal at three particle sizes ranges from 16.8 to 36.0 m³/t. Pulverization affects gas adsorption capacity by influencing micropore volume. The methane desorption velocity within the first 60 s ranged from 0.0091 to 0.0998 ml/g/s, with the minimum particle size being 1.6 to 4.4 times the maximum particle size. Coal pulverization leads to an increase in pore quantity, a reduction in pore length, and the disappearance of high adsorption potential pores, resulting in rapid methane desorption. In the five outbursts, 246 to 25,580 m³ (30°C, 0.1 MPa) of desorbed gas is involved in coal transport. This requires gas desorption velocities ranging from 0.014 to 0.171 ml/g/s, with coal particle sizes reaching 5–875 μm. The abundant presence of micron-sized coal powder is essential for outburst initiation and sustained coal ejection, considerably increasing the risk of outbursts in tectonic coal seams.

KEYWORDS:

• Coal and gas outburst
• coal pulverization
• gas desorption
• coal transportation
• tectonic

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors are grateful to the Key project of the National Natural Science Foundation of China [No.52034008] and project of National Natural Science Foundation of China [No. 52374240].

Notes on contributors

Jia Wang

Jia Wang is a PhD student at the School of Safety Engineering, China University of Mining and Technology. Her research focuses on characterizing gas desorption and diffusion behavior in coal, as well as studying the scale effects of gas diffusion in porous media.

Yuanping Cheng

Yuanping Cheng is a professor at the School of Safety Engineering, China University of Mining and Technology, where he earned his Ph.D. in Safety Technology Engineering in 1990. With over 30 years of teaching and research experience, his primary focus is on the theory and technology for the prevention and control of gas disasters in coal mines.

Chenghao Wang

Chenghao Wang is an Associate Professor at the Artificial Intelligence Research Institute, China University of Mining and Technology. He earned his PhD from the same university in 2023. His main research areas include the mechanisms of coal and gas outburst disasters and the prediction of critical low-probability events.

Minghao Yi

Minghao Yi received his Ph.D. from China University of Mining and Technology in 2023 and is currently a lecturer at the School of Resource & Environment and Safety Engineering, Hunan University of Science and Technology. His research interests include pore characterization of porous media and gas migration in coal.

Xiaoxi Cheng

Xiaoxi Cheng is a PhD student at the School of Safety Engineering, China University of Mining and Technology. Her research areas include adsorption theory of porous adsorbents, pore characterization, and studying microscopic adsorption mechanisms using molecular simulation techniques.

Liang Wang

Liang Wang is a professor at the School of Safety Engineering, China University of Mining and Technology. He received his PhD from China University of Mining and Technology in 2009 and is currently the Dean of the School of Safety Engineering at the same university. His research focuses on the theory and key technologies for the prevention and control of gas disasters in coal mines.