Experimental study on inhibition of coal spontaneous combustion by carbon dioxide and nitrogen

ABSTRACT

Injecting CO₂ and N₂ to reduce the concentration of O₂ in the air is a commonly used measure to prevent coal spontaneous combustion (CSC). To study the difference in inhibitory effects of CO₂ and N₂ on coal oxidation, experiments in this study were conducted using a setup of self-developed gas-bath coal oxidation for low temperatures. The oxidation process of the coal-oxygen system was then analyzed using reaction kinetics. Two different coal samples were tested in experiments under two inert gas environments, i.e. CO₂ and N₂ with various O₂ concentrations, respectively. The changes in O₂ and CO concentrations were measured during the oxidation process. By studying the standard oxygen consumption rate (SOCR) and the apparent activation energy of the coal-oxygen reaction system, inhibitory effects of CO₂ and N₂ on CSC were analyzed and compared. The results showed that the SOCR of the same coal sample remained consistent and independent of the O₂ concentration within the same inert gas environment although under different O₂ levels. In both CO₂-O₂ and N₂-O₂ environments, the SOCR of the coal sample exhibits exponential growth with temperature. The SOCR was found to have a functional connection with temperature, it can be represented as $\mathit{y}=\mathit{a}\cdot e^{\mathit{bT}}$, and the R² (determination coefficients) of the fitting formulas are all greater than 0.94. In the correlation, the inert gas environment has minimal impact on coefficient “b,” while in the CO₂-O₂ environment, reducing the value of coefficient “a” can effectively lower the coal sample’s SOCR. The GBMK sample and YMWK sample have an “a” value that is 20% of the value in the N₂-O₂ environment when oxidizing in the CO₂-O₂ environment. The SOCR in the CO₂-O₂ environment showed a decrement of between 26.0% and 52.1% when compared to that in the N₂-O₂ environment, whereas the activation energy showed an increment between 1.4% and 18.6%. The findings in this work provide an in-depth understanding of the prevention of CSC in the gob for risk mitigation.

KEYWORDS:

• Coal
• CSC
• oxidation
• SOCR
• inhibitory effect

Highlights

• Increased inert gas concentration can enhance the inhibition of coal oxidation

• The standard oxygen consumption rate is independent of the oxygen concentration

• The standard oxygen consumption rate increases exponentially with rising temperature

• Carbon dioxide is a better inhibitor of coal spontaneous combustion than nitrogen

Acknowledgements

This work was completed with the help of the National Natural Science Foundation of China [grant numbers 52074303 and 51874315]. The first author is very grateful for the support from the China Scholarship Council (File: 202206430069).

Disclosure statement

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

Credit authorship contribution statement

Linxiao Yan: methodology, software, writing-original draft. Yueping Qin: supervision, resources, visualization. Changqing Chu: methodology, investigation. Biao Sun: supervision, methodology. Yi Xu: investigation, software. Qiaohong Jiang: investigation, visualization. Yipeng Song: methodology, investigation. Fei Tang: investigation, visualization. Hao Xu: methodology, visualization

Credit author statement

We have reviewed the final version of the manuscript and approve it for consideration of possible publication on your journal. We confirm that the manuscript has not been published in whole or in part nor is it being considered for publication elsewhere.

Additional information

Notes on contributors

Linxiao Yan

Linxiao Yan is a PhD at China University of Mining and Technology, Beijing. He is a visiting scholar at Curtin University. His current research focuses on mine fire prediction and prevention.

Yueping Qin

Yueping Qin is a professor at China University of Mining and Technology, Beijing. His research interests include coal spontaneous combustion in gobs, mine cooling and mine gas control, and he has published many academic papers around the research topics.

Changqing Chu

Changqing Chu is a postgraduate student at China University of Mining and Technology, Beijing. His research includes the spontaneous ignition mechanism and numerical simulation of gob.

Biao Sun

Biao Sun is a professor at Curtin University, and his research focuses on carbon capture.

Yi Xu

Yi Xu is a master at China University of Mining and Technology, Beijing. His research focuses on mine fire.

Qiaohong Jiang

Qiaohong Jiang is a master at Henan Polytechnic University. Her research interests involve emergency response to accidents.

Yipeng Song

Yipeng Song is an associate professor at Shandong Technology and Business University. His research interests include the spontaneous ignition mechanism and numerical simulation of gob and coal spontaneous combustion prevention technologies and methods in gobs.

Fei Tang

Fei Tang is a PhD at China University of Mining and Technology, Beijing. His research focuses on thermal hazard prevention.

Hao Xu

Hao Xu is an associate professor at Shandong University of Science and Technology. His research areas include gas migration patterns in coal seams and gas disaster prevention and control.