Effect of functional groups on spontaneous combustion characteristics of high water-rich coal after long-term soaking and drying

ABSTRACT

Spontaneous combustion of waterlogged coal accounts for many coal mine fire accidents. The soaking process affects the chemical properties of the coal, causing it to be highly susceptible to spontaneous combustion. Changes in functional groups of highly water-rich coals after flooding and drying are discussed, and the structural parameters were characterized by infrared spectroscopy (FTIR). The results show that the highest aliphatic hydrocarbons, oxygenated functional groups, and aromatic hydrocarbons are reached when air-dried after soaking for 30 days. The substitution of the dumb ring is changed with growing immersion time. C-O rose from 13% to 26% at 30 days and remained constant. Methyl and self-conjugated hydroxyl groups are increasing. Analysis of the structural parameters revealed that aromaticity decreases and increases with soaking time, while the degree of fatty chaining increases and decreases. Prolonged water immersion and air-drying change the coal’s aromatization and aliphatic chain structure, resulting in the continuous loss of the branched chains, thus making the skeleton of coal more sparse and the low-temperature oxidation reactions easier to carry out. It is sufficient to show that the theoretical basis for prevention and control of highly water-rich coal combustion after long-term immersion and drying is provided.

KEYWORDS:

• Highly water-rich coals
• immersion
• spontaneous combustion
• FTIR
• functional groups

Highlights

• The chemical characteristics of strong water-rich coal are different from those of low water content coal.

• Water-immersed coal accounts for an essential part of coal spontaneous combustion fire accidents, and water-immersed coal is more accessible to spontaneous combustion.

• FTIR can quantitatively study the changes in functional groups of strong water-rich coal after long-term water immersion and drying.

• The functional groups are involved in the process of coal oxygen reaction, and the change of the content of functional groups in the long-term water-soaked coal affects the spontaneous combustion reaction of coal.

Acknowledgements

The work was supported by China’s National Natural Science Foundation (Grant nos.51874131, 51474106, and 52174163). Thanks for the support and help provided by the above funds during the experiment and writing of this work.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

The work was supported by the China’s National Natural Science Foundation [51874131,51474106, 52174163].

Notes on contributors

Huiyong Niu

Huiyong Niu is a professor in University of Science and Technology Beijing. He is mainly engaged in coal mine fire prevention and control work.

Yikang Liu

Yikang Liu is a doctoral student in University of Science and Technology Beijing. He is mainly engaged in the prevention and control of coal mine fire.

Haiyan Wang

Haiyan Wang is a professor in University of Science and Technology Beijing. He is mainly engaged in coal mine fire prevention and emergency management.

Bo Tan

Bo Tan is a professor of China University of Mining and Technology-Beijing, he is mainly engaged in coal mine fire prevention and control work.

Shilin Li

Shilin Li is a lecturer in Hunan University of Science and Technology. He is mainly engaged in coal mine fire prevention and emergency management.