Thermal Behavior and Microscopic Characteristics of Water-soaked Coal Spontaneous Combustion

ABSTRACT

The current reaction kinetics of coal–oxygen compound in water-soaked coal has not been accurately explained. Therefore, thermal behavior and microscopic characteristics during spontaneous combustion of water-soaked coal samples were analyzed. Five kinds of coal samples were selected with moisture contents of 5%, 10%, 15%, and 20% of the raw coal. Fourier transform infrared (FTIR), thermogravimetric (TG), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were adopted. The results showed that the hydroxyl (–OH) group is greatly affected by the moisture content of coal samples. The area of hydroxyl absorption peaks in coal samples with 5% and 10% moisture content increased by 1.76% and 1.12%, respectively. The critical temperature T₁ decreased the most at 10% moisture content compared with the raw coal, which was about 6.5 °C. This indicated that the heat storage process was accelerated and the activity of the coal samples was increased. According to the thermodynamic analysis, the activation energy of the five kinds of water-soaked coal samples are 148.078 kJ/mol, 147.674 kJ/mol, 146.197 kJ/mol, 145.019 kJ/mol, and 145.934 kJ/mol, respectively. This proves that the activation energy of coal samples is generally reduced after immersion in water, and coal samples with 15% moisture content are most susceptible to spontaneous combustion. As the temperature was raised, aliphatic hydrocarbons (–CH₃, – CH–) and C = O increased rapidly. The above results indicate that water immersion accelerates the spontaneous combustion and oxidation of coal to a certain extent.

KEYWORDS:

• Coal spontaneous combustion
• different moisture content
• reaction thermodynamics
• FTIR
• functional group

Additional information

Funding

The authors appreciate the financial support of project No. 51974015, No. 51904292 and No. 51474017 provided by the National Natural Science Foundation of China, project No. 2018YFC0810600 provided by the National Key Research and Development Program of China, project No. 2017CXNL02 provided by the Fundamental Research Funds for the Central Universities (China University of Mining and Technology), project No. BK20180655 provided by the Natural Science Foundation of Jiangsu Province, project No. WS2018B03 provided by the State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University), and project No. E21724 provided by the Work Safety Key Lab on Prevention and Control of Gas and Roof Disasters for Southern Coal Mines of China (Hunan University of Science and Technology).