Effect of Water Soaking on the Microstructure and Spontaneous Combustion Characteristics of Bituminous Coal During Low−Temperature Oxidation

ABSTRACT

The effects of water soaking on the microstructure and spontaneous combustion characteristics of coal samples were investigated by scanning electronic microscopy (SEM), Fourier transform infrared (FTIR) spectrometer, and temperature programmed testing system (TPTS). The SEM results showed that the pore structures on the surface of water−soaked coal were more developed than raw coal, the pores increased and enlarged, and the phenomenon of water absorption swelling occurred. At the same time, water soaking had a certain influence on the functional groups in coal. The results of FTIR clearly illustrated that the surface functional groups of water−soaked coal were more active, and the contents of functional groups such as hydroxyl, methylene, aliphatic ether and aromatic ether all increased to varying degrees. During the low−temperature oxidation process, the analysis results of TPTS indicated that the oxygen consumption rate and the production of CO, C₂H₄, and other gases of water−soaked coal were higher. Based on the analysis method of CO, CO/CO₂ and C₂H₄ gas growth rate, the three peaks of the curve obtained correspond to the characteristic temperatures of each oxidation stage of the coal samples. The critical temperature, dry cracking temperature and fission temperature of water−soaked coal were 60 ± 10 ℃, 90 ± 10 ℃ and 120 ± 10 ℃, respectively, which was 10 ℃ lower than raw coal. The apparent activation energy (E_a) of coal was calculated by the CO model and fitted in sections. It can be seen that the E_a of water−soaked coal at different stages of low−temperature oxidation was lower, and the maximum difference was 2.1 kJ/mol. Therefore, from the above results, it inferred that the activity of bituminous coal became stronger after soaking in water, which may be due to the effect of soaking on the surface structure and active groups of coal, thus showing a higher risk of spontaneous combustion.

KEYWORDS:

• Water−soaked coal
• functional groups
• low temperature oxidation
• spontaneous combustion characteristics
• apparent activation energy

Disclosure statement

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

Additional information

Funding

This study was sponsored by the National Natural Science Foundation of China [No. 52074218; No. 51804247 No. 52274225 No. 52204236] and Shaanxi Provincial Natural Science Foundation [No.2018JM5071].