A Study on the Spontaneous Combustion Oxidation Properties of Unloaded Coal at Various Surrounding Rock Temperatures

ABSTRACT

Based on effects of the deep surrounding rock temperature (T_sr) on the oxidation properties of mined coal, a thermodynamic experimental system for loaded coal oxidation is employed to examine the oxidation properties of readily oxidizable raw coal samples at various T_srs and comparatively analyze the patterns of change in the oxygen (O₂) consumption rate and the carbon monoxide (CO) concentration (C_CO) with T_sr. The infrared (IR) spectra of unloaded coal samples oxidized at various T_srs were separately fitted to Gaussian curves and Lorentzian curves by using the IR analysis software OMNIC. The following experimental results indicate that T_sr significantly affects the oxidation properties of the coal. The initial T_sr is higher and the rate of increase in the coal temperature is faster during the early stage of oxidation, and the coal–O₂ complex effect is higher and the rate of consumption of O₂ by coal is higher. The C_CO produced by each coal sample continuously increased as T_sr increased. The amount of CO that was produced slowly and linearly increased as T_sr increased during the early stage of oxidation, and it approximately exponentially increases as T_sr increased during the later stage of oxidation. Additionally, the amount of C_CO produced is increased with the increase in initial Tsr during the coal oxidation process. By using Fourier-transform IR (FTIR) spectroscopy, microstructural analysis of oxidized coal samples reveals that the characteristics of dynamic change in the micro-active groups (e.g. hydroxyl groups, O-containing functional groups and aromatic and aliphatic hydrocarbons) of unloaded coal samples at various T_srs, and it also reasonably determines the micro-mechanism of the oxidation properties of unloaded coal samples at various T_srs.

KEYWORDS:

• Deep coal
• Spontaneous combustion of coal
• Surrounding rock temperature
• Oxidation of raw coal
• Microstructure

Acknowledgments

The authors thank the editors and anonymous reviewers for their helpful suggestions for this manuscript.

Additional information

Funding

This work was carried out with funding from the National Key R&D Program of China [Grant No. 2018YFC0808100], National Natural Science Foundation of China [Grant No. 51304070, 51674103] and supported by the Science Research Funds for the Universities of Henan Province.