Spontaneous combustion characteristics and mechanism of water-immersed and air-dried brown coal

ABSTRACT

To reveal the influential laws and mechanism of water immersion on the spontaneous combustion traits of lignite in the low-temperature oxidation stage. Raw coal (HL), water-immersed for 30 days (HL-S₃₀), 90 days (HL-S₉₀) and 150 days (HL-S₁₅₀), were taken as the research objects. The pore evolution characteristics and functional group migration law of coal were explored by Scanning Electron Microscopy (SEM), Low-temperature Nitrogen Adsorption Test (LNAT) and Fourier Transform Infrared Spectroscopy (FTIR). The low-temperature oxidation procedure was simulated by Programmed Heating Test (PHT), and the gas release characteristics, exothermicity and ultimate spontaneous combustion parameters of the relic coal were compared. These findings demonstrated that the discriminant indexes of spontaneous combustion tendency of four specimens change periodically with temperature, but generally the spontaneous combustion intensity of HL-S₃₀ and HL-S₁₅₀ is greater than HL, and HL-S₉₀ is the least. The micro reasons for increasing oxidation activity of HL-S₃₀ and HL-S₁₅₀ are as follows: the number of micropores of water-immersed coal is almost 3 ~ 4 times that of HL, and the pores expanded with immersion which helps to enhance the adsorption of oxygen; the content of broken aromatic hydrocarbon -C = C- reached 50%, the total amount of hydroxy -OH decreased to 2/3 of HL, while the content of carboxyl -COOH and ether-oxygen bond -C-O- of active group doubled which are beneficial to accelerate the process of free radical chain reaction, and promote the gas release and the temperature of residual coal to reach the ignition point. The research findings enrich the basic theory of spontaneous combustion traits of water-impregnated coal, which help reduce the fire accidents and hidden dangers in actual production.

KEYWORDS:

• Coal spontaneous combustion
• exothermic characteristic
• gas release property
• pore structure
• functional group

Acknowledgments

This study was funded by the National Natural Science Foundation of China (51474106, 52174163 & 51874131).

Disclosure statement

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

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51474106, 52174163 & 51874131].