Effect of the sudden change of ambient atmosphere on free radicals in coal body by CO₂ fire prevention gas injection

ABSTRACT

The coal body’s gas environment transforms during the CO2 fire prevention procedure from an oxygenated ambience to a CO2 gas ambience, which in turn prevents the coal body from continuously oxidizing. To investigate the effect of sudden changes in the gas environment to which the coal body is exposed on the microscopic group reactions, the free radical parameters such as ESR in situ spectra, line widths, g-factors, and free radical concentrations of the coal bodies during the gas atmosphere transition at different temperature moments were measured. The findings are as follows: as the injection temperature point for CO2 rises, the spectral peak height increases, and the paramagnetic center of coal shifts at lower temperature in CO₂ atmosphere than in dry air atmosphere. After the abrupt change of gas environment, free radical levels first decrease and subsequently rise. Furthermore, the general development rate of free radicals can be slowed down by injecting CO₂ at lower temperatures. Meanwhile, at lower temperatures, the higher the temperature point of the minimum g value is, the smaller the maximum g value is. Changes in a gas atmosphere, sudden decrease in line width of ESR spectra of coal bodies, and the line width finally stabilizes around 0.45. CO₂ injection at 70°C has the best inhibitory effect on free radicals.

KEYWORDS:

• Coal spontaneous combustion
• free radical reaction
• gas atmosphere
• low temperature oxidation
• carbon dioxide fire prevention

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the China University of Mining and Technology .