Influences of the pre-oxidation time on coal secondary spontaneous combustion behaviors by temperature-programmed technique

ABSTRACT

To reveal the influence of pre-oxidation time on coal spontaneous combustion behaviors, temperature-programmed experiments were carried out to analyze the kinetics characteristics of coal primary and secondary spontaneous combustion from the macro viewpoint. By the growth-rate analysis of gaseous compounds, the critical temperature of raw coal (Y₀) spontaneous combustion was 70°C. At the critical temperature, isothermal oxidation was performed for 2 h, 4 h, 6 h, and 8 h, and the processed samples were named Y₂, Y₄, Y₆, Y₈. It was found that the changing trend of CO concentration increased at first and then decreased with the increase in isothermal pre-oxidation time. Two maximum peak values were found near the 1st and 4th hour in the production of CO₂ gas. Spontaneous combustion characteristic parameters and apparent activation energy of oxidized coal showed staged characteristics compared to raw coal. Below 70°C, the order of spontaneous combustion characteristic parameters and the apparent activation energy was Y₀< Y₂< Y₄< Y₆< Y₈. Above 70°C, the order was Y₆< Y₈< Y₂< Y₄< Y₀. Isothermal pre-oxidation at the critical temperature could slow down coal secondary low-temperature oxidation and speed up high-temperature oxidation. When isothermal pre-oxidation is at the critical temperature, the pre-oxidation time has double effects on the high-temperature oxidation of oxidized coal.

KEYWORDS:

• Pre-oxidation time
• coal spontaneous combustion
• spontaneous combustion characteristic parameters
• oxidation kinetics

Disclosure Statement

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

Additional information

Funding

This work was supported by The Youth Innovation Team of Shaanxi Universities (21JP070), the National Natural Science Foundation of China (No. 51704226, 51974236).