Effect of Low Oxygen Concentrations on the Thermokinetics of Coal Combustion

ABSTRACT

This study evaluated the effects of low oxygen concentrations on the apparent activation energy, reaction mechanism, and kinetic parameters of coal combustion. It was aim to prevent spontaneous combustion of coal. The thermogravimetric analysis and differential scanning calorimetry curves were measured under different heating rates and oxygen concentrations. The effects of oxygen concentration on the apparent activation energy and reaction mechanism were investigated by thermodynamic analysis. As the oxygen concentration decreased, the thermogravimetry-differential thermogravimetry curves of coal combustion began to exhibit obvious hysteresis, the temperature of the exothermic peak increased significantly, and the weight-loss rate and exothermic rate of coal decreased significantly. When the oxygen concentration increased from 5% to 21%, the average ignition temperature decreased by 16°C, indicating that the reduction in oxygen concentration had a significant inhibitory effect on coal combustion. As the conversion rate (temperature) increased, the activation energy first increased and then decreased. The apparent activation energy in the combustion stage gradually increased from 24.4 to 32 kJ/mol as the oxygen concentration increased from 5% to 21%. As the oxygen concentration increased, the reaction mechanism gradually changed from following the A–E equation (two-dimensional diffusion) to the anti-Jander equation (three-dimensional diffusion). When the oxygen concentration reached 21%, the mechanism followed a parabolic model. The research results had important guiding significance for the prevention of coal spontaneous combustion.

KEYWORDS:

• Spontaneous coal combustion
• oxygen concentration
• characteristic temperature
• kinetic parameters
• most probabilistic mechanism function

Highlights

1. Increasing the oxygen concentration would make the TG curve moved to low temperature area gradually.

2. Reaction mechanisms of coal combustion at various oxygen concentrations were studied.

3. Oxygen concentration had an effect on the combustion reaction kinetic parameters of coal.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (Grant Nos. 5180−4247, 5167−4191, 5160−4215, and 5150−4186) and the Industrial Science and Technology Project of Shaanxi Province, China (Grant No. 2017−JM−5114).