Microscopic Structural Evolution of Oxidized Coal Residues with Different Oxidation Degree

Area of Science:

• Environmental Science
• Geochemistry
• Combustion Science

Background:

• Coalfield fires pose significant environmental and safety risks.
• Understanding the reactivity of oxidized coal residues is crucial for fire management.
• Oxidized coal's behavior under fire conditions is complex and requires detailed study.

Purpose of the Study:

• To investigate how oxygen volume fraction and oxidation temperature affect oxidized coal structure.
• To elucidate the mechanisms behind reduced coal reactivity in fire zones.
• To determine representative oxidation conditions for coalfield fires.

Main Methods:

• Industrial and elemental analyses of oxidized coal residues.
• Infrared diffuse reflection spectroscopy.
• Specific surface area and pore size distribution analysis.

Main Results:

• Increased temperature and oxygen volume fraction decrease volatile matter and fixed carbon, especially above 400 °C.
• Hydroxyl groups decrease with rising temperature under high oxygen; carboxyl groups increase at lower temperatures with elevated oxygen.
• Oxygen-lean, high-temperature conditions reinforce coal structure, reducing aromatic hydrocarbon condensation. Oxidation alters pore morphology, consuming the carbon matrix and reducing micropores, thus hindering internal gas diffusion.

Conclusions:

• Elevated temperatures and oxygen levels reduce coal reactivity by modifying its internal structure and pore network.
• Oxygen-deficient combustion and structural reinforcement contribute to decreased reactivity.
• Altered pore morphology and reduced internal gas diffusion are key factors in the diminished reactivity of oxidized coal in fire zones.