Initial exploration on potential fire hazards detection from coal spontaneous combustion applied by acoustic wave

Area of Science:

• Geophysics
• Materials Science
• Combustion Science

Background:

• Coal spontaneous combustion leads to resource waste and environmental pollution.
• Early detection of high-temperature areas in coal is crucial for prevention.
• Acoustic thermometry offers non-contact, high-interference resistance for temperature measurement.

Purpose of the Study:

• To investigate the acoustic wave attenuation characteristics in loose coal.
• To establish the relationship between coal properties (particle size, temperature, metamorphic degree) and acoustic attenuation.
• To provide theoretical support for acoustic thermometry in detecting high-temperature zones in coal.

Main Methods:

• Computer tomography was used to analyze void distribution in four bituminous coal types.
• A self-designed acoustic attenuation test device measured attenuation coefficients under varying temperatures and particle sizes.
• Analysis of acoustic wave propagation and attenuation mechanisms in loose coal.

Main Results:

• Loose coal void distribution is strongly related to particle size; smaller particles yield more uniform voids, while larger particles create larger voids.
• Acoustic attenuation coefficients increase with frequency for all coal samples.
• Coal particle size distribution significantly impacts acoustic attenuation, more so than temperature or metamorphic degree.
• Peak sound attenuation occurred at specific frequencies (400, 700, 1100, 1600 Hz) related to particle size, indicating void distribution as the primary factor affecting acoustic wave propagation.

Conclusions:

• Void distribution, determined by particle size, is the dominant factor influencing acoustic wave propagation and attenuation in loose coal.
• Acoustic wave attenuation results from combined absorption and scattering by loose coal.
• The findings provide a theoretical basis for employing acoustic wave detection to identify high-temperature points in coals prone to spontaneous combustion.