Measurement of Greenhouse Gas Emissions from Spontaneous Combustion in Open Cut Coal Mining

The overall objective of the project was to provide methods, supported by direct measurement, to quantify the emissions of greenhouse gases from spontaneous combustion in Australian open cut coal mining.

Measurements, using a chamber technique, were carried out at eleven mine sites in the Hunter Valley and Bowen Basin. The chamber, placed on selected surfaces collected the emissions of the greenhouse gases CO2 and CH4. The emission rates of the greenhouse gases were determined from the measurements.

Emissions from spoil piles, coal reject and tailings with and without spontaneous combustion were measured. The data provided emission factors for these surfaces broken into the three categories

• Intense spontaneous combustion characterised by smoke and steam, major cracks, surface discolouration and obvious signs of gas venting
  
• Spontaneous combustion with less well pronounced signs, small cracks, surface discolouration and occasional or wisps of smoke or steam
  
• No sign of spontaneous combustion

The data are reported as averages for the individual mines and were then combined to form averages for the Hunter Valley and the Bowen Basin and for both coalfields combined. The rms deviations for all the data are also reported and are approximately the same as the average values indicating the wide scatter in the data. Such scatter is to be anticipated given the inhomogeneous nature of spoil pile material and permeability of surfaces.

A key finding of the research is that the emission rates of greenhouse gases from spoil piles where there is no spontaneous combustion, but only low temperature oxidation of coal and coal waste, are similar to the emission rates due to biological activity from vegetated surfaces. This finding suggests that spoil piles that have no spontaneous combustion might be considered to make minimal net contribution to greenhouse gas emissions. However, further research is required to better define the emission rates from these low temperature processes.

The emission factors presented in this report should be considered interim at this stage as they will be continue to be refined as part of ACARP project C9062 which is currently being undertaken and which will use airborne thermal infra red photography to relate surface expressions of heating to emission rates and may lead to a different method of classifying the emissions.