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In coal mine goaf gas samples the detection of significant concentrations of hydrogen accompanied by carbon monoxide and hydrocarbons is usually a cause for alarm because it is conventionally understood to indicate that there is a well advanced heating taking place in the goaf. Hydrogen is understood to be one of the gases evolved from coal that is being heated at elevated temperatures. From time to time however, in some Australian coal mine goaf gas samples anomalous high concentrations of hydrogen have been detected without accompanying high concentrations of carbon monoxide and hydrocarbons, thus raising questions about the source of this hydrogen. Possible alternative sources of hydrogen in goaf gases could be acid water on metal reactions, partially combusted diesel fuel in engine exhaust gases and perhaps even as a naturally occurring component of some seam gases.
This project was a first trial of using hydrogen isotope ratio analysis methods to determine if they could differentiate between hydrogen samples generated from acid-metal reactions, coal being heated, and from diesel fuel combustion. The work was carried out in the Stable Isotope Geochemistry Laboratory at the University of Queensland under sub-contract arrangements with the North Goonyella Coal Mines Limited.
The study showed that isotope ratio analysis could readily distinguish hydrogen produced from acid-metal reactions from hydrogen produced by combustion of coal or diesel fuel. However, used in isolation, the technique could not differentiate between hydrogen produced from combustion of coal and diesel fuel because there was insufficient difference in the isotope compositions from these organic sources.