Underground » Detection and Prevention of Fires and Explosions
The main objective of the project was to investigate the underlying science of the radon technique by undertaking detailed studies of temperature dependence of radon emanation from coal and radon transport in strata through the studies of theoretical review, laboratory tests and field trials. All planned tasks have been completed and main outcomes of the project are summarized below.
Detailed review of radon transport mechanism in strata
Among the various mechanisms suggested for radon transport in strata, detailed literature review concludes that the geogas microbubble theory seems to be the most in accord with observation. This theory may include widespread occurrence of a microflow of gas, advecting multicomponent gas, rapid gas upflow, bubble flow, and matter transport by geogas bubbles. Underground heating of coal has a profound impact on radon transport in strata. Firstly abundant gaseous productions from the heating act as carrier gases and play a very important role in the ascending microflow of gas through fractures; and secondly the heating generates a temperature gradient (hence pressure gradient) which greatly contribute to the ascending microflow of a gas mixture consisting of carrier gases and rare gases (radon included) and the higher the temperature of coal, the greater the pressure gradient and the more rapid the ascending microflow of a gas.
Laboratory investigation of temperature dependence of radon emanation from coal
In collaboration with Taiyuan University of Technology, a special laboratory was established to investigate the relationship between coal temperature and radon emanation from the coal. Results of laboratory test show that radon concentration (relating to radon emanation from coal) increases with coal temperature, and as coal temperature increases from 30oC to 180oC, measured radon concentration increases eight times from 297 Bq/m3 to 2370 Bq/m3. The results are in accord with those for most minerals as reported in literature, i.e. radon emanation coefficient increases with temperature in a temperature range of between room temperature to 200oC.
Detailed literature review and laboratory investigation indicate that a coal heating event underground will significantly increase the radon concentration from coal, greatly facilitate the radon transport in strata, and contribute to increased radon flux at surface. The radon technique to locate underground heating is therefore theoretically explainable and credible.
Field investigation of the radon technique
Field tests were conducted at both Dartbrook and Southland mines to further verify the radon technique. The field tests successfully identified the underground zones of the elevated coal temperature and these were consistent with those indicated by analysed results of gas sampled from the zones.
Development of appropriate radon detectors and alpha cups and a of specific data processing program
Two KZ-DO2 alpha cup radon detectors and five hundred alpha cups were acquired, meeting preset technical specifications and operation requirements. Main components of the prototype include alpha cups, alpha detection device (ionization chamber, electronic circuit, and alpha detector), amplifier, and alpha counter display. A specific data processing program has been developed. The program has been designed to load, process and display 3D data points. Field tests demonstrated that the acquired prototype and developed data processing program perform well and produce the desired outcomes.