Underground » Ventilation, Gas Drainage and Monitoring
No gas sensor currently employed in underground coal mines is capable of remote sensing. Such a device would be of considerable benefit to the Australian coal mining industry in that it would facilitate methane detection and measurement in difficult-to-access locations.
The spectroscopic method is the only way to provide such sensing. Moreover, it has many other advantages such as high sensitivity, a fast response and molecular selectivity.
Consequently, the objective of the research project was to demonstrate and prove the innovative concept that remote methane detection and measurement can be undertaken by the spectroscopic method using a tuneable laser diode.
The objective of the project was achieved. It was demonstrated that remote methane detection and measurement can be successfully accomplished using a tuneable laser diode to generate an infra-red beam at a wavelength of 1.6179670 µm and coal, or rock types that are typical of coal mine roof strata, as the reflecting medium.
In the near infra-red region of the spectrum, coal was shown to approximate to a Lambertian reflector >>, i.e. its diffuse reflectance is almost independent of incident angle. The implication of this is that, assuming diffuse reflectance, the intensity of an infra-red beam reflected back from a coal face or rib would be almost independent of the condition of the surface and of the angle which the beam makes with the surface.
The challenges that the concept might face when moving from the laboratory to the mine site were identified and solutions proposed. It was concluded that there appears to be no insurmountable impediment to implementing the concept of remote methane detection and measurement in underground coal mines.
It is anticipated that absorption spectroscopy using a tuneable laser diode will lead to a compact and low-cost remote methane detection and measurement device. Recommendations are made for developing the proof-of-concept device into an intrinsically safe prototype capable of detecting and measuring range-integrated methane concentrations as low as 10 ppm m at distances of up to 30 metres.