Underground » Ventilation, Gas Drainage and Monitoring
Infra-red 'open path' methane detection and measurement has been widely adopted by the oil, gas and petrochemical industries. Such systems determine in-situ methane concentration over a path between two points where the path length may vary from 500 mm to more than 200 metres. Coal industry interest in employing the 'open path' technique has centred on those areas of the mine which are not readily accessible for conventional 'point' monitoring devices or where adverse conditions limit their usefulness. However, none of the existing commercially available systems had been trialed in underground coal mines. Nor had an assessment been made as to whether the underground environment precluded the safe use of such systems.
Consequently, the overall aim of the project was to identify and select the most 'promising' of the existing, commercially available infra-red 'open path' systems for use in underground coal mines and to demonstrate it in a simulated mine environment. Research issues that were to be addressed included the cross-sensitivity of such systems to gases other than methane, their speed of response, sensitivity to airborne coal dust and to water droplets and films, and the effects of vibration. Issues of safety including their 'Certifiability' for use in explosive gas atmospheres in Australian underground coal mines and their 'Approvability' for use in hazardous zones in New South Wales coal mines were also to be considered. In addition, potential applications of such systems in underground coal mines were to be identified.
The objectives of the project have been achieved. It has been demonstrated that, subject to detailed safety modifications that have been identified, at least one commercially available system is suitable for use in the following potential applications in Australian underground coal mines.
- Detection and measurement of rapidly changing, transient methane concentrations during wind blasts and outbursts.
- Monitoring of the open goaf behind the roof supports when 'hang ups' occur during longwall mining.
- Monitoring of the face side of the longwall shearer on faces subject to frictional ignition.
- The replacement of multiple 'point' methanometers along belt roads in 'gassy' coal mines
The following further developments will be required before 'open path' monitoring will be useful in all potential coal mining applications. It recommended that the coal industry support efforts to realise such developments.
- 'Single ended operation'. On occasion, access to a site receiver or reflector at the 'far end' of the 'open path' is difficult or impossible. Consequently, it would be necessary for the infra-red beam to be reflected back from the rib or face to the transmitter/receiver. Such a development would require more 'inband' power than is available but could be achieved by substituting a laser diode for the incandescent globe employed in current devices.
- The resolution of methane concentration along the open path.
The comprehensive final report includes all findings relevant to the application of remote methane detection and measurement of Australian coal mines.