Coal mine emissions
All coal contains some level of gas due to the geological processes by which it is formed. The amount of gas varies from location to location and is commonly a mix of carbon dioxide and methane, which is released when coal is mined both in open-cut and underground operations. These escaping gases are referred to as fugitive gas emissions. Coal industry fugitive emissions account for around five per cent of Australia’s total annual greenhouse gas emissions. You can read more about Australia’s greenhouse gas emission estimates in the National Inventory Report 2015: volume one. Of all the gases present in coal, methane is of greatest concern as an emission source due to its relatively high potency as a greenhouse gas. Methane is also a safety concern, particularly in the enclosed working areas of underground mines. Methane can be handled safely if appropriate precautions are taken. Natural gas, which is commonly used in Australian households for heating and cooking, is mostly methane.
Maintaining safe methane levels
Methane in air is explosive in concentrations between 5 and 15 per cent.
Methane levels in underground mines must therefore be kept at levels of less than one per cent to ensure the safety of miners. In underground mines with high levels of methane, the coal is drained prior to mining.
While the drainage process removes most of the methane, some residual gas always remains. This residual gas is managed by maintaining sufficient ventilation air flow to ensure the methane level remains below the designated safety threshold for flammable gases in working areas of a mine.
Safe abatement of methane from coal mines
Methane drained prior to mining is safely confined within the drainage system, in the same way that natural gas delivered to households is safely confined within the pipework.
There are existing commercial technologies for the abatement of this methane, which are widely used by the industry. However, the safety measures used to manage the residual gas lead to ventilation air with very low methane content leaving the mine, contributing to global greenhouse gas emissions.
There are commercially available technologies for the reduction of ventilation air methane. There have been several investigations into applying these technologies at operating underground coalmines, both in Australia and elsewhere in the world.
However, full-scale introduction of these technologies faces severe constraints because they constitute a potential ignition source and their deployment at a coal mine would introduce a hazard that cannot be eliminated using existing mine safety protocols.
An unintended event in an underground coal mine, such as unexpectedly encountering a pocket of coal with very high gas content, could result in methane levels in ventilation air rising into the explosive range for a brief period.
Mine operators go to great lengths to prevent such events, which are exceedingly rare.
Should such an event occur, capturing the ventilation air in an enclosed duct and directing it to an abatement unit could cause the methane content to ignite and potentially cause an explosion back into the mine, resulting severe injury and loss of life to mine workers.
However unlikely, the consequences if this did occur would be catastrophic and the risk must be eliminated before deployment of the abatement technology can be considered.
Finding ways to eliminate this risk is the main focus of COAL21’s investment in fugitive emissions abatement.
COAL21 investment in safe removal of methane
As part of its investment in research and development of low-emissions coal technologies, the COAL21 Fund has invested in two projects aimed at addressing the safety concerns associated with implementing technology for lowering greenhouse emissions from mine ventilation air. Both projects focus on the safety features that would be necessary in the duct work connecting the abatement technology to an operating mine.
University of Newcastle Methane Reduction Project
This project will produce a comprehensive summary of potential safety hazards and elimination options.
This summary will guide coal mine operators considering Ventilation Air Methane (VAM) abatement, recognising that these general principles will need to be adapted to the different conditions at individual mines. Read more about this project.
Centennial Coal: Methane Reduction Demonstration Project
This project aims to demonstrate the safe connection of a VAM abatement unit to a ventilation fan at an operating mine, capturing 100 per cent of the ventilation air flow and achieving 98 per cent abatement of methane.
It will draw heavily on the general principles developed by the University of Newcastle project and apply them to a selected host mine, providing a full-scale, safe demonstration under one set of mine conditions. Read more about this project.
Alternative approaches to removing methane to reduce emissions
While the primary focus for the COAL21 Fund is the safe deployment of commercially available methane abatement technology, emerging technologies that offer an alternative will be examined if there has been sufficient testing to establish their potential.
VAM abatement by chemical looping is one such emerging technology which could offer some advantages, such as more flexible operation and smaller-sized equipment. Read more about this project.
The COAL21 Fund is investing in ongoing research into the safe deployment of VAM abatement technology with the aim of demonstrating safe abatement from an operating coal mine.
The current projects will provide a valuable step towards that goal and will inform future development. Once safe abatement from coal mines has been successfully demonstrated, the industry will have the option to employ such abatement of methane in mine ventilation air at other mines.