Coal mine methane emissions accounted for 5.3 percent of Australia’s net emissions in 2017. However, abatement of emissions from coal mines also represents opportunity to provide clean power, clean gas and clean chemicals to society.
In this third blog of my “Addressing the Safeguard Mechanism” series, I explore coal mine emissions and how substantial value is being generated though abatement.
In my view, coal mine methane represents an excellent opportunity to tap unrealised value whilst also driving emissions reductions.
Sources of emissions
Moranbah North is at the top of the baseline list for coal mines in Queensland with reported covered emissions for 2022 to 2021 of just over 2 million tonnes carbon dioxide equivalent. This is well under their calculated baseline of 4.5 million tonnes carbon dioxide equivalent. Most coal mines also appear to be performing well under their baseline. Oakey Creek for example is at 860 thousand tonnes carbon dioxide equivalent against a baseline of 1.7 million tonnes carbon dioxide equivalent.
The principal emission from coal mining is methane, the main component of natural gas. Methane itself is valuable and can be used for heat, power and as a chemical feedstock. Therefore, there is a value driver to harvest and monetise methane emissions from coal mines which explains the coal industry’s over performance.
Methane’s global warming potential is estimated at 28 times that of carbon dioxide on a 100 year timeframe. This means simply oxidising methane through methods such as combustion in a power station, generates significant reductions in carbon dioxide equivalent emissions. Of course, if you can make some power, heat or fertiliser out of it, all the better.
In Queensland, a number of successful small power stations have been operating on coal mine waste gases for many years, including one at Moranbah North owned and operated by EDL. EDL state that Moranbah North, abates some 2.08 million tonnes of a carbon dioxide equivalent and produces some 450GWh of electricity per annum. This appears to account for the bulk of Moranbah North’s emissions abatement.
How is coal mine methane collected and used?
Coal mine methane is released from the seam prior to mining when the seam to be mined is pre-drained of water. As water is pumped from the seam, the hydrostatic pressure on the coal is reduced and methane adsorbed into the coal is released.
In underground mines, this methane must be removed from the seam before mining starts to prevent explosions. Pre-drained gas is collected using a series of gas wells drilled in advance of mining operations.
Gas generated form pre-draining open cut mines is generally not collected as it simply vents to atmosphere in concentrations well below the lower explosive limits as it is mined. As seams suitable for open cut mining are generally closer to the surface, the hydrostatic pressure is lower and therefore there is generally less gas adsorbed into the coal. Some open cut mines are now considering collecting pre-drain gas as part of their sustainability programs.
Pre-drained gas is typically 25 to 60 percent methane and is generally suitable for use in some spark ignition reciprocating engines. Pre-drained gas can be variable in its constituents and therefore requires a more robust combustion system.
Pre-drained gas can also be processed to pipeline standard and sold as natural gas. Arche Energy’s client, Queensland Pacific Metals have recently acquired the Moranbah Gas Project and intend supplying their Townsville Energy Chemicals Hub (TECH) Project, along with other gas consumers in Moranbah and Townsville with renewable methane sourced from the Bowen Basin’s coal fields.
In areas where the power, or gas network is not available, pre-drained gas is simply flared to take the greenhouse potential from 28 to one times of a carbon dioxide equivalent.
In underground mine continuous ventilation is required is maintain the methane content at levels below one percent because methane continues to de-adsorb from the coal over time. This, very low concentration methane content is more difficult to use, but can be oxidised through a catalytic system, which is concentrated or the ventilation exhaust can be fed directly into the combustion system of a gas engine.
What are the opportunities?
With the value of energy rising, the power generation for both clean and dispatchable is a very attractive option, as well as processing and sale as natural gas. Options also exist for on-site chemical manufacturing from stranded gas. For example a small ammonia plant.
Arche Energy’s Carbon and Energy Reduction Review is intended to set a sustainability pathway strategy that best meets the needs of your business. Arche Energy can help work through the options for monetisation of stranded gas including power generation, connection to the gas network, virtual pipelines and on-site chemical manufacture.
Arche Energy is Australia’s leading owner’s engineer for gas power generation and is able to help you scope, develop and deliver as waste gas to energy project designed to maximise energy market returns.
The Safeguard Mechanism
Click here to understand the basics of the safeguard mechanism and here to read about how the steel industry is managing its obligations.
About the Author
Andrew Murdoch is the Managing Director of Arche Energy and is is a long term energy industry participant, advisor and energy nerd.
