Capturing fugitive methane emissions
Methane poses a unique challenge in the coal industry as risks associated with it are not only a safety hazard, but a significant contributor of greenhouse gas (GHG) into the atmosphere. It is the second most abundant greenhouse gas following carbon dioxide, and 28-times more potent than carbon dioxide per molecule in trapping heat in the atmosphere.
The amount of methane in the atmosphere has more than doubled since pre-industrial times – as a result of human activity – according to recent CSIRO research involving ANSTO, the Australian Antarctic Division and international partners. In Australia fugitive methane emissions from coal mining and handling and decommissioned mines represented 5.3 per cent of Australia’s total net GHG emissions in 2017.
Fugitive gas mitigation technologies – capture, destroy, use
CSIRO has developed a suite of three technologies that aim to mitigate methane emissions by either destroying or enriching the gas or capturing the ventilated air – known in the industry as Ventilation Air Methane (VAM) – from coal mines and using it to generate electricity.
“Our first technology is a mitigation unit called VAMMIT, which is a compact flow reversal reactor with a newly-structured regenerative bed to destroy methane in a cost-effective manner,” CSIRO lead scientist and technology inventor, Shi Su, says.
“Whereas the second technology is a capture and enrichment unit, called VAMCAP, which essentially collects and separates the methane from the ventilated air using carbon composites.
“Our third technology, VAMCAT, uses a catalytic combustion gas turbine to create electricity from an otherwise waste product.”
Dr Su developed several research projects including a $7.1 million project primarily funded by the Department of Industry, and a $1.95 million project funded by Coal Innovation New South Wales, and established a research team to develop the technologies from fundamental studies to pilot scale and mine site trials.
Capturing low concentration methane
CSIRO research engineer, Jon Yin, adds that VAMMIT and VAMCAT work in environments with a low VAM threshold. They can be operated as independent units or be used together in different configurations, which are determined by the needs of the coal mining operations and mine site conditions.
“In practice, the VAM concentration sometimes drops below 0.3 per cent, and that’s where the VAMCAP technology comes into play by treating part of the ventilation air. Its aim is to enrich VAM from very low concentrations, to a much higher concentration, to about 25 or even 30 per cent. The enriched methane can be used to assist the operation of the VAMMIT and VAMCAT units.
“And the waste heat from the VAMMIT and VAMCAT units can be used by VAMCAP for stripping methane in the regeneration process.
“The three VAM technologies are complementary. Depending on the mine site conditions, a company may choose to use one technology or a combination of them.”
This is economical because the units are modular, which makes them easily transportable, reduces the installation costs, and makes it easier for mine operators to scale up their fugitive emissions mitigation efforts.
“They can be easily added to an existing VAM plant and/or to a new ventilation air shaft as the ventilation systems are not going to exist in the long term, so maybe for 10 or 15 years until mining operations finish,’ Dr Yin says.
“So from then on you can move the VAM units to a new ventilation air shaft system, and that’s why we developed the technology at a portable scale. Otherwise you will have problems like the very high cost of relocation, which can be higher than building new units or VAM plants,” Dr Yin says.
World-leading methane capture expertise
CSIRO’s VAM technologies are world‑leading and possess significant advantages over others. They have been developed and successfully proved at a large scale at a mine site. With all necessary operating data, engineering and safety management experience, they are ready for further scale up. They can also be potentially applied in overseas coal mines, such as in the US and China.
Supported by Coal Innovation New South Wales, the team is developing a catalytic version of VAMMIT for mine site trials. These will target a minimum methane concentration of 0.15 per cent and lower operational temperature (below 650 degrees Celsius), suitable for some mines with a VAM concentration of under 0.3 per cent over a substantial period.