Recent news that a gas project in Queensland has been charged with environmental harm has put the spotlight on underground coal gasification, or UCG.
Linc Energy’s Chinchilla project was a pilot UCG project which was completed in October 2013. Following a nine-month government investigation, the project now faces a potential fines of A$2 million over alleged “serious environmental harm”. The company has vowed to fight the charges, and claims regulation favours the rival coal seam gas industry.
UCG, like coal seam gas (CSG), is an unconventional method of extracting gas from coal seams. It is also considered a “clean coal” technology — offering a way to continue exploiting coal resources while reducing greenhouse gas emissions. While it is estimated that Australia has reserves of 1 trillion cubic metres of CSG reserves, there may be 12 trillion cubic metres of UCG.
Despite trialling the technology since the 1980s, UCG has so far failed to achieve the environmental standards needed for commercialisation. So, what is UCG, and are concerns about environmental impacts justified?
What is UCG?
Coal gasification is a technology for producing synthesis gas (a mix of hydrogen and carbon monoxide) from coal before it is burnt. This “syngas” can be processed further for fuel or chemical products.
Unlike fracking, which involves pumping fluid into coal seams to cause fractures, in UCG the entire process takes place underground within the coal body. Coal is ignited by injecting oxygen into the coal seam. The combustion converts carbon in the coal to CO2 and heat. This heat drives secondary reactions between CO2 and water to produce carbon monoxide (CO), hydrogen gas (H2) and methane (CH4). The gases are extracted through a production well, leaving tar, solid char and bottom ashes in the cavity.
These gases can be used to generate electricity, and the hydrogen can be used to power fuel cell vehicles.
UCG is considered a “clean coal” technology. When coupled with electricity generation, UCG produces 25% less greenhouse gases, 80% less nitrous oxides, and 95% less sulphur oxides per megawatt hour than traditional coal-fired power generation.
UCG in Australia
In Australia there are very good prospects for UCG development, particularly in abandoned or exploited CSG fields.
UCG projects were initiated in the 1980s. There have been three pilot projects, all in Queensland — Linc Energy’s Chinchilla project, Cougar Energy’s Kingaroy project, and a study program between Carbon Energy and CSIRO at Dalton.
During its life-time the Chinchilla project successfully produced gas for electricity generation — considered the western world’s ground-breaking UCG achievement — and liquid gas for fuel.
But water contamination from Cougar Energy’s project forced the project to close in 2011, and with pilot stages complete, the Queensland government on the recommendation of an independent scientific panel has refused approval for commercialisation until the industry can prove that UCG projects can be safely decommissioned and prevent groundwater contamination.
The major environmental concerns for UCG stem from subsidence, water contamination and greenhouse gas emissions.
However these issues can be resolved by targeting deeper coal seams; most current UCG projects focus on shallow reserves. Subsidence decreases with the depth of the coal seam, and deeper coal seams are less likely to be in contact with aquifers.
UCG cavities deeper than 800 metres could also be used for CO2 sequestration, where cap rock and overburden layers can restrain the CO2.
Australian and New Zealand UCG projects are regulated under respective Mining Acts. Currently, these are not detailed enough to commercialise UCG.
But in Alberta, Canada, deep UCG pilot projects are ready for commercialisation, and suitable regulation has been provided by the Albertan mining regulator.
Where to from here?
Deep coal deposits are the future for UCG. Coupling UCG with electricity generation and carbon capture and storage is a environmentally safe and economic method for exploiting unconventional coal resources.
In Australia, the coal deposits of Queensland are the most suitable for such projects, and should be an area for further research and development. With 100 years of effort and investment in the technology, we now need governments to update regulation to encompass UCG.