Burning coal underground could be a greener, safer and cheaper way of using it to produce energy, according to engineers at Leeds University.
The engineers plan to conduct a test scheme for deep underground coal seams that are too expensive to mine, as part of a €3m (£2.5m)international project funded by the European Commission.
Waste greenhouse gases will be stored in the rock, which the researchers claim would make the process virtually carbon neutral while opening up large quantities of a high-density energy source.
‘By 2020, all power plants across Europe will have to incorporate some system of carbon capture and storage to meet EU targets on greenhouse gas emissions,’ said Dr Yong Sheng, who is leading the Leeds University part of the project.
‘This two-step process makes it easy to meet these targets, while making the most of coal seams that might otherwise be impossible to exploit.’
Through a process known as underground coal gasification (UCG), oxygen or enriched air would be injected into the un-mined seam together with water, and the coal would be burned underground at high pressure.
This produces streams of combustible gas, rich in hydrogen and/or methane and CO2, which can be extracted from underground through long boreholes.
Once above ground, the hydrogen/methane-rich gas streams could be used to generate power in conventional turbines or fuel cells, or for industrial heating.
Meanwhile, the CO2-rich streams would be compressed and injected back into the space in the rock where the coal had previously been, effectively locking away most of the carbon produced by the underground burning.
UCG has been tested in numerous small-scale trials worldwide. The technology was applied on an industrial scale in the former Soviet Union and is still operating in Uzbekistan. But the proposed scheme for on-site, underground CO2 storage is new.
‘There is a lot of talk about the need for carbon capture and storage, but nearly every suggested system has the same problem: the high cost of capturing and transporting carbon dioxide to the storage site,’ said Dr Sheng.
‘This scheme would be much more cost effective – as well as virtually carbon neutral – because we wouldn’t need to move the gas anywhere.’
Researchers will assess the viability of the scheme at a test site in Bulgaria where coal is buried more than 1,200m underground.
The international team, including the Leeds engineers, will use data from this site to model the complete process – including combustion, gas extraction and CO2 storage.
They will pay particular attention to potential environment hazards, such as the chance of stored CO2 leaking through cracks in the rock.
Bulgarian company Overgas will co-ordinate the project in partnership with the Geological Institute of the Bulgarian Academy of Sciences, Institute for Solid and Fuels Technology Applications (Greece), Instituto Superior Técnico of the Technical University of Lisbon (Portugal), DMT (Germany), Geo-ForschungsZentrum Potsdam (Germany) and UCG Engineering (UK).