Researchers at the University of Leeds are exploring a greener, safer and cheaper way of using coal from deep underground seams as an energy source.
Under the proposed scheme coal would be burned underground to generate energy, offering a new lease of life to coal seams that are too expensive to mine. Waste greenhouse gases would also be stored in the rock, making the process virtually carbon neutral.
Coal-fired power plants still have a sizeable carbon footprint, despite advances in technology that have made them 'greener'. Many of the world's coal reserves are also lying unused because the seams are simply too deep to dig out.
University of Leeds engineers, together with colleagues from across Europe, hope to solve both of these problems in a €3 million project funded by the European Commission.
“The potential environmental impact of this scheme is enormous,” said Dr Yong Sheng, who is leading the University of Leeds part of the project. “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. This two-step process makes it easy to meet these targets, whilst making the most of coal seams that might otherwise be impossible to exploit.”
During the first step – a process known as underground coal gasification (UCG) – oxygen or enriched air are injected into the un-mined seam together with water and the coal is 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- and/or methane-rich gas stream could be used to generate power in conventional turbines or fuel cells, or for industrial heating. Meanwhile, the CO2-rich stream of gas would be compressed and injected back into the rock, filling the space where the coal had previously been. In other words, most of the carbon produced by the underground burning would be locked into the rock. The proposed two-step process consequently provides a source of clean energy with a near-zero carbon footprint.
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. The proposed scheme for on-site, underground CO2 storage is, however, completely 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. This scheme would be much more cost-effective – as well as virtually carbon neutral – because we wouldn't need to move the gas anywhere,” said Dr Sheng.
Researchers will assess the viability of the scheme at a test site in Bulgaria where coal is buried more than 1200m 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.
The project is being coordinated by the Bulgarian company Overgas Inc. AD. The other partners are the Geological Institute of the Bulgarian Academy of Sciences (BAN), Institute for Solid and Fuels Technology Applications (Greece), Instituto Superior Técnico of Technical University of Lisbon (Portugal), DMT GmbH &Co KG (Germany), Geo-ForschungsZentrum Potsdam (Germany) and UCG Engineering Ltd (UK).