Gas guzzlers

Ceramic tubes that could cut most emissions from gas-fired power stations and coal and oil-fired generators have been developed by researchers at Newcastle University.

The tubes are made from an advanced material known as LSCF, or Lanthanum Strontium Cobalt Ferric Oxide.

Originally developed for use as the cathode in fuel cells, LSCF works by controlling the combustion process, as it can filter oxygen out of air. By burning fuel in pure oxygen, it is possible to produce a stream of almost pure carbon dioxide after combustion, which can be reprocessed into useful chemicals rather than having to be captured and stored.

The work was carried out in collaboration with Imperial College London, and has been led by Prof Ian Metcalfe and Dr Alan Thursfield in the School of Chemical Engineering and Advanced Materials at Newcastle.

The tubes have been successfully tested in the laboratory as part of a recent EPSRC project and have created interest within the energy industry, according to the university. Further tests on their durability are now being carried out, and the researchers are in talks with some of the UK's large power generators concerning future partnerships.

'We are looking at the stablility of the tubes are and how they will react to impurities in the gas stage,' said Metcalfe. 'We need to discover how quickly they become unstable and so which impurities we will need to ensure are removed before combustion. All of this has an impact on the cost of using the technology.'

Conventional gas-fired power stations burn methane in air, producing a mixture of nitrogen and greenhouse gases such as carbon dioxide and nitrogen oxides, which are emitted into the atmosphere. Separating the gases is costly and uses energy. However, LSCF tubes would allow only oxygen from the air to reach the methane. The result would be the production of almost pure carbon dioxide and steam, the latter of which would be condensed out as water.

The LSCF tubes look like small, stiff, drinking straws and are permeable to oxygen ions — individual atoms carrying an electrical charge. Most importantly, LSCF is resistant to corrosion or decomposition at typical power station operating temperatures of about 800ºC.

When air is blown around the outside of the tubes, oxygen passes through the wall of the tube to the inside, where it combusts with methane gas that is also being pumped through the tubes.

The oxygen-depleted air is then safe to return to the environment, while pure carbon dioxide can be collected from the inside of the tubes after combustion.

The pure carbon dioxide could be piped to a processing plant for conversion into chemicals such as methanol, a useful industrial fuel and solvent.

Alternatively, the flow of air and methane could be controlled so that only partial combustion took place. The resulting synthesis gas — a mixture of carbon monoxide and hydrogen — could then be converted into a variety of widely used hydrocarbon chemicals.

The team said it should be possible to assemble a power station combustion chamber from a large number of the tubes, with space between them for air to circulate.

They said that as well as gas-fuelled power generation, the technology could also be applied to coal and oil-fired power stations, provided that the solid and liquid fuels were first converted into gas. However, this would add to the cost and complexity of running a power station.

Despite its environmental benefits, the technology's developers say its introduction will be hard to justify on an economic basis without changes to the current carbon credit system.

'Most advanced technologies are not economically feasible as presently, the costs associated with emitting carbon are relatively low,' said Metcalfe. 'In order for the technology to be used, there would need to be the political will to raise the cost associated with carbon emissions.'