UK engineers: Ceramic tubes could cut emissions

Greenhouse gas emissions from power stations could be cut to almost zero by cleaning up the combustion process, British engineers said today.

Using ceramic tubes made from an advanced material called LSCF inside the combustion chamber could revolutionise the way gas is burnt to produce energy.

LSCF has the remarkable property of being able to filter oxygen out of the air and by burning fuel in pure oxygen, it is possible to produce a stream of almost pure carbon dioxide, which has commercial potential for reprocessing into useful chemicals.

Government figures show that the UK’s power stations create more than 200m tonnes of CO2 a year, more than a third of the country’s total output.

The ceramic material was developed for fuel cell technology but engineers at Newcastle University and Imperial College London recognised its potential in power stations.

Conventional gas-fired power stations burn methane in a stream of air, producing a mixture of nitrogen and greenhouse gases including carbon dioxide and nitrogen oxides, which are emitted into the atmosphere.

Separating the gases is not practical because of the high cost and large amount of energy required.

However, the LSCF tubes would allow only the oxygen component of air to reach the methane gas, resulting in the production of almost pure carbon dioxide and steam, which can easily be separated by condensing out the steam as water.

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

Details of the research are given today in two technical publications, Materials World and The Chemical Engineer.

The tubes look like small, stiff drinking straws and are permeable to oxygen ions.

They are resistant to corrosion or decomposition, even at typical power station operating temperatures of 800C.

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

The oxygen-depleted air, which consists mainly of nitrogen, can be returned to the atmosphere with no harmful effects on the environment, while the carbon dioxide can be collected separately from the inside of the tubes after combustion.

Alternatively, the flow of air and methane could be controlled so that only partial combustion took place.

This would result in a flow of “synthesis gas”, a mixture of carbon monoxide and hydrogen, which can easily be converted into a variety of useful chemicals.

The tubes of LSCF, which stands for Lanthanum-Strontium-Cobalt-Ferric Oxide, have been tested successfully in the laboratory and the design is attracting interest from the energy industry.

Tests are now being made to ensure they could withstand commercial use for a reasonable length of time.

In theory 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, although this would add to the cost and complexity of running a power station.

Professor Ian Metcalfe, of Newcastle University, tested the process in the lab.

He said: “The cheapest way to dispose of waste carbon dioxide from combustion is to release it into the atmosphere.

“We have been doing this since humans first discovered how to make fire.

“The technology we have developed may provide a viable alternative, although whether it is economical to introduce it will depend largely upon the carbon credit system that Governments operate in the future.”