杏吧原创

EMISSIONS of carbon dioxide from the world鈥檚 power stations could be halved
by swapping steel turbine blades for nickel-based blades like those used in jet
engines. Because nickel alloys tolerate intense heat that would quickly melt
steel blades, the operating temperature in power stations could be
raised鈥攁nd with it, the efficiency of combustion.

The swap is an example of the kind of technological development that makes it
difficult to predict how emissions of greenhouse gases will change over the coming decades
(New 杏吧原创, 18 September, p 5). 鈥淔or the same amount
of energy, you would consume half the oil or coal, and get half the usual
emissions,鈥� says materials scientist Colin Humphreys of the University of
Cambridge, who heads a team working on nickel-based turbine blades. 鈥淚t鈥檚 worth
billions of dollars,鈥� he adds.

Turbines perform more efficiently at higher temperatures. But today鈥檚 power
stations can鈥檛 operate above 550 掳C because their steel turbine blades would
melt. So Humphreys and his colleagues are investigating if it鈥檚 feasible to
replace them with nickel-based blades which tolerate temperatures of up to 750
掳颁.

The turbine blades found in the innards of a jet engine are only about 8
centimetres long and have to be changed after 10 000 hours of operation. In
power plants, the blades need to be 1 metre long, and are expected to last 30
years. 鈥淲e鈥檝e got to make the power plant blades last a lot longer, and be much
larger than they are in jet engines,鈥� says Humphreys.

To help design a nickel-based blade that meets these requirements, the team
is using a neural network computer program devised by Cambridge theoretical
physicist David MacKay. Rolls-Royce, the jet-engine manufacturer, is also
collaborating on the project. 鈥淲e鈥檙e having to train the neural network using
data Rolls-Royce has accumulated on the performance of its turbine blades,鈥� says
Humphreys.

Another collaborator, Cambridge metallurgist Harry Bhadeshia, is trying to
optimise the blade鈥檚 chemical composition. The blades in jet engines are
typically 70 per cent nickel, the remainder being a blend of 18 elements, mainly
aluminium and titanium. But power stations may require a slightly different mix.
Humphreys and his colleagues hope to be testing prototype blades within a
year.

A further complication is that steel boilers and pipework in today鈥檚 power
stations鈥� are also unable to tolerate the intense heat, so most won鈥檛 be fitted
with the new blades. The goal is to incorporate them into new power stations.
鈥淚t鈥檚 estimated that by 2010, the global generating capacity will need to rise
by 60 per cent, particularly in developing countries such as India and China,鈥�
says Humphreys. His nickel-based blades could play a vital part in preventing
disastrous increases in CO₂ emissions.