Mean machines

 作者:娄章脞     |      日期:2019-03-07 08:14:12
By Andy Coghlan in Sheffield EMISSIONS of carbon dioxide from the world’s 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—and 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 Scientist, 18 September, p 5). “For the same amount of energy, you would consume half the oil or coal, and get half the usual emissions,” says materials scientist Colin Humphreys of the University of Cambridge, who heads a team working on nickel-based turbine blades. “It’s worth billions of dollars,” he adds. Turbines perform more efficiently at higher temperatures. But today’s power stations can’t operate above 550 °C because their steel turbine blades would melt. So Humphreys and his colleagues are investigating if it’s feasible to replace them with nickel-based blades which tolerate temperatures of up to 750 °C. 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. “We’ve got to make the power plant blades last a lot longer, and be much larger than they are in jet engines,” 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. “We’re having to train the neural network using data Rolls-Royce has accumulated on the performance of its turbine blades,” says Humphreys. Another collaborator, Cambridge metallurgist Harry Bhadeshia, is trying to optimise the blade’s 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’s power stations’ are also unable to tolerate the intense heat, so most won’t be fitted with the new blades. The goal is to incorporate them into new power stations. “It’s 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,