High-temperature materials increase efficiency of gas power plants
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Energy Sector Analysis
Improvements to turbine blade materials are making natural gas a more environmentally friendly fuel.
High-temperature materials increase efficiency of gas power plants By Angela Saini Feature Editor Tresa Pollock
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n the global push to adopt more sustainable fuels, change can of 1430°C, which was more than 100 degrees higher than the seem frustratingly slow. Coal still leads the pack as the most previous most efficient combined cycle systems. This in turn popular means of producing electricity in many countries. The was made possible by the materials used to make the turbine disheartened, however, may find some comfort in its runnerblades—the world’s largest single-crystal airfoils made of up—natural gas, a cleaner fossil fuel than coal. By switching nickel-based alloys, known as “superalloys,” with extra heatto gas while also improving the efficiency of gas-fired plants, resistance provided by special thermal coatings made of yttriacarbon emissions could drop significantly in the short term. stabilized zirconia. New materials are at the heart of the challenge of driving “Nickel-based superalloys remain the material of choice,” up efficiency and reducing environmental impact. The turbine said Stephen Balsone, a consulting engineer working on gas is the workhorse of a power plant, and efficiencies of current turbine materials and processes at GE Energy. “They possess coal-fired power plants may be as low as 30 percent. Combined an excellent balance of engineering properties for high-tempercycle plants, which combine a gas turbine and a steam turbine ature structural applications, including high-temperature creep and are fueled by natural gas, are now far leaner than coal and thermal fatigue resistance along with high-temperature technologies. Efficiencies are starting to edge past 60 percent, oxidation resistance.” with each percentage point representing a $20 million savings With up to 10 main alloying elements, Konter said that the in fuel over the lifetime of the plant. difficulty for the materials scientist lies in striking the right The problem is that increasing the size and temperature of balance between them to produce the best qualities. “For exthese combined cycle machines as a way of boosting efficiency ample, chromium is essential to provide sufficient hot corrosion and output puts a deep toll on the turbine blades (known as resistance, but at the same time is detrimental for phase stability “buckets” among industry insiders). “Components are much and strength. Rhenium (which has a melting point of 3180°C) larger and serve at base load temperature much longer than increases high-temperature strength, but is extremely expensive those in aircraft engines,” said Maxim Konter, director of Materials and Materials Processing at Alstom, in Baden, Switzerland. A single blade in one of these industrial gas turbines can be 10 times larger and between 20 and 30 times heavier than that of an aircraft engine. The biggest blades can weigh as much as 20 kilograms. And with rotor inlet temp
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