Thermal barrier coatings issues in advanced land-based gas turbines
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Thermal Barrier Coatings Issues in Advanced Land-Based Gas Turbines W.P. Parks, E.E. Hoffman, W.Y. Lee, and I.G. Wright The Department of Energy's Advanced Turbine Systems (ATS) program is aimed at fostering the development of a new generation of land-based gas turbine systems with overall efficiencies significantly beyond those of current state-of-the-art machines, as well as greatly increased times between inspection and refurbishment, improved environmental impact, and decreased cost. The proposed duty cycle of ATS machines will emphasize different criteria in the selection of materials for the critical components. In particular, thermal barrier coatings (TBCs) will be an essential feature of the hot gas path components in these machines. The goals of the ATS will require significant improvements in TBC technology, since these turbines will be totally reliant on TBCs, which will be required to function on critical components such as the first-stage vanes and blades for times considerably longer than those experienced in current applications. Important issues include the mechanical and chemical stability of the ceramic layer and the metallic bond coat, the thermal expansion characteristics and compliance of the ceramic layer, and the thermal conductivity across the thickness of the ceramic layer.
IKeywords advancedturbine systems, bond coatings, combustion turbines, land-based turbines, thermal barrier coatings
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1. Introduction THE PREDICTEDworldwide need for new electricity generation capacity in the 1990s is 600 GW. In the United States, energy consumption is expected to increase by 46% in the next 10 years or so (Ref 1), which suggests a market in the U.S. alone for new base-load electricity generation capacity of 20 GW per year. Approximately 44% of the current electricity-generating capacity in the U.S. will be more than 40 years old by the year 2010 (Ref 1), and its replacement will be necessary to meet stringent emissions standards. The technology required by conventional fossil fuel-fired steam boilers to meet these demands is ready and available; however, substantial reductions in CO2 emissions will probably necessitate some fuel switching, since approximately 40% of all the carbon emissions in the U.S. currently are produced by the electric utilities (Ref 2). The projected efficiency of the best available coal-fired steam boiler technology, represented by the Electric Power Research Institute's State-ofthe-Art Power Plant (SOAPP) (Ref 3), is 42% (8100 Btu/kW.h net at full load, based on the higher heating value [HHV] of the fuel) when an advanced supercritical steam cycle is employed, which compares with approximately 38% for the best coal-fired plants currently in operation in the U.S. Gas-fired gas turbine combined-cycle systems are expected to account for a significant fraction of the projected new capacity. Such plants area available in a range of sizes, up to more than 200 MW(e) per turbine, which allows the concept of modular buildup of new capacity to meet growth needs. Also, gas t
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