The U.S. Department of Energy and the Ohio Coal Development Office have recently initiated a project aimed at identifying, evaluating, and qualifying the materials needed for the construction of the critical components of coal-fired power plants capable of operating at 50-55 percent efficiency (based on the higher heating value of the fuel). This increased efficiency compared to current coal-fired power plants is achieved principally through the use of ultra-supercritical steam conditions (USC), which implies operation at higher steam temperatures and pressures. The project goal is to increase the operating temperature to 760°C (1400℉), while attention also is given to identifying the materials issues involved in service at temperatures up to 870°C (1600℉). The program is intended to complement alloy development programs now being carried out in Japan and Europe. Those programs have identified ferritic steels capable of meeting the strength requirements of USC plants to approximately 620°C, but it is not clear if such alloys would be capable of further development. In this program, the maximum temperature capabilities of these and other available high-temperature alloys are being assessed to provide a basis for materials selection and application, and to allow confidence in their use. The program approach makes use of developments in understanding and modeling of alloy structure-property relationships to guide the mechanical property measurements needed to evaluate the fabrication issues and long-term microstructural stability issues of concern, and is also addressing concerns about long-term durability in both the anticipated fireside and steam-side environments. Feedback from these various analyses is being used as input to considerations of the viability of alternative paths to alloy modification or new alloy development, should these be needed.
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