Advanced ultra-supercritical (A-USC) is a term used to designate a coal-fired power plant design with the inlet steam temperature to the turbine at 700 to 760C (1292 to 1400F). Average metal temperatures of the final superheater and final reheater could run higher, at up to about 815C (1500F). Nickel-based alloy materials are thus required. Increasing the efficiency of the Rankine regenerative-reheat steam cycle to improve the economics of electric power generation and to achieve lower cost of electricity has been a long sought after goal. Efficiency improvement is also a means for reducing the emission of carbon dioxide (CO2) and the cost of capture, as well as a means to reduce fuel consumption costs. In the United States (U.S.), European Union, India, China and Japan, industry support associations and private companies working to advance steam generator design technology have established programs for materials development of nickel-based alloys needed for use above 700C (1292F). The worldwide abundance of less expensive coal has driven economic growth. The challenge is to continue to improve the efficiency of coal-fired power generation technology, representing nearly 50% of the U.S. production, while maintaining economic electric power costs with plants that have favorable electric grid system operational characteristics for turndown and rate of load change response. The technical viability of A-USC is being demonstrated in the development programs of new alloys for use in the coal-fired environment where coal ash corrosion and steamside oxidation are the primary failure mechanisms. Identification of the creep rupture properties of alloys for higher temperature service under both laboratory and actual field conditions has been undertaken in a long-term program sponsored by the U.S. Department of Energy (DOE) and the Ohio Coal Development Office (OCDO). Ultimately, the economic viability of A-USC power plants is predicated on the comparable lower levelized cost of electricity (LCOE) with carbon capture and sequestration (CCS) using either oxy-combustion or post-combustion capture. Using nickel alloy components will drive the design and configuration arrangement of the steam generator relative to the plant. A-USC acceptance depends on achieving the higher functional value and lowering the perceived level of risks as this generation technology appears in a new form.

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