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Energy and Power Generation Handbook: Established and Emerging Technologies

K. R. Rao
K. R. Rao
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ASME Press
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Advanced Ultra Supercritical (A-USC) is a term being used to describe a coal fired power plant design with the inlet steam temperature to the turbine at 700°C to 760°C (1292°F to 1400°F). Nickel alloy materials are required. The term Ultra Supercritical (USC) is a term for plants currently designed and operating at 600°C (1112°F) using available and suitable ferritic and stainless steels. Increasing efficiency of the Rankine regenerative-reheat steam cycle to improve the economics of electric power generation and achieve lower cost of electricity has been a long sought after goal. Efficiency has more recently been recognized as a means for reducing the emission of carbon dioxide and its capture costs, as well as a means to reduce fuel consumption costs. Programs have been established by nations, industry support associations and private companies to advance the technology in steam generator design and materials development of nickel based alloys needed for use above 700°C. The worldwide abundance of less expensive coal fuel has driven economic growth. The challenge is to continue to advance the improvement of efficiency for coal fired power generation technology, representing nearly 50% of the United States' (U.S.) production, while helping to maintain economic electric power costs with plants that have favorable electric grid system operational characteristics for turndown and rate of load change response.

The Newcomen steam engine operated at about 0.5% thermal efficiency in 1750 [1]. Major efficiency milestones such as James Watt's 1769 patented improvement to a Newcomen steam engine by adding a separate condenser is credited with achieving 2.7% thermal efficiency by 1775 and became a major propellant of the Industrial Revolution due to the economic benefit of the fuel savings attained. Watt's 1782 patent for expansive working, double acting cylinder engine, is credited with achieving 4.5% efficiency by 1792. James Watt, however, is also assailed for causing delay in economic advancement due to his reluctance to raise the working pressure of the steam engine. Lacking in good boiler instrumentation such as reliable water level and pressure gages, Watt's concerns were probably well founded in limiting the operating pressure to about 0.034 MPa (5 psig). After Watt's patents began to expire, Richard Trevithick is credited with engine improvements that permitted increasing steam pressure, to 1MPa (145 psig), to achieve 17% thermal efficiency by 1834.

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