After 17 years of research involving NETL, industry partners, and a high-tech research group known as the AUSC Consortium, significant progress is being made toward scaling up the fabrication of components made from advanced nickel superalloys that will help bring advanced ultrasupercritical (AUSC) power plant technology to the level of readiness for commercial-scale demonstration.
In the 1950s, coal-fired power plants operated at a then cutting-edge steam pressure of 2,400 psi and main steam temperatures of up to 538 degrees Celsius (C). They were known as “subcritical.” Increasing the pressure and temperature of a power plant can increase power plant efficiency, and by the end of the 20th century, new coal-fired power plants were designed for “supercritical” steam conditions where steam conditions and power plant efficiency were as high as 610 degrees C, 4300 psia and 41 percent. Further, increases in power plant efficiency continue to be sought to reduce the cost of power generation and carbon capture. A new generation of AUSC power plants is viewed as a promising way to attain those goals.
AUSC technology is designed to help power plants burn less coal for electricity production while reducing carbon dioxide (CO2) emissions. AUSC power plants can potentially operate at temperatures and pressures higher than current state-of the-art coal-fired power plants — about 25 percent more efficient than the average U.S. coal-fired power plant fleet, and 10 percent more efficient than state-of-the-art coal-fired power plants. AUSC power plants would require less coal per megawatt-hour, resulting in lower emissions of CO2 and mercury, and lower fuel costs per megawatt.
AUSC technology requires fabrication of advanced nickel superalloys into large plant components; development of installation and repair methods for the nickel superalloy components; and enough testing and metallurgical analysis to support the final design of a commercial-scale AUSC demonstration plant.
NETL researchers and program managers began working on AUSC technology in the early 2000s when the Department of Energy (DOE) began funding research projects to identify and develop materials that would be needed to operate coal-fired AUSC steam power cycles to temperatures and pressures as high as 760 degrees Celsius and 5000 psi. That’s when DOE and NETL awarded cooperative agreements with private sector partner Energy Industries of Ohio (EIO) for work on advanced materials for boilers and steam turbines. Manufacturers participating in those early projects including Alstom, Babcock and Wilcox; Foster Wheeler, Riley Power; General Electric and Siemens.
By 2015, research demonstrated that nickel superalloys Inconel 740 and Haynes H282 have the fabricability, castability, long-term mechanical strength, and corrosion/steam oxidation resistance properties necessary for fossil energy power plants operating up to 760 degrees Celsius and 5000 psi steam conditions.
The overall technical goal of the current AUSC project with EIO, “Advanced Ultrasupercritical (AUSC) Component Testing,” is to significantly advance technology readiness of AUSC technology by manufacturing full-scale AUSC components from nickel superalloys and other advanced alloys. The size of the components that will be fabricated correspond to a coal-fired power plant of approximately 800 megawatts generation capacity operating at a steam temperature of 760 degrees Celsius (1400 degrees Fahrenheit) and steam pressure of at least 238 bars (3500 psia). The specific components that will be fabricated under the scope of this project include an AUSC superheater tube assembly, large diameter thick wall pipe and pipe fittings, an AUSC steam turbine rotor and an AUSC steam turbine nozzle carrier casting.
R&D in the last 17 years has resulted in many material development successes and accomplishments that not only impact the progress toward a demonstration AUSC power plant by 2025, but also that are transferable to other industries including development of nickel superalloy casting, development of welding technologies and fabrication processes; identification and testing of alloys and coatings that are resistant to steamside oxidation and fireside corrosion at AUSC conditions; and approval by the American Society of Mechanical Engineers boiler and pressure vessel Code Committee for use of Inconel 740 in power plants.
The AUSC technical achievements over the past 17-years include:
AUSC Plant Design and Economics
Boiler Mechanical Properties
Boiler Steam-Side Oxidation, Exfoliation, and Dew Point Corrosion
Boiler Fireside Corrosion
Steam Turbine Materials and Fabrication
NETL experts explain that by 2021, AUSC materials will be developed to operate at high pressures and temperatures to meet the global electricity demand, reduce overall emissions and increase efficiency in coal-fired power plants. The current AUSC project with EIO will: