Materials Challenges for Advanced Combustion and Gasification Fossil Energy Systems
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TRODUCTION
THE 2010 Energy Outlook Assessment by the U.S. Energy Information Administration (EIA) forecasts that, while nonfossil energy use will grow rapidly, fossil fuels will still provide 78 percent of total U.S. energy use in 2035.[1] However, converting fossil fuels to energy is a major contributor to green house gas (GHG) emissions. According to the U.S. Environmental Protection Agency, in 2006, the total GHG emissions in the United States were estimated at 7100 million metric tons CO2 equivalent.[2] This estimate included CO2 emission as well as other GHGs such as methane, nitrous oxide, and other hydrofluorocarbons. Of this amount, about 53 pct (3800 million metric tons) of the GHG emissions were attributed to stationary fossil fuel combustion sources. Eighty three percent of the stationary sources are from emissions from generating electricity.[2] The U.S. Department of Energy (U.S. DOE) is actively engaged in research and development efforts focusing on carbon capture and storage (CCS) as a means to reduce the emission of CO2 from fossil fueled power plants. Simply, this concept comprises capturing (or separating) the CO2 from the power plant and storing the CO2 in an underground geological formation for permanent sequestration. A key aspect of this strategy is the development of advanced combustion and gasification technologies that are more efficient and produce effluent streams that facilitate the capturing of CO2. S. SRIDHAR, POSCO Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, and is also with the National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, PA 15236. Contact e-mail: [email protected] P. ROZZELLE, Program Manager, is with the Office of Clean Energy Systems, U.S. Department of Energy, Washington, DC 20585. B. MORREALE, Acting Materials Science and Engineering Focus Leader, is with the National Energy Technology Laboratory, U.S. Department of Energy. D. ALMAN, Division Director, is with the Materials Performance Division, National Energy Technology Laboratory, U.S. Department of Energy. Manuscript submitted January 11, 2011. Article published online February 16, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
Higher efficiency boilers and turbines require less fuel and produce electricity, and thus emit less greenhouse gases. Today, the most advanced steam plants are only about 35 pct efficient and operate with steam conditions approaching 893 K (620 C) and 20 MPa.[3,4] The U.S. DOE goal of a 48 pct efficient steam plant will require ultra-supercritical (USC) steam conditions, approaching 1033 K (760 C) and 35 MPa. Operating at these conditions will result in a 20 to 25 pct decrease in CO2 emissions (Figure 1).[3] Identifying cost-effective materials that can operate for long periods of time at extreme temperatures and pressures is a major challenge for implementing USC systems. The combustion process is the highly exothermic chemical reaction of the carbon and hydrogen within the coal in the presence o
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