Corrosion Performance of Fe-Based Alloys in Simulated Oxy-Fuel Environment
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INTRODUCTION
ENERGY production, particularly electricity generation, is expected to continue to increase globally due to population growth and a per capita increase in energy consumption. To meet the energy needs, fossil fuels (coal, oil, and gas) will play a major part in energy production, even with a projected increase in alternative renewable sources. However, to minimize greenhouse gas emissions, the current power plant systems emphasize the capture of carbon dioxide and subsequent sequestration. Oxy-fuel combustion systems (without the diluent nitrogen gas) would enable recycling of the carbon dioxide to the compressor, use of novel gas turbines, and advanced reuse of CO2. The U.S. Department of Energy/Office of Fossil Energy is thus supporting the development of combustion systems that replace air with nearly pure oxygen, with the goal of achieving a coal-based power system with near-zero emissions. For this purpose, turbines and combustor technologies that use pure oxygen in fuel combustion are being developed. The major advantage of combustion under pure oxygen is the potential for the separation and capture of CO2 and for power system efficiencies in the range from 50 to 60 pct. The presence of H2O/CO2 and trace constituents, such as sulfur and chlorine in the gas environment and coal-ash deposits, including alkalis at the operating
ZUOTAO ZENG, Principal Materials Engineer, KEN NATESAN, Senior Scientist, and DAVID L. RINK, Senior Technician, are with the Nuclear Engineering Division, Argonne National Laboratory, Lemont, IL 60439. Contact e-mail: [email protected] ZHONGHOU CAI, Beam Line Scientist, is with the Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439. Manuscript submitted December 14, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
temperatures and pressures, can have adverse effects on the corrosion and mechanical properties of the structural alloys in these plants.[1] The concentrations of CO2, SO2, and H2O in oxy-fuel environments are higher than those under air combustion conditions, because of the absence of airborne N2. Various investigators have studied the alloy corrosion behaviors of steel materials in H2O and CO2 environments. Increasing steam content can lead to breakaway oxidation.[2] Carburization was observed when stainless steel materials were exposed to CO2 at elevated temperature.[3,4] High CO2 and H2O concentrations also assisted in partially oxidizing SO2 to SO3.[5] The concentration of SO3 in the oxy-fuel environment is typically three or more times higher than that under the air combustion condition. This SO3 can react with steam to form sulfuric acid. Subsequently, higher SO3 and H2O concentrations can lead to higher concentrations of corrosive H2SO4 under oxy-fuel conditions. Thus, the response of structural and turbine materials in simulated oxy-fuel environments needs to be evaluated to select materials that have adequate high-temperature mechanical properties and long-term environmental performance. Sulfur can also be transported through oxide scales on a
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