This project will determine the temperature-dependent corrosion mechanisms of candidate high-temperature alloys and coatings in oxy-firing systems. Investigators will use thermo-chemical modeling results to identify the typical and extreme values of the levels of various gases expected to influence high-temperature corrosion behavior of oxy-fired plants. Interactions among the gaseous environments associated with oxy-firing and ash/slag deposits expected from the use of different coals will also be considered. Researchers will perform corrosion testing under realistic combustion gas and ash/slag conditions for materials representative of those expected to be used. Both commercial alloys and model alloy compositions will be evaluated to clearly understand the effect of composition on performance. Coating processes will be selected and samples prepared for environmental exposure and mechanical-environmental testing. A hightemperature creep rig is being constructed for evaluating creep properties in boiler-relevant environments. Researchers will use high-resolution analytical techniques (both pre- and post- corrosion testing) to characterize composition and structures of interest. The results of the testing will be compared to the current state of knowledge of materials corrosion in an air-based combustion environment. The initial testing will focus on ferritic-martensitic steels and model alloys with typical coating compositions. Austenitic steel and Ni-base alloy specimens will be included for reference.
In Oxy-fired Systems, oxygen is used for combustion of coal rather than air. It produces flue (exhaust) gas with concentrated carbon dioxide (CO2), thus facilitating its capture and sequestration. An added benefit of oxy-firing is that it reduces or eliminates nitrogen oxide (NOX) emissions.
Additional energy is required with oxy-firing and subsequent carbon sequestration in order to produce the oxygen, to capture the CO2 from the flue gas, and to process the CO2 for transport and storage. The reduced plant electrical output could be offset by an increase in plant efficiency with the use of an advanced steam cycle usually involving higher steam temperatures. Alloys that can perform under these more extreme conditions are available, but their performance in an oxy-firing fireside environment is not well understood, specifically regarding the role played by water (H2O) and CO2 during the oxy-firing process. Understanding how state-of-the-art alloys perform in an oxy-fired environment would provide a basis for their selection and use in advanced steam cycles, be useful for maintenance planning, and support the development of improved oxidation-resistant alloys and coatings.
The Department of Energy (DOE) National Energy Technology Laboratory (NETL) supports research and development of technologies that will increase efficiency and reduce emissions from power production plants, especially those fueled by coal. To further advance oxy-fired systems, NETL is partnering with Oak Ridge National Laboratory (ORNL) to address such key issues as (1) understanding temperature relevant corrosion mechanisms; (2) determining the role of the combustion environment on the mechanical response of the alloy; (3) evaluating upper temperature limits for new materials; and (4) characterizing corrosion reaction products and alloy degradation.
The primary benefit of this project is the creation of a knowledge base with the potential to support material selection and development for the demanding requirements of advanced, higher-efficiency steam cycles in order to reduce coal consumption and CO2 emissions while reducing the power requirements for CO2 capture, transport, and storage systems.
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