|Content Type||Conference Paper|
|Title||Effect of Oxy-Firing On Corrosion Rates At 600°C|
|Authors||B.A.Pint, Materials Science and Technology Division, Oak Ridge National Laboratory|
|Source||CORROSION 2012, March 11 - 15, 2012 , Salt Lake City, Utah|
|Copyright||2012. NACE International|
|Keywords||high temperature oxidation, coal ash corrosion, boiler, H2O, CO2|
Replacing air with oxygen in coal-fired boilers (i.e. oxy-firing) combined with flue gas recirculation is a leading strategy to concentrate CO2 in the flue gas and assist in carbon capture for subsequent sequestration. A significant area of concern is the fireside corrosion with oxy-firing due to the higher CO2 levels in the combustion gas and potentially higher SOx and H2O levels. In order to investigate this complicated issue, laboratory experiments are being conducted with and without synthetic ash to assess the potential effect of oxy-firing on fireside corrosion rates. The initial results of this project focus on commercial and model Fe-base alloys at 600°C. Without ash, a 50%H2O-50%(CO2-0.15O2) environment was the most aggressive condition, requiring higher Cr contents than 100% H2O or Ar-50%CO2. With the specimens covered in ash, several gas compositions were examined including different levels of H2O and SO2 to simulate various oxy-firing strategies. Box plots were used to present the data for several laser cladding compositions for protecting tubes.
Using oxygen rather than air for coal-fired boilers is a leading concept for enabling large-scale carbon capture and storage.1,2 This strategy potentially could be applied to both new and existing boilers. However, there is considerable concern about the effect of oxy-firing on fireside corrosion rates and several studies have already considered the effect of higher CO2, H2O and SO2 levels.1-7 The fireside environment in which the combustion gas and ash chemistry are dependent on the coal composition is a difficult environment to simulate, since it includes oxidizing and reducing “micro-climates”.8 For the most aggressive conditions experienced by the waterwall tubes in current coal-fired boilers, particularly when substoichiometric low NOx conditions are created, coatings (e.g. weld overlays) are used to protect tubes from fireside corrosion.
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