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5250 |
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Friday, June 09, 2017, Hall 12 12:20 PM Power Generation - Steam |
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HVAF spraying for biomass boiler applications: Oxidation behavior of Ni-based coatings in moisture-laden environment |
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Esmaeil Sadeghimeresht* / University West, Sweden Johan Eklund/ Chalmers University of Technology, Sweden Julien Phother Simon/ Chalmers University of Technology, Sweden Jesper Liske/ Chalmers University of Technology, Sweden Nicolaie Markocsan/ University West, Sweden Shrikant Joshi/ University West, Sweden |
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Reducing CO2 emissions from power generation plants is intimately related to enhancing thermal efficiency, which can be achieved by increasing temperature/pressure of steam. However, any increase in steam temperature is inevitably accompanied by accelerated oxidation of boiler components. The use of renewable fuels such as biomass magnifies the problem by introducing a number of aggressive species into the boiler environment, resulting in more rapid degradation of components. Although thermal sprayed coatings are techno-commercially attractive solutions for augmenting the durability of degradation-prone boiler components and are already being implemented, further improvements in their performance are continuously sought. High-velocity air fuel (HVAF) coatings are promising in this context. In the present work, isothermal oxidation behavior of some candidate HVAF-sprayed Ni-based coatings (NiCr, NiAl, NiCrMo, and NiCrAlY) was studied in N2 + 5% O2 +20% H2O at 600°C. Results were also compared with those obtained from two popular boiler materials, one a chromia-forming alloy and another an alumina-forming alloy. The oxidation kinetics were determined from periodic withdrawal of samples during isothermal exposure and the oxide scale growth mechanisms were studied by SEM/EDX and XRD to evaluate the effectiveness of the coatings. It was found that synergetic effect of Al and Cr in the NiCrAlY coating yielded enhanced oxidation characteristics. The performance of the coatings exhibited the following ranking (most to least damage): NiCrAlY> NiAl> NiCr > NiCrMo. |