Browsing by Author "Bouvet, Justin"
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Item Open Access Fireside and steamside performance in biomass power plant(Taylor & Francis, 2022-01-10) Mori, Stefano; Sumner, Joy; Bouvet, Justin; Simms, Nigel J.To address the challenge of climate change, the energy sector is developing novel strategies to reduce greenhouse gas emissions. One route is to increase steam temperatures and pressures (above 650°C and 350 bar). Another route is the use of potential net zero emissions fuels, like biomass. Both these routes cause issues for the heat-exchanger materials due to the differences in composition of the combustion environments generated, compared to coal. This paper characterises candidate superheater/reheater alloys’ behaviour (Sanicro 25 and IN740) at 700°C. 1,000 h fireside and 10,000 h steamside exposures were carried out, the first using ‘deposit recoat’ techniques. Sample cross-sections were analysed using dimensional metrology and SEM/EDX. Fireside results for Sanicro 25 showed degradation throughout the samples’ thicknesses. In steamside exposures, Sanicro 25 formed a Cr-rich scale, and Nb rich particles (z-phase). IN740 showed lower metal and sound metal damage than Sanicro 25 for fireside and steam oxidation exposures.Item Open Access Impacts of temperature and surface finish upon steam oxidation of austenitic steel TP347HFG(Elsevier, 2017-11-22) Bouvet, Justin; Sumner, Joy; Nigel, SimmsThe effects of the steam oxidation process on an austenitic steel (TP347HFG) exposed under isothermal conditions between 600 and 800 °C for up to 2500 h have been investigated. Samples with both as-received and ground surfaces have been exposed and the impact of surface finish on the oxidation process analysed using scanning electron microscopy with energy dispersive X-ray analysis. Exfoliated oxide flakes have also been examined to characterise their microstructures on fractured sections as well as external and spalled surfaces. Microscopic analyses demonstrated that ground surfaces possess better steam oxidation resistance than as-received surfaces due to their ability to form a more protective chromium-rich layer. The formation of regions of thicker multi-layered oxides was noted on both types of surface finish, covering large areas on as-received surfaces and only nodules on ground surfaces (spreading with increasing exposure temperature and time).Item Open Access Steam oxidation of heat exchanger materials for the new generation of power plants.(2018-11) Bouvet, Justin; Sumner, Joy; Simms, Nigel J.Energy production over recent decades has emitted CO2, linked to an increase in global average temperatures and climate change. Part of the solution to tackle this is through improved power plant flexibility to enable renewable integration, and enhanced generator efficiency. Fossil fuel-based generators’ efficiencies can be improved by increasing steam working temperatures and pressures inside power plants. However, these more severe working conditions can accelerate degradation phenomena, for example, by steam oxidation. To assess the simulate steam oxidation processes at the elevated temperatures required for high efficient power plants, various austenitic steels and nickel-based alloys were exposed to pure steam between 650 and 800°C for up to 10,000 hours. Effects of pressure and surface finish were also investigated. It was observed that, for the different materials, oxide formation increased with increasing oxidation time and steam temperature. Oxidized TP347HFG samples (18.4%wCr and 11.5%wNi) exhibit multi-layered oxide scales susceptible to spallation. Surface finishes applying high compressive stresses drastically enhanced oxidation resistance and promoted chromia layer formation even at elevated temperatures and longer exposure times. Other prepared surfaces, with low compressive stresses, induced increased oxidation resistance only at early exposure times. Sanicro 25 (22.5%wCr and 25%wNi) and nickel-based alloys naturally possess very high oxidation resistances, which results from ready formation of chromia formation on their surfaces; these alloys were not affected by surface preparation. Exposing different materials to increasing pressure in laboratory experiments increased oxidation rates. However, in service exposed materials show the opposite pressure effect. Isotope exposure tests revealed that up to 20% of the anionic species in the oxide layers were hydroxides and/or hydrogen, showing their significant influence on the steam oxidation mechanisms. Finally, models describing mass change and oxide growth for the different materials and surface finishes were developed to contribute to better power plant management.