Corrosion Assessment and Mechanisms of Materials in Advanced Thermal Energy Production Systems

• Author / Creator

  Li, Kaiyang

• Advanced pressurized oxy-fuel combustion and subsequent supercritical CO2 (s-CO2) transportation technologies are being developed for high energy conversion efficiency and significant reduction of greenhouse gas emission at advanced thermal power plants. However, materials knowledge gaps exist on the deployment of these technologies, particularly the selection of suitable alloys for the core components (heat exchangers and flue gas sub-systems) and the upper limits of impurities in the s-CO2 for safe pipeline transportation. This study intends to fill these gaps by investigating the corrosion performance of candidate alloys under various service conditions and advancing the fundamental understanding of how alloys corrode.

  The s-CO2 streams captured from the oxy-fuel combustion plants contain certain amounts of impurities H2O, O2, and SO2, which may cause serve corrosion damages on the transportation pipeline steels. Current study finds that SO2 in H2O-saturated s-CO2 can lead to highly active general corrosion by electrochemical reactions instead of gas chemical reactions, but has a marginal influence on stress corrosion cracking susceptibility of pipeline steel. The maximum allowable limits of impurity contents are also proposed based on a comprehensive literature review and current testing results.

  At the advanced oxy-fired pressurized fluidized bed combustion plants, the flue gas (composed of CO2, H2O, O2, SO2 and HCl) could introduce potential condensed and hot gas chemical corrosion damage on the flue gas components. To address these issues, the corrosion performances of P91 and DSS 2205 steels were investigated in the simulated flue gas condensates at 60-150 C, and the results reveal that the dominant reactions are considerable oxide formation and high chemical dissolution of the formed oxides. Increasing temperature leads to an exponential increase in the long-term corrosion rates of the steels. DSS 2205 exhibited acceptable resistance to the condensates at elevated temperatures because of its high Cr and Mo contents. Besides, the hot flue gas chemical corrosion of 2205 steel was studied in a simulated pressurized hot flue gas environment at 270-320 C. The oxidation kinetics of DSS 2205 follows parabolic law. O2 and H2O act as oxidants while SO2 and HCl are the pitting inducers. In general, DSS 2205 is a suitable candidate for the construction of flue gas components.

  High-temperature s-CO2 Brayton cycle has been recognized as a promising heat transfer method. The corrosion performance of two candidates, SS310 and Alloy 740, were studied in 30 MPa s-CO2 streams with 100 ppm H2O or O2 impurities at 600 C. The addition of H2O remarkably enhances general and localized oxidations while the presence of O2 leads to the opposite change. Compared with H2O, impurity O2 exhibits a more negative impact on the carburization of SS310. Alloy 740 shows much better resistance to carburization than SS310. The two alloys follow near parabolic oxidation law and show acceptable long-term corrosion resistance.

  Depending on the fuel types used, different high-temperature corrosion modes will occur on the fireside of the heat exchangers in the combustion chambers. In pressurized oxy-fuel natural gas-fired system, the fireside of heat exchangers will suffer the attack from high-temperature, high-pressure flue gas mixture (H2O + CO2 + O2). It is found that O2 is the dominant oxidant and has a threshold content (~2%), above which the nodule oxidation of SS347, Alloy 800AT and Alloy 825 will be remarkably suppressed at 600 C and 15 MPa. The three alloys exhibit acceptable corrosion resistance due to the relatively compact Cr2O3 layer. Among them, Alloy 825 shows the best corrosion performance due to its high contents of Cr, Al and Ti.

  For the pressurized oxy-fuel plants fed with coal/biomass, high-temperature molten salt corrosion shall be the dominant reactions on the fireside. Under such service conditions (flue gas + salt mixture of NaCl/KCl/Na2SO4/K2SO4), the corrosion performance of Alloy 800AT and Alloy 740 were studied at 650 C. The alloys suffer oxidation, sulfidation and chlorination attack with porous and fragile corrosion products. Alloy 740 exhibits better corrosion resistance than Alloy 800 AT, as the latter also experience serious internal and intergranular corrosion damage.

• Subjects / Keywords

  • supercritical
  • material selection
  • corrosion
  • flue gas
  • oxy-fuel

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-xje4-hc37

• License

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