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A SCW Flow Apparatus for Material Testing and Electrochemical Measurements

This workshop discusses the background, challenges, and experiments related to Supercritical Water Oxidation (SCWO), including fouling, heat transfer, and corrosion. It also focuses on the development of sensors for monitoring chemistry in the SCWR (Supercritical Water-cooled Reactor) and the measurement of corrosion potentials, pH, and complex impedance.

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A SCW Flow Apparatus for Material Testing and Electrochemical Measurements

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  1. A SCW Flow Apparatus for Material Testing and Electrochemical Measurements Steven Rogak Akram Alfantazi Edouard Asselin University of British Columbia IAPWS/COG Workshop

  2. Outline • Background: Supercritical Water Oxidation (SCWO) experiments in flow systems • Fouling • Heat transfer • Corrosion • Just starting: Sensor development for supercritical water (fouling and corrosion for relatively clean water) IAPWS/COG Workshop

  3. SCWO Pilot Plant • 1990’s Supercritical Water Oxidation (SCWO) waste destruction “ready to move from chemist’s lab to engineering” • UBC-NORAM pilot plant built 1997-1998 for • waste destruction pilot plant tests • heat transfer measurements (eg. H2O/O2) • fouling measurements • Corrosion experiments: unintended bonus! IAPWS/COG Workshop

  4. 1.5 Kg/min 600C 25 MPa IAPWS/COG Workshop

  5. Fouling in SCWO • Salts (ppm% conc.) insoluble in low-density water precipitate; can form hard or soft deposits (surface growth or bulk nucleation) Sodium carbonate growth on heated tube wall IAPWS/COG Workshop

  6. Corrosion in SCWO of “Redwater” • Ammonium sulphate solution (high pH at room temperature) destroys Alloy 625 preheater in hours (in presence of oxygen) • Literature give no indication that this would happen! IAPWS/COG Workshop

  7. Corroded Tube Cross Sections IAPWS/COG Workshop

  8. What did we learn from SCWO? • Tough technical challenges! • Viable only in niche applications (may not justify huge R&D programs) • Practical experimental techiques for SCWO might benefit Gen IV (SCWR), where the large “payoff” may justify the effort. IAPWS/COG Workshop

  9. Sensors for monitoring chemistry in the SCWR • NSERC CRD with AECL; • Team: • Akram Alfantazi (Materials Eng.) • Steve Rogak (Mechanical Eng.) • Walter Merida (Mechanical Eng.) • Edouard Asselin (Materials Eng.) • Glenn Mcrae (AECL) • Feb 2009 start; 3 years x $100K • Recruiting students and learning more about SCWR reactor requirements IAPWS/COG Workshop

  10. Broad Objectives • Develop reliable reference electrodes • Measure corrosion potentials, pH, complex impedance • Detect fouling and/or in-stream solids IAPWS/COG Workshop

  11. UBC SCW Flow Systems • Big system (discussed earlier) • Realistic flow regimes for pilot studies (heat transfer) • Expensive to operate • Small system (<0.1 kg/min) • low tube velocities, but can integrate special materials and test sections easily IAPWS/COG Workshop

  12. UBC SCWO • Put pictures here IAPWS/COG Workshop

  13. UBC SCW Electrochemical Cell • Unfinished idea from Ed Asselin’s PhD thesis: electrochemistry cell for the flow system. • Design completed by Ed’s student; ready to be tested this summer. IAPWS/COG Workshop

  14. Non-flow reference electrode • Used by Ed Asselin in PhD • Potential drift from KCl diffusion through plug • ~300 mV bias from thermodiffusion (Oh et al 2004) IAPWS/COG Workshop

  15. Flow Loop & Flow-Through Reference Electrode FTRE IAPWS/COG Workshop

  16. Uncertainty in RE Potential • Liquid Junction Potential (ELJP) – few mV • Thermal Liquid Junction Potential (ETJP) – 300 mV? HT/HP Electrochemistry

  17. Working/Counter Electrode • Design Consideration • Electrical isolation of the electrodes from the cell body • Sealing/Leakage: what material to use? October 21, 2019 IAPWS/COG Workshop

  18. Working/Counter Electrode IAPWS/COG Workshop

  19. Ideas for work this summer • EIS for coated and uncoated working electrodes (precursor to fouling detection) • Sensitivity of reference electrode to flow, concentration and temperature differences IAPWS/COG Workshop

  20. Conclusions • SCWO has technical problems analogous to the proposed SCWR – we can offer something! • SCWR contaminants are dilute and have slow effects – some new challenges (for us). • Many, diverse corrosion and fouling problems in existing and proposed SCWR plants – where should we start? IAPWS/COG Workshop

  21. FEM Safety Factor5000 PSI/500°C – 316 SS IAPWS/COG Workshop

  22. Liquid Junction Potential (ELJP) • Henderson Equation: Case 1 Reference Solution 0.01M KCl Test Solution : 1M Na2SO4 ELJP = -10.7mV Case 3 Reference Solution 0.01M KCl Test Solution : 0.05M Na2SO4 ELJP =-3.74mV Case 2 Reference Solution 0.01M KCl Test Solution : 0.1M Na2SO4 ELJP =- 5.35mV IAPWS/COG Workshop

  23. Thermal Junction Potential Thermal junction potential = combined effect of heat and ion flux Depends on electrode configuration and flow rates (if any) Soret Effect (Thermal Diffusion) Concentration Gradient Migration of Ion Diffusion Potential Internal Electric Field Thermal Junction IAPWS/COG Workshop

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