1. University of British Columbia
A SCW Flow Apparatus for Material Testing and Electrochemical Measurements
Steven Rogak
Akram Alfantazi
Edouard Asselin
University of British Columbia
May 12, 2009
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)
May 12, 2009
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 for
waste destruction pilot plant tests
heat transfer measurements (eg. H2O/O2)
fouling measurements
Corrosion experiments: unintended bonus!
May 12, 2009
IAPWS/COG Workshop

4. 1.5 Kg/min
600C
25 MPa
May 12, 2009
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
May 12, 2009
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!
May 12, 2009
IAPWS/COG Workshop

7. Corroded Tube Cross Sections
May 12, 2009
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.
May 12, 2009
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
May 12, 2009
IAPWS/COG Workshop

10. Broad Objectives Develop reliable reference electrodes
Measure corrosion potentials, pH, complex impedance
Detect fouling and/or in-stream solids
May 12, 2009
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
May 12, 2009
IAPWS/COG Workshop

12. UBC SCWO
Put pictures here
May 12, 2009
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.
May 12, 2009
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)
May 12, 2009
IAPWS/COG Workshop

15. Flow Loop & Flow-Through Reference Electrode
FTRE
May 12, 2009
IAPWS/COG Workshop

16. Uncertainty in RE Potential
Liquid Junction Potential (ELJP) – few mV
Thermal Liquid Junction Potential (ETJP) – 300 mV?
May 17, 2019
HT/HP Electrochemistry

17. Working/Counter Electrode
Design Consideration
Electrical isolation of the electrodes from the cell body
Sealing/Leakage: what material to use?
May 17, 2019
May 12, 2009
IAPWS/COG Workshop

18. Working/Counter Electrode
May 12, 2009
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
May 12, 2009
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?
May 12, 2009
IAPWS/COG Workshop

21. FEM Safety Factor 5000 PSI/500°C – 316 SS
May 12, 2009
IAPWS/COG Workshop

22. Liquid Junction Potential (ELJP)
Electrochemical Engineeringa nd Technology
Liquid Junction Potential (ELJP)
Henderson Equation:
Case 1
Reference Solution 0.01M KCl
Test Solution : 1M Na2SO4
ELJP = -10.7mV
Case 3
Test Solution : 0.05M Na2SO4
ELJP =-3.74mV
Case 2
Reference Solution 0.01M KCl
Test Solution : 0.1M Na2SO4
ELJP =- 5.35mV
Case 1
May 12, 2009
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
May 12, 2009
IAPWS/COG Workshop