Transcript A SCW Flow Apparatus for Material Testing and Electrochemical Measurements Steven Rogak

A SCW Flow Apparatus for Material
Testing and Electrochemical
Measurements
Steven Rogak
Akram Alfantazi
Edouard Asselin
University of British Columbia
May 12, 2009
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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)
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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!
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1.5 Kg/min
600C
25 MPa
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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
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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!
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Corroded Tube Cross Sections
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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.
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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
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Broad Objectives
• Develop reliable reference electrodes
• Measure corrosion potentials, pH, complex
impedance
• Detect fouling and/or in-stream solids
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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
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UBC SCWO
• Put pictures here
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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.
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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)
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Flow Loop & Flow-Through Reference Electrode
FTRE
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Uncertainty in RE Potential
1. Liquid Junction Potential (ELJP) – few mV
2. Thermal Liquid Junction Potential (ETJP) – 300 mV?
Ecell  ENernst  ELJP  ETJP
May 23, 2016
HT/HP Electrochemistry
16
Working/Counter Electrode
• Design Consideration
– Electrical isolation of the electrodes from the cell
body
– Sealing/Leakage: what material to use?
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Working/Counter Electrode
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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
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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?
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FEM Safety Factor
5000 PSI/500°C – 316 SS
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Liquid Junction Potential (ELJP)
• Henderson Equation:
E LJP
| zi | i
i z [(Ci1  Ci2 )] RT  | zi |  i Ci2
i

In i
1
2
 | zi |  i [(Ci  Ci )] F  | zi |  i Ci1
i
i
Case 1
Reference Solution 0.01M KCl
Case 2
Test Solution : 1M Na2SO4
Reference Solution 0.01M KCl
ELJP = -10.7mV
Test Solution : 0.1M Na2SO4
Case 3
Reference Solution 0.01M KCl
Test Solution : 0.05M Na2SO4
ELJP =-3.74mV
ELJP =- 5.35mV
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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
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