1. CEA’s assessment of the sulfur-iodine cycle for hydrogen production
Fourth OECD-NEA Information Exchange Meeting on the Nuclear Production of Hydrogen
CEA’s assessment of the sulfur-iodine cycle for hydrogen production
P. Carles, X. Vitart, P. Yvon

2. The sulfur-iodine cycle
H2SO4 ↓
H2O + SO2 + ½ O2
[850 °C]
2 HI → H2 + I2
[330 °C]
I2 + SO2 + 2 H2O → H2SO4 + 2 HI
[120 °C]
Sum of the reactions
H2O → H2 + ½ O2

3. alkaline electrolysis
Project objectives
Objective : assess the technical and economic viability of massive hydrogen production processes using water as raw material
Reference process:
alkaline electrolysis
Cost components

4. Hydrogen production cost estimation
Technico- economical assumptions
Components
Plant design
Other
cost
components
Investment
cost
Flowsheet
Thermodynamic data
Materials
Hydrogen
Production
cost
Energy consumption

5. Bunsen section optimization for improved efficiency
(x+1)I2 + SO2 + (n+2)H2O → [H2SO4 + (n-m)H2O] + [2HI + xI2 + mH2O]
H2SO4 phase
HIx phase
Reference: x = 8 / n = 14
120°C
Studies of H2SO4/HI/I2/H2O mixtures:
Reduction of iodine and water overstoichiometry seems possible
Counter-current reactor
Better yield
Better purity of the phases
Lower level of side reactions

6. S-I cycle efficiency Assumptions Energy consumption: 39.3 % efficiency
Optimized Bunsen reaction
Reactive distillation for iodine section
Modified Neumann model for HIx description
Energy consumption:
7 I2 + SO H2O → [H2SO4 + 4 H2O] + [2 HI + 6 I2 + 9 H2O]
39.3 % efficiency
Allows 2 kg/s hydrogen production with a 600 MWth V/HTR

7. Iodine section flowsheet3
EAU BUNSEN 1
100°C – 50 bars 13 L2 9
L23 3b
HIx BUNSEN
130°C – 3 bars 2
EAU 9b 8
L12 L1
L10
L13 1b 7 12 7b 7c
L24
IODE BUNSEN
130°C – 50 bars 5c
HYDROGENE
120 bars 4 4b
L14
L200
L210
L201
L211
L21
L20
L22 5 5b 6 10
10b 11
11b
P301
50 bars
E302
E304
E301 He
E307
C302
E305
E303
E306
234,2 kJth
4,4 kJélec
2,7 kJélec
E308
E309
E310
D301
D302
PAC
2/0,3 bar
52,5/102,7 bar
C301 / T301
Total: 353,8 kJ th
(He: 234,2 kJ
Elec: 59,8 kJ)
52,7 kJélec
261°C
313°C
312,3°C
270°C
244,6°C
108,3°C 1
Reactive distillation column:
10 x (23 trays, F4m x H26 m)
Heat exchanges: 1950 kJ/mol

8. Materials for iodine section
Nb-1%Zr

9. S-I plant investment cost
1 shop (0.2 kg/s)
2.5 G€
for a 1st of a kind plant

10. Main assumptions for hydrogen production cost
General assumptions
Discount rate: 8%
Construction period: 3 yrs
Operating life: 30 yrs without replacing any equipment (cf. maintenance)
Start-up / stopping phases: none
Load factor: 80%
Investment cost
Process unit investment cost: assessed according to the flowsheet
Contingency: 30% of the principal equipment
General facilities: 15% of the installed base price
Engineering fees: 12% of the installed base price
Contractor fees: 5% of the installed base price
Initial loads include the initial stock of sulphuric acid and iodine
O&M costs
Energy:
Electricity: 40 €/MWh
Heat: 20 €/MWh
Labor:
Number of operators: 30
Labor cost: 0.4 M€/op./year
Maintenance: 7%/year of the installed real equipment cost
Taxes and insurance: 2%/year of the installed real equipment cost
Plant overhead costs: 1%/year of the installed base equipment cost

11. Hydrogen production cost
~10 €/kg of H2 for a Nth of a kind plant

12. Discussion Uncertainties remain large Costing methods accuracy 30%+
€-$ conversion rate and material prices fluctuations

13. Steel prices and $ exchange rate do fluctuate a lot!
Material prices
Steel prices and $ exchange rate do fluctuate a lot!
$ / tonne
Jan 2006
Jan 2008
Jul 2008
Ordinary steel price:
0,86 $ / kg
Exchange rate:
1 $ = 0,63 €

14. Discussion Uncertainties remain large Costing methods accuracy 30%
€-$ conversion rate and material prices fluctuations
Catalyst cost and efficiency poorly known
Iodine section remains poorly known and understood

15. Iodine section: some LVE measurement results
LT : less iodine more HI
HT : more iodine less HI
than reference model
Total pressure measurements around 130°C
for various mixtures with 39 % I2
Experimental evidence of
hydrogen formation:
liquid phase decomposition?
Results to be included in new thermodynamic model

16. Discussion Uncertainties remain large
Costing methods accuracy 30%
€-$ conversion rate and material prices fluctuations
Catalyst cost and efficiency poorly known
Iodine section remains poorly known and understood
Are assumptions made pessimistic?
Simplified chemistry
Effect of a 45% efficiency?
Chemical flows are high
Corrosion resistant materials are expensive
New technologies?
Low temperatures?

17. Conclusion
S-I cycle
Efficiency 39-40%, likely to be revised to a lower value
Hydrogen production cost around 10 €/kg
Competitiveness seems difficult to achieve with today’s state of the art knowledge and technology
Uncertainties remain, but breakthroughs are required!
New material technologies
Low temperature distillation
Liquid phase HI decomposition
Bunsen reaction optimization …
CEA’s strategy:
Continue ongoing international collaborations (GIF, HYCYCLES, BARC, I-NERI…)
Publish results and discuss them with international partners
Update the assessment with results from international research