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CEA ASSESSMENT OF THE SULPHUR-IODINE CYCLE FOR HYDROGEN PRODUCTION
acid concentration only use heat which is recovered from another part of the section (Buckingham,
2009). The overall optimised heat requirement of the section amounts to 365 kJ/mol, with negligible
electricity requirements.
In terms of thermodynamic models, the sulphur section appears to be the best known of the
three sections, and no specific developments were undertaken in this field by CEA.
Iodine section
CEA quickly selected reactive distillation as its reference process for the iodine section (Goldstein,
2005), because of its simplicity and potential efficiency. In reactive distillation, iodine stripping from
the HI/I 2 /H 2 O mixture produced by the Bunsen section is performed in the same column as HI gas
phase decomposition, taking advantage of iodine condensation into the liquid phase to displace the
thermodynamically limited decomposition equilibrium.
In its most recent assessment of the cycle, which is reported here, CEA chose to make an
optimistic assumption about the composition of the HI/I 2 /H 2 O mixtures that are treated inside the
iodine section. A 2 HI/6 I 2 /9 H 2 O composition, instead of the usual 2 HI/8 I 2 /10 H 2 O mentioned above,
was assumed to be produced from Bunsen section, thanks to the counter-current reactor described
above. Although not proven, this assumption is consistent with experimental results obtained so far
on HI/H 2 SO 4 /I 2 /H 2 O mixtures, in CEA (Lovera, 2009) as well as elsewhere (Lee, 2008).
With this assumption, and using a modified Neumann model for HI/I 2 /H 2 O mixtures description,
CEA (Leybros, 2009) devised a flow sheet for the iodine section which decomposes almost all incoming
HI and therefore returns relatively pure products (the iodine return flow contains only 4 molar% water
and less than .3 molar% HI) to the Bunsen section, an important feature for the counter-current reactor.
Secondary helium heat is provided to the boiler of the column (235 kJ/mol), whereas all other heat needs
are fulfilled through internal heat recovery, with the help of a heat pump which transfers heat from
the products of the distillation column to its feed. Mainly because of the presence of this heat pump,
the iodine section uses 60 kJ/mol of electric power on top of the helium heat.
Figure 2: CEA’s iodine section flow sheet
170 NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010