Nuclear Production of Hydrogen, Fourth Information Exchange ...

EXECUTIVE SUMMARY
sulphur deposition is a key technical objective. A new operating method with an SO 2 -limited
condition shows no voltage degradation or sulphur build-up. Flow sheet design results in a process
thermodynamic efficiency of 37%. Hydrogen costs are estimated to be in the range of USD 4.15-7.10/kg
H 2 . Next demonstration steps should include an integrated lab-scale experiment, followed by a
MW-scale pilot plant.
Overall, the presentations were well received, though it was clear that significant technical and
economic challenges remain for sulphur-based thermochemical cycles. For the S-I thermochemical
cycle, some ILS experiments were carried over the past few years. The HIx decomposition section
largely affects the overall efficiency and the hydrogen production cost. Currently there are significant
differences in predicted efficiency, from 39% to 43% depending on the HIx decomposition process and
the flow sheet. The cost also depends largely on the materials to be used for the HIx section.
For the hybrid sulphur cycle, current researches are focused on the SDE cell development to
overcome the sulphur deposition in cathode. The next step should be ILS experiments followed by a
MW-scale pilot plant.
Session 4: Thermochemical copper chloride and calcium bromide processes
Chairs: Karl Verfondern (FZJ), Paul Pickard (SNL)
Session 4 focused on recent advances in the thermochemical copper chloride and calcium bromide
cycles. Much of the current research on thermochemical cycles for hydrogen production involves the
sulphur cycles (sulphur-iodine, hybrid sulphur), however, these cycles require very high temperatures
(~800-900°C) to drive the acid decomposition step. The interest in the Cu-Cl and Ca-Br cycles is due to
the lower peak temperature requirements of these cycles. The peak temperature requirement for the
Cu-Cl cycle is about 550°C, which would allow this cycle to be used with lower temperature reactors,
such as sodium- or lead-cooled reactors, or possibly supercritical water reactors. Ca-Br requires peak
temperatures of about 760°C. Both of these cycles are projected to have good efficiencies, in the range
of 40%. Work on Cu-Cl is ongoing in France, Canada and the United States. Work on Ca-Br has been
done primarily in Japan and the US, with the more recent work being done in the US at ANL. The
papers presented in this session summarised the recent advances in these cycles.
Five papers were given on the Cu-Cl cycle, focusing on the key technical issues for this cycle.
Canadian research activities on Cu-Cl include study of the chemical processes and also the development
of component designs, material corrosion studies, and the development of heat exchanger technologies
for coupling the nuclear heat source and the hydrogen production plant. Work on the important
hydrolysis reaction of the Cu-Cl cycle was reported in CEA and ANL papers. Since the hydrolysis
reaction requires excess steam to obtain high yields, these papers describe parametric studies to
quantify the steam to Cu molar ratio and minimise the formation of the unwanted CuCl reaction
product. The high steam to Cu ratios also imply higher capital costs to deal with the higher volumetric
flows, and preliminary engineering approaches to mitigate these costs were also discussed. Penn State
researchers summarised recent work on the development and characterisation of the electrolyser
for the Cu-Cl cycle. Several commercially available options for the anion exchange membrane were
evaluated for membrane swelling, ion exchange capacity and conductivity. The membrane that
displayed the highest conductivity was used to fabricate membrane electrode assemblies for
electrolysis tests. These MEA showed current efficiencies of 98%. The last Cu-Cl paper in this session
summarised the recent CEA analysis of the energy efficiency of this cycle.
Recent advances on the Ca-Br cycle were presented in an ANL paper. The original concept for this
cycle involved solid phase reactions in a semi-continuous batch operation. The ANL paper reported
on experiments that used a direct sparging reactor in the hydrolysis reaction to allow continuous
production of HBr which is then electrolytically decomposed to produce hydrogen. The sparging steam
was introduced into the molten bath of CaBr 2 which yielded HBr in a stable and continuous operation.
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 13