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PROHYTEC, THE FRENCH INDUSTRIAL PLATFORM FOR MASSIVE HYDROGEN PRODUCTION
One of the most challenging sections of the sulphur-based plants concerns the thermal
decomposition of sulphuric acid. The EU FP7 project HYCYCLES (2008-2010) aims at giving an ultimate
answer as concerns the industrial feasibility of the H 2 SO 4 decomposer (sulphuric acid evaporation and
sulphur trioxide splitting) made of SiC ceramics (Poitou, 2008). Experimental demonstration of the
thermal-hydraulic performance of SiC heat exchangers operating as sulphuric acid decomposer will
be conducted by CEA and the French company BOOSTEC due to their broad expertise in that field.
This demonstration is a prerequisite to the global demonstration of the integrated sulphur-based
thermochemical cycles.
Thus it has been chosen to firstly specify PROHYTEC for high-temperature steam electrolysis
demonstration. Depending on the results of HYCYCLES some particular components of sulphur-based
thermochemical cycle could also be qualified in a second time. The fact is that HTSE meets well the
required modularity of PROHYTEC since the minimal electrical and thermal powers for HTSE industrial
demonstration are still debated. The reliability of the electrolyser is of major importance in the final
cost of the produced H 2 . It depends not only on the durability of the performance (say more than
50 000 h to be competitive with alkaline electrolysis) but also on the probability of failure of one stack.
For both reasons it is of great interest to have the capability to test for a long time a sufficiently high
number of stacks for statistics analysis. Depending on the design of the stacks the required electrical
power should be above several hundreds of kW corresponding to the 1-10 MW prototypes required in
the European H 2 roadmap. In a first step the thermal power of the heat source of PROHYTEC has thus
been fixed at 1 MWth potentially increasable to 5 MWth.
The heat source
Basically this heat source has to be representative of any nuclear source including the present light
water reactors or possible next generation nuclear reactors as VHTR, GFR or SFR. Pragmatic design
considerations have led to first simulate a PWR since the supplementary heat input required for
future reactors could be brought by additional superheater simply implemented in the process part of
PROHYTEC (see § The process part). Thus the reference design of PROHYTEC simulates the coupling of a
PWR with an HTSE of about one thermal MW. The temperature of the heating source is thus about 270°C.
For environmental and physical considerations this “PWR-like” heat source should use electricity
instead of other energy sources (fuel, biomass, natural gas…). Preliminary design studies using water
for the heat coupling with the process part have shown that the water working pressure should be
about 45 atm in order to fulfil the power requirement of 1 thermal MW at the electrolyser or at the
intermediate heat exchanger levels. On another hand a thermal fluid capable to work under 300°C will
present the essential advantage to be operated at a moderate pressure (about 2 atm). A strong constraint
concerns the duration of the tests; the objective is to have the heat source (including pump…) worked
with no disturbance for at least 5 000 h and possibly 10 000 h.
Conservative estimations have been performed for taking into account the transient phase of
starting up; all the heat retrieved in the low- and high-temperature (recuperative) exchangers and
part of the heat required for the steam generator is supposed to be furnished to the process fluids as
electricity. Except the steam flow rate which will have to be reduced during this phase all other
operating conditions remain identical to those prevailing in the normal functioning mode of the HTSE.
Based on this assumption it has been shown that the required power of the heat source (about 1 MW)
is compatible with the available electrical power even during the heating up phase of the platform.
The process part
Due to its required versatility, the platform should not be dependent on a particular design of the HTS
electrolyser. Beyond the different possibilities of steam and air feeding the cathodic and anodic
compartments of the electrolyser (mixed or not with H 2 ) some key components are generic as the
steam generator, both low- and high-temperature (recuperative) heat exchangers, the superheater.
As a function of the type of stacks plugged in PROHYTEC different gas distribution can be
implemented without major difficulties. Nevertheless, particular attention must be paid to the
conception of process parts where temperature exceed 600°C since plumbing fixtures for gas
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