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Participants:
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CNRS-PROMES (F)
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ETH (CH)
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PSI (CH)
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WIS (IL)
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CERTH/CPERI
(GR)
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DLR (D)
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TIMCAL (B)
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SOLUCAR
R&D (E)
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CREED (F)
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N-GHY (F)
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Achievements
in 2006
At CNRS-PROMES,
a high-temperature lab-scale solar chemical reactor (1 kWth) has been
successfully modeled and tested. The solar receiver consists of a tubular
graphite cavity which absorbs the solar power and transfers the heat to the
reactant flow. Several parameters such as receiver geometry, temperature,
gas flow rates and CH4 composition in the feed were studied. Maximum
chemical conversion of methane was higher than 95%. Conversion increased
with temperature or gas residence time. Reactor simulations showed that the
reaction occurred near the hot wall where the gas velocity is minimal and
the temperature is maximal, since the coldest gas temperatures were found at
the center of the laminar flow profile.
Contour plots of
(a) temperature and (b) H2 molar concentration in the small-scale solar
reactor.
In addition,
work at CNRS has focused on the design and development of a medium-scale
solar reactor (10 kWth) based on the indirect heating concept without the
need for an optical window. For the purpose of predicting the temperature
and species concentration profiles in the reactor, a reactor model has been
developed, taking into account the hydrodynamics of the two-phase flow as
well as the heat and mass transfer coupled to the chemical reaction. Solar
reactor experimental testing is scheduled for 2007.
At WIS, a
directly heated solar reactor (10 kWth) for solar thermal methane splitting
(STMS) is being developed. The reactor window is protected from contact with
incandescent CB particles by maintaining a confined cyclonic flow inside the
reaction chamber. The reactor is designed for operation at temperatures of
up to 2300 K since valuable CB nanotubes are expected to be produced by STMS
at such high temperatures. The reactor development is based on previous
experience with solar reactors using volumetric gas heating by seeding the
reaction chamber with radiation-absorbing particles.
At ETH, a
numerical model of a CH4-flow laden with carbon particles is being developed
for simulating its behavior under direct exposure to concentrated solar
radiation. A joint PSI-ETH experimental campaign with a small-scale 5 kWth
solar reactor was performed in the High-Flux Solar Simulator to
experimentally validate simulation results. The solar reactor concept proven
for thermal decomposition of methane features a vortex-flow laden with
carbon particles. In previous solar experiments, the best chemical
conversion was 67%. Nano-filamentary carbon was produced. Some experimental
results were evaluated to find the kinetic parameters. A mixed flow (MFR)
and a plug flow (PFR) reactor model were distinguished, and the influence of
temperature, CH4 concentration and residence time on the chemical conversion
was examined. Finally, a model was developed using the Monte Carlo method to
understand and predict the heat transfer phenomena in a vortex-flow laden
with particles flowing through a cylindrical cavity.
Publications
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Objectives
The project
aims at designing, constructing, and testing innovative solar reactors
at different scales (10 kWth and 50 kWth) for operating conditions at
1500-2300 K and 1 bar. Methane conversion over 80% and CB properties
equivalent to industrial products are targeted. At the 50 kWth scale,
production of 3 sm3/h H2 and 1 kg/h CB is expected. Three main
scientific and technical challenges are faced: 1) design and operation
of high temperature solar chemical reactors containing nano-size
particulates; 2) production of two valuable products (H2 and CB) in the
same reactor; 3) solar reactor scale-up based on modeling and
experimental validation.
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