Philipp Haueter

The production of zinc by thermal dissociation of zinc oxide—solar chemical reactor design

We describe the design, fabrication, and preliminary test of a novel solar chemical reactor for conducting the thermal dissociation of ZnO into zinc and oxygen at above 2000 K. The reactor configuration features a windowed rotating cavity-receiver lined with ZnO particles that are held by centrifugal force. With this arrangement, ZnO is directly exposed to high-flux solar irradiation and serves simultaneously the functions of radiant absorber, thermal insulator, and chemical reactant. The reactor design respects the constraints imposed by both the chemistry of the decomposition reaction and the transitory nature of solar energy. A 10 kW prototype reactor, made from conventional reliable materials, was tested at PSI’s high-flux solar furnace and exposed to peak solar radiation fluxes exceeding 3500 kW m−2. The reactor system proved to have low thermal inertia and resistance to thermal shocks.

A New High-Flux Solar Furnace for High-Temperature Thermochemical Research

A new high-flux solar furnace, capable of delivering up to 40 kW at peak concentration ratios exceeding 5000, is operational at PSI. Its optical design characteristics, main engineering features, and operating performance are described. This solar concentrating facility will be used principally for investigating the thermochemical processing of solar fuels at temperatures as high as 2500 K.

Thermoelectric Oxide Modules (TOMs) for the Direct Conversion of Simulated Solar Radiation into Electrical Energy

The direct conversion of concentrated high temperature solar heat into electrical energy was demonstrated with a series of four–leg thermoelectric oxide modules (TOM). These temperature stable modules were not yet optimized for high efficiency conversion, but served as proof-of-principle for high temperature conversion. They were constructed by connecting two p- (La1.98Sr0.02CuO4) and two n-type (CaMn0.98Nb0.02O3) thermoelements electrically in series and thermally in parallel. The temperature gradient ΔT was applied by a High–Flux Solar Simulator source (HFSS) which generates a spectrum similar to solar radiation. The influence of the graphite layer coated on the hot side of the Al2O3 substrate compared to the uncoated surface on ΔT, Pmax and η was studied in detail. The measurements show an almost linear temperature profile along the thermoelectric legs. The maximum output power of 88.8 mW was reached for a TOM with leg length of 5 mm at ΔT = 622 K. The highest conversion efficiency η was found for a heat flux of 4–8 W cm-2 and the dependence of η on the leg length was investigated.

Optical Design of a Novel Two-Stage Solar Trough Concentrator Based on Pneumatic Polymeric Structures

An innovative concept for fabricating solar trough concentrators based on pneumatic polymer mirrors supported on precast concrete frames is presented. Optical aberration is corrected by means of a secondary specular reflector in tandem with a primary cylindrical concentrator. The optimal design is formulated for maximum solar flux concentration. The Monte Carlo ray-tracing technique is applied to determine the effect of reflective surface errors and structural beam deformations on the performance of the combined primary and secondary concentrating system. The numerical results are validated with field measurements on a 49.4 m length, 7.9 m width sun-tracking prototype system. Theoretical maximum solar concentration ratio is 151 suns; the measured one with a flat secondary reflector was 55 suns.

Metal oxide reduction using a solar-driven vacuum thermogravimeter

We present a kinetic study performed in a solar-driven vacuum thermogravimeter (solar-TG), in which solid reactants are directly exposed to high-flux irradiation while their weight change is continuously monitored. The system allows testing under a total vacuum pressure as low as 10 mbar. With this arrangement, the rate of thermochemical reactions can be examined under the same radiative heat transfer characteristics and heating rates typical of solar reactors. The solar-TG System is used to investigate metal oxides redox cycles for Splitting H2O and CO2 and for high-temperature heat storage. Operation of the metal oxide reduction under vacuum pressures is of special interest because it eliminates the need for purge gas, thus simplifying the process and avoiding energy penalties associated with inert gas Recycling.

Hydrogen Production by Steam-Gasification of Petroleum Coke Using Concentrated Solar Power: Reactor Experimentation With Slurry Feeding

We report on the experimental evaluation of a 5 kW solar chemical reactor for the steam-gasification of petcoke, carried out at PSI’s solar furnace. A petcoke-water slurry was continuously injected into a solar cavity-receiver to create a vortex flow directly exposed to concentrated solar radiation. For a nominal reactor temperature of 1500 K, a residence time of 2.4 s, and a water-petcoke molar ratio of 4.8, the maximum degree of petcoke conversion was 87%. Typical syngas composition produced was 62% H2 , 25% CO, 12% CO2 , and 1% CH4 . The energy conversion efficiency — defined as the portion of solar energy absorbed as chemical energy and sensible heat — attained 17%. The effect of varying the particle size (range 8.5–200 μm) and slurry stoichiometry (range 2.1–6.3) on the degree of chemical conversion and energy conversion efficiency was examined.Copyright

A High-Flux Solar Parabolic Dish System for Continuous Thermochemical Fuel Production

A high-flux solar parabolic dish coupled to a rotating secondary reflector enables to alternate the focus of concentrated solar radiation between two thermochemical redox reactors. The design, fabrication and on-sun characterization is presented.