Design of a Lab-Scale Rotary Cavity-Type Solar Reactor for Continuous Thermal Reduction of Volatile Oxides Under Reduced Pressure

The investigated two-step M_xO_y/ M_xO_y−1 solar thermochemical cycles consist of two redox reactions. Net result is watersplitting with concentrated solar energy as the source of high temperature process heat: The M_xO_y−1 species produced in reaction (1) is gaseous in the case of the ZnO/Zn cycle. The oxide (ZnO) is injected in a solar thermochemical reactor and undergoes a thermal reduction reaction (oxygen release). Dilution/quenching with a neutral gas at the reactor exit yields nanoparticles of metal by condensation. The particles have a high specific surface area that leads to a high reactivity in the 2^nd step. The reduced species (Zn) can then be fed to another reactor to react with water steam. The reaction produces pure H₂ and forms the original metal oxide. A high-temperature lab-scale solar reactor prototype was designed, constructed and operated, allowing continuous metal oxide processing under controlled atmosphere. It is based on a cavity-type rotating receiver absorbing solar radiation. The reactant powder is injected continuously inside the cavity and the produced particles (Zn) are recovered in a downstream filter. The solar reduction of ZnO has been achieved, the reaction yields were quantified, and a first concept of solar reactor was qualified.