We report on the improved operational performance and energy conversion efficiency of a 5 kW solar chemical reactor for the combined ZnO-reduction and CH4-reforming “SynMet” process. The reactor features a pulsed vortex flow of CH4 laden with ZnO particles, which is confined to a cavity-receiver and directly exposed to solar power fluxes exceeding 2000 kW/m2. Reactants were continuously fed at ambient temperature, heated by direct irradiation to above 1350 K, and converted to Zn(g) and syngas during mean residence times of 10 seconds. Typical chemical conversion attained was 100% to Zn and up to 96% to syngas. The thermal efficiency was in the 15–22% range; the exergy efficiency reached up to 7.7% and may be increased by recovering the sensible and latent heat of the products. The Synmet process avoids emissions of greenhouse-gases and other pollutant derived from the traditional fossil-fuel-based production of zinc and syngas, and further converts solar energy into storable and transportable chemical fuels.

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