A solar-driven thermochemical pilot plant for the high-temperature thermal dissociation of ZnO has been designed, fabricated, and experimentally demonstrated. Tests were conducted at the large-scale solar concentrating facility of PROMES-CNRS by subjecting the solar reactor to concentrated radiative fluxes of up to 4477 suns and peak solar radiative power input of 140 kW_th. The solar reactor was operated at temperatures up to 1936 K, yielding a Zn molar fraction of the condensed products in the range 12–49% that was largely dependent on the flow rate of Ar injected to quench the evolving gaseous products.

A 100-kWth receiver-reactor designed for the thermal dissociation of ZnO into metallic Zn is separated from atmosphere by use of a transparent quartz window, through which concentrated solar radiation is admitted. Protection of such windows from reactant and product particle deposition is critical for successful reactor operation. Usingin-situ visualization techniques, the effectiveness of an auxiliary flow of inert gas in aerodynamically protecting a 600-mm-diameter quartz window mounted on the receiver-reactor has been directly assessed during high-temperature experimentation. This work has shown that: (i) high-temperature, in-situ flow visualization is possible and effective in assessing flow patterns developed inside the reactor;(ii) there exist three characteristic flow patterns inside the reactor that can be dynamically controlled by use of a set of tangential and radially oriented jets; and (iii) a region of stable protective flow, under a wide range of experimental and operational conditions, is capable of repeatedly and fully suppressing detrimental particle depositions on the quartz window

A dynamic numerical model of a solar cavity-type reactor for the thermal dissociation of ZnO is formulated based on a detailed radiative heat transfer analysis combining the Monte Carlo ray-tracing technique and the radiosity enclosure theory. The quartz window is treated as a semitransparent glass layer with spectrally and directionally dependent optical properties. Model validation is accomplished by comparison with experimental results obtained with a 10-kW solar reactor prototype in terms of cavity temperatures, reaction extents, and quartz window temperature distribution measured by IR thermography. The solar-to-fuel energy conversion efficiencies obtained experimentally are reported, and the various energy flows are quantified.