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Research Papers

# Solar Carbothermic Reduction of ZnO in a Two-Cavity Reactor: Laboratory Experiments for a Reactor Scale-Up

[+] Author and Article Information
S. Kräupl, U. Frommherz, C. Wieckert

Solar Technology Laboratory, Paul Scherrer Institute, CH-5232 Villigen, Switzerland

J. Sol. Energy Eng 128(1), 8-15 (Jun 20, 2005) (8 pages) doi:10.1115/1.2147585 History: Received July 13, 2004; Revised June 20, 2005

## Abstract

Solar energy can be stored chemically by using concentrated solar irradiation as an energy source for carbothermic ZnO reduction. The produced Zn might be used for the production of electricity in Zn-air fuel cells or of $H2$ by splitting water. In either case the product is again ZnO which can be reprocessed in the solar process step. This innovative concept will be scaled up to $300kW$ solar input power within the so-called SOLZINC-project. In this paper we report on experimental results obtained with a two cavity reactor operated at solar power inputs of $3–8kW$ in a solar furnace. The objective was to generate input data which are necessary for designing the scaled up reactor, such as the effect of process temperature $(1100–1300°C)$ and carrier gas ($N2$ and CO) on the overall reaction rate. Furthermore, construction materials were tested and a variety of carbonaceous materials were screened for their use as reducing agents by means of thermogravimetric measurements. As a result, beech charcoal was chosen as the standard reducing agent.

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## Figures

Figure 1

Sketch of the laboratory solar reactor

Figure 2

Experimental setup in the solar furnace of PSI

Figure 3

Results of TG experiments for screening of carbon materials (molar ratio Cfix: ZnO=0.8:1)

Figure 4

Micrographs of a beech charcoal ash sample (dark) during heating. Until the softening temperature of 1210°C is reached there is no change of shape. Between 1210°C and the fusion temperature of 1415°C strong deformation of the sample takes place. At 1415°C the ash is molten completely.

Figure 5

Solar power input, product gas flow rates and reactor temperatures during a representative batch run of the reactor (500g mixture of beach charcoal powder and ZnO with molar ratio Cfix: ZnO=0.9:1)

Figure 6

Overall reaction rate as a function of temperature for different carrier gas flows (Cfix: ZnO=0.9:1)

Figure 7

Mass change of separation wall materials used in solar reactor tests

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