No abstract

Direct solar reduction of CO 2 to CO and oxygen has been demonstrated using only solar energy. Known thermochemical, kinetic, and spectral properties of the CO 2 /CO/O 2 system enable the process. In this first prototype system, a solar focusing mirror and secondary concentrator were used to provide high solar intensity around a ceramic rod. This high-temperature, high solar irradiance environment provided strong heating of CO 2 with the resultant dissociation to CO and oxygen. Quenching of the back reaction was provided by the geometry and gas dynamics of the system and by cool gas quencher jets just downstream. The best measured net conversion of CO 2 to CO was near 6%, which is compared to a plant design target of 12%. The peak observed conversion of solar energy to chemical energy was 5%. Calculations indicate that a mature system will yield 20% solar-to-chemical energy conversion with an additional 25% electrical energy.

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No abstract

At high temperatures (greater than 2300 K), CO 2 is known to dissociate to CO and O. A prototype solar collector was previously demonstrated to achieve such high temperatures, achieving 4-6 mol % CO in the product stream from an inlet stream of pure CO 2 . This paper describes the results of computer modeling performed to determine the flow, temperature, and reactions occurring in the prototype device. Of particular interest are the heat-transfer and reaction mechanisms involved and how much photolysis occurs in the prototype. Predictions were performed with two different computational fluid dynamic codes (Fluent and PCGC-3). The solar flux heated a zirconia rod at the throat of the device to 2625 K, which in turn heated the surrounding gas by convection. All CO formation reactions occurred in the boundary layer of the zirconia rod and just beyond the region of high solar flux. Predictions of CO concentrations exiting the reactor, performed using three reversible reactions, matched experimentally observed values.