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CO2 Splitting in a Hot-Wall Aerosol Reactor via the Two-Step Zn/ZnO Solar Thermochemical Cycle

[+] Author Affiliations
Peter G. Loutzenhiser, Anastasia Stamatiou

Paul Scherrer Institute, Villigen PSI, Switzerland

M. Elena Gálvez, Illias Hischier, Aldo Steinfeld

ETH Zurich, Zurich, Switzerland

Paper No. ES2009-90048, pp. 415-420; 6 pages
doi:10.1115/ES2009-90048
From:
  • ASME 2009 3rd International Conference on Energy Sustainability collocated with the Heat Transfer and InterPACK09 Conferences
  • ASME 2009 3rd International Conference on Energy Sustainability, Volume 2
  • San Francisco, California, USA, July 19–23, 2009
  • Conference Sponsors: Advanced Energy Systems Division and Solar Energy Division
  • ISBN: 978-0-7918-4890-6 | eISBN: 978-0-7918-3851-8
  • Copyright © 2009 by ASME

abstract

Using concentrated solar energy as the source of high-temperature process heat, a two-step CO2 splitting thermochemical cycle based on Zn/ZnO redox reactions is applied to produce renewable carbon-neutral fuels. The solar thermochemical cycle consists of: 1) the solar endothermic dissociation of ZnO to Zn and O2 ; 2) the non-solar exothermic reduction of CO2 with Zn to CO and ZnO; the latter is the recycled to the 1st solar step. The net reaction is CO2 = CO + 1/2 O2 , with products formed in different steps, thereby eliminating the need for their separation. A Second-Law thermodynamic analysis indicates a maximum solar-to-chemical energy conversion efficiency of 39% for a solar concentration ratio of 5000 suns. The technical feasibility of the first step of the cycle has been demonstrated in a high-flux solar furnace with a 10 kW solar reactor prototype. The second step of the cycle is experimentally investigated in a hot-wall quartz aerosol flow reactor, designed for in-situ quenching of Zn(g), formation of Zn nanoparticles, and oxidation with CO2 . The effect of varying the molar flow ratios of the reactants was investigated. Chemical conversions were determined by gas chromatography and X-ray diffraction. Chemical conversions of Zn to ZnO of up to 88% were obtained for a residence time of ∼ 3.05 s. For all of the experiments, the reactions primarily occurred outside the aerosol jet flow on the surfaces of the reaction zone.

Copyright © 2009 by ASME

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