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TECHNICAL PAPERS

Solar Thermal Reduction of ZnO Using CH4:ZnO and C:ZnO Molar Ratios Less Than 1

[+] Author and Article Information
Christian Wieckert

Solar Process Technology, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerlande-mail: christian.wieckert@psi.ch

Aldo Steinfeld

ETH-Swiss Federal Institute of Technology, Department of Mechanical and Process Engineering, Institute of Energy Technology, ETH-Zentrum, CH-8092 Zurich, Switzerlande-mail: aldo.steinfeld@psi.ch

J. Sol. Energy Eng 124(1), 55-62 (Mar 01, 2001) (8 pages) doi:10.1115/1.1434980 History: Received November 01, 2000; Revised March 01, 2001
Copyright © 2002 by ASME
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References

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Steinfeld, A., and Palumbo, R., 2000, “Solar Thermal Process Technology,” Encyclopedia of Physical Science and Technology, R. A. Meyers (Ed.), Academic Press, 15 , pp. 237–256.
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Palumbo,  R., Lédé,  J., Boutin,  O., Elorza Ricart,  E., Steinfeld,  A., Möller,  S., Weidenkaff,  A., Fletcher,  E. A., and Bielicki,  J., 1998, “The Production of Zn from ZnO in a High Temperature Solar Decomposition Quench Process—I. The Scientific Framework for the Process,” Chem. Eng. Sci., 53, pp. 2503–2517.
Haueter, P., Möller, S., Palumbo, R., and Steinfeld, A., 2000, “The Production of Zinc by Thermal Dissociation of Zinc Oxide—Solar Chemical Reactor Design,” Sol. Energy, in Press.
Steinfeld,  A., Frei,  A., Kuhn,  P., and Wuillemin,  D., 1995, “Solar Thermal Production of Zinc and Syngas via Combined ZnO-Reduction and CH4-Reforming Process,” Int. J. Hydrogen Energy, 20, pp. 793–804.
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Steinfeld,  A., Brack,  M., Meier,  A., Weidenkaff,  A., and Wuillemin,  D., 1998, “A Solar Chemical Reactor for Co-Production of Zinc and Synthesis Gas,” Energy (Oxford), 23, pp. 803–814.
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Bale,  C., and Pelton,  A., 1999, “Software package FACT-WIN, see http://www.crct.polymtl.ca/FACT/fact.htm for a description; Pelton, A. (1997), “Thermodynamic Databases and Equilibrium Calculations in Metallurgical Processes,” Pure Appl. Chem., 69, pp. 969–978.
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Figures

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Schematics showing two applications of processing zinc from ZnO using concentrated solar radiation: ZnO-Zn-cycle process for electricity production and solar thermal production of zinc as commodity (in italic)
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Carbothermic reduction of ZnO: Minimal temperature without ZnO(s) in thermodynamic equilibrium as a function of the stoichiometries of CH4:ZnO and of C:ZnO
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Thermodynamical equilibrium gas composition of the molar system ZnO+0.277CH4 as a function of temperature
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Reductive fractions rC and rH2 according to Eq. (6) as well as ratio between heating value of the offgas (after zinc-removal) and heating value of methane fed as a function of the temperature. It is assumed, that the amount of methane is αmin(T).
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Gas composition as a function of the stoichiometry α for Tmin(α)
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Enthalpy change ΔH of cold reactants in the furnace (left axis) and relative production rate of Zn per ΔH and heating value of methane as a function of temperature using αmin(T) (right axis). ΔH is supplied by the solar energy.
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Partitioning of the energy in the gas leaving the furnace as a function of the stoichiometry α (for Tmin(α))
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Re-radiation loss correction factor frerad as a function of the reactor temperature for different flux concentrations (1 sun=1 kW/m2 )
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Partitioning of the total energy input into the furnace as a function of the temperature for an incident flux concentration C=4000 suns and α=αmin(T)
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Total reactor efficiency ηreactor=(QZn+Qoffgas)/Qintotal and solar fraction fsolar as a function of the temperature (for an incident flux concentration C=4000 suns and α=αmin(T))
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Comparison of specific CO2-emissions for different processes for Zn-production from ZnO (direct emissions during operation only)
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Electricity from solar processing of ZnO+αCH4 for ηZn-electricity=68%,ηsyngas-electricity=40% and C=4000 suns. Different types of efficiency indicators are shown as a function of temperature using α=αmin(T).Δsolar denotes the difference to values for the case that the methane is alternatively burned with ηmethane-electricity=40%.
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Comparison of specific CO2-emissions from electricity production using fossil and solar chemical fuels (direct emissions during operation only)
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Variation of electricity production efficiencies for treatment of a molar mix of ZnO with 0.277CH4 at 1400°C as a function of ηZn-electricity for different values of ηoffgas-electricitymethane-electricitysolar denotes the difference to values for the case that the methane is alternatively burned with ηmethane-electricity.

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