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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

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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