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Research Papers

A Receiver-Reactor for the Solar Thermal Dissociation of Zinc Oxide

[+] Author and Article Information
L. O. Schunk, P. Haeberling, S. Wepf, D. Wuillemin, A. Meier

Solar Technology Laboratory, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

A. Steinfeld

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerlandaldo.steinfeld@eth.ch

1sun=1kWm2

J. Sol. Energy Eng 130(2), 021009 (Mar 11, 2008) (6 pages) doi:10.1115/1.2840576 History: Received May 14, 2007; Revised August 28, 2007; Published March 11, 2008

An improved engineering design of a solar chemical reactor for the thermal dissociation of ZnO at above 2000K is presented. It features a rotating cavity receiver lined with ZnO particles that are held by centrifugal force. With this arrangement, ZnO is directly exposed to concentrated solar radiation and serves simultaneously the functions of radiant absorber, chemical reactant, and thermal insulator. The multilayer cylindrical cavity is made of sintered ZnO tiles placed on top of a porous 80%Al2O320%SiO2 insulation and reinforced by a 95%Al2O35%Y2O3 ceramic matrix composite, providing mechanical, chemical, and thermal stability and a diffusion barrier for product gases. 3D computational fluid dynamics was employed to determine the optimal flow configuration for an aerodynamic protection of the quartz window against condensable Zn(g). Experimentation was carried out at PSI’s high-flux solar simulator with a 10kW reactor prototype subjected to mean radiative heat fluxes over the aperture exceeding 3000suns (peak 5880suns). The reactor was operated in a transient ablation mode with semicontinuous feed cycles of ZnO particles, characterized by a rate of heat transfer—predominantly by radiation—to the layer of ZnO particles undergoing endothermic dissociation that proceeded faster than the rate of heat transfer—predominantly by conduction—through the cavity walls.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 2

Reactor’s cavity made from ZnO tiles (1) and 80%Al2O3–20%SiO2 insulation (2). Not seen here are the ZnO tiles on the lateral back and front walls. The cavity’s inner diameter is 160mm.

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Figure 3

Velocity (left, in ms−1), temperature (center, in K), and Zn(g) mole fraction (right) fields in the central cross section of the reactor for the optimal flow configuration

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Figure 4

Experimental setup of the solar reactor and peripherals at PSI’s HFSS

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Figure 5

Radiation power input, cavity temperature, and O2 molar flow rate in the product gases measured during experimental Run No. 1, with one feed cycle of 284g ZnO

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Figure 6

Radiation power input, cavity temperature, and O2 molar flow rate in the product gases measured during experimental Run No. 3, with one feed cycle of 398g ZnO

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Figure 7

Radiation power input, cavity temperature, and O2 molar flow rate in the product gases measured during experimental Run No. 4, with two feed cycles of 158g ZnO each

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Figure 8

Radiation power input, cavity temperature, and O2 molar flow rate in the product gases measured during experimental Run No. 6, with five feed cycles of 120g ZnO each

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Figure 9

Radiation power input, cavity temperature, and O2 molar flow rate in the product gases measured during experimental Run No. 7, with seven feed cycles of 133g ZnO each

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Figure 10

Radiation power input, cavity temperature, and O2 molar flow rate in the product gases measured during experimental Run No. 8, with nine feed cycles of 131g ZnO each

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Figure 1

Schematic of the solar chemical reactor configuration: 1, rotating cavity lined with sintered ZnO tiles; 2, 80%Al2O3–20%SiO2 insulation; 3, 95%Al2O3–5%Y2O3 CMC; 4, alumina fibers; 5, Al reactor shell; 6, aperture; 7, quartz window; 8, dynamic feeder; 9, conical frustum; and 10, rotary joint

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