Research Papers

Pilot Scale Demonstration of a 100-kWth Solar Thermochemical Plant for the Thermal Dissociation of ZnO

[+] Author and Article Information
A. Meier

Solar Technology Laboratory,
Paul Scherrer Institute,
Villigen PSI 5232, Switzerland

A. Steinfeld

Solar Technology Laboratory,
Paul Scherrer Institute,
Villigen PSI 5232, Switzerland
Department of Mechanical and
Process Engineering,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: aldo.steinfeld@ethz.ch

The mean concentration ratio is defined as Cmean = Qaperture/(IA), where Qaperture is the solar radiative power intercepted by the aperture of area A. Cmean is often expressed in units of suns when normalized to I = 1 kW m−2.

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received August 14, 2013; final manuscript received August 23, 2013; published online November 8, 2013. Editor: Gilles Flamant.

J. Sol. Energy Eng 136(1), 011016 (Nov 08, 2013) (11 pages) Paper No: SOL-13-1230; doi: 10.1115/1.4025512 History: Received August 14, 2013; Revised August 23, 2013

A solar-driven thermochemical pilot plant for the high-temperature thermal dissociation of ZnO has been designed, fabricated, and experimentally demonstrated. Tests were conducted at the large-scale solar concentrating facility of PROMES-CNRS by subjecting the solar reactor to concentrated radiative fluxes of up to 4477 suns and peak solar radiative power input of 140 kWth. The solar reactor was operated at temperatures up to 1936 K, yielding a Zn molar fraction of the condensed products in the range 12–49% that was largely dependent on the flow rate of Ar injected to quench the evolving gaseous products.

Copyright © 2014 by ASME
Topics: Solar energy
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Fig. 1

Schematic longitudinal (left) and transversal (right) cross sections of the 100-kWth solar reactor. Indicated are the temperature measurement locations of type-K and type-B thermocouples.

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Fig. 2

Left: Schematic side view of the MWSF, comprised of a field of 63 heliostats, a parabolic concentrator, and a tower. Incident solar radiation is reflected by the heliostats onto the parabolic concentrator, which in turn focuses the sunrays into the solar reactor located in the tower. Right: Schematic north-facing front view of the MWSF heliostat field. The 39 dark-shaded heliostats represent those used during the experimental campaign. The number labels are used to designate each heliostat.

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Fig. 3

3D schematic view of the 100-kWth solar pilot plant mounted on a transportable platform, including the solar reactor, the dynamic screw feeder, and the filter system.

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Fig. 4

Schematic layout of the entire solar pilot plant, showing the receiver-reactor (quench unit and rotary joint attached to the reactor outlet), peripheral equipment (particle filters, side channel blower, ZnO screw feeder) and instrumentation (flow controllers, pressure transducers, thermocouples, gas chromatograph, control and data acquisition system). FM: gas/water volumetric flow meter, MFC: mass flow controller, PI/PIC: pressure transducer indicator/controller, TC: type-K/B thermocouple, TS: temperature sensor Pt100, V: valve.

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Fig. 5

Cross-sectional side and front views of the heat-flux measurement system, comprised of an array of five water-cooled gauges mounted on a water-cooled rotating plate. The shaded area represents the covered measurement domain.

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Fig. 6

Time evolution of experimental runs #3 (top) and #4 (bottom). Tcavity corresponds to the measurement location B3 in Fig. 1 (right), measured ∼15 mm behind the irradiated Al2O3-brick surface. The arrows on the top indicate the timespans when filters 1 and 2 were active.

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Fig. 7

Reactor temperatures measured during experimental runs #3 (top) and #4 (bottom). The measurement locations of the type-B and type-K thermocouples are indicated in Fig. 1 (left). The DNI is plotted until sunset, with solar noon indicated by the vertical arrow. The vertical lines indicate the points in time at which the supply of Qsolar to the solar reactor was interrupted.

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Fig. 8

SEM images of (a) unreacted ZnO particles, and (b)–(d) solid products collected in filter 2 after experimental runs #1, 3, and 4 (in the same order of appearance).

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Fig. 9

XRD patterns of unreacted ZnO (Grillo) and solid products collected in filter 2 after the solar thermal dissociation of ZnO. The labeled experimental runs #1–4 correspond to those listed in Table 1.

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Fig. 10

Zn molar fraction of collected solid products versus Zn partial pressure in the quench unit, for both the 100-kWth scale-up solar reactor (solid line) and the 10-kWth solar reactor equipped with different quench units (dashed lines)

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Fig. 11

Heat-flux measurement data acquired at the focal plane of the MWSF for heliostat 28. Left: solar flux curves obtained with each of the five flux gauges, along with the measured DNI (numbering of gauges corresponds to that of Fig. 5). Right: rendered heat-flux map over the irradiated target. The dashed circle represents the area of the 19 cm-diameter aperture.




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