Pilot-scale solar reactor operation and characterization for fuel production via the Zn/ZnO thermochemical cycle

Solar Thermochemical Hydrogen (STCH) Processes

“…4 Reaction 2, recovery of ZnO, can also be carried out in a tubular reactor, and research has demonstrated that this reaction can be driven nearly to completion with increased residence time. 4 Efficiencies around 40% have been demonstrated for the zinc oxide cycle, 6 with quenching under an inert atmosphere (typically Ar) critical to recovery of Zn (i.e., Zn(g) and O 2 may coexist, but quenching avoids recombination and aids Zn recovery). 7 In fact, this aspect is one of the primary challenges of the ZnO cycle; recombination of Zn and O 2 (back-reaction 1) limits overall conversion, and the necessity of quenching limits recovery of sensible heat from the solar reactor.…”

“…4,8,9 Despite these challenges, a 100-kW system has been developed to demonstrate the zinc oxide process on a pilot scale. 7 In this study, the solar reactor was designed for concentrated solar radiation up to 6 In general, given the high temperature of Reaction 1 (common to metal oxide thermochemical cycles), materials selection is important and a key metric over process feasibility. 10 A quartz window separates the solar reactor from the atmosphere, and the entire reactor rotates to uniformly expose ZnO to the concentrated solar radiation.…”

“…The maximum recorded solar-to-fuel efficiency was 0.17%. 6 On the other hand, solar-tochemical efficiency was typically on the order of 3%. Low Zn yield was attributed primarily to damage to the reactor during operation.…”

High-flux optical systems for solar thermochemistry

“…Volumetric absorption increases the penetration of the flux into the reactant, reducing the temperature gradient through the reactant and allowing the heat to penetrate deeper for a more homogeneous heating. If the reactant is a powder, surface reaction is obtained by forming pellets which are fed to the hot cavity, or by lining the cavity inner surface with the powder (even dispersion can be obtained by rotation) (Abanades et al, 2007;Koepf et al, 2016;Levêque and Abanades, 2013;Möller and Palumbo, 2001;Alonso et al, 2013). This approach is generally satisfactory for reactions with consumption of the reactant.…”

Effect of Zr doping on the electrical and optical properties of ZnO

“…ZnO usually manifests n-type semiconductor. However, different-element doping enables ZnO to own many new functions, for example, transparent electrodes, flat-panel display, light-emitting diode, solar cell and surface acoustic wave device [1][2][3][4][5][6][7]. Effective element doping has a stable structure in ZnO semiconductor [8], so photoelectric properties of ZnO doping system have been a current research hotspot [9][10][11][12].…”