Solar Thermal Production of Zinc - Final Step Toward Scale-Up

• Research unit: SFOE
• Project number: 101050

Key words (German)

TP0065;F-Industrielle Solarenergienutzung

Short description (German)

Solar Thermal Production of Zinc - Final Step Toward Scale-Up

Final report (English)

A 10 kW receiver-reactor prototype (called ZIRRUS) was further improved and tested for the solar thermal decomposition of ZnO, which is the 1st step of the two-step water-splitting thermochemical ZnO/Zn cycle. The rotating cylindrical cavity was made of either sintered ZnO or sintered Al2O3 tiles placed on top of a multi-layer Al2O3-SiO2-Y2O3-based ceramics for thermal shock resistance, mechanical stability, gas diffusion barrier, and thermal insulation. Pre-heated Ar gas was injected for aerodynamic window protection and for minimizing recombination of product gases in the cavity. Experimentation was carried out at PSI’s High-Flux Solar Simulator with the direct heating 10 kW reactor prototype subjected to peak radiative fluxes exceeding 5800 suns. The reactor operated without incident for a total of more than 40 h at maximum temperatures – measured behind the ZnO and Al2O3 tiles – ranging from 1807-1907 K. Thermal dissociation of ZnO(s) near 2000 K was demonstrated for experimental runs over 4 h in transient ablation mode with up to nine semi-continuous feed cycles of ZnO particles. A working Zn/O2 separation device based on the rapid quenching of the Zn/O2 mixture is ready to be incorporated at the exit of the solar reactor. Zinc yields of up to 94% were obtained when using total Ar/Zn(g) dilution of 530 and a cooling rate of about 105 K/s. The fully integrated solar reactor will be scaled up to the pilot scale of 100 kW. A newly developed reactor model that couples radiation, conduction, and convection heat transfer to the reaction kinetics will allow determining optimal operational conditions for matching the feeding rate to the reaction rate and for maximizing solar-to-chemical energy conversion efficiency. The 2nd step of the ZnO/Zn cycle has been experimentally demonstrated at ETH using an aerosol-flow reactor for in situ formation and hydrolysis of Zn nanoparticles. The reactor was operated continuously at 1 bar and 573-1263 K, yielding up to 90% chemical conversion for a residence time of about 1 s, and producing nanoparticles with mean crystallite sizes in the 40-100 nm range, containing up to 80 wt% ZnO. A Life Cycle Assessment (LCA) confirmed that the ZnO/Zn cycle is a promising option for storing solar energy in hydrogen aimed at substituting fossil-based fuels in sustainable future transportation systems.

Auftragnehmer/Contractant/Contraente/Contractor:
Paul Scherrer Institut (PSI) - Labor für Solartechnik

Autorschaft/Auteurs/Autori/Authors:
Meier,Anton

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• Solar Thermal Production of Zinc - Final Steps Toward Scale-Up - Final Report [PDF] 2'122 kB