A cavity-receiver containing a tubular absorber for high-temperature thermochemical processing using concentrated solar energy

Abstract

A solar chemical reactor consisting of a cylindrical cavity-receiver containing a tubular ceramic absorber is considered for performing thermochemical processes using concentrated solar radiation as the energy source of high-temperature process heat. The model chemical reaction selected is the thermal dissociation of ZnO into its elements, which proceeds endothermically at above 1800 K and is part of a 2-step H 2O-splitting thermochemical cycle for H 2 production. A lab-scale 5 kW reactor prototype is fabricated and subjected to high-flux solar irradiation in the range 448–2125 kW/m 2. A heat transfer reactor model is formulated that encompasses the governing mass and energy conservation equations coupling radiation/convection/conduction heat transfer to the chemical kinetics, and their solution by Monte Carlo ray-tracing and finite difference techniques. Validation was accomplished by comparing numerically computed and experimentally measured temperatures and reaction rates in the 1780–1975 K range. The reactor model is further applied to simulate a continuous thermochemical process, identify major sources of irreversibility, and predict solar-to-chemical energy conversion efficiencies.