The Development of a Solar Chemical Reactor for the Direct Thermal Dissociation of Zinc Oxide

Abstract

A solar chemical reactor was designed, constructed and tested for the direct thermal decomposition of zinc oxide at temperatures as high as 2250 K using concentrated sunlight. Along with the reactor, a 1-dimensional numerical model was developed to predict the reactor’s thermal performance under various solar flux levels and to identify the physio-chemical properties of ZnO that are critical for designing the reactor. An experimental study was also conducted to ascertain how best to employ a curtain of inert gas to keep the reactor’s window clean of Zn and ZnO. The reactor proved to be a reliable research tool for effecting the decomposition reaction and it possesses many features characteristic of a reactor scale-able to an industrial level: it is resilient to thermal shock; it has a low effective thermal inertia, and it can operate in a continuous mode when ZnO as a powder is fed to the reactor. Furthermore, experimental work led to insight on how best to keep the window clean in the course of an experiment. Also, comparisons between output from the numerical model and experimental results show that the solar flux and the ZnO’s thermal conductivity and emissivity are the most critical variables affecting the exergy efficiency of the reactor and the mass flux of product gases. The comparison further reveals the need to investigate whether or not the magnitude of the published pre-exponential term in the decomposition rate equation used in the numerical model should be reduced for improving agreement between the model and the experimental results.