Fluid-wall effectiveness for preventing oxidation in solar-thermal ZnO reactors



Computational fluid dynamics simulations of a “fluid-wall” solar reactor for the dissociation of ZnO were performed to determine the effectiveness of the fluid-wall strategy at preventing oxygen from reacting with the reactor wall. An axial boundary layer near the porous wall was found to exist where ZnO concentrations were essentially zero, demonstrating that the concept was effective at preventing particle contact with the reactor wall. ZnO particles were found to heat nearly instantaneously (>105 K/s), and ZnO conversions were found to be significant (>50%) in the short residence times employed. Conditions for high levels of oxidation of the tube wall coincided with those for high levels of ZnO conversion, and oxidation levels were high (>50%). This was confirmed in solar experiments, where all oxygen products reacted with the tube wall. Although an effective concept for keeping particles from contacting the wall, the fluid-wall strategy was not effective for preventing oxidation. © 2007 American Institute of Chemical Engineers AIChE J, 2007