Simulation of a Volumetric Solar Receiver-Reactor for Hydrogen Producing Thermochemical Cycles

Abstract

Sulfur based thermochemical cycles for hydrogen generation from water have one reaction step in common which is the decomposition of sulfuric acid as one of the most energy consuming steps. The present work deals with the development of a dynamic mathematical model of a solar reactor for this key step. One of the core parts of the model is a part model of the reaction kinetics of the decomposition of sulfur trioxide, which is based on experiments investigating the kinetics of the used catalyst platinum coated on a ceramic solar absorber. Other part models describe e. g. the absorption of solar radiation, heat conduction in the absorber, convection between gas and the absorber walls and energy losses due to heat radiation. A comprehensive validation of the reactor model is performed using measured data which is gained in experiments with a prototype reactor. The operating behavior of the real reactor is compared with the results of the numerical simulation with the model. The validation is in particular done by reproducing the influences of individual parameters on the chemical conversion and the reactor efficiency. The relative deviations between experimental data and simulation results are mostly within the range of measurement accuracy. In particular the good agreement of calculated values of the derived parameters SO3 conversion and reactor efficiency with those determined from the experiments qualify the model for optimization purposes.