Solar Thermochemical Generation of Hydrogen: Development of a Receiver Reactor for the Decomposition of Sulfuric Acid

A key step in the sulfur based thermochemical cycles for hydrogen production is the highly endothermic decomposition of sulfuric acid at temperatures between 800 °C and 1200 °C. This reaction can be carried out in a receiver-reactor which is irradiated with concentrated solar radiation from a heliostat field. To investigate this process a test reactor was developed and built. The reaction takes place on the surface of a catalytically coated porous absorber irradiated through a quartz pane of the receiver-reactor. This concept has the advantage of a minimum number of heat transferring steps. Experiments with the test reactor were performed in the DLR solar furnace in Cologne. Firstly the feasibility of a solar decomposition of sulfuric acid in a receiver-reactor containing volumetric absorbers was investigated and proven. Then the reactor was qualified at different operating points. Finally the receiver-reactor and strategy of operation was iteratively optimized with respect to chemical conversion and reactor efficiency. Several test series were performed with variation of the absorber temperature, the mass flow and the dilution rate. Partial pressure of SO₃, residence time, absorber temperature, and the kind of catalyst applied were identified and quantified as parameters with the most relevant influence on chemical conversion and reactor efficiency. The operation behavior observed and the detailed knowledge of dependencies of different operation parameters assist in evaluating the potential of scaling up the described technology.