A two-chamber solar receiver-reactor for sulfuric acid decomposition

Kurzfassung

Fossil energy carriers may be replaced in the future by hydrogen to save fossil resources and to avoid emission of carbon dioxide. To achieve this, a technology for a sustainable and environmentally friendly mass production of hydrogen is needed. A promising way is the application of a thermochemical cycle with solar heat as the energy source offering potentially higher efficiency and economical advantages over other processes. Especially, the Hybrid Sulfur Cycle is a promising candidate for the solar production of hydrogen from water. A key step in this process 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. The reactor contains two chambers with two different porous absorbers to transform the solar radiation into heat. The first absorber is a ceramic foam which enables the evaporation of the liquid H2SO4. The second absorber is a parallel channel monolith with a catalyst coating dedicated for the SO3-dissociation. Experiments with the test reactor were carried out in DLR’s solar furnace in Cologne. Firstly the feasibility of a solar decomposition of sulfuric acid in a porous absorber reactor was investigated and proven. Then the reactor was qualified at different operating points and with different catalyst coatings. Finally, the receiver-reactor and strategy of operation was stepwise improved 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. Mass flow of sulfuric acid, space velocity, and the absorber temperature 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.