Methane Decarbonization in Indirect Heating Solar Reactors of 20 and 50 kW for a CO₂-Free Production of Hydrogen and Carbon Black

Solar methane decarbonization is an attractive pathway for a transition toward an hydrogen-based economy. In the frame of the European SOLHYCARB project, it was proposed to investigate this solar process extensively. At CNRS-PROMES, two indirect heating solar reactors (20 and 50 kW) were designed, built, and tested for methane decarbonization. They consist of graphite cavity-type receivers approaching the blackbody behavior. The CH₄ dissociation reaction was carried out in tubular sections inserted in the solar absorber receiving concentrated solar irradiation. The 20 kW solar reactor (SR20) was especially suitable to study the chemical reaction and methane conversion performances depending on the experimental conditions (mainly temperature and residence time). The 50 kW solar reactor (SR50) was operated to produce significant amounts of carbon black for determining its properties and quality in the various possible commercial applications. The main encountered problem was the particle evacuation. Solutions were proposed for large-scale industrial applications. A process analysis was achieved for a 14.6 MW solar chemical plant on the basis of a process flow-sheet. A production of 436 kg/h of hydrogen and 1300 kg/h of carbon black could be obtained for 1737 kg/h of methane consumed, with an hydrogen cost competitive to conventional methane reforming. This paper summarizes the main results and conclusions of the project.