Hydrogen production from CO2-free thermal decomposition of methane: Design and on-sun testing of a tube-type solar thermochemical reactor

• Solar thermal methane decomposition for hydrogen and carbon black production
• A lab-scale solar chemical reactor was designed and operated on-sun.
• Thermal performance of the reactor was analyzed using CFD simulation.
• Experimental CH4 conversion and H2 yield of 90% and 85% were reached at 1400 °C.
• The formation of pyrocarbon deposit in the graphite/ceramic absorber tube was avoided.

This study addresses the development of a solar thermochemical reactor for CO2-free production of hydrogen from solar-aided methane decomposition. The developed lab-scale solar reactor basically pertaining to the indirect heating concept is chiefly based on a tube-type configuration in tandem with a cavity receiver. The reactor design and performance prediction were first appraised via 3-dimensional CFD thermal simulation as a function of internal geometry. The model including coupled heat/mass transfer and chemical reaction aimed to simulate the reactor in order to determine the temperature distribution and the conditions for maximum reactor efficiency. The designed 1 kW solar reactor was then constructed and installed for reaction testing at the focus of a 2 m-diameter parabolic solar concentrator. Solar CH4 decomposition experiments were performed between 1300 and 1400 °C to demonstrate the feasibility of hydrogen production and the reliability of the solar process using the developed reactor concept, and the results were used to validate simulations. Regarding the estimated kinetic parameters, the best fitting was obtained for an activation energy of 320 kJ/mol and a pre-exponential factor of 1011 s− 1. The chemical conversion was improved when increasing the temperature or decreasing the inlet gas flow rate or the CH4 mole fraction. A maximum CH4 conversion (resp. H2 yield) of 90% (resp. 85%) was achieved at 1400 °C and the thermochemical reactor efficiency reached 5% for the highest CH4 content in the feed.