(325a) Experimental Demonstration of Heat Recovery in a Solar Redox Reactor with an Integrated Thermal Energy Storage

We consider the production of solar fuels via a thermochemical redox cycle for splitting H₂O and CO₂, driven by concentrated sunlight. The product is a specific mixture of H₂ and CO – syngas – which can be further processed downstream by the established Fischer-Tropsch synthesis to liquid hydrocarbons such as kerosene (jet fuel). The entire solar fuel process chain has been successfully demonstrated with a solar reactor concept based on a cavity-receiver containing reticulated porous ceramic (RPC) ceria structures. The key performance metric of the solar reactor is its solar-to-fuel energy efficiency, which is strongly dependent on the ability to recover heat during the temperature-swing redox cycle.

In previous work, we reported on an experimental investigation of a novel heat recovery method based on coupling the solar reactor with two thermocline energy storage (TES) units made of a packed bed of alumina spheres and using an inert heat transfer fluid (HTF). With this arrangement, the heat rejected from the solar reactor during the switching from the reduction to the oxidation step can be recovered, stored in the TES units, and recuperated back to the solar reactor for the switching from the oxidation to the reduction step. Experimental campaigns with two versions of the setup were able to demonstrate efficient heat extraction from the reactor following reduction, with HTF temperature over 1300°C and up to 70% of the rejected heat transferred to the HTF. However, severe heat losses in the piping manifold between the reactor and TES units prevented storing heat at sufficiently high temperature for the recuperation stage.

In this work, a new system has been developed, combining the solar receiver-reactor and a single TES unit into an integrated assembly, thus removing the need for high-temperature piping and valves. In a preliminary experimental demonstration, using a solar receiver with an inert porous absorber material, successful heat recovery was demonstrated, for the first time, for this type of cavity receiver-reactors, to the best of the authors’ knowledge. The new system and the experimental results will be presented.