(264a) Dynamic Model of a Solar Fuel System for the Thermochemical Production of Syngas from H2o and CO2

We report on a dynamic model of a solar fuel system for the solar thermochemical production of syngas – a specific mixture of CO and H₂ − from CO₂ and H₂O via a ceria-based redox cycle using concentrated solar energy.

The system is driven by concentrated solar process heat to effect the simultaneous co-splitting of CO₂ and H₂O via a ceria-based thermochemical redox cycle. The solar reactor for effecting this redox cycle consists of a cavity-receiver containing a reticulated porous ceramic (RPC) foam structure made of pure CeO₂. The characteristic redox cycle is operated under a temperature/pressure-swing mode, consisting of three phases: 1) The reduction phase, during which the solar reactor is heated with concentrated sunlight up to the desired reduction end temperature of up to 1500°C to release O₂ from CeO₂, assisted through lowered total pressure by a vacuum pump and an Ar sweep gas flow. 2) A cool-down phase under atmospheric pressure during which the solar reactor, re-pressurized by injecting CO₂, cools down to the oxidation start temperature. 3) The oxidation phase, during which CO₂ and H₂O are co-injected into the reactor’s cavity, react with the reduced ceria to form syngas. An in-depth experimental parametric study of the system has previously been carried out and the presented dynamic model allows further parameter analysis and offers additional insight to the system performance.

The dynamic reactor model is a grey box model based on energy and mass conservation equations within predefined model domains and considers mass and energy transfer between the domains and over the system boundaries. Model domains contain solid, gaseous and porous volumes with the redox reaction taking place in the porous volumes representing the RPC structure inside the cavity. The model follows a lumped parameter approach to describe the mass and energy reservoirs and is implemented using MATLAB. Unknown system parameters are determined empirically through comparing numerically simulated results to experimental data collected over multiple characteristic cycles with varying process parameters. Model validation is done by comparing simulated results to a different data set of reactor cycles.

Apart from the model description, we present the parameter identification and validation as well as first model applications. We look at system behaviour when linking two or more reactors together in continuous operation and study the reactor behaviour under intermittent solar conditions.