Session: 08-01: Solar Chemistry: Thermochemical Fuel Production I

Paper Number: 130505

130505 - High-Fidelity Thermomechanical Modeling of a Novel Indirectly Irradiated Reactor for Solar Thermochemical Fuel Production 

Abstract: 

Solar thermochemical hydrogen production (STCH) is a process which uses heat to split water through a redox reaction, typically using a metal oxide such as ceria. While STCH is promising due to its use of thermal energy, which can be efficiently harvested from the sun and stored, existing experimental prototypes fall short of the heat-to-hydrogen efficiency necessary for widespread adoption¹ . We have previously proposed a novel Reactor Train System (RTS) which has the potential to significantly increase heat-to-hydrogen efficiency². A principal reason for the high efficiency of the RTS is internal heat recovery by radiative heat exchange between reactors. In contrast to receiver-reactors STCH systems which have been demonstrated before, the RTS is not exposed to concentrated solar radiation and is ‘indirectly irradiated’ instead. This enables the use of stored thermal energy, eliminates hot spots, and potentially reduces thermal shock.

 

We have previously analyzed heat and mass transfer within RTS reactors using simplified 1-D models^2,3. In this work we extend the modeling capabilities to 3D to enable geometry optimization and material selection. Previous STCH receiver-reactors have been optimized for direct irradiation with concentrated sunlight and feature small apertures with actively cooled quartz windows^4,5. On the other hand, RTS reactors are irradiated with non-collimated, infrared spectrum (IR) radiation supplied by a high-temperature source like a heated plate. This results in a novel set of reactor design constraints and opportunities: e.g., the need for larger, IR transmissive windows, uncooled window and flanges to reduce heat loss and prevent steam condensation, novel redox material cavity shapes for higher mass loading, etc. This reactor will need to operate at up to 1500°C with significant temperature and pressure swings, while exposed to steam, carbon dioxide and oxygen. Thus, in addition to heat and mass transfer, considering thermo-chemo-mechanical stresses is crucial to ensure safe operation and long lifetime of RTS reactors. As far as we know, such an analysis has not been reported for STCH reactors.

 

In this presentation we will report our work combining heat transfer with structural mechanics for high-fidelity modeling and optimization of a prototype RTS reactor to evaluate material stresses in the harsh working environment. Of particular interest is the high-temperature infrared-transmitting window and the flanges and gaskets which will hold it. This is a key design difference compared to existing directly irradiated reactors, which commonly use actively cooled quartz windows that have high transmission in the solar spectrum. We will conduct parametric heat transfer studies to optimize the geometry of components such as the ceria receiver, window, flanges, and emitter. The use of state-of-the-art high-temperature materials such as ceramic matrix composites will be investigated for use in critical components of the reactor, like the window’s flanges. The thermal and mechanical properties of these structural materials will be compared, and trade-offs will be considered to optimize the overall efficiency of the reactor. These analyses will culminate in a reactor design that is optimized for reactor-to-reactor radiative heat transfer and is structurally robust at the target working environment.

 

1. Moretti et al., Science of The Total Environment 901, 166005, 2023

2. Patankar et al., Journal of Solar Energy Engineering 144(6), 061014, 2022

3. Patankar et al., Solar Energy 264, 111960, 2023

4. Zoller et al., Journal of Solar Energy Engineering 141(2), 021014, 2019

5. Sack et al., Solar Energy 135, 232-241, 2016

Presenting Author: Peter Scott Massachusetts Institute of Technology

Presenting Author Biography: Peter Scott is a graduate student in the Reacting Gas Dynamics lab at MIT. He obtained a B.S. in Mechanical Engineering and a minor in Energy Studies from MIT in June 2023. Peter first joined the lab during his senior year, in which he contributed to numerical modeling of mass transfer and early-stage reactor design for the Reactor Train System (RTS), which is a solar thermochemical hydrogen (STCH) project. He is continuing his work on the RTS project as a master's student by performing high-fidelity multiphysics modeling that will contribute to key design decisions for system optimization.

Authors:

Peter Scott Massachusetts Institute of Technology
Aniket Patankar Massachusetts Institute of Technology
Ziyao Wu Massachusetts Institute of Technology
Henrik Haussmann Massachusetts Institute of Technology
Ahmed Ghoniem Massachusetts Institute of Technology