Session: 17-03: Symposium Steinfeld - Solar fuels via an external energy addition

Paper Number: 122052

122052 - Modeling of the Ceria-Based Redox Cycle for Dry Reforming of Methane: Towards Optimized Thermochemical Syngas Production 

Abstract: 

Thermochemical processes using concentrated solar energy as the source of high-temperature heat offer an efficient pathway for producing sustainable fuels. A precursor to these liquid fuels is syngas (H₂ and CO), which can be produced via dry reforming of CH₄ with CO₂.

 

Within this framework, CeO₂ is introduced as a redox material over which the dry redox reforming reaction can occur, represented by:

reduction: CeO₂ + δCH₄ ↔ CeO_2-δ + δCO + 2δH₂

oxidation: CeO_2-δ + δCO₂ ↔ CeO₂ + δCO

 

where δ represents the non-stoichiometry and reduction extent of CeO₂. The process operates isobarically and isothermally around 1000°C, and serves as an interim technology preceding the solar-driven production of syngas from H₂O and CO₂ which requires higher temperatures (1500°C) as well as temperature and pressure swings between the redox steps. The thermodynamics of the dry redox reforming process have been extensively studied [1][2] and its on-sun feasibility was demonstrated with a 10 kW solar reactor mounted in a solar tower [3].

 

We report on the development of a solar reactor model that implements the reaction thermodynamics into a computational fluid dynamic scheme using a customized solver in OpenFOAM. The solver considers the species mass, continuity, energy, and momentum conservation equations in both gas and solid phases, and incorporates the thermodynamics of reversible heterogenous reactions of a non-stoichiometric metal oxide solid whose inherent properties are dependent on δ. A tubular reactor (⌀=19 mm, l=200 mm) filled with a packed bed of CeO₂ pellets is used to validate the model in terms of the experimentally measured versus numerically computed outlet gas product composition. Experiments are conducted with standard operating conditions at 1L_n/min, 1000°C, and 5% reactive gas concentrations. Subsequently, the model is used in parametric studies to build towards an optimized system with a focus on syngas selectivity and rates of fuel production.

 

References

[1]          B. Bulfin et al., "Statistical thermodynamics of non-stoichiometric ceria and ceria zirconia solid solutions," Phys Chem Chem Phys, vol. 18, no. 33, pp. 23147-54, Aug 17 2016, doi: 10.1039/c6cp03158g.

[2]          Bulfin, B., et al., “Thermodynamic comparison of solar methane reforming via catalytic and redox cycle routes,” Solar Energy, 2021. 215: p. 169-178.

[3]          M. Zuber et al., "Methane dry reforming via a ceria-based redox cycle in a concentrating solar tower," Sustainable Energy & Fuels, 2023, doi: 10.1039/d2se01726a.

Presenting Author: Mario Zuber ETH Zürich

Presenting Author Biography: Mario Zuber began his PhD under the supervision of Prof. Dr. Steinfeld in 2019, where his thesis focusses on renewable energy carriers, notably solar fuels. His research investigates the system on the theoretical, experimental, and computational fronts. Prior to his doctorate studies, Mario received his BASc from the University of Toronto where he studied mechanical engineering, and later continued his studies at ETH Zürich where he received his MSc in the mechanical engineering department.

Apart from academics Mario has spent time as a combustor trainee at Alstom/General Electric Power, stress intern at UTC Aerospace Systems, and was an active member in the Baja SAE design and build team during his bachelor studies. In his free time, he enjoys riding his motorcycle, playing ice hockey, or skiing in the mountains.

Authors:

Mario Zuber ETH Zürich
Simon Ackermann Synhelion
Aldo Steinfeld ETH Zürich