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

Paper Number: 140968

140968 - Solar Thermochemical Jet Fuel Production From Air-Captured H2o and Co2 – Reactor Modelling, Upscaling, and Techno-Economic Analysis 

Abstract: 

We report on the solar thermochemical fuel production from H₂O and CO₂ obtained by direct air capture [1]. We present a heat and mass transfer model of the solar reactor. We further present the results of an energy efficiency and techno-economic analysis of an industrial-scale fuel plant [2].

The core of the process is the simultaneous co-splitting of CO₂ and H₂O via a ceria-based thermochemical redox cycle driven by concentrated solar process heat. 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 O₂ partial pressure by a vacuum pump and 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 – a tailored mixture of CO and H₂. The syngas can then be further processed to liquid hydrocarbon fuels via established gas-to-liquid processes such as Fischer-Tropsch synthesis. We present the results of a dynamic grey-box model of the solar reactor for solving the governing energy and mass conservation equations. The analysis compares the implementation of the modelled reactors in a 2-reactor versus 3-reactor system under different solar input conditions and compares the findings to experimental results obtained with a 2-reactor pilot demonstration plant.

We present an energy efficiency analysis of an industrial-scale solar fuel plant that uses the concentrated solar energy of a heliostat field as the source of high-temperature process heat and integrates a thermal energy storage system for round-the-clock continuous operation. We further report on the techno-economic assessment of such an industrial-scale plant. Two scenarios are considered for a location with high direct normal irradiation (e.g. annual DNI > 3400 kW/m2): near-term future by the year 2030 and long-term future beyond 2030 with advancements in solar receiver, redox reactor, high-temperature heat recovery and direct air capture technologies. The minimum fuel selling price is estimated at around 2.5 €/L jet fuel in the near-term future, and 0.6-1.3 €/L jet fuel in the long-term future. Greenhouse gas savings can exceed 70% already in the near-term future.

References:

1.         Schäppi R., Rutz D., Dähler F., Muroyama A., Haueter P., Lilliestam J., Patt A., Furler P., Steinfeld A. Drop-in fuels from sunlight and air. Nature 601, 63-68, 2022. https://doi.org/10.1038/s41586-021-04174-y

2.         Moretti C., Patil V., Falter C., Geissbühler L., Patt A., Steinfeld A. Technical, economic and environmental analysis of solar thermochemical production of drop-in fuels. Science of the Total Environment 901, 166005, 2023. https://doi.org/10.1016/j.scitotenv.2023.166005

Presenting Author: Remo Schäppi ETH Zurich

Presenting Author Biography: Remo Schäppi is a postdoctoral researcher from ETH Zurich and is focusing his
research activities on the production of solar fuels and the demonstration of the entire
production chain from sunlight and air to liquid hydrocarbons.

Authors:

Remo Schäppi ETH Zurich
Christian Moretti ETH Zurich
Vikas Patil Synhelion AG
Christoph Falter Synhelion AG
Lukas Geissbühler Synhelion AG
Anthony Patt ETH Zurich
Aldo Steinfeld ETH Zurich