Session: 17-02: Symposium Steinfeld - Solar fuels via two-step cycles + the addition

Paper Number: 141898

141898 - Countercurrent Chemical Reactor for Solar Thermochemical Fuel Production 

Abstract: 

Solar thermochemical fuel production is considered a potential alternative pathway for sustainable fuel production. By using concentrating solar thermal (CST) heat, a 2-step reduction-oxidation (redox) cycle is performed, splitting CO₂ and H₂O into syngas – a mixture of H₂ and CO. The syngas can be converted into various hydrocarbons via gas-to-liquid (GTL) processes such as Fischer-Tropsch. While significant work is being performed on increasing the reactor efficiency (also called solar-to-fuel efficiency even though it does not include solar collection losses, product separation, and other necessary system operations), this is but one of several important performance metrics for an industrial chemical process, other common metrics being conversion extent, power output, and power density. To date, even the most successful demonstrations have exhibited conversion extent values of less than 0.2 (usually less than 0.01) and power densities of less than 50 kW/m³ while considering the volumes of the reactive material and cavity only. These parameters are directly related to the size of energy intensive unit operations such as syngas conditioning and steam generation, and lower values require large units, adding cost and complexity to the plant.

We have developed a new reactor concept based on a packed-bed design, that could achieve high conversion extents under operating conditions comparable to the state-of-the-art. The design utilizes the continuous chemical potential of nonstoichiometric oxides such as ceria-based oxides, ferrites, and perovskites, achieving similar performance to that of countercurrent systems, but without the complexity and limitations of high-temperature membranes or moving oxide systems. The design also allows to decouple the reactor from the solar receiver and enables the possibility of a hybrid CST-electrical heating system, benefiting from the superior performance of each method at different temperatures. A higher capacity factor than directly irradiated reactors can be obtained using a thermal energy storage (TES) system. Considering that CST systems are deployed in areas with high solar resources, there is a great potential synergy with PV-based heating. A 1D numerical model of the reactor has been developed, with initial results predicting conversion extents over 0.5 (in some cases up to 0.9) using CeO₂ as the oxide material. With peak conversion reaching values over 0.9, optimization of the operating conditions can lead to an improved performance on the system level. The reactor concept and its predicted performance will be presented, together with a comparison of the energy and equipment cost saving due to the high conversion compared to previous works.

Presenting Author: Alon Lidor National Renewable Energy Laboratory

Presenting Author Biography: Dr. Lidor is a Senior Research Engineer at the National Renewable Energy Laboratory (NREL) since 2023 working in the Thermal Energy Science & Technologies Group. He received his B.Sc. (2011) from the Department of Mechanical Engineering at Ben-Gurion University, and his M.Sc. (2013) and Ph.D. (2017) from the Faculty of Aerospace Engineering at the Technion – Israel Institute of Technology. He was a DLR-DAAD Postdoctoral Fellow at the German Aerospace Center (DLR) in 2018-2019, before winning a Marie-Curie Individual Fellowship and joining ETH Zürich where he worked as a Postdoctoral Associate and later Senior Research Associate until 2023. His research interests include solar thermochemical processes, high-temperature heat recovery, thermal energy storage, small-scale propulsion units, and fundamental topics in thermodynamics. His work combines theoretical, numerical and experimental approaches, and includes expertise in the design and testing of high-temperature solar reactors and thermal energy storage systems.

Authors:

Alon Lidor National Renewable Energy Laboratory
Zachary Hart National Renewable Energy Laboratory