Session: 05-04: Concentrating Solar Power I -- Receiver Simulations/Analysis

Paper Number: 142170

142170 - Thermochemical Oxygen Pumping for Enhanced Solar Fuel Production: A Modeling Approach 

Abstract: 

Thermochemical oxygen pumping for enhanced solar fuel production: A modeling approach

Jens Keller^1,2, Nicole Neumann¹, Mathias Pein¹, Stefan Brendelberger¹, Christian Sattler^1,2

¹Institute of Future Fuels, German Aerospace Center,

²RWTH Aachen, Chair for Solar Fuel Production
Jens.Keller@dlr.de

Solar fuel production via the two-step thermochemical redox cycle is one of the most promising methods for converting solar energy into green hydrogen or synthesis gas, because it has the ability to utilize a wide range of the solar spectrum and it omits lossy energy conversion steps compared to other fuel production methods.

The high-temperature heat required for the underlying redox cycle is provided by concentrated solar energy and is used in a cyclic two-stage process. In a reduction step, the heat is used for the endothermic reduction of a metal oxide at high temperatures. In a temperature swing step, the pre-reduced metal oxide is cooled to a lower temperature and reoxidised exothermically by reacting with water or carbon dioxide to form hydrogen and/or carbon monoxide. [1]  

The high oxygen affinity of the metal oxide required to split water and carbon dioxide leads to the fact that these materials are difficult to reduce, even at high temperatures. In order to increase the reduction extend during the reduction step and thus the cyclic yield of the process, it is necessary to provide a controlled reducing atmosphere with a low partial pressure of oxygen. While the conventional vacuum pump is still state of the art, alternative methods such as the thermochemical oxygen pumping (TCOP) have great potential to increase the efficiency of the fuel production process with comparatively low energy consumption. [2] TCOP uses a second two-stage thermochemical redox cycle to reduce the oxygen partial pressure during the reduction stage. [5]

Compared to conventional vacuum pumps, a TCOP requires up to 90% less energy at pressures below 1 mbar and can therefore increase the overall efficiency of thermochemical fuel production. This pumping process also uses redox metal oxides, which can be circulated at much lower temperatures than splitting materials such as cerium oxide. [1] In addition, no mechanical components are required and the heat recovered from the thermochemical splitting process can be used to power the pumping system. [2]

Proof of concept for this TCOP process has already been demonstrated [2,3] and efforts have been made to identify suitable potent TCOP pumping materials. [4]

Modelling of different operating modes and simulation of practical TCOP scenarios is crucial to identify optimised operating parameters and suitable pumping materials. As part of ongoing work, this thesis outlines a sophisticated modelling approach and compares it with experimental results. Furthermore, first results in the context of solar fuel production are presented and an extension of the application of TCOPs to other reactor concepts such as membrane reactors for solar hydrogen production is discussed.

 

[1] Y. Lu et al., Progress in Energy and Combustion Science, 75, 2019, 100785

[2] S. Brendelberger et al., Solar Energy, 2017, 91-102

[3] M. Pein et al., Solar Energy, 2020, 612-622

[4] J. Vieten, Energy Environ. Sci., 2019, 1369-1384

[5] B. Bulfin, Energy Fuels, 2015, 1001−1009

Presenting Author: Jens Keller DLR e.V., Institute of Future Fuels

Presenting Author Biography: Jens Keller has received a Master degree in Chemistry and in Energy- and Materials Physics both from the University of Clausthal. Since 2023, he has been employed as a doctoral student at the German Aerospace Center at the Institute of Future Fuels under the supervision of Prof. Christian Sattler. The topic of his dissertation is the development of a thermochemical oxygen pump.

Authors:

Jens Keller DLR e.V., Institute of Future Fuels
Nicole Neumann DLR e.V., Institute of Future Fuels
Mathias Pein DLR e.V, Institute of Future Fuels
Stefan Brendelberger DLR e.V, Institute of Future Fuels
Christian Sattler DLR e.V, Institute of Future Fuels