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Counter flow sweep gas demand for the ceria redox cycle

Brendelberger, Stefan and Roeb, Martin and Lange, Matthias and Sattler, Christian (2015) Counter flow sweep gas demand for the ceria redox cycle. Solar Energy, 122, pp. 1011-1022. Elsevier. DOI: 10.1016/j.solener.2015.10.036 ISSN 0038-092X

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Abstract

The exploitation of solar radiation as abundant energy source and its utilization in solar fuels are crucial for a large scale deployment of a sustainable energy economy. In the search for related efficient, scalable, and economic technologies several two-step solar thermochemical redox cycles are under assessment. Generic thermodynamic process assessments have identified the parasitic power consumption for maintaining low partial pressures of oxygen during the reduction of the redox material as possibly critical efficiency limiting factor. Two options are generally considered for maintaining low oxygen pressures: reduction of the total pressure and sweeping. In case of sweeping with an inert gas, the parasitic power demand is proportional to the sweep gas amount and comprises the pumping power as well as the power for heating the sweep gas to the targeted reduction temperature and the power related to the provision of clean sweep gas. Different models have been proposed in literature to predict the required sweep gas amount for the redox cycle – with highly diverging results. A proposed counter flow model leads to negligible sweep gas demands over a wide set of operational conditions while another model leads to prohibitively high sweep gas demands below 5 kPa. In this study a refined counter flow model is proposed, which considers the actual oxygen release characteristic of ceria and the oxygen uptake capability of the sweep gas stream. While the model predicts much higher values of required sweep gas than the previous counter flow model, the application of a counter flow still leads to considerable savings. In addition, a numerical model is used to analyze different operational implications for a counter flow arrangement, showing that a significant additional reduction of the sweep gas demand can be reached by keeping the reduction extent below the thermodynamic equilibrium value. The derived counter flow sweep gas model is compared to the alternative reduction of the total pressure by the use of vacuum pumps on a system level. The results show the relative performances and operational window of sweep gas for redox cycles.

Item URL in elib:https://elib.dlr.de/99496/
Document Type:Article
Title:Counter flow sweep gas demand for the ceria redox cycle
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Brendelberger, Stefanstefan.brendelberger (at) dlr.deUNSPECIFIED
Roeb, MartinMartin.roeb (at) dlr.deUNSPECIFIED
Lange, Matthiasmatthias.lange (at) dlr.deUNSPECIFIED
Sattler, Christianchristian.sattler (at) dlr.deUNSPECIFIED
Date:9 October 2015
Journal or Publication Title:Solar Energy
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:122
DOI :10.1016/j.solener.2015.10.036
Page Range:pp. 1011-1022
Editors:
EditorsEmail
Epstein, MichaelUNSPECIFIED
Publisher:Elsevier
ISSN:0038-092X
Status:Published
Keywords:Water and CO2 splitting; Ceria redox cycle; Sweep gas; Counter flow model
HGF - Research field:Energy
HGF - Program:Renewable Energies
HGF - Program Themes:Concentrating Solar Systems (old)
DLR - Research area:Energy
DLR - Program:E SF - Solar research
DLR - Research theme (Project):E - Solar Process Technology (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Solar Research > Solare Verfahrenstechnik
Deposited By: Sattler, Prof. Dr. Christian
Deposited On:18 Nov 2015 10:05
Last Modified:18 Nov 2015 10:05

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