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With a view to elevated operating temperatures in thermal energy storage - Reaction chemistry of Solar Salt up to 630°C

Sötz, Veronika and Bonk, Alexander and Bauer, Thomas (2020) With a view to elevated operating temperatures in thermal energy storage - Reaction chemistry of Solar Salt up to 630°C. Solar Energy Materials and Solar Cells, 212, p. 110577. Elsevier. doi: 10.1016/j.solmat.2020.110577. ISSN 0927-0248.

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Official URL: https://www.sciencedirect.com/science/article/abs/pii/S092702482030180X

Abstract

Sensible heat storage is a cost-efficient and scalable technology for energy storage. The state-of-the-art storage systems in concentrating solar power (CSP) plants use the storage material Solar Salt, which is a nitrate salt mixture. Chemical stability of this salt material is crucial for lifetime reliance, and for development of the storage technology towards higher temperatures. High temperatures enhance the storage capacity, but also promote decomposition reactions. For instance, harmful gases can evolve, and oxide ions are produced, which aggravate corrosion. Up to now, it is unclear how to describe the salt chemistry, and how to quantitatively predict the problematic decomposition products. The experimental method in this study is chosen with regard to the exclusion of mass transport limitations. Thin films of salt are heated to 560-630 °C. The salt composition is analyzed by ion chromatography and acid-base titration. The ratio of nitrite to nitrate ions stabilizes, which indicates chemical equilibrium of the nitrite forming reaction. The oxide content increases continuously over time, and is interpreted in terms of a kinetic rate law. A consistent mathematical description of Solar Salt chemistry at high temperatures (≥560 °C) in contact with air is presented. It includes thermodynamic parameters, in particular the reaction enthalpy of 95 ± 4 kJ·mol-1 and entropy of 86 ± 5 J·mol-1·K-1 for the nitrate-nitrite reaction. The microkinetics of the oxide ion formation are characterized by an activation energy of 42 ± 3 kJ·mol-1. The work presented finally contributes to a forecast of material stability at and above 560 °C.

Item URL in elib:https://elib.dlr.de/137740/
Document Type:Article
Title:With a view to elevated operating temperatures in thermal energy storage - Reaction chemistry of Solar Salt up to 630°C
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Sötz, VeronikaVeronika.Soetz (at) dlr.dehttps://orcid.org/0000-0002-8309-6612
Bonk, AlexanderAlexander.Bonk (at) dlr.dehttps://orcid.org/0000-0002-0676-7267
Bauer, ThomasThomas.Bauer (at) dlr.dehttps://orcid.org/0000-0003-4080-7944
Date:August 2020
Journal or Publication Title:Solar Energy Materials and Solar Cells
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:212
DOI :10.1016/j.solmat.2020.110577
Page Range:p. 110577
Publisher:Elsevier
ISSN:0927-0248
Status:Published
Keywords:Concentrating solar power (CSP); thermal energy storage (TES); Solar Salt; nitrate salt; salt decomposition; reaction kinetics
HGF - Research field:Energy
HGF - Program:Storage and Cross-linked Infrastructures
HGF - Program Themes:Thermal Energy Storage
DLR - Research area:Energy
DLR - Program:E SP - Energy Storage
DLR - Research theme (Project):E - Thermochemical Processes (Storage) (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Engineering Thermodynamics > Thermal Process Technology
Deposited By: Sötz, Veronika
Deposited On:07 Dec 2020 11:37
Last Modified:07 Dec 2020 11:37

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