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In- and ex-situ monitoring of extremely low MgOHCl in molten chloride salt for next-generation CSP

Gong, Qing and Ding, Wenjin and Bonk, Alexander and Bauer, Thomas (2022) In- and ex-situ monitoring of extremely low MgOHCl in molten chloride salt for next-generation CSP. EUCHEMSIL-2022, 05.-10. Jun.2022, Patras, Griechenland.

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Abstract

Molten chloride salt (MgCl2-KCl-NaCl) is seen as a promising thermal energy storage medium for next-generation concentrating solar power (CSP) plant, due to its advantages of relatively low melting point (~385 °C), high thermal stability (stable at >800 °C), low vapor pressure (~ 1 kPa at 800 °C) and low cost (0.22 USD/kg) [1, 2]. However, molten MgCl2-KCl-NaCl is strongly corrosive to Fe-Cr-Ni alloys even under protective inert gas atmospheres, attributing to hygroscopicity and corrosive hydrolysis products [3]. MgOHCl (MgOH+) is the main corrosive hydrolysis product, which is soluble in MgCl2-containing molten salt [4]. Hence, monitoring of MgOHCl is essential to evaluate the redox potential (i.e. corrosivity) of MgCl2-KCl-NaCl. In other words, monitoring of MgOHCl is a prerequisite for quantitative control of corrosion. In previous work, the MgOHCl concentration was in-situ measured with cyclic voltammeter (CV) and was ex-situ measured with acid-base back titration (BT). The ex-situ BT results were used to calibrate the in-situ CV results. With this approach, concentration of MgOHCl in molten chloride can be converted into electrical signal, which has been used for lab-scale to understand purification methods[5, 6]. In addition, CV could be a potential method for automatic corrosion control system (CCS) in molten salt loops. However, when the concentration of MgOHCl was measured by BT, the results were interfered with MgO mixed in chloride salts. This makes the measure limit of MgOHCl concentration above 0.1 wt.%, which is not sufficiently low to study the acceptable impurity level in molten chlorides. In this work, a more accurate ex-situ measurement, direct titration (DT), was adopted and will be reported. With the post calibration by DT, it is demonstrated that the extremely low (~0.02 wt.%, 39 ppm O) MgOHCl is quantifiably detectable in-situ by CV at 700 °C.

Item URL in elib:https://elib.dlr.de/187254/
Document Type:Conference or Workshop Item (Speech)
Title:In- and ex-situ monitoring of extremely low MgOHCl in molten chloride salt for next-generation CSP
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Gong, QingQing.Gong (at) dlr.deUNSPECIFIED
Ding, WenjinWenjin.Ding (at) dlr.deUNSPECIFIED
Bonk, AlexanderAlexander.Bonk (at) dlr.deUNSPECIFIED
Bauer, Thomasthomas.bauer (at) dlr.dehttps://orcid.org/0000-0003-4080-7944
Date:June 2022
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:MgOHCl measurement, In-situ measurement, Direct titration, Thermal energy storage
Event Title:EUCHEMSIL-2022
Event Location:Patras, Griechenland
Event Type:international Conference
Event Dates:05.-10. Jun.2022
HGF - Research field:Energy
HGF - Program:Materials and Technologies for the Energy Transition
HGF - Program Themes:High-Temperature Thermal Technologies
DLR - Research area:Energy
DLR - Program:E SP - Energy Storage
DLR - Research theme (Project):E - Thermochemical Processes
Location: Stuttgart
Institutes and Institutions:Institute of Engineering Thermodynamics > Thermal Process Technology
Deposited By: Gong, Qing
Deposited On:22 Jul 2022 14:53
Last Modified:22 Jul 2022 14:53

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