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Design and evaluation of a continuous electrochemical purification reactor for corrosion control in flowing molten chloride salts
Witteman, Liam
Witteman, Liam
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2023
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2024-11-29
Abstract
The global energy system is evolving due to increasing demands for sustainable and affordable
carbon-free energy. With this energy transition comes the energy storage grand challenge - the need to
develop, commercialize, and utilize sustainable grid scale energy storage systems. Concentrating solar
power (CSP) with thermal energy storage (TES) is one proposed technology to answer the grand challenge.
However, widespread deployment of CSP-TES has been slow due to high levelized cost of electricity
(LCOE).
One avenue for cost reduction is to increase the operating temperatures (500-720 ◦C) of the CSP-TES
plant to enable higher efficiency power cycles. To operate at these temperatures requires finding a new salt
blend; a ternary Mg-K-Na chloride salt blend has been considered a prime candidate. However, its
commercial deployment has been challenged due to the lack of corrosion control strategies at scale. This
thesis evaluated an electrochemical purification reactor using Mg anodes and W cathodes to remove the
corrosive impurity MgOHCl. A series of studies were conducted and assessed the feasibility of scaling up
the electrochemical purification reactor for commercial utility. First, key properties of MgOHCl were
obtained via various electroanalytical techniques. Then, the batch kinetics of the relevant reactions were
studied to obtain necessary rate constants. A continuous purification reactor based on the batch kinetics
was built and tested in a molten salt flow system. The flow tests validated the continuous purification
reactor design to maintain MgOHCl concentrations below 1,000 ppm — the required concentration to
achieve less than 20 μm year− corrosion rates for Fe- and Ni-based alloys. Lastly, a preliminary scale-up
design, integration, and techno-economic analysis was conducted for purification system integrated into a
100 MWe CSP-TES plant.
The thesis answered the vital questions required for the success of commercial deployment of Mg-K-Na
chloride salts as a TES media. The knowledge generated in the thesis benefits other industries looking
towards molten chloride salts as well, such as nuclear fusion, nuclear fission, Carnot batteries, and
stand-alone thermal energy storage systems. Furthermore, the thesis serves as a road map for any future
researchers that wish to design and scale up molten salt reactors.
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