PROJECT PROFILE: National Renewable Energy Laboratory 2 (Gen3 CSP Lab Call)

Project Name: Molten Chloride Thermophysical Properties, Chemical Optimization, and Purification
Funding Opportunity: Generation 3 Concentrating Solar Power Systems Lab Call
SETO Subprogram: Concentrating Solar-Thermal Power
Location: Golden, CO
SETO Award Amount: $1,000,000
Awardee Cost Share: N/A

This project will characterize molten salts that can be used as high-temperature heat-transfer fluids and thermal energy storage media in Generation 3 concentrating solar power (Gen3 CSP) plants, as well as established protocols for purifying them. The project team will work with a molten salt mixture that consists of three salts—magnesium chloride, potassium chloride, and sodium chloride—to find the optimal composition based on melting point, high-temperature stability, and ability to store energy. Characterizing different salt compositions and removing salt impurities will also minimize corrosion of plant components.

APPROACH

The project team will perform tests to establish levels of corrosion caused by different chemical compositions of molten chloride salts. They will also explore cost-effective thermal, chemical, and electrochemical salt-purification processes to make molten salt an effective heat-transfer fluid for CSP plants. Salts can be purified thermally by evaporating water, making the salts chemically react, or applying an electric voltage to remove impurities. The team will examine physical properties such as the density and heat capacity of various salt mixtures, which can be adjusted to raise thermal conductivity, lower viscosity, and improve stability at CSP plant operating temperatures as high as 750° Celsius.

INNOVATION

Studying new and traditional purification technologies will enable the project team to create a cost-effective sensing technology that can be deployed directly into industrial CSP plants to provide real-time data on impurities that lead to corrosion. This project will be key to accurately documenting properties of molten salts, providing reliable data that engineers can use to design Gen3 CSP plants.

PROJECT PROFILE: National Renewable Energy Laboratory (Gen3 CSP Lab Call) Photos

Proposed electrochemical sensor to detect the salt composition during operation, with a thermocouple, which creates an electrical signal that can be used to measure temperature. Photo courtesy of National Renewable Energy Laboratory.

Thermally purified chloride salt. The pink color occurs after thermal purification, potentially due to dehydration and interaction of salt with the purification container. Photo courtesy of National Renewable Energy Laboratory.

Chemically purified chloride salt. The pink color after thermal purification disappears because elemental magnesium is added to help purify the salt purification agent. Then, sodium chloride is added for optimal heat capacity, density, and viscosity measurement by NREL and other research partners. Photo courtesy of National Renewable Energy Laboratory.

Graphic courtesy of National Renewable Energy Laboratory.