Molten Eutectic Salt STES for Stable Thermal Storage Above 565°C
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Solution Overview
Problem
Current thermal energy storage systems for concentrated solar power (CSP) are limited by the thermal instability of existing molten salt and synthetic oil heat transfer fluids above 565°C, requiring new materials and methods for efficient energy storage and transfer at higher temperatures.
Innovation Solution
A multi-chamber sensible thermal energy storage system using molten eutectic salt mixtures as both thermal energy storage medium and heat transfer fluid, with an immiscible inert gas for direct contact heat transfer, enabling efficient energy storage and transfer at temperatures up to 1000°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If solar salt is used as TES medium and HTF for power tower, then thermal energy storage up to 565°C is achieved, but thermal instability occurs above this temperature
Solution Approach 1:
The patent changes the chemical composition parameters of the molten salt from conventional solar salt (NaNO3-KNO3) to a eutectic mixture containing lithium carbonate, sodium carbonate, and potassium carbonate. This parameter change enables the system to operate stably at temperatures above 565°C, with the new composition maintaining thermal stability up to 1000°C while achieving the desired high-temperature energy storage capability.
2Temperature
If synthetic oil is used as HTF for parabolic trough collectors, then operation up to 400°C is achieved, but thermal instability occurs above this temperature
Solution Approach 1:
The patent fundamentally changes the HTF from organic synthetic oil to inorganic molten eutectic salt. This parameter change transitions the system from a carbon-based fluid with limited thermal stability to an inorganic salt mixture that maintains stability at temperatures exceeding 1000°C, thereby resolving the thermal degradation issue that limits synthetic oil operation to 400°C.
3Ease of operation
If molten solar salt is used as HTF for power tower, then freezing protection is provided, but thermal instability occurs above 565°C
Solution Approach 1:
The patent modifies the chemical composition parameters of the molten salt to create a eutectic mixture with a lowered freezing point while simultaneously achieving high-temperature stability. The specific ratio of lithium carbonate, sodium carbonate, and potassium carbonate creates a composition that remains liquid at operating temperatures and maintains thermal stability above 565°C, unlike conventional solar salt.
4Reliability
If carbonate salts are used as TES medium for high temperature applications, then thermal stability up to 1000°C is achieved, but decomposition occurs without CO2 atmosphere
Solution Approach 1:
The patent implements a CO2 atmosphere control system that maintains a carbon dioxide environment around the molten carbonate salt. This inert atmosphere prevents the decomposition of carbonate salts at high temperatures by suppressing carbon loss through oxidation. The system includes CO2 injection or circulation mechanisms that ensure the molten salt remains in a stable chemical environment, enabling operation up to 1000°C without decomposition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system achieves high heat storage and recovery efficiencies, reduces installation costs, and allows for dispatchable energy generation, particularly suitable for lower electricity generation capacities, while maintaining system stability and minimizing maintenance efforts.
Implementation Method 1
sensible thermal energy storage (STES) systems containing molten eutectic salt liquids at temperatures above 565° C., the stored thermal energy being used for generation of electricity
Implementation Method 2
with an immiscible inert gas for direct contact heat transfer
Data Source
AI summary
Two sensible thermal energy storage (STES) systems in multiple chambers containing molten eutectic salts have been devised for use at temperatures above 565° C. For the first type, the thermal energy of low specific heat of an immiscible gaseous heat transfer fluid (HTF) at temperatures above 900° C. is readily converted to dispatchable heat of high specific heat in the molten eutectic salt liquid layers operating at high temperatures, which can again produce a gaseous HTF at a constant temperature of 700° C. or higher for the lower electricity generation capacities. For the second type, the molten eutectic salt liquids are used as a thermal energy storage (TES) medium and also a HTF at temperatures above 700° C. for the higher electricity generation capacities. These STES systems provide an effective cushion against the disturbances of heat supply from the sun.