1. Material and Corrosion Issues
- Molten salts are highly corrosive at high temperatures and tend to dissolve alloy constituents of containment vessels, leading to fouling and deterioration of thermophysical properties of the salts, which can impair heat transfer efficiency and system reliability. This corrosion especially affects ferrous and nickel alloys commonly used in storage tanks and piping.
- Protection against corrosion requires specialized coatings, such as fractal-textured nickel coatings, which can reduce corrosion and fouling but add complexity and cost to system design.
2. Thermal Stability and High-Temperature Operation
- Molten salts must operate at high temperatures, typically around 290°C to 565°C in concentrated solar power (CSP) plants, to stay in liquid form and maintain performance. Thermal stability of salts at these temperatures is a concern, especially for traditional nitrate-based salts which can degrade or suffer from phase changes that affect storage efficiency.
- The need to maintain molten salts at such high temperatures means equipment must be designed to handle thermal stresses and avoid phase separation or solidification during downtime or fluctuations, posing engineering challenges.
3. Tank and System Design Challenges
- The design of molten salt storage tanks lacks standardized codes or guidelines, leading to inconsistent designs that may compromise safety, efficiency, and reliability. Failures of tanks in central receiver CSP plants have been reported due to stress relaxation cracking, fabrication errors, and operational stresses, resulting in significant economic losses.
- Materials such as stainless steel 347H used in tanks are vulnerable to cracking under thermal and mechanical stress at high temperatures.
4. Operational and Economic Considerations
- The infancy of high-temperature molten salt technology in CSP has resulted in operational failures related to commissioning and aggressive operation conditions.
- Maintaining molten salts at operational temperatures requires continuous heating, leading to energy consumption and associated costs.
- There are additional costs related to the development of improved molten salt formulations (e.g., additives, nanofluids) and protective materials to enhance performance and reduce corrosion.
In summary, the main challenges are corrosion and material degradation at high temperatures, ensuring thermal stability of the salts, designing robust and safe storage tanks, and managing the energy and cost implications of operating at high temperatures. Addressing these requires advances in materials science, tank design standards, and optimized salt chemistries.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/what-are-the-main-challenges-associated-with-using-molten-salts-for-thermal-energy-storage/
