Advanced Materials for CSP Molten Salt Storage
Because solar power is variable and intermittent, methods of energy storage are required to shift power production to match demand and power prices. Currently, the cost and availability of MW-GW scale energy storage and load leveling are major limitations to the general acceptance of renewable power generation. Unfortunately, current materials technologies limit state of the art molten salt storage and power transfer operations to a maximum of around 565°C (mixed nitrate salts, Solar Reserve Co). Rankine cycle power turbines operating at these conditions have a thermal efficiency around 41%, while ultra-supercritical steam turbines operating at 600°C operate at around 47% efficiency, a 15% increase. 700°C turbine operation increases this further to 51%, or a 24% increase in thermal efficiency. Transitioning to higher temperature power cycles can dramatically improve plant efficiencies, reduce the size of the solar field, and reduce salt storage tank size and pumping requirements, reducing costs - Thus, increasing the hot tank or thermocline (small systems) storage and heat exchanger (HX) temperature to 700-750°C can dramatically reduce the size of required tanks, HX, and pump systems (reducing construction cost), while increasing thermodynamic efficiency (decreasing operating costs) of concentrating solar power plants. This advantage is offset by the lack of durable materials, including piping, tanks, pumps, and heat exchangers capable of performing at 750°C in chloride salts for a desirable performance life span of 30 years. A specific challenge with heat exchangers is limited operational temperatures imposed by material limitations like reduced oxidation resistance, thermal stresses, creep, and reduced thermal conductivity at higher temperatures. Under this program of material and process manufacturing development, Powdermet seeks to evaluate and develop design data for the use of multifunctional thermal composites for a highly conductive metal matrix composite alloy for superheater and reheater HX applications. This proposed program’s material development towards high temperature, high pressure, and highly compact heat exchangers will enable efficient and power dense power generation cycles. The material is based on Powdermet’s metal matrix composite, also known as cermets, technology, which has been demonstrated for ballistic impact energy mitigation (Al, Mg alloy base) and thermally constrained high temperature systems (Ti, Ni, FeCrAlY, Nb based). In considering heat exchangers for this program, substituting high conductivity carbides, diamond, or BN in place of insulating microballoons enables high conductivity, corrosion- and wear-resistant composite materials. Powdermet’s HybriMet™ hierarchically engineered nanocomposite materials combine the hardness of ceramics (1600VHN), with the toughness of metals (>20MPa/m(1/2)). Under a prior Phase I, and ongoing Gen 3 CSP program, Powdermet’s HybriMet™ nanocomposite cermets have demonstrated near zero corrosion in 750°C molten salts. This project utilized the proven matrix materials used in HybriMet’s ongoing testing, and their evolution to include high oxidation resistance in sCO2 systems, to resolve heat exchanger life and reliability issues as well as to provide size reduction in high temperature molten salt thermal energy storage systems. A joint multi-disciplinary team comprised of material experts (Powdermet), heat exchanger design (University of Wisconsin and Brayton Energy) and scale up processing/manufacturing (Powdermet) extended Powdermet’s HybriTherm™ metal matrix composite material into the HX market – overcoming material, design, and manufacturing technical barriers. A cost-effective material and manufacturing process was developed for HX for modular power cycles, thermal energy storage and energy-waste recovery systems.
- Research Organization:
- Powdermet Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Contributing Organization:
- University of Wisconsin – Madison Brayton Energy LLC
- DOE Contract Number:
- SC0019953
- OSTI ID:
- 2287635
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-PMT-19953
- Country of Publication:
- United States
- Language:
- English
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