Low-melting point inorganic nitrate salt heat transfer fluid
| DWPI Title: Composition used as heat transfer fluid and thermal energy storage media in solar energy application comprises specific amount of sodium nitrate, potassium nitrate, lithium nitrate and calcium nitrate |
| Abstract: A low-melting point, heat transfer fluid made of a mixture of four inorganic nitrate salts: 9-18 wt % NaNO3, 40-52 wt % KNO3, 13-21 wt % LiNO3, and 20-27 wt % Ca(NO3)2. These compositions can have liquidus temperatures less than 100 C; thermal stability limits greater than 500 C; and viscosity in the range of 5-6 cP at 300 C; and 2-3 cP at 400 C. |
| Use: As low-melting point, heat transfer fluid and thermal energy storage media in solar energy application, such as solar parabolic trough electrical power plant systems. |
| Advantage: The compositions i.e. molten salt compositions have improved properties compared to the oil-based heat transfer fluid (HTF) currently used in solar power plants. The molten salt costs significantly less. The molten salt is relatively benign in terms of environmental impact, whereas the oil is toxic and carries cleanup and waste disposal penalties when leaks occur. The molten salt has a higher density and heat capacity, requiring lower flows, much lower pressure drops in the system piping (which reduces pumping costs) and enhanced heat transfer capability. The molten salt HTF allows a higher operating temperature differential in the solar field and greater temperature gradients in thermal storage systems which greatly enhances efficiency and thermal storage utilization. The molten salt can be operated at higher temperatures which, leads to higher power cycle and power plant efficiencies. The molten salt has virtually no inherent vapor pressure, which allows its use in thermal energy storage tanks that are vented to atmosphere versus using high-cost pressure vessels that would be required for other HTF types. The molten salt HTF is stable in contact with air and is not flammable. |
| Novelty: A composition comprises (mol.%, cation basis) sodium nitrate (NaNO 3 ) (11, 14, 16, 20), potassium nitrate (KNO 3 ) (47, 49, 38, 50), lithium nitrate (LiNO 3 ) (20, 25, 27, 30), and calcium nitrate (Ca(NO 3 ) 2 ) (10, 17, 12). |
| Filed: 5/14/2008 |
| Application Number: US2008120257A |
| Tech ID: SD 10676.1 |
| This invention was made with Government support under Contract No. DE-NA0003525 awarded by the United States Department of Energy/National Nuclear Security Administration. The Government has certain rights in the invention. |
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