Development of Molten Salt Heat Transfer Fluid With Low Melting Point and High Thermal Stability

Journal of Solar Energy Engineering (Impact Factor: 1.13). 08/2011; 133(3). DOI: 10.1115/1.4004243

ABSTRACT This paper describes an advanced heat transfer fluid (HTF) consisting of a novel mixture of inorganic salts with a low melting point and high thermal stability. These properties produce a broad operating range molten salt and enable effective thermal storage for parabolic trough concentrating solar power plants. Previous commercially available molten salt heat transfer fluids have a high melting point, typically 140 °C or higher, which limits their commercial use due to the risk of freezing. The advanced HTF exploits eutectic behavior with a novel composition of materials, resulting in a low melting point of 65 °C and a thermal stability limit over 500 °C. The advanced HTF described in this work was developed using advanced experiment design and data analysis methods combined with a powerful high throughput experimental workflow. Over 5000 unique mixtures of inorganic salt were tested during the development process. Additional work is ongoing to fully characterize the relevant thermophysical properties of the HTF and to assess its long term performance in realistic operating conditions for concentrating solar power applications or other high temperature processes.

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    ABSTRACT: One of the major challenges preventing the concentrated solar power (CSP) industry from occupying a greater portion of the world's energy portfolio are unattractive start up and operating costs for developers and investors. In order to overcome these reservations, plant designers must be able to achieve greater efficiencies of power production. Molten salt nitrates are ideal candidates for CSP heat transfer fluids and have been proposed to offer significant performance advantages over current silicone based oil heat transfer fluids. Ternary molten salt nitrates offer high operating temperatures while maintaining low freezing temperatures. However, a shortage of important thermophysical property data exists for these salts. Previous work has shown the ternary compositions of LiNO3-NaNO3-KNO3 salts offer the widest possible temperature range for use in a CSP system. The present work contains data for the viscosity, specific heat, and latent heat of some mixtures of these salts at various temperatures, providing vital information for plant designers to optimize power generation and attract future investment to CSP systems.
    Journal of Solar Energy Engineering 08/2013; 135(3). DOI:10.1115/1.4024069 · 1.13 Impact Factor
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    ABSTRACT: In order to obtain molten salt with lower melting point, higher thermal stability and reduced cost relative to previously available materials, a variety of molten salt mixtures of alkali nitrates are investigated by experimental methods. However, since measurements are generally expensive and time-consuming, it is of interest to be able to predict melting point and the component of multi-component systems by using the numerical methods. In this paper, eutectic point and component of a new kind of the quaternary reciprocal system (K, Na/NO2, Cl, NO3) are determined firstly by conformal ionic solution theory. Then thermal stability of the mixtures that show a lower melting point is measured by thermogravimetric analysis device. Experimental results show the agreement between measurements and calculations is found to be very good. This kind of molten salt has a lower melting point, 140 °C. It is thermally stable at temperatures up to 500 °C, and may be used up to 550 °C for short periods. Besides, this molten salt has a reduced cost relative to previous low-melting nitrate mixtures due to the elimination of cesium nitrate and lithium nitrate.
    Applied Energy 12/2013; 112:682-689. DOI:10.1016/j.apenergy.2012.10.048 · 5.26 Impact Factor
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    ABSTRACT: Recently several new heat transfer fluids (HTF) have been proposed and analyzed with the aim of reducing the levelized costs of electricity (LCOE) of parabolic trough power plants. An existing simulation model at Fraunhofer ISE has been adapted to the use Solar Salt and HITEC ® as HTF in parabolic trough power plants. This model uses steady-state and semi-transitional methods to calculate the annual electrical energy yield of solar power plants at different locations including thermal energy storage. Finally rough cost-estimations in order to compare the LCOEs of the novel media and the conventionally applied thermal oil – Therminol VP-1 ® [3] are drawn. It turns out, that the freeze protection has significant impact on the net energy production of systems with molten salt. For a reference plant with a configuration similar to the Andasol 3 power plant, but located in Daggett/USA the net energy yield of Solar Salt varies between +5.6 % and −4.3 % compared to thermal oil, depending on the implemented freeze-protection strategy. Systems using Solar Salt as HTF are allowed to have up to 14.4 % higher investment costs to achieve the same LCOE as the conventional systems with thermal oil Therminol VP-1, but simulation results indicate that for an economic use of molten salt as HTF alternative freeze protection strategies should be investigated. Another key factor is the geographic location of the site, as sites with better solar resource seem more suited for use of molten salt as heat transfer fluid.
    18th SolarPACES Conference, SolarPACES 2012, 11.-14. Sept. 2012, Marrakesch, Marokko; 09/2012


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