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Research Papers

The Thermal Stability of Molten Lithium–Sodium–Potassium Carbonate and the Influence of Additives on the Melting Point

[+] Author and Article Information
Rene I. Olivares1

 CSIRO Energy Centre, Mayfield West, Newcastle, NSW 2304, AustraliaRene.Olivares@csiro.au

Chunlin Chen, Steven Wright

 CSIRO Process Science and Engineering, Clayton, Melbourne, Vic 3169, Australia

7 wt. % NaNO3 , 53 wt. % KNO3 and 40 wt. % NaNO2 , Reg. U.S. Patent - Coastal Chemical Company.

1

Corresponding author.

J. Sol. Energy Eng 134(4), 041002 (Jun 27, 2012) (8 pages) doi:10.1115/1.4006895 History: Received November 23, 2011; Accepted May 06, 2012; Published June 26, 2012; Online June 27, 2012

The thermal stability of a molten LiNaK carbonate salt, potentially suitable for thermal energy storage, was studied up to a temperature of 1000 °C. The salt investigated was the eutectic Li2 CO3 –Na2 CO3 –K2 CO3 in the proportions 32.1–33.4–34.5 wt. % and the study was done by simultaneous differential scanning calorimetry (DSC)/thermogravimetric–mass spectrometric (TG–MS) analysis in gas atmospheres of argon, air, and CO2 . It was found that (i) under a blanket gas atmosphere of CO2 the LiNaK carbonate salt is stable up to at least 1000 °C. (ii) In an inert atmosphere of argon, the salt evolves gaseous CO2 soon after melting and begins to decompose at between 710 °C and 715 °C with acceleration in the CO2 evolution rate from the melt. An increase in the rate of weight loss is also observed after 707 °C. (iii) Under a blanket atmosphere of air, the gaseous CO2 evolution from the salt is observed to commence at 530 °C, the onset of decomposition detected by DSC analysis at 601 °C and the rapid rate of weight loss determined by TG analysis at 673 °C. The melting point of the LiNaK carbonate studied was between 400 °C and 405 °C. Thermodynamic modeling with Multi-Phase-Equilibrium (MPE ) software developed in CSIRO Process Science and Engineering indicated that additives such as NaNO3 , KCl, and NaOH lower the melting point of the LiNaK carbonate eutectic, and this was experimentally verified.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Hydroxide and carbonate interactions optimized by fitting published phase diagrams [10]

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Figure 2

Model prediction of the effect of hydroxide on the melting point of LiNaK carbonate

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Figure 3

DSC/TG-MS analysis for thermal decomposition of LiNaK carbonate salt in argon atmosphere

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Figure 4

DSC/TG-MS analysis for thermal decomposition of LiNaK carbonate salt in air atmosphere

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Figure 5

DSC/TG-MS analysis for thermal decomposition of LiNaK carbonate salt in CO2 atmosphere

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Figure 6

DSC/TG-MS analysis for the effect of 10 wt. % NaNO3 addition to LiNaK carbonate salt in argon atmosphere

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Figure 7

DSC/TG-MS analysis for the effect of 10 wt. % KCl addition to LiNaK carbonate salt in argon atmosphere

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Figure 8

DSC/TG-MS analysis for the effect of 10 wt. % NaOH addition to LiNaK carbonate salt in argon atmosphere

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