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 Li2CO3–Na2CO3–K2CO3 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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Nitrate based salts have application as a heat transfer fluid and thermal energy storage media in solar field installations and are normally used from 200 °C up to maximum temperatures of ∼550 °C. Molten K2CO3-Na2CO3-Li2CO3 could potentially be used as heat transfer fluid and thermal energy storage media to replace nitrate salts due to its wider temperature operating window (400–900 °C), which improves the heat transfer efficiency. There will be improved operability and the process will be more economical viable if the lower temperature at which carbonate salts can operate could be decreased. This paper explores the melting point and high temperature stability of K2CO3-Na2CO3-Li2CO3 based salt mixtures, the effect of atmosphere and the effect of additives to the melt using experimental investigation and thermodynamic modeling.

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The reduction of hematite iron ore fines by different carbonaceous materials in composite pellets in a one-layer bed under nonisothermal asymmetric heating from above is studied. Temperature measurements at various points in the bed show that there are large gradients both inside and outside the pellets, with the reduction fastest at the top where the temperature is highest. The relative difference between the degree of metallisation between the top and the bottom of the pellet can be even greater during the reduction. The pellets undergo nonuniform swelling/shrinking towards the end of the reduction, and their height is less than their width. Reoxidation can start at the top of the pellet while the bottom has not yet been fully reduced. Those with a higher initial volatile content but with the same amount of fixed carbon as other pellets, gave a significantly higher degree of reduction without the involvement of fixed carbon gasification reactions.

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