Lithium nitrate purity influence assessment in ternary molten salts as thermal energy storage material for CSP plants

The addition of lithium nitrate is assumed to improve the performance of molten salts, extending the work temperature range. This paper presents an evaluation of the influence of different degrees of purity of LiNO3, in a ternary mixture with composition 30 wt%LiNO3 + 13 wt%NaNO3 + 57 wt% KNO3 including a Chilean mixture obtained from the Atacama Desert brines. In addition, the use of synthetic lithium nitrate obtained from the chemical synthesis using Li2CO3 and HNO3, was incorporated in the comparison. The melting point results of the 30 wt% LiNO3 + 13 wt% NaNO3 + 57 wt% KNO3 mixture for different purities (128 °C, 124 °C), show a reduction of 92–96 °C with respect to the 223 °C of the solar salt and thermal stability results show maximum temperature are around 594 and 596 °C, which means that this mixture could work at maximum operating temperatures similar to those of solar salt. Finally, it was also determined that for the use of the proposed ternary mixture would mean a reduction of 35% in the volume of inventory with respect to solar salt since the proposed ternary salt presents an improvement about 14–21% in the heat capacity.