Molten salt selection methodology for medium temperature liquid air energy storage application

Power production research in the recent years is moving towards renewable energy sources with the aim to reduce CO2 emissions. A potential means to overcome the obstacles placed by the intermittent nature of the most common sustainable energy sources is represented by the Liquid Air Energy Storage (LAES) systems. In order to improve its round trip efficiency, which is currently at 50%, the use of a common thermal medium for thermal storage and heat transfer fluid is considered as an effective solution. Molten salts were selected as the common thermal medium in this work, where a novel methodology for identifying and evaluating alternative mixtures is introduced. Firstly, various literature correlations were collected to form a thermo-physical property database of low melting temperature molten salts. These correlations were integrated in Aspen+ by implementing a hybrid simulation technique for property estimation. These simulations were followed by a parametric analysis where 70 molten salt mixtures were evaluated in terms of thermo-physical properties by means of a performance and system index parameter. Following this process, 16 new molten salt mixtures were selected for the experimental campaign to measure their melting point temperature. As a result, two new alternative molten salt mixtures were found to have a low melting point of 95 °C and 105 °C, whilst providing a 37% and 34% increase in the performance indicator value. Hence, the presented methodology was proven to be an effective and versatile tool in identifying alternative salt mixtures, and can be adapted for comparable applications.