(557d) Long Term Stability and Operational Limits of Lithium Sulphate for Thermal Energy Storage

This work explores the
experimental feasibility of lithium sulphate as a
thermal energy storage material for concentrated solar power (CSP)
technologies. This salt has a crystalline phase change between cubic and
monoclinic at temperatures around 576°C. By operating with a minimum cycle temperature,
both sensible and latent thermal energy can be utilised.
The operating temperatures of the proposed system are appropriate for current
CSP technologies based on subcritical steam Rankine or supercritical CO₂
power cycles.

Current phase change materials
(PCMs) under investigation utilize solid-liquid transformations which can
achieve a higher storage performance than sensible storage materials within a low
temperature difference. However, these PCMs suffer from some technical problems
such as supercooling, corrosion and volume expansion.
Such disadvantages can be overcome when solid-solid PCM is used as the storage
material as it is less corrosive and undergoes a much smaller volume change.

In this work, the long
term performance and stability of lithium sulphate
has been evaluated. This involved long term experiments using 55 g of salt in
an air furnace, with characterization of material properties before and after
cycling using TGA-DSC, XRD and SEM. From experiment, it was determined that the
highest temperature at which the thermal properties and volume of the salt were
unchanged after repeated cycles was equivalent to its melting point (859°C). At
temperatures lower than 130°C, the material is prone to hydration reducing the
performance through significant changes to volume, density and consequently
thermal conductivity.