High temperature chloride carbonate phase change material: thermal performances and modelling of a packed bed storage system

Molten salts eutectics are promising candidates as phase change materials (PCMs) for thermal storage applications, especially considering the possibility to accumulate and release heat at high temperatures. Although many compounds have been proposed at this purpose in the scientific literature, very few data are available regarding actual applications. In particular, there is a lack of information concerning thermal accumulation at temperatures around 600°C, necessary for the coupling with a highly efficient Rankine cycle. For these reasons, the present work deals with the investigation of the thermophysical behaviour of a storage heat exchanger containing a cost effective and safe ternary eutectic, composed by sodium chloride, potassium chloride and sodium carbonate. This material was preliminarily and appositely selected and characterized to comply with the necessary melting temperature and latent enthalpy. In turn, an indirect heat exchanger was considered for the simulation, assuming Aluminium capsules to confine the PCM, thus obtaining the maximum possible heat exchange surface. Pressurized air at 5 bar was taken into account as heat transfer fluid (HTF). The modelling was carried out setting the inlet and outlet air temperatures at, respectively, 290 °C and 550°C and the results show a realistic storage efficiency of around 0.6. Finally, a conservative investment cost was estimated for the storage system, demonstrating a real possible economic benefit in using these types of materials and heat exchange geometries, with the results varying, according to possible manufacturing prices, in a range from 25 to 40 €/kWh.