Investigation of Cascaded Shell and Tube Latent Heat Storage Systems for Solar Tower Power Plants

Solar thermal electricity generation is taking up increasing proportions of future power generation worldwide. Recent research indicates that a closed-loop Brayton cycle using supercritical carbon dioxide (s-CO2) offers the potential of higher power cycle efficiency versus the conventional superheated steam cycle at temperatures relevant for CSP applications. Thermal energy storage solves the time mismatch between the solar energy supply and the electricity peak demand and allows for a more efficient use of the turbine and other power block components. The narrow storage temperature range required for the s-CO2 cycle advantages the use of latent heat storage, which has a higher storage density compared to the conventional two-tank storage. This paper demonstrates a design of a cascaded shell and tube phase change storage system potentially applicable for the s-CO2 cycle. A previously developed effectiveness-number of transfer unit method is employed as a design guide and computational fluid dynamics modelling is performed to examine the sensible energy extraction. The results prove that the effectiveness of the extracted sensible energy can be increased by increasing the number of phase change storage systems in series. Stainless steel (SS) AISI 316 as well as a creep resistant SS AISI 446 is considered as the tube material in the design and results suggest that using AISI 446 can minimize the overall amount of storage and tube materials.