An innovative concept of a thermal energy storage system based on a single tank configuration using stratifying molten salts as both heat storage medium and heat transfer fluid, and with an integrated steam generator

摘要

The proposed innovative thermal energy storage system is based on a single tank containing a mixture of nitrate salts (60% NaNO3 and 40% KNO3 in weight; this mixture gradually changes from solid to liquid in the temperature range between about 220°C and 240°C, becoming completely melted above this temperature), with an integrated steam generator directly contained inside it. The system is operated exploiting the thermal stratification of the salts mixture in the temperature range between 550°C (hot temperature) and 290°C (cold temperature). The experimental work conducted at ENEA has revealed that the thermal stratification of the molten salts mixture can be maintained quite constant for several hours and the presence of the integrated steam generator actively guarantees and maintains the stratification during the operation time, avoiding mixing of the stratified layers. The single-tank system with stratification of the molten salts and an integrated steam generator is an important improvement in terms of efficiency, reliability and cost reduction, with respect to the two-tank thermal energy storage system. This report has the aim of giving an overview of this new technology but, given the fact that the experimental activities are still ongoing, the description of the system remains at a qualitative level. The complete set of experimental results will be presented in the future when the Projects that are framework of this research will have been completed.