Concrete based molten salt storage tanks

Abstract

High-temperature molten salt mixtures such as chloride-based salts have been widely investigated in recent years as alternate thermal energy storage media since they can enable higher temperature power cycles with higher thermodynamic efficiencies in concentrated solar power plants. They can also be used to decarbonize industrial processes requiring high-grade heat for industries located in electrical grids with increasing penetration of intermittent renewable energy. However, molten salts in general, and chloride salts in particular, are highly corrosive towards metals and thus require special stainless steel grades for storage tank construction. These grades, such as nickel-based alloys, can be up to four times more expensive than a regular grade stainless steel. Therefore, the primary cost driver for high-temperature chloride salts is the tank material instead of the salt itself which limits the commissioning of high-temperature thermal energy storage plants. Until now, a low-cost tank material which can effectively overcome the problems associated with molten salts operating above 670 °C has not been reported. In this work, we present low-cost engineered concrete-based thermal energy storage tanks for molten salts capable of operating at high temperatures even in corrosive environments. The engineered concrete composites are developed using commercially available additives and coatings. Tank prototypes, filled with moderate-temperature nitrate salts, are rigorously tested under thermal cycling conditions to demonstrate that the tanks can effectively withstand thermal shocks experienced during daily salt charge/discharge cycles. Moreover, salt diffusion through the porous concrete walls is shown to be suppressed by using external coatings. Finally, the compatibility of engineered composites with high-temperature chloride salts is qualitatively evaluated under a high-flux solar simulator.