Researchers from Beijing University of Technology built an experimental thermal storage system with a new type of molten salt as a thermal energy storage medium to assess the temperature distribution of molten salt inside the tank
Concentrated solar power (CSP) systems use mirrors or lenses to generate solar power by concentrating a large area of sunlight onto a small area. This renewable energy technology is commercially viable and has the ability to be combined with a thermal energy storage (TES) system unlike wind power generation and solar photovoltaic power generation. The ability can enhance the dispatch ability of plants. The indirect two-tank molten salt storage system is one of the TES systems that absorbs excess energy from the solar field, which is stored for later use. The molten salt tank determines the thermal storage of the system and has a strong impact on the productivity of the power plant.
Although the tank is highly insulated, the high operation temperature leads to heat losses, which may cause the temperature to drop. This in turn can induce a decline in the thermal efficiency of the TES system. Now, a team of researchers from Beijing University of Technology built an experimental TES system to study the thermal property of a high-temperature molten salt tank during the cooling down process. The experimental molten salt tank is made of stainless steel 304 in order to avoid corrosion from the molten salt. The wall and roof of the tank were insulated by alumina silicate fiber boards to reduce heat losses of the tank. The team set 15 sensors to measure the temperature distribution and a new kind of quaternary nitrate molten salt: Hitec salt with a Ca(NO3)2 additive was used as the molten salt material.
The team recorded an irregular temperature distribution of molten salt. This can be attributed to natural convection due to the heat losses of the tank to the surrounding environment. The team found that thermal stratification exists in the tank and that the position of initial solidification is located at the lower edge of the tank. The maximum temperature appears at the middle upper of the foundation and radially decreases. The total heat losses of the tank were calculated to be 3.75 kW to 1.82 kW as the temperature decreased from 500 °C to 310 °C. The research was published in the journal MDPI Energies on May 21, 2019.