Abstract
Two-tank molten salt heat storage systems are considered to be the most mature thermal storage technology in solar thermal power plants. As the key part of the system, the thermal performance of molten salt tanks is of great importance. An experimental thermal storage system with a new type of molten salt as a thermal energy storage medium has been built to investigate the temperature distribution of molten salt inside the tank during the cooling process from 550 °C to 180 °C. The temperature distribution of the salt was obtained, which reveals that temperature stratification appears at the bottom of the tank within the height of 200 mm. The position, with the maximum temperature difference of 16.1 °C, is at the lower edges of the molten salt storage tank. The temperature distribution was also measured to deepen our understanding of the insulation foundation, which shows that the maximum temperature appears at the middle upper part of the foundation and decreases radially. The heat losses of the molten salt tank were calculated by the classical equation, from which it was found that the heat loss decreases from 3.65 kWh to 1.82 kWh as the temperature of the molten salt drops from 550 °C to 310 °C. The effect of temperature stratification on the heat losses of the tank’s bottom was also analyzed.
Highlights
Concentrating Solar Power (CSP), as one of the renewable energy technologies, has been successfully applied commercially in several plants, and is entering a commercial ramp-up period [1]
The highest operating temperature of molten salt solar power tower plants is 535~565 ◦ C; there may be some that operate at a temperature from 380 to 300 ◦ C during the cooling down process, but no experimental study on the temperature distribution of molten salt inside the tank at that temperature range is available
During the cool down process, heat losses to the environment offer enough buoyancy forces to drive the molten salt to natural convection, with the result that the molten salt near the tank walls cools down
Summary
Concentrating Solar Power (CSP), as one of the renewable energy technologies, has been successfully applied commercially in several plants, and is entering a commercial ramp-up period [1]. The highest operating temperature of molten salt solar power tower plants is 535~565 ◦ C; there may be some that operate at a temperature from 380 to 300 ◦ C during the cooling down process, but no experimental study on the temperature distribution of molten salt inside the tank at that temperature range is available. The objectives are: (a) to obtain the temperature distribution of the molten salt and the insulation foundation during the natural cooling process from 550 ◦ C to 310 ◦ C; (b) to confirm or deny through the experiments whether thermal stratification appears and the influence of thermal stratification; (c) to obtain the temperature distribution of the molten salt during the solidification process; and (d) to analyze the heat loss of the experimental TES tank
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