Abstract
Thermal energy storage (TES) systems are key components for concentrated solar power plants to improve their dispatchability and for shifting the energy production efficiently to high revenue periods. The commercial state of the art is the molten salt two tank storage technology. However, this TES confronts some issues like freezing and decomposition, which require continued technical attention. Furthermore, the molten salt itself is very expensive compared to other storage materials. A TES option that possesses a high cost reduction potential and the ability to increase the whole power plant efficiency is the regenerator-type energy storage. Here, a packed bed inventory of waste metallurgical slag from electric arc furnace (EAF) can achieve further cost reduction. Despite previous studies regarding the use of steelmaking slag as an inventory material for thermal energy storages, there are still basic questions to be answered. This work presents experimental thermal performance and thermo-structural stability studies of slag-based TES, obtained during the European project REslag. The EAF slag and different insulation options were tested for their thermomechanical strength in a uniaxial compression test rig. The thermal cyclic behavior was investigated in a pilot TES plant with temperatures up to 700 °C. The experimental results confirm the suitability of steelmaking slag as thermal energy storage inventory material. Furthermore, a comparison of experimental and simulation model results shows an agreement of over 90%.
Highlights
A concentrated solar power (CSP) tower converts the sun’s light energy into heat and electricity.Sun tracing mirrors are used to focus the sunlight onto a receiver located on the top of a tower.There, the solar energy is used to heat up a heat transfer fluid (HTF)
Plant charging and discharging leads to steady state storage operation after six cycles. This is clearly shown by the fluctuations of the discharge outlet temperature, which afterend sixTES-section
This results from thermalresults lossesarecaused bysolid the small pilot tests during thermalcan cycling is depicted in black
Summary
A concentrated solar power (CSP) tower converts the sun’s light energy into heat and electricity. There, the solar energy is used to heat up a heat transfer fluid (HTF) This fluid serves to generate high-temperature steam in a steam boiler, to drive a turbine which is connected to an electrical power generator. The power generation is related to the availability of the sun. To increase the independence of CSP systems, thermal energy storage (TES) systems are used. Those systems are able to mitigate short load fluctuations during transient weather conditions, can shift the generation period to peak hours of demand and can extend the energy supply when the sun is not available. One representative is the two-tank molten salt thermal energy storage, which is extensively deployed and currently the state of the art [1]
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