High Operating Temperature Transfer and Storage (HOTTS) System for Concentrated Solar Power Generation and Metals Production

High Operating Temperature Transfer and Storage (HOTTS) is a solar energy-based process currently under development, designed to provide high-quality heat to industrial processes.  This system includes a dry, particle-based heat transfer fluid (pHTF) that can be heated to temperatures of 1,100°C, some 400°C higher than molten salt-based systems.  The pHTF can store thermal energy to enable continuous operation through day and night cycles.  The HOTTS system also contains Mo-Si-B composites and coatings as the material of construction (MOC), which resists oxidation and particle erosion at these elevated operating conditions. 

In this study, we report the heat-transfer performance of different materials as pHTFs in a low temperature (up to 200°C) bench-scale unit.  Heat-transfer coefficients are determined for mass fluxes up to 75 kg/m²-s.  We also correlate the flow rate of the particles to the outlet size of the bench-scale unit.  The flowability of the pHTFs after high-temperature thermal cycling is also reported.  In addition, we discuss the oxidative resistance of hot-pressed, Mo-Si-B composites at temperatures up to 1650°C in air.  One Mo-Si-B composition is examined after long-term (100 h) isothermal conditions, as well as thermal cycling to simulate solar-thermal operation.  Engineering approaches to implement the pHTF and Mo-Si-B MOC into a pilot-scale HOTTS process are also discussed.