Heat transformation based on reversible chemical reactions has gained significant interest due to the high achievable output temperatures. This specific type of chemical heat pump uses a reversible gas–solid reaction, with the back and forward reactions taking place at different temperatures: by running the exothermic discharge reaction at a higher temperature than the endothermic charge reaction, the released heat is thermally upgraded. In this work, we report on the experimental investigation of the hydration reaction of strontium bromide (SrBr2) with regard to its use for heat transformation in the temperature range from 180 °C to 250 °C on a 1 kg scale. The reaction temperature is set by adjusting the pressure of the gaseous reactant. In previous experimental studies, we found the macroscopic and microscopic properties of the solid bulk phase to be subject to considerable changes due to the chemical reaction-. In order to better understand how this affects the thermal discharge performance of a thermochemical reactor, we combine our experimental work with a modelling approach. From the results of the presented studies, we derive design rules and operating parameters for a thermochemical storage module based on SrBr2.
Thermal storages can contribute to decarbonization in storing energy of fluctuating renewables and waste heat of industrial processes by decoupling supply and demand. A great opportunity to decrease the cost of high temperature storage is given by single tank thermocline storage systems, where large fractions of cost-intensive high-temperature fluids are replaced by a low-cost filler material. Besides low cost, a suitable filler material must meet various other criteria such as suitable thermal conductivity, high heat capacity, high volumetric density of the packed bed of fillers, sufficient mechanical stability and compatibility with high temperature fluids in the temperature range of the application. For one promising type of ceramic filler, the compatibility with a solar salt mixture of 60 wt% sodium nitrate (NaNO 3 ) and 40 wt% potassium nitrate (KNO 3 ) was investigated. The filler is composed of additives, such as metallic slag and various other low-cost recycled materials, and a phosphatic binder resistant to the high temperatures. For testing, fillers were immersed in the corresponding fluids in a crucible under air atmosphere. The samples were thermally cycled in an oven up to the maximum foreseen temperature (250-550 °C for the salt). Overall, the ceramics tested show good compatibility with solar salt and have the potential to significantly reduce the cost of the storage systems.
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