Abstract
The scope of our study was to examine the potential of regeneration mechanisms of an aged molten Solar Salt (nitrite, oxide impurity) by utilization of reactive gas species (nitrous gases, oxygen). Initially, aging of Solar Salt (60 wt% NaNO3, 40 wt% KNO3) was mimicked by supplementing the decomposition products, sodium nitrite and sodium peroxide, to the nitrate salt mixture. The impact of different reactive purge gas compositions on the regeneration of Solar Salt was elaborated. Purging the molten salt with a synthetic air (p(O2) = 0.2 atm) gas stream containing NO (200 ppm), the oxide ion concentration was effectively reduced. Increasing the oxygen partial pressure (p(O2) = 0.8 atm, 200 ppm NO) resulted in even lower oxide ion equilibrium concentrations. To our knowledge, this investigation is the first to present evidence of the regeneration of an oxide rich molten Solar Salt, and reveals the huge impact of reactive gases on Solar Salt reaction chemistry.
Highlights
Thermal energy storage with molten nitrate salts at 565 ◦ C is currently employed in several Concentrating Solar Power (CSP) plants to provide dispatchable and renewable electricity in the MW-scale
To exclude the effect of the nitrate–nitrite equilibrium, for the first set the results of molten salt purged with p(O2 ) = 0.2 atm are discussed
We demonstrated the regeneration of a decomposed oxide ion rich molten
Summary
Thermal energy storage with molten nitrate salts at 565 ◦ C is currently employed in several Concentrating Solar Power (CSP) plants to provide dispatchable and renewable electricity in the MW-scale. The influence of nitrous gases on the nitrite-oxide equilibrium becomes more tangible through Equation (2) In this regard, Sötz et al reported the stabilization of molten Solar Salt with a purge gas flow containing nitrous gases at temperatures of 600 ◦ C and even 620 ◦ C in terms of stable nitrate-nitriteand low oxide ion concentrations. The reduction of high oxide ion levels (0.15 wt% or 1 mol%) in Solar Salt-based mixtures (60 wt% NaNO3 , 40 wt% KNO3 ) by reversing Equation (2), is demonstrated These mixtures are artificially aged by adding unusually high concentrations of nitriteand oxide ions (10 mol% and 1 mol%, respectively) and the effect of different purge gas compositions (20 % and 80 % O2 , with and without 200 ppm NO) on the salt chemistry are investigated.
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