Alexander Bonk

Material investigations on the thermal stability of solar salt and potential filler materials for molten salt storage

The thermal and chemical stability of solar salt during isothermal tests is assessed under manifold conditions. Solar salt stored at 560°C under synthetic air stabilizes readily after a few days with both nitrate and nitrite content remaining relatively stable over time. A nitrogen atmosphere enhances degradation due to a continuous reduction of nitrate to nitrite. In an open atmosphere CO2 formation is pronounced owing to the reaction of the molten nitrates with atmospheric CO2. The stability of some filler materials, as potential candidates to be used in thermocline storage concepts, was investigated in long term experiments up to 5.000h. Additional anionic traces in the melt as corrosion products from the filler due to the reaction of instable mineral species with nitrates/nitrites were identified. However, No impact on the the thermal properties of the salt could be determined. These properties remain to be unchanged over a time frame up to 5.000h which is confirmed by relatively stable nitrate/nitrit...

Round robin test on the measurement of the specific heat of solar salt

Solar salt (SS), a well-known non-eutectic mixture of sodium nitrate (60% w/w) and potassium nitrate (40% w/w), is commonly used either as Thermal Energy Storage (TES) material (double tank technology) or Heat Transfer Fluid (HTF) (solar tower) in modern CSP plants worldwide. The specific heat (cp, kJ kg−1 °C−1) of SS is a very important property in order to support the design of new CSP Plants or develop novel materials based on SS. A high scientific effort has been dedicated to perform a suitable thermophysical characterization of this material. However, there is still a great discrepancy among the cp values reported by different authors1. These differences may be due to either experimental errors (random or systematic) or divergences in the starting material (grade of purity, presence of impurities and/or water). In order to avoid the second source of uncertainty (the starting material), a Round Robin Test (RRT) was proposed starting from a common material. In this way, the different methods from each ...

Corrosion behavior of metallic alloys in molten chloride salts for thermal energy storage in concentrated solar power plants: A review

Recently, more and more attention is paid on applications of molten chlorides in concentrated solar power (CSP) plants as high-temperature thermal energy storage (TES) and heat transfer fluid (HTF) materials due to their high thermal stability limits and low prices, compared to the commercial TES/HTF materials in CSP-nitrate salt mixtures. A higher TES/HTF operating temperature leads to higher efficiency of thermal to electrical energy conversion of the power block in CSP, however causes additional challenges, particularly increased corrosiveness of metallic alloys used as containers and structural materials. Thus, it is essential to study corrosion behaviors and mechanisms of metallic alloys in molten chlorides at operating temperatures (500–800 °C) for realizing the commercial application of molten chlorides in CSP. The results of studies on hot corrosion of metallic alloys in molten chlorides are reviewed to understand their corrosion behaviors and mechanisms under various conditions (e.g., temperature, atmosphere). Emphasis has also been given on salt purification to reduce corrosive impurities in molten chlorides and development of electrochemical techniques to in-situ monitor corrosive impurities in molten chlorides, in order to efficiently control corrosion rates of metallic alloys in molten chlorides to meet the requirements of industrial applications.

Materialaspekte bei der thermischen Energiespeicherung in Flüssigsalz

Thermische Energiespeicher auf Basis von Flussigsalzen spielen eine wichtige Rolle bei der zeitlichen Zwischenspeicherung von uberschussiger thermischer Energie. Diese Speicher werden derzeit kommerziell in solarthermischen Kraftwerken eingesetzt. Ein umfassendes Verstandnis fur die Salzchemie ist unabdingbar fur die Auslegung und den Betrieb von sensiblen thermischen Flussigsalzspeichern mit und ohne Feststoff als Fullmaterial. Die Zersetzungsreaktionen der Nitratsalze bei der maximalen Betriebstemperatur sind Forschungsgegenstand. Bei Temperaturschichtspeichern, die Fullermaterialien auf Mineralbasis nutzen um teures Salzvolumen zu verdrangen, werden grundlegende Fragen zur Bestandigkeit der eingesetzten Fullermaterialien gegenuber dem Salz beantwortet. Insgesamt befasst sich die hier vorgestellte Arbeit somit umfassend mit Materialaspekten bei der thermischen Energiespeicherung und beantwortet Fragestellungen uber die Degradationsmechanismen von Nitratsalzen und der Fullermaterialien mit der Anwendungstemperatur und Gasatmosphare als wesentlich Parameter.