High Temperature Corrosion Resistance in Molten Salts in Solar Power Concentration Plants: High Temperature Corrosión Monitoring in Dynamic and Static Conditions

Abstract

The actual technology for solar power plants-CSP have termal storage system composed by molten salts. Molten salts technology means electrochemical electrolytes in contact with materials, and in this case high temperature molten salts. which are an ionic electrolyte. In order to follow up the evolution of the sal chemistry, i.e. concentrating the impurities such as chlorides and sulphates, and to monitor the corrosión rate and corrosión mechanism of structural materials, electrochemical sensors have been developed and patented. On the other hand, in order to check the reliabilify and performance of the sensors, static and dynamic test have been performed in a pilot plant.Moreover, his study assessed the behaviour of a constructive material in CSP plants, namely ferritic-martensitic steel, with molten NaNO3/KNO3 (60/40 wt%), also known as Solar Salt. To this end, EIS is presented as a suitable technique to evaluate and monitor the resistance of this material to Solar Salt at 580 °C. Tests were performed up to 1000 h and results were also supported by gravimetric and microstructural characterisation of the samples and chemical analysis of the salt. According to the EIS results, a diffusion-controlled reaction occurred during contact, which indicates that the corrosion process follows a porous layer mechanism. The results also indicated variations in corrosion layer thickness and instability of the salt during the whole test. The EIS results were also used for determining the corrosion rate, this being estimated at ~300 µm year−1. Results obtained by EIS were in line with the behaviour of P91 steel as measured by gravimetric, morphological and chemical analysis. Thus, the results confirm the suitability of EIS for monitoring corrosion processes in real-time of constructive materials in CSP plants.