Corrosion of alloys in a chloride molten salt (NaCl-LiCl) for solar thermal technologies

Abstract

a b s t r a c tNext-generation solar power conversion systems in concentrating solar power (CSP) applications require high-temperature advanced fluids in the range of 600-800°C. Current commercial CSP plants use molten nitrate salt mixtures as the heat transfer fluid and the thermal energy storage (TES) media while operating with multiple hours of energy capacity and at temperatures lower than 565°C. At higher temperatures, the nitrates cannot be used because they decompose. Molten chloride salts are candidates for CSP applications because of their high decomposition temperatures and good thermal properties; but they can be corrosive to common alloys used in vessels, heat exchangers, and piping at these elevated temperatures. In this article, we present the results of the corrosion evaluations of several alloys in eutectic 34.42 wt% NaCl -65.58 wt% LiCl at 650-700°C in nitrogen atmosphere. Electrochemical evaluations were performed using open-circuit potential followed by a potentiodynamic polarization sweep. Corrosion rates were determined using Tafel slopes and Faraday's law. A temperature increase of as little as 50°C more than doubled the corrosion rate of AISI stainless steel 310 and Incoloy 800H compared to the initial 650°C test. These alloys exhibited localized corrosion. Inconel 625 was the most corrosionresistant alloy with a corrosion rate of 2.80 7 0.38 mm/year. For TES applications, corrosion rates with magnitudes of a few millimeters per year are not acceptable because of economic considerations. Additionally, localized corrosion (intergranular or pitting) can be catastrophic. Thus, corrosion-mitigation approaches are required for advanced CSP plants to be commercially viable.

Corrosion resistance of alumina-forming alloys against molten chlorides for energy production. I: Pre-oxidation treatment and isothermal corrosion tests

“…Each alloy was subjected to pre-oxidation for certain periods of time. work [10]. The electrochemical tests were performed using a potentiostat (AUTOLAB-PGSTAT302N).…”

“…Protective alumina scales have been shown to be a more effective barrier to the inward penetration of aggressive components such as chlorine and chloride molten salts [9]. Chromia-forming alloys have been shown to not be corrosion resistant in chloride molten salt environments [10]. Alumina grows at a slower rate than chromia, is more stable thermodynamically with oxygen, and affords a significantly higher degree of protection in the presence of many aggressive oxidizing species.…”

Investigation on static and dynamic corrosion behaviors of thermal energy transfer and storage system materials by molten salts in concentrating solar power plants

“…This was due to chloride ions remained in the 3# molten salt mixture during production process. Chloride ions are reported to have general aggressiveness to many alloys in large amounts of cases …”

Review of supercritical CO2power cycles integrated with CSP

“…Chloride and carbonate salt blends have been proposed and tested, but coming after new challenges . The corrosion mechanisms of candidate salts and corresponding mitigation approaches are still an area of ongoing which are badly needed for component designers . Nickel alloys are decided to be adopted in the receiver and TES, as shown in Table .…”

“…[124][125][126] The corrosion mechanisms of candidate salts and corresponding mitigation approaches are still an area of ongoing which are badly needed for component designers. [127][128][129][130][131] Nickel alloys are decided to be adopted in the receiver and TES, as shown in Table 7. Compared with molten salt, particle as heat carrier is cheaper and more stable at high temperatures.…”