Molten Chloride Salt for Thermal Energy Storage in Next Generation CSP: Mg Inhibitory Effect in Corrosion Control System (CCS)

Abstract

Molten MgCl2-KCl-NaCl chloride salts are promising next generation thermal energy storage (TES) materials in concentrated solar power (CSP) plants. Both advantages of high operating temperature (>800 °C) and low costs of chloride salts contribute to achieve the target TES cost for next generation CSP (15 USD/kWhth) and reduce the levelized cost of electricity (LOCE) [1]. However, the corrosive impurities (e.g. MgOHCl) from hydrolysis of chloride salts will lead to severe corrosion of commercial Fe-Cr-Ni based alloys and limit the application of chloride salts in CSP. A Corrosion Control System (CCS) is proposed based on the previous work [2]-[6], for the purpose of mitigating the corrosion attack of MgCl2-KCl-NaCl on Fe-Cr-Ni-based alloys. As shown in Figure 1, the CCS is composed of three parts: impurity monitoring, controller and corrosion inhibition. The electrical signal of corrosive impurities MgOHCl measured by Cyclic Voltammetry (CV) is fed back to CCS controller [5]-[6]. The controller controls the addition of corrosion inhibitor. The Mg shown in Figure 1 is a promising inhibitor for controlling the concentration of corrosive impurities in MgCl2-KCl-NaCl chloride salt [2]. In this work, we designed experiments to study the corrosion inhibition effect of Mg up to 2000 hours. The samples are divided into 5 groups, each of which includes Incoloy 800H and SS 310. All metal samples were immersed in MgCl2-NaCl-KCl salt with excessive 2.8 wt.% Mg at 700°C under inert atmosphere. The metal samples with salts were taken out after 100h, 250h, 500h, 1000h, and 2000h exposure, respectively and were characterized by XRD, SEM and EDX. The salts were analyzed by titration to determine the effect of inhibitor on reducing the corrosive impurities. Through the analysis of the corrosion behavior of metal samples with different exposure time, the anti-corrosion effect of Mg addition will be shown at different periods.