Corrosion evaluation of alumina-forming alloys in carbonate molten salt for CSP plants

Abstract

The use of carbonate molten salts for the new generation of concentrated solar power (CSP) plants have been considered and analysed during the last years to improve the efficiency of energy generation. However, the high temperature and corrosivity of the salts pose a risk on safety and profitability of the technology requiring more resistant materials. In this study, two alumina-forming austenitic (AFA) alloys corresponding to modified OC4 and HR224 grades, were exposed to the eutectic ternary Li2CO3-K2-CO3-Na2CO3 (32.1-34.5-33.4 wt%) salt mixture at 650 ºC for 1000 h. The evolution of weight change along the exposure time and analysis of the resulting scales by means of scanning electron microscopy (SEM), X-Ray diffraction (XRD), and glow discharge optical emission spectroscopy (GDOES) revealed a good performance of both steel grades associated with the formation of multi-layered corrosion products. Whereas both alloys undergo external oxidation with the formation of NiO, internal oxidation with the formation of two spinels is the case of HR224. The rate of corrosion is significantly lower than those reported in molten carbonated in non-AFA alloys, allowing to recommend OC4 and HR224 for use in the carbonate-based CSP.

The research leading to these results has received funding from Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group GREiA (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. Angel G. Fernández would like to acknowledge the financial support provided by CONICYT/FONDAP 15110019 “Solar Energy Research Center” SERC-Chile. Additionally, the authors would like to acknowledge Fondequip EQM160091 for funding Glow Discharge Optical Emission Spectroscopy (GD-OES) and CONICYT-PAI “Concurso inserción en el sector productivo, segunda convocatoria 2017, ISP i78170200020”.