Vapor pressure and corrosivity of ternary metal-chloride molten-salt based heat transfer fluids for use in concentrating solar power systems

Abstract

h i g h l i g h t sApplicability of NaCl-KCl-ZnCl 2 salts for CSP applications is evaluated. Corrosion rates are estimated by electrochemical and immersion methods. Hastelloys show corrosion rates of <10 lm/year at 800°C under anaerobic conditions. g r a p h i c a l a b s t r a c t a b s t r a c t Higher operating temperatures increase efficiency of the concentrating solar power plants but promote faster corrosion of the pipes and vessels made of Hastelloy or stainless steel materials for the moltensalt mixtures. Hastelloys C-276 and C-22 and stainless steel 304 coupons evaluated in the present study in a eutectic molten salt consisting of 13.4 mol% NaCl, 33.7 mol% KCl and 52.9 mol% ZnCl 2 showed substantially lower corrosion rates in the absence versus presence of air from 200 to 800°C as determined by electrochemical and gravimetric methods. In the presence of air, the corrosion rate for the Hastelloy C-276 in the molten salt was found to diminish with immersion time and converges around $50 lm per year after 4 weeks of immersion at 500°C, which is close to the value $40 lm per year obtained using the electrochemical method at 500°C. For anaerobic corrosion rate estimation, the corrosivity of an alloy sample was examined by immersing in molten salt inside a sealed quartz container without any contact with air, which is possible because the vapor pressure of the eutectic molten salt is only about 0.7 atm at 800°C. The corrosion rate of the Hastelloy C-276 was only 10 lm per year in the molten salt in the absence of air at 800°C, which is extremely low compared to 500 lm per year in conducting corrosion studies in the presence of air at 800°C. The Hastelloy coupons after immersion testing in the absence of air have then been examined also by SEM, and the images did not show any http://dx.

Re‐establishing the paradigm for evaluating halide salt compatibility to study commercial chloride salts at 600°C–800°C

“…A recent literature review concluded that purified salts and sealed containers had a significant effect on corrosion rates . Also, in the recent chloride salt literature, it is common to extrapolate isothermal results and report an annualized rate of attack (i.e., µm/yr) as a performance metric . That is inappropriate for two main reasons: first, an assumption must be made about the kinetics and the assumption of a linear extrapolation is not based on any mechanistic understanding or data.…”

A simple method for the inhibition of the corrosion of carbon steel by molten nitrate salt for thermal storage in concentrating solar power applications

“…In this context, numerous studies have explored the corrosion behaviour of potential construction materials with different storage media or heat transfer fluids. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Molten nitrate salt, known as Solar Salt, is the most technologically mature solution for CSP. It consists of 60 wt% NaNO 3 -40 wt%KNO 3 .…”

“…The ternary salt Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 was investigated for compatibility with HR3C steel (25%Cr-20%Ni-53%Fe), demonstrating that oxidation is the main corrosion mechanism. 21 Hastelloy C-276 and C-22 and stainless steel 304 with chloride salts were studied at temperatures up to 900°C in the presence 22,23 and absence 23 of air. The authors concluded that the corrosion rates decrease with the absence of oxygen in the atmosphere.…”

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

“…Immersion method was most widely used by researchers to describe the corrosion behaviors of alloys in the molten salt mixtures . Vignarooban et al have studied the corrosion behaviors for Hastelloys and stainless steels in ternary molten salt system, calculated the corrosion rates for different alloys with and without air and ranked the corrosion resistance of each alloy for potential applications. Fernandez et al have studied corrosion products and corrosion layer formed in a ternary nitrate/nitrite molten salt system for alloys such as 122 steels.…”